[fpc-pascal] JSON stream load/save recursive structure

[Xiangrong Fang]

Hi there,

Can fpjson handle load AND save of the following structure from/to json:

PTreeStructure = ^TTreeStructure;
TTreeStructure = class
  name: string;
  value: Integer;
  items: array of PTreeStructure;
end;

Thanks!

xrfang
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[fpc-pascal] libevent for socket

[Xiangrong Fang]

Hi All,

Could anyone help me with some samples of writing socket program with
libevent, or is there any adapter/wrapper already exists for freepascal?

Thanks!
Xiangrong
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Re: [fpc-pascal] FPC 3 inclusion for debian/ubuntu?

[Xiangrong Fang]

>
>
> ​T​
> he experimental repository​
>
> ​contains a file
> fpc_3.0.0+dfsg-1_all.deb
> ​which is only 38Kb, and is for "all" architecture.
>
> ​Sorry I digged inside and found the actual file. That's a "meta" package.

However, there is no MIPS build.  To build fpc executables for MIPS, I have
to do cross-compiling?​
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Re: [fpc-pascal] FPC 3 inclusion for debian/ubuntu?

[Xiangrong Fang]

On Mon, Dec 14, 2015 at 5:27 PM, Jonas Maebe 
wrote:


> It's already in the Debian experimental repository:
> https://packages.debian.org/search?searchon=names=fpc
>
> You will have to ask the Debian/Ubuntu project when they plan to include
> it in which release.
>

The experimental repository​

​contains a file
fpc_3.0.0+dfsg-1_all.deb
​which is only 38Kb, and is for "all" architecture.

As a matter of fact, I usually get the latest version of fpc from the
download site of Lazarus.

The reason I ask is that I expect to get non-intel architecture (armhf,
mips etc.) builds of fpc-3.​

Thanks!

Xiangrong​
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[fpc-pascal] FPC 3 inclusion for debian/ubuntu?

[Xiangrong Fang]

Hi There,

Just curious, will the freshly release FPC 3 be included in the current or
next release of debian/ubuntu repository?

Thanks!
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[fpc-pascal] status of fpc-mips

[Xiangrong Fang]

Hi All,

I plan to port my program to a MIPS based openwrt router.
The hardware is based on Atheros AR9331.  I wonder if FPC for MIPS linux
cross
compiler is usable or not and what FPC version it currently support?

Also, btw, last time I asked similar question about the RaspberryPi,
and know that there are ARMEL/ARMHF.   Is there similar concept
on MIPS platform? i.e. if I successfully compile a program for MIPS,
is it guaranteed to work on all MIPS compliant CPUs?

Thanks a lot.

Xiangrong
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Re: [fpc-pascal] Linking failed on RaspberryPi

[Xiangrong Fang]

Another problem is, as I downloaded the wrong version and ran its
install.sh (as root), how can I uninstall it?

Thanks!



2015-09-16 9:29 GMT+08:00 Xiangrong Fang <xrf...@gmail.com>:

> I asked on the list before.  The version shipped with Pi is 2.6.0, and is
> said to be very buggy, I need version 2.6.4, so I downloaded from official
> site.
>
>
>
> 2015-09-15 19:52 GMT+08:00 Jonas Maebe <jonas.ma...@elis.ugent.be>:
>
>> On 15/09/15 13:28, Xiangrong Fang wrote:
>>
>>> I downloaded arm linux distribution from freeepascal website
>>> (sourceforge).  So, I should get it work by fixing crti as suggested by
>>> PB, or I shall get the compiler from Pi website as suggested by Jonas?
>>>
>>
>> You don't get it from the Pi website, but by using the package manager of
>> your linux distribution (apt).
>>
>> The version from the FPC website is not appropriate for your Linux
>> distribution, as it is for ARMEL and you have ARMHF.
>>
>>
>> Jonas
>>
>>
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Re: [fpc-pascal] Linking failed on RaspberryPi

[Xiangrong Fang]

Hi Peter,

xrfang@pi ~ $ grep FI /etc/fpc.cfg
# nested #IFNDEF, #IFDEF, #ENDIF, #ELSE, #DEFINE, #UNDEF are allowed
# -d is the same as #DEFINE
#DEFINE NEEDCROSSBINUTILS

xrfang@pi ~ $ ls /usr/lib/**/crti.o
/usr/lib/arm-linux-gnueabihf/crti.o

Thanks!




2015-09-15 20:06 GMT+08:00 Peter :

> It would be useful to see the output of these two commands
>
> grep Fl /etc/fpc.cfg
> ls /usr/lib/**/crti.o
>
>
> Jonas knows a lot more about FPC than I do!
>
> Regards,
> PB
>
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Re: [fpc-pascal] Linking failed on RaspberryPi

[Xiangrong Fang]

I asked on the list before.  The version shipped with Pi is 2.6.0, and is
said to be very buggy, I need version 2.6.4, so I downloaded from official
site.



2015-09-15 19:52 GMT+08:00 Jonas Maebe <jonas.ma...@elis.ugent.be>:

> On 15/09/15 13:28, Xiangrong Fang wrote:
>
>> I downloaded arm linux distribution from freeepascal website
>> (sourceforge).  So, I should get it work by fixing crti as suggested by
>> PB, or I shall get the compiler from Pi website as suggested by Jonas?
>>
>
> You don't get it from the Pi website, but by using the package manager of
> your linux distribution (apt).
>
> The version from the FPC website is not appropriate for your Linux
> distribution, as it is for ARMEL and you have ARMHF.
>
>
> Jonas
>
>
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Re: [fpc-pascal] Linking failed on RaspberryPi

[Xiangrong Fang]

I downloaded arm linux distribution from freeepascal website
(sourceforge).  So, I should get it work by fixing crti as suggested by PB,
or I shall get the compiler from Pi website as suggested by Jonas?




2015-09-15 19:11 GMT+08:00 Peter <pe...@pblackman.plus.com>:

> On 14/09/15 21:09, Mark Morgan Lloyd wrote:
> > Peter wrote:
> >> On 04/09/15 02:15, Xiangrong Fang wrote:
> >>> .
> >>> Is there anything missing from my FPC installation?
> >>> TIA for any hint.
> >>
> >> To build FPC programs on linux one generally needs a variant of
> >> libc-dev, which is not part of FPC itself.
> >> The package you need might be libc6-dev, or some other combination of
> >> 'libc' and 'dev'.
> >>
> >> Please post the solution if/when you find it for the benefit of others.
> >> This same question seems to keep poping up on this list.
> >
> > You mean like I did [checks] on the 31st?
> > http://lists.freepascal.org/pipermail/fpc-pascal/2015-August/045157.html
> >
> > And that was without any particular additions, other than what came with
> > Raspbian 2014 as standard; Raspbian 2015 doesn't need most of those
> > options (i.e. either miss out the -FL and -Fl options, or follow
> > Martin's procedure).
> >
>
>
> The symbols the OP is missing are defined in crti.o
> Without further information from him, its impossible to know whether the
> problem is that
> 1) crti.o is not installed (its libc..dev not FPC)
> 2) The -Fl option does not use the right path for the system in use.
>
> I would suggest the following;
> try the command
> ls /usr/lib/**/crti.o
>
> If it works, use the given path for -Fl (as per the links already given
> in this thread.
> If it does not work, install the libc package that contains crti.o, and
> repeat the test.
>
>
> Regards,
> PB
>
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[fpc-pascal] Linking failed on RaspberryPi

[Xiangrong Fang]

Hi All,

I try to compile my program on Pi, with the official FPC 2.6.4 for arm
linux, but get the following error:

/usr/lib/fpc/2.6.4/units/arm-linux/rtl/cprt0.o: In function
`_haltproc_eabi':
(.text+0x88): undefined reference to `_fini'
/usr/lib/fpc/2.6.4/units/arm-linux/rtl/cprt0.o: In function
`_haltproc_eabi':
(.text+0x90): undefined reference to `_init'

Is there anything missing from my FPC installation?

TIA for any hint.
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[fpc-pascal] Fatal: Internal error 200305103

[Xiangrong Fang]

Hello,

I got Fatal: Internal error 200305103 while try to compile the attached
file on my raspi.

The file is a class helper. I wonder if that is supported on FPC 2.6.0 or
not? And whether this problem has anything to do with ARM?
unit cipher;
{$mode objfpc}{$H+}
interface
uses sysutils, BlowFish;
type
  TBlowFish = BlowFish.TBlowFish;
  TBlowFishModes = class helper for TBlowFish
  private
procedure CryptCTR(IV: QWord; buf: Pointer; len: Integer); inline;
  public
constructor Create(key: Pointer; KeySize: Integer);
procedure EncryptCTR(IV: QWord; buf: Pointer; len: Integer);
procedure DecryptCTR(IV: QWord; buf: Pointer; len: Integer);
procedure EncryptCBC(IV: QWord; buf: Pointer; len: Integer);
procedure DecryptCBC(IV: QWord; buf: Pointer; len: Integer);
  end;

implementation

constructor TBlowFishModes.Create(key: Pointer; KeySize: Integer);
begin
  inherited Create(PBlowFishKey(key)^, KeySize);
end;

procedure TBlowFishModes.EncryptCTR(IV: QWord; buf: Pointer; len: Integer);
begin
  CryptCTR(IV, Buf, len);
end;

procedure TBlowFishModes.DecryptCTR(IV: QWord; buf: Pointer; len: Integer);
begin
  CryptCTR(IV, Buf, len);
end;

procedure TBlowFishModes.CryptCTR(IV: QWord; buf: Pointer; len: Integer);
var
  i, cnt, res: Integer;
  ipt: QWord;
  iptb: array[0..7] of Byte absolute ipt;
  ptb: PQWord;
  ptr: PByte;
begin
  cnt := len div 8;
  res := len mod 8;
  for i := 0 to cnt - 1 do begin
ipt := IV xor i;
Encrypt(TBFBlock(ipt));
ptb := PQWord(buf + i * 8);
ptb^ := ptb^ xor ipt;
  end;
  if res  0 then begin //process last block less than 8 byte
ipt := IV xor cnt;
for i := 0 to res - 1 do begin
  ptr := PByte(buf + cnt * 8 + i);
  ptr^ := ptr^ xor iptb[i];
end;
  end;
end;

