asked on

URGENT: Problem with threads

I have input file - plain text in the format:
1
2
3
...

I use this file for open URL, submit the value as a parameter, retrieve some info and save it to file. I use a dynamic array of TMyThread type. Let's say I set its length to 30. Then loop through Low() and High() and check if the element is nil - create the thread. If it is not - check if it is running (public var in the thread). I set FreeOnTerminate = True, but somehow the thread is not nil after it finished.

I the loop if the thread has finished (it should be nil because FreeOnTerminate = True) I create a new instance. But Somehow the finished thread is not nil... I create it with CreateSuspended = False...

vadim_ti

FreeOnTerminate only destroy thread, but will not assign nil to thread variable,
you can nil array element in onDestroy method of your thread

vadim_ti

think abot it, you can save Thread object in number of different variables, thread could not to nil them (and even to know
about them)
but in your on destory event you can loop through your array
for (....) {
if (ThreadArr[i] = Self) then begin
ThreadArr[i] := nil;
break;
end

Russell Libby

It would actually be better to set the OnTerminate method handler for the thread, as this will run in the context of the main thread.

OnTerminate
---------------
Occurs after the thread's Execute method has returned and before the thread is destroyed.

property OnTerminate: TNotifyEvent;

Description

Write an OnTerminate event handler to execute code after the thread finishes executing. The OnTerminate event handler is called in the context of the main VCL thread, which means VCL methods and properties can be called freely. The thread object may also be freed within the event handler.

---

Regards,
Russell

Ivanov_G

ASKER

I think I have to clarify few things

type
ThreadArr : array of TMyThread;

for counter := Low(ThreadArr) to High(ThreadArr) do
begin
if ThreadArr[counter] = nil then
begin
if InputStrings.Count > 0 then
begin
ThreadArr[counter] := TMyThread.Create(False, ThreadOptions, InputStrings[0]);
InputStrings.Delete(0);
end;
end
else
if ThreadArr[counter].IsFinished then
begin
ThreadArr[counter].Terminate;
ThreadArr[counter] := nil;
end;
end;

This is the case here... Is finished is public variable in the thread which shows me if everything with the HTTP ended correctly...

SOLUTION

vadim_ti

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ASKER CERTIFIED SOLUTION

Russell Libby

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Russell Libby

Oops, posted too quick...

another example of execute without looping

procedure TMyThread.Execute;
begin

// perform first step
....

if not(Terminated) then
begin
// next step
....
if not(Terminated) then
begin
// next step
....
etc....
end;
end;

end;

----
Regards,
Russell

Lee_Nover

weird pooling scheme if it is ment to be one
for a thread pool check for example Indy's ThreadPool
the threads that finish just get suspended .. when needed nonworking threads get returned, if no thread is free a new one is created
think of something in the lines of:
while InputStrings.Count > 0 do
begin
thd:=ThreadPool.GetAvailableThread(true {allow create});
thd.ProcessURL(InputStrings[InputStrings.Count-1]);
InputStrings.Delete(InputStrings.Count-1);
end;

with proper locking you could make this 'live' :)

Ivanov_G

ASKER

somehow ... some of the thread fails. If I run it once, it can finish successfully, but the second time, some thread will fail and this will stop the whole application...

I am trying to debug this now, but with so many threads ... grrr