dispatch_context_alloc()

Updated: May 06, 2022

Return a dispatch context

Synopsis:

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

dispatch_context_t* dispatch_context_alloc( dispatch_t * dpp );

Arguments:

dpp
A dispatch handle created by a successful call to dispatch_create().

Library:

libc

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

Description:

The dispatch_context_alloc() function returns a dispatch context pointer. The function is passed in the handle dpp from dispatch_create(). The dispatch context is used by dispatch to do its work. It's passed as an argument to dispatch_block() and dispatch_handler().

Note:
  • The dispatch_context_alloc() function fails if you haven't attached any events to dispatch yet (i.e., you didn't call message_attach(), pulse_attach(), resmgr_attach(), or select_attach()).
  • Once you've called dispatch_context_alloc(), don't call message_attach() or resmgr_attach() specifying a larger maximum message size or a larger number of message parts for the same dispatch handle. In QNX Neutrino 7.0 or later, these functions indicate an error of EINVAL if this happens.
  • The returned dispatch_context_t* value is a pointer to a union of various callback-specific structures, in particular: a resmgr_context_t, a message_context_t (which is identical to a resmgr_context_t), and a select_context_t.

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.

Returns:

A pointer to a dispatch context, or NULL if an error occurs (errno is set).

Errors:

EINVAL
No events were attached.
ENOMEM
Insufficient memory to allocate context.

Examples:

#include <sys/dispatch.h>
#include <stdio.h>    
#include <stdlib.h>   
    
int main( int argc, char **argv ) {
   dispatch_t           *dpp;
   dispatch_context_t   *ctp;

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

   ...

   ctp = dispatch_context_alloc( dpp );

   ...

   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