procedure TBlowFishModes.EncryptCBC(IV: QWord; buf: Pointer; len: Integer);
var
  i, cnt, res: Integer;
  ptb: PQWord;
  last, prelast: QWord;
begin
  if len = 8 then begin
CryptCTR(IV, buf, len);
Exit;
  end;
  cnt := len div 8;
  res := len mod 8;
  if res = 0 then begin
prelast := PQWord(buf+(cnt-2)*8)^;
last := PQWord(buf+(cnt-1)*8)^;
res := 8;
Dec(cnt, 2);
  end else begin
prelast := PQWord(buf+(cnt-1)*8)^;
last := PQWord(buf+cnt*8)^;
Dec(cnt);
  end;
  for i := 0 to cnt - 1 do begin
ptb := PQWord(buf + i * 8);
ptb^ := ptb^ xor IV;
Encrypt(TBFBlock(ptb^));
IV := ptb^;
  end;
  prelast := prelast xor IV;
  Encrypt(TBFBlock(prelast));
  Move(prelast, PByte(buf+(cnt+1)*8)^, res);
  last := last xor prelast;
  Encrypt(TBFBlock(last));
  PQWord(buf+cnt*8)^ := last;
end;

procedure TBlowFishModes.DecryptCBC(IV: QWord; buf: Pointer; len: Integer);
type
  QWB = array[0..7] of Byte;
var
  i, cnt, res: Integer;
  ptb: PQWord;
  ctx: QWord;
  last, prelast: QWord;
begin
  if len = 8 then begin
CryptCTR(IV, buf, len);
Exit;
  end;
  cnt := len div 8;
  res := len mod 8;
  if res = 0 then begin
prelast := PQWord(buf+(cnt-2)*8)^;
last := PQWord(buf+(cnt-1)*8)^;
Dec(cnt, 2);
  end else begin
prelast := PQWord(buf+(cnt-1)*8)^;
last := PQWord(buf+cnt*8)^;
Dec(cnt);
  end;
  for i := 0 to cnt - 1 do begin
ptb := PQWord(buf + i * 8);
ctx := ptb^;
Decrypt(TBFBlock(ptb^));
ptb^ := ptb^ xor IV;
IV := ctx;
  end;
  Decrypt(TBFBlock(prelast));
  if res  0 then begin
for i := res to 7 do QWB(last)[i] := QWB(prelast)[i];
  end else res := 8;
  prelast := prelast xor last;
  Move(prelast, PByte(buf+(cnt+1)*8)^, res);
  Decrypt(TBFBlock(last));
  PQWord(buf+cnt*8)^ := last xor IV;
end;

end.

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[fpc-pascal] shift right operation with variables

[Xiangrong Fang]

Hi All,

I noticed a strange behavior with the following program:

program tt;
{$mode objfpc}{$H+}
uses sysutils;
var
  res: Integer;
  mask1, mask2: QWord;
begin
  mask1 := $ shr 24;
  WriteLn(IntToHex(mask1, 16));
  res := 24;
  mask2 := $ shr res;
  WriteLn(IntToHex(mask2, 16));
end.

The output is:

00FF
00FF

Why they are different? How can I ensure the result is like SHR with
constant.

Thanks!
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[fpc-pascal] quality of FPC random

[Xiangrong Fang]

Hi All,

I need to generate random numbers to be used as IV of block ciphers.  My
question is: is FPC built-in PRNG good enough as comparing to /dev/urandom?

On the other hand, /dev/urandom in my impression is fairly slow, how is the
speed of Random() comparing to that?

Thanks!
Xiangrong
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Re: [fpc-pascal] quality of FPC random

[Xiangrong Fang]

2015-08-14 21:47 GMT+08:00 Jonas Maebe jonas.ma...@elis.ugent.be:


 Xiangrong Fang wrote on Fri, 14 Aug 2015:

 I need to generate random numbers to be used as IV of block ciphers.  My
 question is: is FPC built-in PRNG good enough as comparing to
 /dev/urandom?


 No PRNG is suited for that purpose, because every PRNG is by definition
 predictable and you need unpredictable numbers for IVs.


​Well, practically, how can I get totally unpredictable numbers? On
stackoverflow, someone suggested using hash value of data as IV, but that's
still flawed somehow.

Without introduce hardware source like a dongle or other devices (which is
not acceptable for my purpose), I suppose good quality PRNGs​ are the only
thing that I can use?

​Also, why FPC random number are not comparable to /dev/urandom?  Despite
the difference in their quality and speed (if any), what's the difference
between them? especially, what are the typical use cases of these 2 PRNGs
when they are designed?​
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Re: [fpc-pascal] alignment of records

[Xiangrong Fang]

 By using the correct types for the fields:
 http://www.freepascal.org/docs-html/rtl/ctypes/index-3.html

 E.g., unsigned long is not (always) the same as dword.
 ​

 ​OK, as a matter of fact, the stuff was copied from output of h2pas
conversion program. :-)  I will use ctypes to test again.

However, another issue: if I use this :

​{$CODEALIGN RECORDMIN=4}

It worked. i.e. output size same as C version.   I wonder what's the
difference between $CODEALIGN and $A/$PACKRECORDS?

Also, if I use packed records, alignment will never take place,
regardless of $A settings, right?

Thanks!
​Xiangrong​




 Jonas
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[fpc-pascal] alignment of records

[Xiangrong Fang]

Hi All,

I try to port a program from C to Pascal, see the following example:

#include stdio.h
#include sys/socket.h
#include linux/if.h
void main() {
printf(ifmap=%ld\n, sizeof(struct ifmap));
}

I converted it to:

est.c  test.pas

   X
program test;
{$mode objfpc}{$PACKRECORDS C}
type
  ifmap = record
mem_start: dword;
mem_end: dword;
base_addr: word;
irq: byte;
dma: byte;
port: byte;
  end;
begin
  WriteLn('ifmap=', SizeOf(ifmap));
end.

The C struct's size is 24, but pascal record is 16.The ifmap struct is
defined as:

struct ifmap {
unsigned long mem_start;
unsigned long mem_end;
unsigned short base_addr;
unsigned char irq;
unsigned char dma;
unsigned char port;
/* 3 bytes spare */
};

How can I instruct FPC to align records exactly same as GCC?

Thanks!
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Re: [fpc-pascal] alignment of records

[Xiangrong Fang]

It seems that $packrecord does not work at all.  I did some research and
found this document:

http://www.freepascal.org/docs-html/ref/refsu19.html

compiled and ran the example on that page, I got:

​​Size Trec1 : 4 Offset B : 2
Size Trec2 : 3 Offset B : 1
Size Trec3 : 2 Offset B : 1
Size Trec4 : 2 Offset B : 1
Size Trec5 : 5 Offset B : 1 Offset C : 4
Size Trec6 : 5 Offset B : 1 Offset C : 4
Size Trec7 : 9 Offset B : 1 Offset C : 8
Size Trec8 : 9 Offset B : 1 Offset C : 8

While the expected output, as stated in the document above, should be:

Size Trec1 : 4 Offset B : 2
Size Trec2 : 3 Offset B : 1
Size Trec3 : 2 Offset B : 1
Size Trec4 : 2 Offset B : 1
Size Trec5 : 8 Offset B : 4 Offset C : 7
Size Trec6 : 8 Offset B : 4 Offset C : 7
Size Trec7 : 12 Offset B : 4 Offset C : 11
Size Trec8 : 16 Offset B : 8 Offset C : 15



2015-08-07 10:48 GMT+08:00 Xiangrong Fang xrf...@gmail.com:

 Hi All,

 I try to port a program from C to Pascal, see the following example:

 #include stdio.h
 #include sys/socket.h
 #include linux/if.h
 void main() {
 printf(ifmap=%ld\n, sizeof(struct ifmap));
 }

 I converted it to:

 est.c  test.pas

  X
 program test;
 {$mode objfpc}{$PACKRECORDS C}
 type
   ifmap = record
 mem_start: dword;
 mem_end: dword;
 base_addr: word;
 irq: byte;
 dma: byte;
 port: byte;
   end;
 begin
   WriteLn('ifmap=', SizeOf(ifmap));
 end.

 The C struct's size is 24, but pascal record is 16.The ifmap struct is
 defined as:

 struct ifmap {
 unsigned long mem_start;
 unsigned long mem_end;
 unsigned short base_addr;
 unsigned char irq;
 unsigned char dma;
 unsigned char port;
 /* 3 bytes spare */
 };

 How can I instruct FPC to align records exactly same as GCC?

 Thanks!





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[fpc-pascal] manipulate tun/tap in free pascal

[Xiangrong Fang]

Hi there,

Is there any example to write a tun/tap driver (or adapter, whatever) on
Linux using free pascal?

Thanks!
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[fpc-pascal] fcl-net and fpasync

[Xiangrong Fang]

Hi All,

I try to write a tcp client program, and found this page:

http://pascalgeek.blogspot.com/2012/06/encryption-decryption-and-asynchronous.html

which is the only resource I found using fcl-net.

But there is a big problem: it did not tell how to receive message back
from the server.

I tried to write something like:

EventLoop.Run;
while true do begin
  Stream.WriteAnsiString('Hello');
  WriteLn('Server Reply: ' + Stream.ReadAnsiString);
  Sleep(1000);
end;
//Active := false;
And at the server side,

  Msg := FClientStream.ReadAnsiString;
  WriteLn(AddrToString(FClientStream.PeerAddress) + ': ' + Msg);
  FClientStream.WriteAnsiString('World!');   //added by me

It simply generated a runtime error: EReadError : Stream read error

As a matter of fact, I also tried to create a thread like this:

procedure TMyTCPClient.ConnStateChanged(Sender: TClientConnectionSocket;
  OldState, NewState: TConnectionState);
begin
  if NewState = connConnected then begin
WriteLn('Connected!');
TMsgReceiver.Create(Stream);
  end;
end;

constructor TMyTCPClient.TMsgReceiver.Create(AStream: TSocketStream);
begin
  inherited Create(False);
  FStream := AStream;
  FreeOnTerminate := True;
end;

procedure TMyTCPClient.TMsgReceiver.Execute;
var
  s: string;
begin
  while True do begin
WriteLn('Now try to receive something...');
s := FStream.ReadAnsiString;
WriteLn('Received: ', s);
  end;
end;

But it did not receive anything!

How can I enable **bi-directional**, asynchronous (event driven)
communication using fcl-net, also, is there any document on fpasync??

Thanks a lot!

xrfang
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[fpc-pascal] SQLDB: how to use TSQLTransaction

[Xiangrong Fang]

Hi All,

Sorry that I don't know if SQLDB belongs to fpc or lazarus, so I posted to
both lists.

I am confused about the use of transaction in SQLDB. I tried to use in in
my non-gui app. Here is the code:

function TPortfolio.ConfirmTransaction(id: Integer): Boolean;
begin
  with qr do begin
SQL.Text := Format('UPDATE records SET status=%d WHERE id=%d AND
status=%d',
  [TR_SUCCESS, id, TR_PENDING]);
ExecSQL;
WriteLn('Confirming: ', id, ', affected: ', RowsAffected);
//tr.Commit;
//WriteLn('Confirming: ', id, ', affected: ', RowsAffected);
Result := RowsAffected  0;
  end;
end;
It seems that I must assign a TSQLTransaction object to the TSQLQuery
object, otherwise it doesn't work. I also found that without call
tr.Commit, the ExecSQL will not take effect, at least for INSERT
statements.

