Function DestroyParallelContext

src/backend/access/transam/parallel.c:964–1033

* Destroy a parallel context. * * If expecting a clean exit, you should use WaitForParallelWorkersToFinish() * first, before calling this function. When this function is invoked, any * remaining workers are forcibly killed; the dynamic shared memory segment * is unmapped; and we then wait (uninterruptibly) for the workers to exit. */

 * is unmapped; and we then wait (uninterruptibly) for the workers to exit.
 */
void
DestroyParallelContext(ParallelContext *pcxt)
{
	int			i;

	/*
	 * Be careful about order of operations here!  We remove the parallel
	 * context from the list before we do anything else; otherwise, if an
	 * error occurs during a subsequent step, we might try to nuke it again
	 * from AtEOXact_Parallel or AtEOSubXact_Parallel.
	 */
	dlist_delete(&pcxt->node);

	/* Kill each worker in turn, and forget their error queues. */
	if (pcxt->worker != NULL)
	{
		for (i = 0; i < pcxt->nworkers_launched; ++i)
		{
			if (pcxt->worker[i].error_mqh != NULL)
			{
				TerminateBackgroundWorker(pcxt->worker[i].bgwhandle);

				shm_mq_detach(pcxt->worker[i].error_mqh);
				pcxt->worker[i].error_mqh = NULL;
			}
		}
	}

	/*
	 * If we have allocated a shared memory segment, detach it.  This will
	 * implicitly detach the error queues, and any other shared memory queues,
	 * stored there.
	 */
	if (pcxt->seg != NULL)
	{
		dsm_detach(pcxt->seg);
		pcxt->seg = NULL;
	}

	/*
	 * If this parallel context is actually in backend-private memory rather
	 * than shared memory, free that memory instead.
	 */
	if (pcxt->private_memory != NULL)
	{
		pfree(pcxt->private_memory);
		pcxt->private_memory = NULL;
	}

	/*
	 * We can't finish transaction commit or abort until all of the workers
	 * have exited.  This means, in particular, that we can't respond to
	 * interrupts at this stage.
	 */
	HOLD_INTERRUPTS();
	WaitForParallelWorkersToExit(pcxt);
	RESUME_INTERRUPTS();