Re: Problem interrupting threads in PR_Accept() wiht PR_Interrupt()

Wan-Teh Chang wrote:
> I/O functions that may block indefinitely, for example, PR_Recv and PR_Send,
> can also be interrupted.  Your handle_call function must be calling
> such functions.

Yes, they call PR_Send() and PR_TransmitFile().

> You can also just use a global variable:
> 
> PRBool stopping = PR_FALSE;
> 
> Change your worker thread's while loop to test it:
> 
>     while(!stopping)

Yes, this works. Thank you!

The original task as given by my project leader was to write a portable
demo server that does not loose any request (except for the ones caused
by network timeouts or network problems, which cannot be avoided). That
is, after a request has been PR_Accept()ed, it must run to full
completion, even in the case that the time to serve the request is long
and that during this time the administrator signals the server to go down.

So I formulated the while loop now as follows, including your hint and
introducing Boolean variables worker_busy[]:

  while( !shutdown_workers ){

    if((fd = PR_Accept( sock, NULL, PR_INTERVAL_NO_TIMEOUT ))
       == NULL) {
      if(PR_GetError() == PR_PENDING_INTERRUPT_ERROR)
        break; /* that's OK: master has signaled an interrupt */
      else {
        oops("PR_Accept in thread_start()");
        continue;
      }
    }

    /* RACE HERE */

    worker_busy[nthread] = 1;
    handle_call(fd, nthread);
    PR_Close( fd );
    worker_busy[nthread] = 0;
  }


The master thread first checks that all workers are not busy before
sending PR_Interrupt(). But I realize that there is a tiny race
condition in this approach, namely that the interrupt signal occurs
exactly while the thread is in the line indicated by "RACE HERE". Then
the request is accepted, but the thread will be interrupted later in
PR_Send() or PR_TransmitFile(). I cannot combine PR_Accept() and setting
worker_busy to TRUE into an atomar operation.

Is there any solution to this problem? Can I make PR_Send() and
PR_TransmitFile() ignore the PR_Interrupt()?

Greetings,
Joachim