In the above function, I found the first WriteLn will output rows-affected
as 1, and the 2nd (after tr.Commit) will output rows-affected as -1!  I
then commented out the tr.Commit; statement, it STILL worked.

Now my questions are:

1. How to control the use of transactions in SQLDB? Sometime I do NOT want
transaction, but want the DDL/DML statement to be executed immediately.
Why sometime SQLDB's ExecSQL won't take effect if not followed by a Commit?
BTW, I tried to set tr.Active to true/false before execute the sql, but it
seems not making a difference?

2. What is the meaning of -1 as returned by RowsAffected?

Thanks!

Xiangrong
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[fpc-pascal] load a library twice

[Xiangrong Fang]

Hi All,

Is the following correct:

var
  h1, h2: TLibHandle;
  lib1, lib2: string;
begin
  lib1 := 'library.so';
  lib2 := 'library.so';
  h1 := LoadLibrary(lib1);
  h2 := LoadLibrary(lib2);
end.

The reason I need this is that I would like to keep the possibility to
provide different group of functions in the same or two different
libraries. For example, lib1 provides function A, lib2 provide function B,
or, lib3 provide both function A and B.

If I open the same library via 2 different handles, are they actually
pointing to the same memory address internally, so that if I UnloadLibrary,
it will cause something like access violation in the second call?

Thanks!

Xiangrong
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Re: [fpc-pascal] how to use signals in freepascal?

[Xiangrong Fang]

2015-03-17 17:06 GMT+08:00 Michael Schnell mschn...@lumino.de:

 IPC between applications or within an application ?

 ​between application.
​


 If between application are both don in fpc and under your control ?


​actually, multiple instance of the same application.
​



 Lazarus or pure fpc ?

 ​pure fpc.​
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Re: [fpc-pascal] how to use signals in freepascal?

[Xiangrong Fang]

2015-03-17 16:28 GMT+08:00 Michael Schnell mschn...@lumino.de:

 As there are similar concepts implemented in fpc and Lazarus in a
 cross-platform manner, could you give the reason why you want too use
 platform-specific (low level) concepts like Unix-Signals (or Windows
 messages) ? (I don't doubt there are in some special projects.)

 Actually, I do *not* insist on using unix signals in a cross-platform way.
I just need a simple IPC mechanism, without the hassle of e.g. a socket
server.​
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Re: [fpc-pascal] how to use signals in freepascal?

[Xiangrong Fang]

 You should not use this in fact, it is meant for internal use.

 To write a signal handler on unix, see

 http://www.freepascal.org/docs-html/rtl/baseunix/fpsigaction.html

 there is an example.


​I tried example57, it worked, but I still do not know some peculiar
behaviors in it​. I will ask later, after some investigations.

However, what is HookSignal for? How to use it? Or it is just a stub and
not functional yet?

Thanks!
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[fpc-pascal] how to use signals in freepascal?

[Xiangrong Fang]

Hi All,

I have some questions regarding event and signals:

1) RTLEventWaitFor

can a program waiting for an RTLEvent be notified by an RTLEventSet from
ANOTHER process?

2) Unix Signals

I see HookSignal() in the sysutils documentation, but there is nothing said
on how to use it. Is it used to write my own signal handler on Linux?
Could anyone give a sample program?

Also, is there a list of defined RtlSigNums?

3) Unix-style Signals on Windows

If possible, I would like to have cross platform signal handling in my app.
I found this:

https://github.com/graemeg/freepascal/blob/master/rtl/win32/signals.pp

Does it mean that if I uses signals, I will have same capability on both
linux and windows?

Thanks!

Xiangrong
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[fpc-pascal] how to use procedure of object in C

[Xiangrong Fang]

Hi all,

I define a procedure like this:

type
  TDataHandler = procedure(data: Pointer) of object;

procedure SetHandler(h: TDataHandler); external cdecl;

Now, can I implement SetHandler in a library written in C, then call h in C?

Thankyou.



-- 
Sent from Gmail Mobile
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Re: [fpc-pascal] how to use procedure of object in C

[Xiangrong Fang]

2015-03-10 0:33 GMT+08:00 OBones obo...@free.fr:


 How about using TMethod?

 procedure DataHandler(DummySelf: Pointer; data: Pointer);
 begin
   // do what you want to do, DummySelf is always nil.
 end;

 var
   Method: TMethod;
 begin
   Method.Data := nil;
   Method.Code := @DataHandler;

   SetHandler(TDataHandler(Method));
 end;


​I'm not sure how this works, but it seems that you are deliberately
converting a normal procedure to a method. What I want is exactly opposite
- I want to convert a method to a normal procedure.

If I define the interfact of DataHandler like this:

​TDataHandler = procedure(data: Pointer); cdecl;

It is very easy to use in an so, no matter it is written in C or pascal.

But the problem is, I want to do this:

SetHandler(h);

where h is a METHOD, not a normal procedure​.

Because I want to use the handler wrapped in my Class.

However, like in my first mail, if I define THandler a procedure of object,
it makes easier to SetHandler(AMethod); but how can I use that procedure
of object pointer in the so?

Thanks!


​
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Re: [fpc-pascal] Use sleep in thread

[Xiangrong Fang]

2015-02-26 21:53 GMT+08:00 Marco van de Voort mar...@stack.nl:


 No, basically a sleeping thread is marked in the scheduler as do not
 schedule for nn
 ticks. The thread doesn't run to evaluate if it should contiue. That is
 the
 scheduler/kernel's task.

 ​That's even better. And the key point is, after nn ticks, it is
**AUTOMATICALLY** re-scheduled,
without the need of knowledge of other threads/processes running on the
system!

​This is the effect of a thread voluntarily gives up its cpu share, but not
let other thread to control its fate. ​
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Re: [fpc-pascal] Use sleep in thread

[Xiangrong Fang]

2015-02-26 18:50 GMT+08:00 Henry Vermaak henry.verm...@gmail.com:

 
  Sleep is for granting the CPU for other processes for (at least) a
  predefined time.
 
  See the mail of the original poster: this is what he asked for.


​Thats ri​ght.


 This is incorrect, since if you pause a thread with sleep(), you'll have
 to loop to check when you're supposed to wake up.


​I use rtlevent, but only meant to maintain a pool of threads, while there
is no task for a thread it is blocked waiting for an event.

BUT, that cannot be used to prioritize a thread. While you block a thread
using rtlevent, it can only be unblocked from another thread. While you use
sleep(), it still get time share of the CPU, only that it does nothing
until sleep finishes, right?  That way, it only consume a tiny amount of
computing power while sleeping. This, in my view, is the price I have to
pay to achieve my purpose?
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[fpc-pascal] Use sleep in thread

[Xiangrong Fang]

Hi All,

Can I use Sleep() in a thread to give up cpu time to other threads running
at the same time, so as to adjust the relative niceness of a group of
workers working on the same subject (in which each thread take part of the
whole task).

Thanks!

Xiangrong
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Re: [fpc-pascal] Use sleep in thread

[Xiangrong Fang]

2015-02-25 22:47 GMT+08:00 Dmitry Boyarintsev skalogryz.li...@gmail.com:

 I presume most of the systems would make the sleeping thread to yield the
 execution time for other threads.
 The questionable behavior might occur in case of  sleep(0); (should it
 yield the remaining time or just return immediately - up to the OS).
 And multi-cpu might also do something different.

 ​Yes, I am particularly interested in behavior of SMP system. i.e. my
purpose of using threads is to take full advantages of all CPU cores.

As far as I know, setting thread priority does not always work, it may
require root privilege for example.  I would like to use Sleep() to control
relative time share of all threads in the pool.  For example, I run 3
threads on a dual-core system, with thread 1 and 2 share core-1, and thread
3 taking all computing power of core-2...

Now the problem is, can I use Sleep to control thread 1 to run at 50% of
the speed of thread 2 (which is not throttled), providing that all threads
are doing same kind of task, so that they are comparable?

Xiangrong​
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Re: [fpc-pascal] Use sleep in thread

[Xiangrong Fang]

2015-02-25 23:16 GMT+08:00 hinsta...@yandex.ru:

 not sure if this helps, but:
 for example, if you want thread T to run using approx. 70% of max.
 available capacity, try this:

 repeat
   T.Resume;
   Sleep(70);
   T.Resume;
   Sleep(30);
 until ...


​This seems not what I want. I would like to schedule it from within the
thread.  My demo program is here:

https://github.com/xrfang/fpcollection/blob/master/src/demos/asyncdo/demo.lpr

TAsyncDo is the class I wrote to have a procedure run in parallel.

I want to control priority of the thread from within the worker, not from
the main thread. ​
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Re: [fpc-pascal] compare currency and double

[Xiangrong Fang]

Thank you!  I have changed all occurrences of Currency to Double in my
program.

2014-12-08 21:25 GMT+08:00 Jonas Maebe jonas.ma...@elis.ugent.be:


 On 07 Dec 2014, at 16:07, Jonas Maebe wrote:

  That's because currency has a bigger range than double.


 Or rather: a double cannot exactly represent every possible currency value.


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[fpc-pascal] compare currency and double

[Xiangrong Fang]

Hi All,

I have the following code:

var
  val: Currency;
  res: Double;
begin
  val := 2345.67;
  res := 1e300;
  if val = res then WriteLn('val =res')
  else WriteLn('val  res');
end;

The program compile and runs correctly on Linux x64, and Win7 32bit, but
failed (SIGFPE) on Win7 64bit.

Can I safely compare a Currency against a Double?

Thanks!

Xiangrong
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[fpc-pascal] Problem with heaptrc

[Xiangrong Fang]

Hi All,

I use heap trace utility to see if there are memory leak in my program.
The source is here:

https://github.com/xrfang/fpcollection/blob/aefa04f0374c94298facd8d57d4a25dafe10b753/src/demos/cache/demo.lpr

My problem is, at the beginning of the main program, I have a costant
definition:

const
  ITEM_COUNT = 500;
If I set ITEM_COUNT to a small value, say 50 or 5000, everything is OK, no
memory leak. But with the above value, it will cause HEAPTRC to fall in an
endless loop, generating messages like:

Call trace for block $7F41693AA680 size 40
  $0040071F line 29 of demo.lpr
  $00400180

While line 29 is this:

27  for i := 0 to ITEM_COUNT - 1 do begin
28for j := 0 to 4 do key[j] := $deadbeef + i + j;
29h.Add(@key, SizeOf(PtrUInt) * 5, Pointer($deadbeef + i));
30  end;
Could anyone tell me why heaptrc will fall in an endless loop, and does my
program have memory leak?

Thanks!

