Hi, Wilfried - thanks for the explanation - I've been looking at the code
for hours and just couldn't see the cause. I've now changed the code to
this which should solve the problem if I understood correctly:
function ReadMessage: PAnsiChar; stdcall;
var
Note: AnsiString;
begin
EnterCriticalSection(CritSectn);
if (NotesList.Count > 0) then
begin
Note := NotesList.Strings[0];
NotesList.Delete(0);
Result := PAnsiChar(Note);
end
else
Result := '';
LeaveCriticalSection(CritSectn);
end;
Regarding the critical section issue, there are 2 threads involved ... the
main DLL thread which services the calls from the client application and the
worker thread which is running the TWSocket message loop.
As I saw things, there were two areas that could be problematic:
1) the Readmessage function above which is checking the list count and
deleting the string after reading it.
2) the worker thread that would be trying to add strings to the end of a
list which might be 1 string shorter at the end of the process than it was
at the beginning i.e. the string count is 5 as the worker thread prepares to
add NotesList.Strings[5] but before that task has completed, the main thread
has deleted NotesList.Strings[0] so the count is then only 4
Is that a possibility or is the Strings class smart / thread-safe enough to
prevent those situations causing an issue?
Regards, Adam
-----Original Message-----
From: twsocket-boun...@elists.org [mailto:twsocket-boun...@elists.org] On
Behalf Of Wilfried Mestdagh
Sent: 15 September 2011 22:34
To: 'ICS support mailing'
Subject: Re: [twsocket] DLL implementation advice (or example)...
Hi Adam,
> despite tearing out some hair and losing a
Hopefully you have spare :)
> Result := PAnsiChar(NotesList.Strings[0]);
> NotesList.Delete(0);
The problem is that you give a pointer to the return value of that function
to something that not exists anymore after the functions exit:
> Result := PAnsiChar(NotesList.Strings[0]);
You give a pointer to a string
> NotesList.Delete(0);
And here you destroy the string you point to
> critical section code or not... I thought I might as the worker thread
You only need Critical section if you access same data from out different
thread context. So if this is not the case then you don't need it.
Was this clear to answer your questions?
--
mvg, Wilfried
http://www.mestdagh.biz
http://www.comfortsoftware.be
http://www.expertsoftware.be
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