Threads & Mutexs & Things

[Terry Keep]

I have created a small DLL that creats threads to do slow
network tasks, however, I wanted to put a thread pool control
into it e.g. I request 100 threads to run but only have 10
at anyone time. So I did som'it like the following

'Implement a currently running thread pool manager
DO WHILE ThreadCnt > %MaxConcurrentThreads
CALL SwitchToThread
LOOP

THREAD CREATE ThreadRoutine(pHeap) TO hThreadID
IF hThreadID <> 0 THEN
CALL WaitForSingleObject(ThreadCntMutex, 1000)' %INFINITE)
INCR ThreadCnt
CALL ReleaseMutex(ThreadCntMutex)
END IF

Then in the ThreadRoutine I have
CALL WaitForSingleObject(ThreadCntMutex, %INFINITE)
DECR ThreadCnt
CALL ReleaseMutex(ThreadCntMutex)
ExitThread 0

The problem is that when it gets into the Do loop, the child threads
don't appear to get a look in, hense, they can't do their bit
and exit..........

what am I missing ???

------------------

[Trevor Lane]

Terry,

I haven't done this, I am just going from the win32 System
Services manual.

All threads can be given a priority using the SetThreadPriority API
This means that you have complete control over the amount of processor
time taken by your threads without having to write your own code.

Trevor

P.S. If you cannot find information about the SetThreadPriority API
watch this space, I am sure you will get a few real gems on this
thread in the not too distant future.

------------------

[Terry Keep]

Thanks, but I didn't want to up the priority of child threads,
I don't understand why the main thread isn't given control to
it's child threads. I thought SwitchToThread did a simular thing
as DoEvents does in VB.

Terry

------------------

[Tom Hanlin]

VB's DoEvents basically just drops program control back to VB's hidden
message pump, allowing Windows (and other) messages to be processed.
It's not clear that your DLL provides any similar mechanism, in which
case the program may be blocked waiting to process necessary messages.

------------------
Tom Hanlin
PowerBASIC Staff

[Fred Oxenby]

What OS are you using (NT/4 Win2000/Pro) ?

The SwitchToThread function causes the calling thread to yield execution to
another thread that is ready to run on the current processor.
The operating system selects the thread to yield to.
Remarks
The yield of execution is in effect for up to one thread-scheduling time slice.
After that, the operating system reschedules execution for the yielding thread.
The rescheduling is determined by the priority of the yielding thread and
the status of other threads that are available to run.

I am not sure that your 'DoThread' is able to do what you want it to
I suppose processing of your threads will be lengthy,
that is more than a few seconds...

1) Create the thread-scheduler in its own thread.
   (this could be your main thread)
   In this thread create a invisible window (modal)
   make two 'functions' AddThread and RemoveThread
   AddThread will Resume The Thread(let it run and end) 
   RemoveThread will close the thread
   Use the DlgProc callback to 'remember' suspended threads
   waiting for execution
   
2) Create your worker-thread in suspended mode
   call the "AddThread" function with ThreadId and
   let the Thread-Scheduler Resume execution 
   (according to your rules)

3) When a worker-thread is ending, let it call
   RemoveThread to Close the Thread and activate a 
   suspended thread

------------------
Fred
mailto:[email protected][email protected]</A>
http://www.oxenby.se



[This message has been edited by Fred Oxenby (edited January 09, 2001).]

[Terry Keep]

Fred,

Thanks for that, but I'm not sure I follow the advantage of
creating a Window and usign DDT (this is because I have not used
DDT before). Can you put a quick and dirty example together so
that I can try to understand.

Thanks


------------------

[Fred Oxenby]

This is not working code, but tells you what I mean.

Global ghWnd_Scheduler&
Global Abort_Scheduler&
Global gThread_Suspend&()
Global gThread_Running&()
%AddThread    = %WM_APP + 1
%RemoveThread = %WM_APP + 2
%FreeThreads  = %WM_APP + 3
  
Function WindowThread(ByVal x&)As Long
'create a modal scheduler-window
Local WinCnt&
  Dialog New %HWND_DESKTOP,"",0,0,0,0 TO ghWnd_Sheduler&
  Dialog Show State ghWnd_Sheduler&,%SW_HIDE
  Dialog Show ModeLess ghWnd_Sheduler& Call DLGPROC_SCHEDULER
  
  Do             
   Dialog DoEvents To WinCnt&
   If Abort_Scheduler <> 0 Then Dialog End ghWnd_Sheduler&
  Loop While WinCnt& > 0
  
End Function                    
  
CallBack Function DLGPROC_SCHEDULER
Local Nr&,Nr1&,Rc&
  
  Select Case CBMsg
    Case %WM_INITDIALOG
     ReDim gThread_Suspended&(1 To 100)
     ReDim gThread_Running&(1 To 10)
    Case %AddThread
     Array Scan gThread_Running(),= 0, To Nr&
     If Nr& <> 0 Then 
      gThread_Running&(Nr&) = CBwParam
      Thread Resume CBwParam TO rc&
     Else
      Array Scan gThread_Suspended&(),=0, To Nr&
      If Nr& = 0 Then 'Fatal Error, more than 100 requests
      gThread_Suspended&(Nr&) = CBwParam
     End if 
    Case %RemoveThread
     Array Scan gThread_Running&(), =CBwParam, To Nr&
     If Nr& = 0 Then 'Something is wrong here
     Thread Close gTread_Running&(Nr&) To rc&
     gThread_Running&(Nr&) = 0
     Array Scan gThread_Suspended&(),<>0, To Nr1&
     If Nr1& <> 0 Then
      Swap gThread_Running&(Nr&), gThread_Suspended&(Nr1&)
      Thread Resume gThread_Running&(Nr&) TO rc&
     End if
    Case %FreeThreads
     Nr2& = 0
     For Nr& = 1 to 100
      If gThread_Suspended&(Nr&)=0 then incr Nr2&
     Next
     Function = Nr&
  End Select   
  
End Function
   
'--When you create a new workerthread----------------
  
  Dialog Send ghWnd_Scheduler&,%FreeThread,0,0 To ThreadCnt&
  If ThreadCnt& > 0 then
   Thread Create Worker(Parameter) Suspend To ThreadId&
   If ThreadId& <> %NULL Then 
    Dialog Send ghWnd_Scheduler&,%AddThread,ThreadId&,0
   End If
  End If 
  ....
  
    
'--In your worker thread, when it is about to end----
  
  Dialog Send ghWnd_Scheduler&,%RemoveThread,GetCurrentThreadId(),0

You can add code for threads to query sceduler for abort if your
app is terminating etc.


------------------
Fred
mailto:[email protected][email protected]</A>
http://www.oxenby.se


[This message has been edited by Fred Oxenby (edited January 10, 2001).]