Xiangrong
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Re: [fpc-pascal] Problem with heaptrc

[Xiangrong Fang]

2014-11-09 22:05 GMT+08:00 Tomas Hajny xhaj...@hajny.biz:

 On 9 Nov 14, at 21:58, Xiangrong Fang wrote:

 Are you sure that it really is endless (i.e. did you let to run for a
 sufficiently long time)? If you increase the amount of allocated
 blocks (which is what happens in case of increasing your constant),
 traversing through all the blocks (especially if they are not freed
 at the end) may indeed take fairly long time...


​You are right Tomas, it finished, generated a 300M+(!) trace file, looks
like this:
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Re: [fpc-pascal] Problem with heaptrc

[Xiangrong Fang]

2014-11-09 22:14 GMT+08:00 Xiangrong Fang xrf...@gmail.com:

 2014-11-09 22:05 GMT+08:00 Tomas Hajny xhaj...@hajny.biz:

 On 9 Nov 14, at 21:58, Xiangrong Fang wrote:

 Are you sure that it really is endless (i.e. did you let to run for a
 sufficiently long time)? If you increase the amount of allocated
 blocks (which is what happens in case of increasing your constant),
 traversing through all the blocks (especially if they are not freed
 at the end) may indeed take fairly long time...


 ​You are right Tomas, it finished, generated a 300M+(!) trace file, looks
 like this:

 ​Heap dump by heaptrc unit
8137678 memory blocks allocated : 258591549/258591552
5226767 memory blocks freed : 142155109/142155112
2910911 unfreed memory blocks : 116436440
True heap size : 951812096
True free heap : 392917184
Should be : 462779048
Call trace for block $7F57C456D680 size 40
  $0040071F line 29 of demo.lpr
  $00400180

The last 3 likes repeated until the end of 300M log data!

Why when ITEM_COUNT is small, there is no memory leak, but when it is
large, there are so many leaks?

Xiangrong​
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Re: [fpc-pascal] Problem with heaptrc

[Xiangrong Fang]

2014-11-09 22:38 GMT+08:00 Michael Van Canneyt mich...@freepascal.org:


 Code like this:

ci := PCacheItem((buf + SizeOf(Pointer) * Random(FDepth))^);
 for i := 0 to FDepth - 1 do begin
   slot := buf + SizeOf(Pointer) * i;
   if Pointer(slot^) = nil then begin
 Inc(N);
 Pointer(slot^) := GetMem(SizeOf(TCacheItem));
 ci := PCacheItem(slot^);

 makes me frown, because the first assignment to ci is useless, so highly
 suspect.


​You are right Michael.  I just found that if there is no free slot, I use
Random Replacement to dump one of the existing cached item, whose key is
not freed, which caused memory leak.

Thanks!

Xiangrong.​
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Re: [fpc-pascal] Effective memory allocation

[Xiangrong Fang]

2014-11-03 23:40 GMT+08:00 Adriaan van Os f...@microbizz.nl:

 Xiangrong Fang wrote:

 Hi All,

 I am programming a Bloom Filter and need a high-performance way to


 On what platform are you doing this ?


​I am programming on Linux, but it will be used on both Windows and Linux,
Windows is the primary target.​
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Re: [fpc-pascal] Effective memory allocation

[Xiangrong Fang]

2014-11-04 6:35 GMT+08:00 Nico Erfurth n...@erfurth.eu:


 Well, the first thing you should ask yourself is Do I REALLY need such
 a large bloom filter. Everything larger than the last level cache will
 seriously harm your performance as you are going to trigger a lot of
 cache and TLB misses. In general you should target for typical L1-Cache
 sizes (16-32KByte) or if REALLY necessary L2-Cache-sizes
 (256KByte-32MByte). Everything above that will make the performance go
 down rapidly, especially in hashing-application the CPU can't prefetch
 data properly as the access-patterns are erratic.


​I didn't think of things like cache and TLB misses. Because I try to use
BloomFilter and HASH to avoid repeated calculation ​and/or lookups which
are time consuming. So, I don't think it will harm performance, unless
bloom filter lookup is slower than the calculation, am I right?

Thanks!
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[fpc-pascal] Effective memory allocation

[Xiangrong Fang]

Hi All,

I am programming a Bloom Filter and need a high-performance way to allocate
and wipe large block of memory.  I did the following test:

program getmem;
{$mode objfpc}{$H+}
uses epiktimer;
const
  SIZE = 1024 * 1024 * 1024;
  CNT = 10;
var
  a: array of Byte;
  p: Pointer;
  et: TEpikTimer;
  i: Integer;
  t1, t2: TimerData;
begin
  et := TEpikTimer.Create(nil);
  et.Clear(t1); et.Clear(t2);
  for i := 1 to CNT do begin
et.Start(t1);
p := GetMemory(SIZE);
//SetLength(a, SIZE);
et.Stop(t1);
et.Start(t2);
FillQWord(p^, SIZE div 8, 0);
//FillQWord(a[0], SIZE div 8, 0);
et.Stop(t2);
FreeMem(p);
//a := nil;
  end;
  WriteLn('Alloc: ', et.Elapsed(t1) / CNT);
  WriteLn('Clear: ', et.Elapsed(t2) / CNT);
end.

The result is:

Using GetMemory:

Alloc:  9.40781697E-0001
Clear:  2.13420202E-0001

Using SetLength:

Alloc:  2.8100E-0005
Clear:  7.74975504E-0001

It is understandable that GetMemory() is faster than SetLength(), but why
the difference in FillQWord()?

Also, I usually use pointer to pass block of memory to functions.  How do I
implement a function with the following signature:

procedure MyProc(var Buf; Len: Integer):

I mean, how to handle var Buf inside the procedure body?

Thanks!

Xiangrong
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Re: [fpc-pascal] Effective memory allocation

[Xiangrong Fang]

Sorry, the results in previous mail was mis-labeled.

​
The result is:

Using SetLength:

Alloc:  9.40781697E-0001
Clear:  2.13420202E-0001

Using GetMemory:

Alloc:  2.8100E-0005
Clear:  7.74975504E-0001
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Re: [fpc-pascal] Effective memory allocation

[Xiangrong Fang]

2014-11-03 2:50 GMT+08:00 Sven Barth pascaldra...@googlemail.com:

 If you use SetLength the dynamic array consists not only of the array
 data, but also of an information record in front of it. This will likely
 lead to the data not being aligned correctly (FillQWord works best with
 8-Byte alignment). So what about testing FillDWord or FillChar? Just to see
 whether they would be faster.

 ​It is quite strange that if I use SetLength+FillByte, it is really faster
(for the FillByte), but if I use GetMemory+FillByte, it is not faster than
using FillDWord or FillQWord.

I found this in FPC doc (for $ALIGN switch):

This switch is recognized for Turbo Pascal Compatibility, but is not yet
implemented. The alignment of data will be different in any case, since
Free Pascalis a 32-bit compiler.

​It is a pity that this switch is not recognized yet. But I need to
understand the last statement, will alignment be different or not?

Thanks!

Xiangrong​
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Re: [fpc-pascal] Effective memory allocation

[Xiangrong Fang]

2014-11-03 14:39 GMT+08:00 Sven Barth pascaldra...@googlemail.com:


 Would you mind to show the timings that you got for FillChar? :)


​Using FillChar is always about 5% (or less) faster than FillQWord when
used with GetMemory, but will be around 20%-40% faster if the memory is
allocated by SetLength.

Additionally this switch won't help you. The memory buffer that is
 allocated by SetLength is also allocated using GetMemory. So the buffer
 itself *is* aligned. But you don't get the start byte of the buffer in case
 of SetLength, but the first byte after the information record which might
 not be aligned correctly and *no* compiler switch will help you with that.


​Then the problem remains with SetLength vs. GetMemory... Why SetLength is
about 1x (!) slower than GetMemory?​


​allocating 1G memory took about 0.1 second by SetLength​, but is about
1E-5 via GetMemory.
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Re: [fpc-pascal] Is TFPList thread safe?

[Xiangrong Fang]

2014-10-02 14:16 GMT+08:00 Michael Van Canneyt mich...@freepascal.org:


 TFPList is not thread-safe. You need to use TThreadList if you want a
 thread-safe list.

 Critical sections use OS calls, so there is always a performance penalty.


I think the only thread-critical operation I need is to add item to the
list, so I will use critical section myself, not replace TFPList with
TThreadList, for simplicity and performance reason...

Xiangrong
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Re: [fpc-pascal] Is TFPList thread safe?

[Xiangrong Fang]

2014-10-02 22:09 GMT+08:00 Michael Schnell mschn...@lumino.de:


 AFAIR, in Linux, the fpc RTL calls the pthread library mutex...
 function. This library uses Futex, if the arch supports that, and uses the
 plain old MUTEX system call if the arch does not support FUTEX.


I need my program to work on both Linux and Windows, can I still use
FUTEX?  For Critical Sections, FPC has the TCriticalSection object, is
there a TMutex object?

Xiangrong
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Re: [fpc-pascal] Is TFPList thread safe?

[Xiangrong Fang]

2014-10-02 22:23 GMT+08:00 Xiangrong Fang xrf...@gmail.com:


 2014-10-02 22:09 GMT+08:00 Michael Schnell mschn...@lumino.de:


 AFAIR, in Linux, the fpc RTL calls the pthread library mutex...
 function. This library uses Futex, if the arch supports that, and uses the
 plain old MUTEX system call if the arch does not support FUTEX.


I found some quotes online:

For Windows, critical sections are lighter-weight than mutexes.
 Mutexes can be shared between processes, but always result in a system
 call to the kernel which has some overhead. Critical sections can only be
 used within one process, but have the advantage that they only switch to
 kernel mode in the case of contention.


I only need lock WITHIN my own application, so, it seems that critical
sections are better.

Xiangrong
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Re: [fpc-pascal] Is TFPList thread safe?

[Xiangrong Fang]

2014-10-02 23:07 GMT+08:00 Jonas Maebe jonas.ma...@elis.ugent.be:


 On 02 Oct 2014, at 15:59, Xiangrong Fang wrote:

 It will make your program unstable (adding an element to an fplist can
 cause the entire internal array to move, so if you are in the middle of a
 read operation at the same time, that read operation will either read
 invalid data or crash). Unless you are an expert at multithreaded
 programming, don't try to optimise existing thread-safe structures (and
 definitely don't perform premature optimisations).

 I don't intend to do any optimization. I just think that I need to enter a
critical section, add item to the list, then leave the critical section.

I am definitely not expert in thread programming, but I am clear about the
logic of my class and program.   Actually, it is a TTree object I wrote,
using TFPList to store sibling nodes. There are a lot of TFPList (one per
tree node).   I just need to make sure that there are no more than one
thread operating on the same node at the same time.

Xiangrong
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[fpc-pascal] Is TFPList thread safe?

[Xiangrong Fang]

Hi,

I would like to know if TFPList is thread-safe or not? And if I make a
component thread-safe by using critical sections etc. Is the performance
penalty noticeable?

