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

On Wed, Aug 6, 2008 at 7:38 AM, Joachim Ziegler <[email protected]> wrote:
> Hello,
>
> to get familiarized with NSPR, I have written a little demo web server.
>
> The server has master thread that creates 5 worker threads. Each worker
> thread blocks in PR_Accept() to wait for a new request, then serves the
> request, the goes on in an endless loop. This loop looks like this:
>
>
>  while( 1 ) {
>    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;
>      }
>    }
>    handle_call( fd );
>    PR_Close( fd );
>  }

I found a problem in your code, which should explain what you observed.

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.
So you also need to check for the PR_PENDING_INTERRUPT_ERROR error
in handle_call, and exit the worker thread's while loop if you get that error.

You can also just use a global variable:

PRBool stopping = PR_FALSE;

Change your worker thread's while loop to test it:

    while(!stopping)

And your master thread sets 'stopping' to PR_TRUE before interrupting
the worker threads:

stopping = PR_TRUE;
for(nthread = 0; nthread < NTHREADS; nthread++)
 if( PR_Interrupt(worker[nthread]) == PR_SUCCESS )
   printf("MASTER[%d]: Thread %d is blocked. Sent PR_Interrupt.\n",
myPID, nthread);
 else
   printf("MASTER[%d]: Thread %d is not blocked. Sent PR_Interrupt\n",
myPID, nthread);

Wan-Teh