[fpc-pascal] More memory leaks and other problems: request for review of probably stupid mistake

2010-03-31 Thread Jim 
Hi all,

I'm trying to learn FreePascal by writing a file indexer a la locate and
I'm hitting more walls after receiving quick and clear help from Michael
Van Canneyt  regarding memory leaks.

In the last couple of hours I've seen memory leaks cropping up in the
main LPR file, invalid pointer problems (= think I was too aggressive
cleaning up memory),  list index out of bounds, reading past end of file
errors (faulty improvement of data types in exif code?).

1. Could some kind soul tell me what I've been doing wrong if possible?
It's probably in the search as well as in the exif code.
I'd love to start with something that I can understand and work up from
there - at this moment I feel like I'm chasing smoke.
The code is at:
http://bitbucket.org/jb/flocate/downloads/

... but I'd rather prefer getting better at figuring out what I did
wrong, however, when setting some breakpoints on my
Lazarus 0.9.29 r23972 FPC 2.4.1 x86_64-win64-win32/win64
Free Pascal Compiler version 2.4.1 [2010/03/13] for x86_64
system, every time the IDE would inform me that the debugger had crashed.
I didn't see instructions for debugging with Lazarus x64 on Windows.
(I've also been running the fpc compiler only on Linux to see the
effects of the compiler conditionals).

2. Is there anything I need to do to get visual debugging working? Some
project options? I've fiddled with dwarf output etc but am not sure what
should be enable and disabled? Should I switch to Lazarus 32bit?
Please see heaptrc dump as well as last part of my debug output below.

Seems like I still need to get some basic details about the language
regardless of checking the fpc reference manual, Marco Cantu's Essential
Pascal/Delphi and the Delphi basics website...

Thanks in advance,
jb

stdout message:
exception at 00010003EFE3:
Read past end of file.

stderr output snipped:
Debug: 31-3-2010 19:38:37: starting exif info
for:C:\Windows\Microsoft.NET\Framework64\v2.0.50727\ASP.NETWebAdminFiles\Images\ASPdotNET_logo.jpg
Heap dump by heaptrc unit
156639 memory blocks allocated : 13406733/14127240
156636 memory blocks freed : 13406173/14126672
3 unfreed memory blocks : 560
True heap size : 1343488 (224 used in System startup)
True free heap : 1342208
Should be : 1342312
Call trace for block $035662A0 size 432
  $000100038E2D  TFILESEARCH__SEARCHPERFILTER,  line 659 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $00010003915B  TFILESEARCH__SEARCH,  line 714 of search.pp
  $00011AF5  FLOCATE__DORUN,  line 140 of flocate.lpr
Call trace for block $035CAEF0 size 35
  $000100030659
  $0001000324B1
  $000100032616
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
Call trace for block $011A5340 size 93
  $000100038CBB  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
  $00010003915B  TFILESEARCH__SEARCH,  line 714 of search.pp
  $00011AF5  FLOCATE__DORUN,  line 140 of flocate.lpr
  $000100034148

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Re: [fpc-pascal] More memory leaks and other problems: request for review of probably stupid mistake

2010-03-31 Thread José Mejuto 
Hello FPC-Pascal,

Wednesday, March 31, 2010, 7:52:43 PM, you wrote:

J I'm trying to learn FreePascal by writing a file indexer a la locate and
J I'm hitting more walls after receiving quick and clear help from Michael
J Van Canneyt  regarding memory leaks.
[...]
J Call trace for block $035CAEF0 size 35
J   $000100030659
J   $0001000324B1
J   $000100032616
J   $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
J   $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
J   $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
J   $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp
J   $000100038CCF  TFILESEARCH__SEARCHPERFILTER,  line 638 of search.pp

Your code looks too tricky, specially the AddFileToResult. You are
using records to store the item, in theAddFileToResult you assign an
ansistring to one or more fields, in this process a reference to the
ansistring is generated, and this references are quite sure your
memory leaks in some way as the allocation point by heaptrc is in the
RTL (no traceback).

Instead using records, use a class and instead TList use TObjectList,
this way when you invoke Res.Free all objects inside will be freed
also, or when you delete an object it is automagically freed.

Working with records allocated with New and adding them to a list is a
complex task to keep the track of each one, specially if you have to
mix different record types.

If you still want to use records, before the Dispose(APResultRecord)
set the ansistring fields to '', this will garantee that the reference
is freed.

-- 
Best regards,
 José

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Re: [fpc-pascal] More memory leaks and other problems: request for review of probably stupid mistake

2010-03-31 Thread Flávio Etrusco 

 If you still want to use records, before the Dispose(APResultRecord)
 set the ansistring fields to '', this will garantee that the reference
 is freed.


Or call Finalize() on them.

Flávio
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Re: [fpc-pascal] More memory leaks and other problems: request for review of probably stupid mistake

2010-03-31 Thread Jim 
On 31-3-2010 20:47, Flávio Etrusco wrote:
 If you still want to use records, before the Dispose(APResultRecord)
 set the ansistring fields to '', this will garantee that the reference
 is freed.

 
 Or call Finalize() on them.

 Flávio
   
Thanks José  Flávio,

Sounds like a good plan, though I liked the beauty/simplicity of dealing
with records - unless you forget that ansistrings also have pointers ;)
I had completely forgotten about them and assumed the compiler would
deal with them behind the scenes. Obviously it doesn't.

I'll give it a go and get back to the list if I hit more troubles.

All, any advice/tricks on debugging? I think I'll try setting up Lazarus
in an Ubuntu VM to see how that works in any case. Maybe that works...

Regards,
jb
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