Thanks.

Xiangrong
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[fpc-pascal] key-value engine for FPC

[Xiangrong Fang]

Hi All,

Is there any good performance Key-Value storage engine written in free
pascal, or can be linked with FPC application?

I need an embedded storage engine with good performance for a generic
(non-binary) tree structure with the following properties and operations:

- tree node has 2 properties: data (byte array), and 0~N sub-nodes
- a fast way to iterate through all leaf nodes
- find parent, and parent of parent, until root
- get / iterate all siblings of a node (order is NOT important)
- insert node / set parent of a node
- cut-off or free (delete) a sub-tree

Thanks!

Xiangrong
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[fpc-pascal] PostMessage vs. QueueAsyncCall

[Xiangrong Fang]

Hi,

In a previous email asking about PostMessage, Michael suggested I used
QueueAsyncCall instead, because although it's OK to use PostMessage, but it
is considered a Windows Legacy, or only for Delphi compatibility.

However, in actual use, I feel that PostMessage does a better job for code
separation. Because when use PostMessage, GUI (or main thread) related code
are written in the main form, and the thread will not need to use the Forms
unit.

My question is, why cannot Lazarus just use PostMessage, but invent the
QueueAsyncCall() method?  What is the rationale, or, why PostMessage is
considered windows-ish (read: not fit into LCL very well?), apart from the
fact that it is a Windows API?

Thanks,
Xiangrong
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Re: [fpc-pascal] Random thread lockup. QueueAsyncCall??

[Xiangrong Fang]

2014-09-18 23:10 GMT+08:00 Xiangrong Fang xrf...@gmail.com:


 I suspect that it is blocked on the RTLeventWaitFor, because if I use this:

 RTLeventWaitFor(Barrier, 1000);

 It will periodically pause for 1 second, then continue.


I found the problem myself. Instead of writing:

while not Terminated do begin
  RTLeventWaitFor(Barrier);
  if not IsPrime then Number := 0;
  Application.QueueAsyncCall(@AddPrime, PtrInt(Self));
  RTLeventResetEvent(Barrier);
end;

I should write:

while not Terminated do begin
  RTLeventWaitFor(Barrier);
  RTLeventResetEvent(Barrier);
  if not IsPrime then Number := 0;
  Application.QueueAsyncCall(@AddPrime, PtrInt(Self));
end;

Because when doing the AsyncCall, the main thread may have called
RTLeventSetEvent BEFORE the RTLeventResetEvent() is called.

Xiangrong
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[fpc-pascal] EpikTimer: maximum elapsed seconds

[Xiangrong Fang]

Hi there,

I would like to know the maximum number of seconds EpikTimer can count.  I
put a program running for over 24 hours, but epiktimer told me only about
less than 2000 seconds passed, when I click the finish button.

Thanks.

Xiangrong
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[fpc-pascal] Optimal number of threads for SMP

[Xiangrong Fang]

Hi All,

If my application needs SPEED, i.e. take full advantage of CPU
capabilities, and the application has no I/O operation at all (neither disk
nor network), it seems no need to create threads more than the number of
CPU cores （hyper-threads)?

Am I right?

Xiangrong
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[fpc-pascal] detect CPU cores

[Xiangrong Fang]

Hi All,

Is there a platform independent (specifically Windows and Linux) way to
detect cores and hyper-threads of the CPU? I am writing a calculation
intensive app and would like to fully utilize SMP capability of the CPU.

Thanks!
Xiangrong
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Re: [fpc-pascal] detect CPU cores

[Xiangrong Fang]

I found this code on the net:

http://code.google.com/p/fpos/source/browse/kernel/cpuid.pas?r=c387b381d7a05f9328693cdcf59b0b4f633294e4

It's part of the FreePascal Operationg System project. I suppose it is
compatible with FreePascal of course. But while compiled, I got lots of
errors, such as:

cpuid.pas(28,3) Error: Unrecognized opcode pushfd
cpuid.pas(29,10) Error: Unknown identifier EAX
cpuid.pas(30,13) Error: Unknown identifier EDX

Even I added {$mode objfpc}{$H+} does not help.

I tried to compile this code on this platform:

CPU: i3 M 390
OS: Ubuntu x64
FPC: 2.6.4

How to use assembly in fpc anyway?

Thanks.

2014-09-12 22:28 GMT+08:00 Dmitry Boyarintsev skalogryz.li...@gmail.com:

 If you're talking bout x88_64, i386 platforms, you should be able to do it
 using CPUID instruction

 http://en.wikipedia.org/wiki/CPUID

 thanks,
 Dmitry

 On Fri, Sep 12, 2014 at 10:07 AM, Xiangrong Fang xrf...@gmail.com wrote:

 Hi All,

 Is there a platform independent (specifically Windows and Linux) way to
 detect cores and hyper-threads of the CPU? I am writing a calculation
 intensive app and would like to fully utilize SMP capability of the CPU.

 Thanks!
 Xiangrong


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Re: [fpc-pascal] detect CPU cores

[Xiangrong Fang]

2014-09-13 0:28 GMT+08:00 Dmitry Boyarintsev skalogryz.li...@gmail.com:

 You're compiling for x64, You need to replace eax and edx with rax
 and rdx, since e?x are available for i386 only.


My situation is, I program and test on Ubuntu x64 on a i3-M390. Then
compile it to Windows 32bit on a VirtualBox on this machine, then run it on
a Windows 32bit running on a rather old pentium dual core (T-something, I
don't know if it is 32bit or 64bit processor).

regarding e?x vs. r?x, is it only related to the CPU, or also has something
to do with the OS (32bit or 64bit)?  How to do conditional compiling for
assembly code?
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[fpc-pascal] cthread and cmem

[Xiangrong Fang]

Hi All,

which one should be the *first* unit to use? cthread or cmem?

Thanks!

Xiangrong
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[fpc-pascal] Handling virtual abstract method in case of generics

[Xiangrong Fang]

Hi all,

I am having trouble with the following code:

  generic TVectorT = class
  type
DataType = array of T;
  private
//...
  protected
//...
  public
//...
  end;

  generic TSortableVectorT = class(specialize TVectorT)
  protected
function OnSort(v1, v2: T): Integer; virtual; abstract;
//...
  public
procedure Sort(Reversed: Boolean = False; OldOrder: PIntegerDynArray =
nil);
//...
  end;

  TIntegerVector = class(specialize TSortableVectorInteger)
  protected
function OnSort(v1, v2: Integer): Integer; override;
  end;

The error I got is:

Error: Forward declaration not solved
TIntegerVector.TSortableVector$LongInt.OnSort(LongInt,LongInt):LongInt;

The original code of vector is here:

https://github.com/xrfang/fpcollection/blob/master/src/units/vector.pas

I am having trouble with the original code while specializing TVector with
a Record type that does not have comparison operators.  So I decide to make
OnSort() abstract, and add it whenever needed.

I am running FPC 2.6.4 on Linux x64.

Thanks!

Xiangrong
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[fpc-pascal] Operator overloading and generic class

[Xiangrong Fang]

Hi All,

While I try to compile this code:

program demo;
{$mode objfpc}{$H+}
uses tree;
type
  TIntTree = class(specialize TTreeInteger)
  end;
  TITTree = class(specialize TTreeTIntTree)
  end;

operator (it1, it2: TIntTree): Boolean;
begin
  Result := it1.Data  it2.Data;
end;

var
  itt: TITTree;
begin
end.

I got the following error:

tree.pas(324,11) Error: Operator is not overloaded: TIntTree  TIntTree

The complete code for tree.pas is here:

https://github.com/xrfang/fpcollection/blob/master/src/units/tree.pas


Even I defined the needed operator like above, it still refuse to compile.

How to solve this?

Thanks in advance!

Xiangrong
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Re: [fpc-pascal] Operator overloading and generic class

[Xiangrong Fang]

Sorry, I asked similar question long time ago, I found it in my gmail.

Please ignore this question. However, I hope FPC will add this feature in
future release anyway.



2014-08-26 16:17 GMT+08:00 Xiangrong Fang xrf...@gmail.com:

 Hi All,

 While I try to compile this code:

 program demo;
 {$mode objfpc}{$H+}
 uses tree;
 type
   TIntTree = class(specialize TTreeInteger)
   end;
   TITTree = class(specialize TTreeTIntTree)
   end;

 operator (it1, it2: TIntTree): Boolean;
 begin
   Result := it1.Data  it2.Data;
 end;

 var
   itt: TITTree;
 begin
 end.

 I got the following error:

 tree.pas(324,11) Error: Operator is not overloaded: TIntTree  TIntTree

 The complete code for tree.pas is here:

 https://github.com/xrfang/fpcollection/blob/master/src/units/tree.pas


 Even I defined the needed operator like above, it still refuse to compile.

 How to solve this?

 Thanks in advance!

 Xiangrong




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[fpc-pascal] warning about hiding method in ancestor class

[Xiangrong Fang]

Hello All,

I have a unit here:

https://github.com/xrfang/pastats/blob/master/src/units/datalist.pas

which report this error:

/home/xrfang/git/pastats/src/units/datalist.pas(61,17) Warning: An
inherited method is hidden by constructor TDataFrame.Create;

However, the following code, which also define a new constructor without
using overload, does NOT have such warning.

program Project1;
{$mode objfpc}{$H+}
type
  TBase = class
  public
constructor Create(AName: string);
  end;
  TDerived = class(TBase)
  public
constructor Create;
  end;

constructor TDerived.Create;
begin
  WriteLn('Creator of TDerived... anonymous');
end;

constructor TBase.Create(AName: string);
begin
  WriteLn('Creator of TBase: ', AName);
end;

var
  obj: TDerived;
begin
  obj := TDerived.Create;
end.

If I use reintroduce, I can suppress this warning. But my question is, why
is this warning NOT displayed in the above sample code? In general, shall I
use reintroduce keyword? Is it related to generics?

Thanks!

Xiangrong
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[fpc-pascal] why constructor of TObject is NOT virtual but destructor is?

[Xiangrong Fang]

Hi All,

I would like to know the benefit of making constructor / destructor
virtual.  As described here:

http://c2.com/cgi/wiki?VirtualConstructor

The benefit of virtual constructor seems related to class reference. As
far as I understand, it is related to how LCL works, like:

CreateComponent(AComponent: TComponentClass);

My questions are:

1) if the above understanding is correct AND COMPLETE, why the constructor
of TObject is not virtual? What problem will appear IF we make it virtual?

2) What is the purpose of making destructor of TObject virtual?

Thanks!

Xiangrong
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[fpc-pascal] override or virtual override

[Xiangrong Fang]

Hi All,

Is the property of virtual inherited? i.e. if a method in parent class is
virtual, same method in child class is also virtual, right?

