[fpc-pascal] LoadLibrary, FreeLibrary & Threads (win32)
Dear all,
I have spent 2 days now tracking an access violation in my app which I couldn't
debug well because it occured somewhere where no debug info was available, but
obviously during a call to FreeLibrary.
I don't know whether I am allowed to do this or not, but as far as I have read
from the Microsoft docs about using libraries [1,2] I didn't find a note that
my approach is forbidden. (Of course, I may have overread it.)
[1]
https://learn.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-best-practices
[2]
https://learn.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-loadlibrarya
What I did is to call LoadLibrary in a different thread than the main thread.
The corresponding call to FreeLibrary on the other hand was done in the main
thread.
Question 1: Is this legal on Windows? If not, we're finished here and you can
skip the rest ;)
However, if it *is* legal, I'd need some help with FPC. Here's a minimal
example:
***
library dummylib;
uses
Classes;
begin
end.
***
program project1;
uses SysUtils, Types, Classes;
type TLoadLibThread = class(TThread)
procedure Execute; override;
var FHandle: THandle;
end;
procedure TLoadLibThread.Execute;
begin
FHandle := LoadLibrary('dummylib.dll');
end;
var h: THandle = NilHandle;
begin
with TLoadLibThread.Create(FALSE) do begin
WaitFor;
h := FHandle;
Free;
end;
Assert (h <> NilHandle);
FreeLibrary (h);
end.
***
The call to FreeLibrary causes an "access violation writing to address $14".
I also tried to follow the advice in the "multithreaded application tutorial"
in the wiki ("initialize the FPC's threading system by creating a dummy
thread"), but this doesn't make any difference.
I assume that I have some obviouy error and am just too blind to see, so I'd
appreciate someone pointing me to it.
Thanks,
Thomas
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Re: [fpc-pascal] Subscript pointers
On Thu, 22 Jun 2023, Hairy Pixels via fpc-pascal wrote: On Jun 22, 2023, at 8:41 PM, Michael Van Canneyt via fpc-pascal wrote: It's for easier pointer math, a construct which has been used in FPC since day 1 (AFAIK). Use with care, since no boundary checks are done. You mean instead of doing p + 1 or you can do p[1]? Yes. It may have been used for C compatibility too since an array in C is just a pointer. Yes, the concepts are similar. Michael. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Subscript pointers
> On Jun 22, 2023, at 8:41 PM, Michael Van Canneyt via fpc-pascal > wrote: > > It's for easier pointer math, a construct which has been used in FPC since > day 1 (AFAIK). > Use with care, since no boundary checks are done. You mean instead of doing p + 1 or you can do p[1]? It may have been used for C compatibility too since an array in C is just a pointer. Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Subscript pointers
On Thu, 22 Jun 2023, Hairy Pixels via fpc-pascal wrote: I've forgotten entirely, what does subscripting a pointer do in Pascal? p[0] returns 100 but after that garbage. Seems like a c-style array which doesn't feel right in the language. var i: Integer; p: PInteger; begin p := @i; p^ := 100; writeln(p[0]); writeln(p[1]); writeln(p[2]); It's for easier pointer math, a construct which has been used in FPC since day 1 (AFAIK). Use with care, since no boundary checks are done. Michael. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
[fpc-pascal] Subscript pointers
I've forgotten entirely, what does subscripting a pointer do in Pascal? p[0] returns 100 but after that garbage. Seems like a c-style array which doesn't feel right in the language. var i: Integer; p: PInteger; begin p := @i; p^ := 100; writeln(p[0]); writeln(p[1]); writeln(p[2]); Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Legitimate use of for and break
On 6/21/23 10:54 AM, Steve Litt via fpc-pascal wrote: wkitty42--- via fpc-pascal said on Wed, 21 Jun 2023 08:07:59 -0400 On 6/20/23 10:54 PM, Steve Litt via fpc-pascal wrote: It was a long time ago, but if I remember correctly the Whitesmith Pascal and Turbo Pascal 2 and 3 had either break or continue. If I remember correctly, I first learned about those when learning C. i'm confused about your statement... first you say break/continue existed in one of two pascal dialects but then you say you first learned about the two keywords in C... u, wut? I meant to say "neither" instead of "either". Sorry for the confusion. that does make a difference :) thanks... -- NOTE: No off-list assistance is given without prior approval. *Please keep mailing list traffic on the list where it belongs!* ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
