Delphi - timer inside thread generates AV

Question

I have the following thread code which executes correct first time. After that from time to time I get an AV on the Execute method of the thread, e.g

Answer 1

First, in constructor TProcesses.Create(aGrid : TJvStringGrid); you have:

FTimer.OnTimer := OverrideOnTerminate;
FTimer.OnTimer := OverrideOnTimer;

Here OverrideOnTerminate never fires. Probably you want to catch thread OnTerminate.

Second, you create thread in running state inherited Create(false); so Execute is called automatically. When Execute is finished it calls DoTerminate and thread is destroyed.

Next, when timer fire OnTimer you call multiple times Execute; Here Thread already may not exists. Timer is not freed, and you try to start a dead thread.

You need to rewrite your code following some rules:

1. Execute should run continuously. You may put thread to "sleep" using WaitForSingleObject/WaitForMultipleObjects. Take a look at MSDN help.
2. These functions have Timeout parameter, so you don't need TTimer at all.

[EDIT] I found some useful sample for you (sorry, it's not tested by me):

procedure TProcesses.Execute;
const  
 _SECOND = 10000000;  
var  
 lBusy : LongInt;  
 hTimer : LongInt;  
 liWaitTime : LARGE_INTEGER;  
begin  
  hTimer := CreateWaitableTimer(nil, True, 'WaitableTimer');
  liWaitTime.QuadPart := _SECOND * YOUR_NumberOfSeconds;
  SetWaitableTimer(hTimer, TLargeInteger(liWaitTime ), 0, nil, nil, False);  
  repeat  
    lBusy := MsgWaitForMultipleObjects(1, hTimer, False, INFINITE, QS_ALLINPUT);
    // CODE EXECUTED HERE EVERY YOUR_NumberOfSeconds
   Until lBusy = WAIT_OBJECT_0;  
   CloseHandle(hTimer);  
end;  

You need to slightly adjust this. Add one more object to wait for: an event created with CreateEvent function. When you need to instantly terminate thread just call SetEvent function.