TBase = class
public
  destructor Destroy; override; //-- is this enough
  destructor Destroy; virtual; override; //or this to ensure it is still
virtual?
end;

Thanks,

Xiangrong
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Re: [fpc-pascal] Double specialization of generic class

[Xiangrong Fang]

Hi Sven,

I am using fpc 2.6.2.  I am very sorry that I don't have time to compile
and install 2.7.1 at this time.

It's good to know that it works, at least in 2.7.1.   I will report the
problem again while I start using 2.7.1 or when it is released as 2.8 :-)

For now, another suggestion regarding this error is the error message it
gave out, which is not understandable (error -139), I only find out the
cause of this by comparing my source code in git.

I hope this is also improved in 2.7 or later.

Thanks!
Shannon


2014-04-15 13:34 GMT+08:00 Sven Barth pascaldra...@googlemail.com:

 On 15.04.2014 03:51, Xiangrong Fang wrote:

 Hi,

 I got strange ppcx64 error: -139, which I found is caused by this:

 type
TNodeStack = specialize TVectorTNodeHash;

 where TNodeHash itself is a specialization:

 type
PNode = ^TNode; //TNode is a plain record
TNodeHash = specialize TTreapInteger, PNode;

 Is it true that specialization of a generic class using another
 specialized generic class is not allowed?


 No, that should work. Maybe some bug. Is there any error message? Could
 you present the full compiler output, please? You are using 2.7.1, right?

 Regards,
 Sven

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Re: [fpc-pascal] Double specialization of generic class

[Xiangrong Fang]

2014-04-15 17:21 GMT+08:00 Sven Barth pascaldra...@googlemail.com:

 Am 15.04.2014 08:47 schrieb Xiangrong Fang xrf...@gmail.com:
   It's good to know that it works, at least in 2.7.1.   I will report the
 problem again while I start using 2.7.1 or when it is released as 2.8 :-)

 That's the point: I don't know wether it compiles in 2.7.1 as I did not
 test it. If you could provide a minimal sample (which fails in 2.6.2) and
 report that as a bug I could ensure that 2.7.1 works correctly there.


​I cannot replicate the problem using a minimal program, because it gives
out different error message.  The following minimal program compiles OK:

program vectr;
type
  generic TGeneric1T = class

  end;
  generic TGeneric2T = class

  end;
  TSpec1 = specialize TGeneric1Integer;
  TSpec2 = specialize TGeneric2TSpec1;
begin
end.

While the following program generate different error:

program vectr;
uses
  treap, vector;
type
  TNodeHash = specialize TTreapInteger, string;
  TNodeVector = class(specialize TVectorTNodeHash)
  protected
function OnSort(v1, v2: T): Integer; override;
  end;

operator (nh1, nh2: TNodeHash): Boolean;
begin
  Result := nh1.Count  nh2.Count;
end;
operator (nh1, nh2: TNodeHash): Boolean;
begin
  Result := nh1.Count  nh2.Count;
end;

function TNodeVector.OnSort(v1, v2: T): Integer;
begin
  Result := 0;
end;

begin
end.​

gives error message:

vector.pas(149,9) Error: Operator is not overloaded:
TTreap$LongInt$AnsiString  TTreap$LongInt$AnsiString
vector.pas(151,14) Error: Operator is not overloaded:
TTreap$LongInt$AnsiString  TTreap$LongInt$AnsiString
vectr.lpr(28) Fatal: There were 2 errors compiling module, stopping

The two used units can be downloaded here:

https://github.com/xrfang/fpcollection/

While in my real program, I have this:

type
  TCmhWaves = specialize TVectorTCmhWave;

The thing is, even if I do NOT use this definition at all, it still crashes
the compiler.  By crash I mean I get this from lazarus:

Compiling wmodel.lError: /usr/bin/ppcx64 can't be executed, error message:
Failed to execute /usr/bin/ppcx64, error code: -139

TCmhWave is a specialized subclass of My TTreap class (also on github), it
does NOT overload the  and  operators either.

So my question is:

1) why my simplified example still require overloaded operator, although I
have already done so?

2) If this is the cause of error (TCmhWave does not have these operators
defined), why the compiler returns error code: -139 instead of more
detailed errors?

BTW, on my first attempt to debug this problem in lazbuild (command line) I
get some error related to VMA, but unfortunately I forgot what it is and
cannot get it shown again. Is there any way to customize the lazbuild by
some switches to let it output more messages?

Thanks.
xrfang@OP380:~/Sync/wmodel$ lazbuild wmodel.lpi
primary config path: /home/xrfang/.lazarus
TPkgManager.CheckCompileNeedDueToDependencies  State file of LCL 1.2.0.3 is 
newer than state file of Package: cairocanvas_pkg 0.0
TLazPackageGraph.CheckIfPackageNeedsCompilation normal output dir is not 
writable: /usr/share/lazarus/1.2.0/components/cairocanvas/lib/x86_64-linux/gtk2/
TLazPackageGraph.GetFallbackOutputDir  cairocanvas_pkg: 
/home/xrfang/.lazarus/lib/cairocanvas_pkg/lib/x86_64-linux/gtk2
TParsedCompilerOptions.SetOutputDirectoryOverride 
New=/home/xrfang/.lazarus/lib/cairocanvas_pkg/lib/x86_64-linux/gtk2
TLazPackageGraph.CheckIfCurPkgOutDirNeedsCompile  Compiler params changed for 
Printer4Lazarus 0.5
  Old= -MObjFPC -Scgi -O1 -g -gl -vewnhi 
-Fi/usr/share/lazarus/1.2.0/components/printers/unix 
-Fi/usr/share/lazarus/1.2.0/components/printers/win32 
-Fi/usr/share/lazarus/1.2.0/components/printers/carbon 
-Fi/usr/share/lazarus/1.2.0/components/printers/qt 
-Fu/usr/share/lazarus/1.2.0/components/printers/unix 
-Fu/usr/share/lazarus/1.2.0/components/printers/win32 
-Fu/usr/share/lazarus/1.2.0/components/printers/carbon 
-Fu/usr/share/lazarus/1.2.0/components/printers/qt 
-Fu/usr/share/lazarus/1.2.0/packager/units/x86_64-linux 
-Fu/usr/share/lazarus/1.2.0/components/lazutils/lib/x86_64-linux 
-Fu/usr/share/lazarus/1.2.0/lcl/units/x86_64-linux 
-Fu/usr/share/lazarus/1.2.0/lcl/units/x86_64-linux/gtk2 
-Fu/usr/share/lazarus/1.2.0/components/cairocanvas/lib/x86_64-linux/gtk2 
-Fu/usr/share/lazarus/1.2.0/components/printers/ 
-FU/usr/share/lazarus/1.2.0/components/printers/lib/x86_64-linux/gtk2/ -l -dLCL 
-dLCLgtk2 -dUseCache -dNativePrint -dUSEUNICODE printer4lazarus.pas
  Now= -MObjFPC -Scgi -O1 -g -gl -vewnhi 
-Fi/usr/share/lazarus/1.2.0/components/printers/unix 
-Fi/usr/share/lazarus/1.2.0/components/printers/win32 
-Fi/usr/share/lazarus/1.2.0/components/printers/carbon 
-Fi/usr/share/lazarus/1.2.0/components/printers/qt 
-Fu/usr/share/lazarus/1.2.0/components/printers/unix 
-Fu/usr/share/lazarus/1.2.0/components/printers/win32 
-Fu/usr/share/lazarus/1.2.0/components/printers/carbon 
-Fu/usr/share/lazarus/1.2.0/components/printers/qt 
-Fu/usr/share/lazarus/1.2.0/packager/units

Re: [fpc-pascal] Double specialization of generic class

[Xiangrong Fang]

2014-04-15 20:26 GMT+08:00 Sven Barth pascaldra...@googlemail.com:

  Compiling wmodel.lError: /usr/bin/ppcx64 can't be executed, error
 message: Failed to execute /usr/bin/ppcx64, error code: -139

 Is there really a ppcx64 in /usr/bin? And is it really executable? (try
 /usr/bin/ppcx64 -i in a shell) Also check you Lazarus settings that
 you've setup the correct fpc binary and that you project's target
 settings are set to the correct platform (maybe you are trying to compile
 for x86_64 without having a x84_64 compiler installed).

​No problem with the executable. I run it from command line, which is ok.
i.e. ppcx64 is not corrupted, nor there is any authorization problem.
Also, if I remove the unused declaration, the error is gone.​

Doesn't -139 have any meaning to you?

Regards,
Xiangrong
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[fpc-pascal] Double specialization of generic class

[Xiangrong Fang]

Hi,

I got strange ppcx64 error: -139, which I found is caused by this:

type
  TNodeStack = specialize TVectorTNodeHash;

where TNodeHash itself is a specialization:

type
  PNode = ^TNode; //TNode is a plain record
  TNodeHash = specialize TTreapInteger, PNode;

Is it true that specialization of a generic class using another specialized
generic class is not allowed?

Thanks!

Xiangrong
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[fpc-pascal] function mapping to array?

[Xiangrong Fang]

Hi All,

Is the following possible:

type
  TFunc=function(x: Double): Double;

procedure apply(f: TFunc; var x: array of Double);
var
  i: Integer;
begin
  for i := 0 to Length(x) - 1 do x[i] := f(x[i]);
end;

apply(@sqrt, x); -- how can I apply() to built-in functions?

Thanks!

Xiangrong
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[fpc-pascal] reference counting of multi-dimensional array

[Xiangrong Fang]

If I have this:

var
  a2: array of array of Integer;
  i, j: Integer;
begin
  SetLength(a2, 3);
  for i := 0 to 2 do begin
SetLength(a[i], 3);
for j := 0 to 2 do a[i][j] := 1;
  end;
  a2 := nil; -- will this free all memory of a[0]...a[2]?
end;

Thanks!

Xiangrong
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[fpc-pascal] Two double related question

[Xiangrong Fang]

Hi All,

I am trying to convert an R program to pascal. Having 2 problems:

1. In R, ln(0) is -Inf (negative infinity) and ln(-1) is NaN, while in FPC
(2.6.2), ln(0) is NaN, and ln(-1) is -Inf, why? Mathematically, I think R's
rationale is better because ln(x) approaches -Inf while X approaches 0.

2. How can I tell the compiler NOT to generate EDivideByZero or any similar
stuff, but just return the IEEE Infinity NegInfinity or Nan accordingly? I
know that they are defined in the math unit.

Thanks!

Xiangrong
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[fpc-pascal] procedure modifiers

[Xiangrong Fang]

Hi All,

I wonder where should I put procedure modifiers, in the interface section,
or implementation section, or both?

e.g.

interface
function test(data: Integer): Integer; inline; -- here?
implementation
function test(data: Integer): Integer; inline; -- here?
begin
  //..
end;

Thanks,
Xiangrong
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[fpc-pascal] nested inline

[Xiangrong Fang]

Hi All,

Is nested inline allowed? i.e. will the compiler generate inlined code for
the following source:

procedure a; inline;
begin
end;

procedure b; inline;
begin
  a;
end;

if I call b() in the main program, will the compile copy code for both a
and b to avoid function calls?

