dispatch_timeout()

Updated: May 06, 2022

Set a timeout

Synopsis:

#include <sys/iofunc.h>
#include <sys/dispatch.h>

int dispatch_timeout( dispatch_t *dpp,
                      struct timespec *reltime );

Arguments:

dpp
A dispatch handle created by a successful call to dispatch_create().
reltime
A pointer to a timespec structure that specifies the relative time of the timeout, or NULL to cancel the timeout.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The function dispatch_timeout() sets a timeout that's used when blocking with dispatch_block().

CAUTION:
Applying timeouts in a multi-threaded resource manager may not have the expected effect. Some, but not all, threads may be servicing many client requests while another thread is completely inactive. If a regular wake-up is needed for sanity or health checking, a timer delivering a pulse might be a better choice.

This function is part of the dispatch layer of a resource manager. For more information, see Layers in a resource manager in the Bones of a Resource Manager chapter of Writing a Resource Manager.

This affects all future calls to dispatch_block() with the same dispatch handle, unlike the similar TimerTimeout() and timer_timeout() calls, which affect only the next blocking call.

If you're using dispatch_timeout() with a thread pool created with thread_pool_create(), you will need to provide a custom handler_func because dispatch_handler() silently ignores the unblock case. It should look something like the following:
int my_handler_func( dispatch_context_t *ctp ) {
   if ( ctp->message_context->rcvid == -1 ) {
      return my_handle_unblock(ctp);
   } else {
      return dispatch_handler(ctp);
   }
}

Returns:

0
Success.
-1
An error occurred.

Examples:

#include <sys/dispatch.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
    
int main( int argc, char **argv ) {
   dispatch_t           *dpp;
   struct timespec      time_out;
   int                  timedout;
   time_out.tv_sec = 1;
   time_out.tv_nsec = 2;

   if( ( dpp = dispatch_create() ) == NULL ) {
     fprintf( stderr, "%s: Unable to allocate \
              dispatch handle.\n",argv[0] );
     return EXIT_FAILURE;
   }
    
   …

   if ( (timedout = dispatch_timeout ( dpp, &time_out ))
         == -1 ) {
       fprintf ( stderr, "Couldn't set timeout );
       return EXIT_FAILURE;
   }
   /* else successful timeout set */

   …
   return EXIT_SUCCESS;
}

For examples using the dispatch interface, see dispatch_create(), message_attach(), resmgr_attach(), and thread_pool_create().

Classification:

QNX Neutrino

Safety:  
Cancellation point No
Interrupt handler No
Signal handler No
Thread Yes