Thanks,
Xiangrong
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[fpc-pascal] dynamic array reference count

[Xiangrong Fang]

Hi there,

I just want to confirm one thing:

var
  a, b: array of Integer;
begin
  SetLength(a, 100);
  SetLength(b, 100);
  a := b;
end.

Now a will point to the same memory block as b. Since dynamic arrays
are ref counted, I don't need to worry about the memory originally
allocated for a, right?

Thanks,
Xiangrong
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Re: [fpc-pascal] dynamic array reference count

[Xiangrong Fang]

​Thanks, this is important to know!​
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Re: [fpc-pascal] weird compiler(?) problem

[Xiangrong Fang]

2014-02-14 14:45 GMT+08:00 Sven Barth pascaldra...@googlemail.com:


 @Xiangrong Fang: do you use 2.6.2 or 2.7.1?

 I use 2.6.2
​​
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[fpc-pascal] weird compiler(?) problem

[Xiangrong Fang]

Hi All,

I encountered a very strange problem.  The code looks like this:

//In Unit1.pas:

//sel is an object of TIntVector and
//TIntVector = specialize TVectorInteger

*sel.Sort([soEliminateNA, soReversed]); *

//In vector.pas:

procedure TVector.Sort(Options: SortOptions);
var
  i, gap, order, first, last, pos: Integer;
  Temp: T;
begin
  *if FCount  2 then** Exit;  -- problem here*
  if soReversed in Options then order := 1 else order := -1;
  ... ...

My purpose is to skip sorting if the vector's element count is less than 2.

Now the problem is that this statement does not have any effect (see
attached screenshot).  The debugger refuse to stop on the breakpoint, but
goes directly to the line below it!

What's more strange is that if I change the line to break after “then”,
i.e.:

begin
  *if FCount  2 then*
*Exit;*
  if soReversed in Options then order := 1 else order := -1;
  ... ...

Now it worked!

I also wrote a simple test program, but can NOT reproduce this bug there.

My TVector source code is here:
https://github.com/xrfang/fpcollection/blob/master/src/units/vector.pas


Any help is greatly appreciated.

Sincerely,
Xiangrong
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Re: [fpc-pascal] weird compiler(?) problem

[Xiangrong Fang]

Hi Sven,

I don't know how to find that, could you please explain?  Attached
dbg.tar.bz2 is the demo program and assembly code generated by the compile.
Where is the point of specialization in that file?

My working program is quite complex, I copied part of the code related to
this problem in snippet.pas

Thank you!
Xiangrong


2014-02-13 23:53 GMT+08:00 Sven Barth pascaldra...@googlemail.com:

 Am 13.02.2014 16:42, schrieb Xiangrong Fang:

 Hi All,

 I encountered a very strange problem. The code looks like this:

 //In Unit1.pas:

 //sel is an object of TIntVector and
 //TIntVector = specialize TVectorInteger
 *sel.Sort([soEliminateNA, soReversed]);

 *

 //In vector.pas:

 procedure TVector.Sort(Options: SortOptions);
 var
 i, gap, order, first, last, pos: Integer;
 Temp: T;
 begin
 *if FCount  2 then**Exit; -- problem here*

 if soReversed in Options then order := 1 else order := -1;
 ... ...

 My purpose is to skip sorting if the vector's element count is less than
 2.

 Now the problem is that this statement does not have any effect (see
 attached screenshot). The debugger refuse to stop on the breakpoint, but
 goes directly to the line below it!

 What's more strange is that if I change the line to break after “then”,
 i.e.:

 begin
 *if FCount  2 then***
 *Exit;*

 if soReversed in Options then order := 1 else order := -1;
 ... ...

 Now it worked!

 I also wrote a simple test program, but can NOT reproduce this bug there.

 My TVector source code is here: https://github.com/xrfang/
 fpcollection/blob/master/src/units/vector.pas


 Any help is greatly appreciated.

 Could you please check/compare the generated assembler code? Use -al to
 have the compiler generate it and you'll need to look at the file where you
 specialized the TVector.

 Regards,
 Sven
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dbg.tar.bz2
Description: BZip2 compressed data
type
  TWaveStack = specialize TVectorPointer;
  TIntVector = specialize TVectorInteger;
... ...

var
  i: Integer;
  cw: TCmhWave;
  n: TTreeNode;
  ws: TWaveStack;
  sel: TIntVector;
  had_first: Boolean;
  procedure RecNodeIndex(node: TTreeNode);
  begin
if (node.Level = 0) and (node.Text  '') then sel.Push(node.Index);
  end;
begin  
  ws := TWaveStack.Create(nil);
  with tvb, tvb.Items do try
if SelectionCount = 1 then begin
  n := Selected;
  if n  nil then begin
while n.Parent  nil do n := n.Parent;
tbCfm.Enabled := TCmhWave(n.Data).Mode = 0;
  end;
  for i := 0 to TopLvlCount - 1 do begin
if TopLvlItems[i].Text = '' then Continue;
ws.Push(TopLvlItems[i].Data);
  end;
end else begin
  had_first := False;
  sel := TIntVector.Create(-1);
  try
for i := 0 to SelectionCount - 1 do begin
  n := GetSelections(i);
  if n.Index = Selected.Index then had_first := True;
  RecNodeIndex(n);
end;
if (not had_first) then RecNodeIndex(Selected);
sel.Sort([soEliminateNA, soReversed]);
while sel.Count  0 do ws.Push(TopLvlItems[sel.Pop].Data);
  finally
sel.Free;
  end;
end;
... ...
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Re: [fpc-pascal] weird compiler(?) problem

[Xiangrong Fang]

2014-02-14 0:16 GMT+08:00 Martin Frb laza...@mfriebe.de:


 Is it just the debugger does not stop? But the statement is executed
 (stopping in the next line never happens with FCount = 2)?

 Check your setup
 http://wiki.lazarus.freepascal.org/Debugger_Setup
 - NO smartlinking
 - NO optimization
   -O1 is often, but not always ok, so if there is an issue, then use -O-

 Your image does not show the blue dots in the gutter (where the
 breakpoint ,and green arrow are). That indicates there is something wrong
 with the debug info.

 Or maybe you have 2 units of the same name ,and use relative path ( ../ )?
 This can cause problems in some cases. Because gdb does not always deal
 with the .. , and then the IDE must specify the unit by name only, which is
 ambiguous.


​Debugger problem is minor.  I know I am missing the blue dots here. But
the MAJOR problem is that in the attached screenshot, FCount is 0, which is
of course smaller than 2, but it does NOT Exit!

This caused a SIGSEGV because in the code below I do this:

last := FCount - 1;
FItems[last] ...  //-- which results in FItems[-1];

And smartlinking never turned on, switching off optimization in lazarus
does not help either.

Regards,
Xiangrong​
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Re: [fpc-pascal] weird compiler(?) problem

[Xiangrong Fang]

Hi Sven,

Sorry that I overlooked the problem.  It is indeed a debugger problem. It
just stopped on the next line, but if I continue it just quit the function
nicely.

So, now the minor problem is, I don't have the blue dots :)

Sincerely,
Xiangrong
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Re: [fpc-pascal] weird compiler(?) problem

[Xiangrong Fang]

blue dots comes back after I switch back to O1...

Sorry for the false alarm... but this seems a debugger problem in lazarus
anyway...


2014-02-14 0:34 GMT+08:00 Xiangrong Fang xrf...@gmail.com:

 Hi Sven,

 Sorry that I overlooked the problem.  It is indeed a debugger problem. It
 just stopped on the next line, but if I continue it just quit the function
 nicely.

 So, now the minor problem is, I don't have the blue dots :)

 Sincerely,
 Xiangrong

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Re: [fpc-pascal] weird compiler(?) problem

[Xiangrong Fang]

Hi Martin,

2014-02-14 1:14 GMT+08:00 Martin Frb laza...@mfriebe.de:


 With -O2 and above the debugger does not always work.

 In case of such optimization the debug info compiled into the exe by fpc
 is not always accurate.

 It is not just blue dots, inspecting variables may show random data, 

 Debugging with O2 and up, if you must, requires to only look at the
 disassembler and register window. registers can only be trusted in the ttop
 stackframe. selecting any other may not show correct info.


I never use optimization option other than O1, I think O1 is the default.
 As Sven suggested, I tried turning off optimization, and back on, still at
O1 level.
​​
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[fpc-pascal] Memory leak in GetEnumerator

[Xiangrong Fang]

Hi All,

I used HeapTrc on my TTreap class:

https://github.com/xrfang/fpcollection/blob/master/src/units/treap.pas

It reported memory leak in the following procedure:


function TTreap.GetEnumerator: TTreap;
begin
  Result := TTreap.Create;  //-- memory leak here
  Result.ProxyFor := Self;
  ... ...
end;

Typical usage of the TTreap enumerator is:

 for n in aTreap do begin
   //do something with n
 end;

My question is: will the for-loop automatically free the enumerator after
usage?  How to fix leaks in my ttreap class?

Thanks a lot!

Xiangrong
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Re: [fpc-pascal] Memory leak in GetEnumerator

[Xiangrong Fang]

You are right, the bug is fixed, and another bug in the GetEnumerator are
also found and fixed.

This is my first time using heaptrc.

Thanks a lot.


2013/12/27 Jeppe Græsdal Johansen je...@j-software.dk

  Den 27-12-2013 10:16, Xiangrong Fang skrev:

  Hi All,

  I used HeapTrc on my TTreap class:

  https://github.com/xrfang/fpcollection/blob/master/src/units/treap.pas

  It reported memory leak in the following procedure:

 function TTreap.GetEnumerator: TTreap;


 begin
   Result := TTreap.Create;  //-- memory leak here


   Result.ProxyFor := Self;


   ... ...
 end;


   Typical usage of the TTreap enumerator is:

for n in aTreap do begin


//do something with n
  end;


   My question is: will the for-loop automatically free the enumerator
 after usage?  How to fix leaks in my ttreap class?

  Thanks a lot!

  Xiangrong

  Your constructor allocates a new NullNode, which gets overwritten in
 GetEnumerator, and hence the enumerator NullNode is never freed.


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[fpc-pascal] Is this behavior related to calling convention?

[Xiangrong Fang]

I have this function:

function Compare(v1, v2: Integer): Integer;

And called like this:

Result := Compare(stack.Pop, stack.Pop);

The behavior is that the second Pop is evaluated first, thus reversed the
meaning of the function.

Is it true that all parameter evaluation goes from right to left?

Thanks!
Xiangrong
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[fpc-pascal] virtual method and generics

[Xiangrong Fang]

Hi,

In my TTree class:
https://github.com/xrfang/fpcollection/blob/master/src/units/tree.pas

I have the following method:

function TTree.Load(s: TStream): Integer;
var
  lv, c: QWord;
  node: TTree;
  buf: Pointer;
begin
  Clear;
  if not ReadNodeData(s, lv, buf, c) then Exit(0);
  DoRestore(buf);
  OnRestore;//-- CALL#1
  FreeMem(buf, c);
  Result := 1;
  node := Self;
  while ReadNodeData(s, lv, buf, c) do begin
while (node  nil) and (lv  node.Level) do node := node.Parent;
if (lv = node.Level) and (node  Self) then
  node := TTree.Create(Data, node.Parent)
else
  node := TTree.Create(Data, node);
node.DoRestore(buf);
node.OnRestore;  //-- CALL#2
FreeMem(buf, c);
Inc(Result);
  end;
end;

Now I have a problem. CALL#1 is virtual as expected (sub-class's OnRestore
is called), but CALL#2 is not virtual, it just call the (empty) OnRestore
method defined in TTree.

How to solve this problem?

Thanks!
Xiangrong
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[fpc-pascal] Re: virtual method and generics

[Xiangrong Fang]

2013/11/19 Xiangrong Fang xrf...@gmail.com


 Now I have a problem. CALL#1 is virtual as expected (sub-class's OnRestore
 is called), but CALL#2 is not virtual, it just call the (empty) OnRestore
 method defined in TTree.

 How to solve this problem?


BTW, this also does NOT solve the problem:

TSelfType(node).OnRestore; ​​
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Re: [fpc-pascal] optionally uses a unit

[Xiangrong Fang]

2013/11/18 Mark Morgan Lloyd markmll.fpc-pas...@telemetry.co.uk

 There are definitely hazards, but I think that an exists() predicate of
 some form would definitely be useful. For example, inside an {$ifdef
 persist} it would give the developers the ability to have a tailored error
 message advising the maintainer that if persists.pas didn't exist he should
 also get such-and-such a project from local svn, and set up appropriate
 symlinks.

 The major issue would be directories and search paths.


That's also what I want to achieve.  My original purpose is to reduce
dependencies by put non-critical functions into a separate aux unit while
make the main unit still workable without the aux unit.​​

As to the search path, I would suggest searching the current path (which
*this* unit resides in), plus the path defined in project options.  I also
suggest to disable path component in this proposed directive, i.e.:

{$ifexists some/relative/path/filename.pas} and
{$ifexists /some/absolute/path/filename.pas}

are BOTH NOT allowed, only {$ifexists filename.pas} is allowed.

I don't know if this conforms to fpc traditions or not.

As to the concern about existing ppu or .o file, I think it is not a
problem, because you just follow the normal rule to compare file datetime
of the .o and .pas file. I don't like to rely on make files as fpc has its
own building system.

Xiangrong
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[fpc-pascal] optionally uses a unit

[Xiangrong Fang]

Hi All,

Is it possible to optionally use a unit? e.g.

unit myunit;
uses {$ifexists persist.pas}persist,{$endif} Classes;

type
  TMyClass = class
  public
{$ifexists persist.pas}
procedure SaveToStream(s: TStream);
{$endif}
  end;

Thanks,
Xiangrong
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[fpc-pascal] use of inherited keyword

[Xiangrong Fang]

Hi,

Is it OK to use inherited in any instance method? i.e.

It is OK to do this:

procedure TChildClass.DoIt；//override
begin
  inherited DoIt;
end;

But is it ok to do this:

procedure TChildClass.SomethinElse；//NOT DoIt
begin
  inherited DoIt;
  //... ...
end;

I tried, it seems ok, but I am not sure, because I had a strange access
violation in my code which I cannot reproduce in simplified version of the
code, so I suspect this might be an invalid use and correct by
coincidence?

Thanks!
Xiangrong
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[fpc-pascal] The overload keyword

[Xiangrong Fang]

Hi All,

According to http://www.freepascal.org/docs-html/ref/refsu72.html,

the overload keyword is mostly optional and for delphi compatiblity only.
But on Oct. 27, Sven replied my question about hide a public constructor in
base class:

  I don't understand why this does not work:
 f := TFileStream.Create;

 I know that TFileStream's Create require a file name parameter, but as
TFileStream is
 inherited from TObject, which has a Create without parameter.  This is
why I feel that it
 is possible to HIDE a public constructor from ancestor.

 No, I don't think so. If you want users to use the original constructor
as well you'd need to
 declare yours as overload. If it would be possible to call 
 TFileStream.Create
without
 parameters then the instance would be in an inconsistent state, so only
calling the
 constructor with arguments should be possible (which is the case for
TFileStream.

 So this is definitely by design.

Now my question is: in this case overload keyword DO make a difference?
Then, how to overload? e.g.:

In base class:

constructor Create;

In child class:

constructor Create(param1:...; param2: ...): overload;

i.e. overload does NOT require functions to have same parameter list or
return type? Also, it does not require the overload keyword in base class?
Otherwise programmers need to modify the base class, which is not good.

Thanks,

Xiangrong
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[fpc-pascal] private type and type compatibility

[Xiangrong Fang]

Hi All,

I have the following class:

type
  generic TVectorT = class
  private type
TDataType = array of T;
  private
FData: TDataType;
... ...
  public
... ...
function Slice(APos: Integer = -1; ACount: Integer = -1): TDataType;
  end;

The Slice() method return a portion of the data as a dynamic array.

My question is, as I define TDataType as PRIVATE type, why it is still
usable outside of the class?  In the main program I did:

type
  TIntVector = specialize TVectorInteger;
var
  iv: TIntVector;
  ia: array of Integer;
begin
  iv := TIntVector.Create;
  ... ...
  ia := iv.Slice;
end.

This will assign a TDataType (is it TVector$TDataType or
TIntVector$TDataType? I don't know) to an array of Integer. Why this
assignment works?

i.e. how does the type system work?!

Best Regards,
Xiangrong
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Re: [fpc-pascal] private type and type compatibility

[Xiangrong Fang]

2013/10/30 Sven Barth pascaldra...@googlemail.com

 I think it is an error. You declare something as private, and then you use
 it in a public function ? If that is not a visibility clash, I don't know
 what is :)

 I agree, but the question is should we declare this as a bug in the
 language and thus fix it which might lead to adjustments of legacy (2.6.x)
 code or use a warning. I personally would do the former (and better sooner
 than later). We need to keep the current behavior in mode Delphi however...
 (Note: Delphi additionally allows to access protected types from external
 units; could be related to the point that helper types allow access to
 protected types and fields as well...)


​I also agree that it is a bug. That's why I am confused.​
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Re: [fpc-pascal] private type and type compatibility

[Xiangrong Fang]

2013/10/30 Jonas Maebe jonas.ma...@elis.ugent.be

 The tdynarray type is not visible in the program because u1 is not in its
 uses clause (it's not in scope whatsoever), and nevertheless there is no
 problem to use it. It's of course not exactly the same (tdynarray isn't
 declared as private to u1), but at the scope visibility level it is the
 same situation as far as I am concerned.


​I don't think they are the same.  tdynarray​
 is not usable in main program because you did not uses u1, NOT because the
type is defined as PRIVATE!

​As a matter of fact, if you define tdynarray as private (not in interface
section), there is no way you can use it as a return type of an exported
(public) function. ​This is a very consistent scoping rule!

In my example, if the code is like this:

generic TVectorT = class
private type
  TDataType = array of T;
private
  function proc: TDataType;
end;

Then I think it is ok, because this PRIVATE type is used by PRIVATE
function.

What do you think?

Sincerely,
Xiangrong
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Re: [fpc-pascal] private type and type compatibility

[Xiangrong Fang]

2013/10/30 Sven Barth pascaldra...@googlemail.com

 It's a bit annoying that the usage private/protected types in
 public/published functions is allowed... (this is however Delphi
 compatible) Maybe this should be adjusted for non-Delphi modes for language
 consistency... (maybe at least as a warning which could be elevated to an
 error if someone wants)


​Alternatively, consider do NOT allow access modifiers for NESTED types,
instead, the visibility of nested types follow the class they are embeded
in.  Anyway, what is the purpose of HIDE a nested type?

Regards,
Xiangrong​
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Re: [fpc-pascal] private type and type compatibility

[Xiangrong Fang]

2013/10/30 Martin laza...@mfriebe.de


 I think there is no problem with:

 var
   a: array of Integer
 begin
   A:= obj.proc;

 You are NOT using the type. You are using the value.


pascal is strong-typed.  You are actually using type along with its value.
 e.g.

var
  a: array of Double;
begin
  a := obj.proc;​​

This will emit a COMPILE time error because compiler know these 2 types are
not compatible.
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Re: [fpc-pascal] private type and type compatibility

[Xiangrong Fang]

2013/10/30 Jonas Maebe jonas.ma...@elis.ugent.be


 This is not equivalent. A private type declaration in a class adds a new
 identifier that is visible inside that class. You then use it, still in
 that class, to declare the return type of a function. Next, in a scope
 where that type identifier is no longer visible, you call the function.

 My example is a complete match to that scenario as far as identifier
 visibility is concerned (you use a type in a scope where it is visible to
 declare a function return type, and then call the function in a scope where
 it is not visible). In your example, the type is not visible in the place
 where the function is declared but only where it is defined
 ​.


​This is logically WRONG. Because to the machine, any function return value
can be seen as an array of bytes, for example, a pointer is array[0..3] of
Byte on a 32-bit machine.  The purpose of type system is to explain what
these bytes stands for. So, if a type is out-of-scope, how do you interpret
the data?​

The current delphi compatible implementation IS using the type
information to compile the program, i.e. although it is not visible, it is
indeed used by the compile, which, in my opinion, violates visibility rules.

Standing on your view point, if a type is no longer visible, but a variable
(function return value) of that type is in current scope, and understood by
the program, this means, this value itself carries type information!  Is is
kind of meta data available in Pascal? If so, I think RTTI should work for
ANY kind of primitive data types.

Regards,
Xiangrong
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Re: [fpc-pascal] private type and type compatibility

[Xiangrong Fang]

2013/10/30 Martin laza...@mfriebe.de


 Since the type is part of value, and the value is public, all of the type
 that is accessed through the value is available.
 Same as you can access a private field through a public property.


Access a private variable via public property is analogous to function​​
calls, isn't it?
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Re: [fpc-pascal] WHY compiler should be public?

[Xiangrong Fang]

2013/10/27 Michael Van Canneyt mich...@freepascal.org



 Ah. The 'private' constructor is called FROM ANOTHER INSTANCE. You didn't
 say that.

 That currently can't be done.

 Michael.


​So, in this case, can/should I make my constructor private, ignoring the
warning, or just make it public to play it safe?

Regards,
Xiangrong​
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