Function LaunchParallelWorkers

src/backend/access/transam/parallel.c:587–673

* Launch parallel workers. */

 * Launch parallel workers.
 */
void
LaunchParallelWorkers(ParallelContext *pcxt)
{
	MemoryContext oldcontext;
	BackgroundWorker worker;
	int			i;
	bool		any_registrations_failed = false;

	/* Skip this if we have no workers. */
	if (pcxt->nworkers == 0 || pcxt->nworkers_to_launch == 0)
		return;

	/* We need to be a lock group leader. */
	BecomeLockGroupLeader();

	/* If we do have workers, we'd better have a DSM segment. */
	Assert(pcxt->seg != NULL);

	/* We might be running in a short-lived memory context. */
	oldcontext = MemoryContextSwitchTo(TopTransactionContext);

	/* Configure a worker. */
	memset(&worker, 0, sizeof(worker));
	snprintf(worker.bgw_name, BGW_MAXLEN, "parallel worker for PID %d",
			 MyProcPid);
	snprintf(worker.bgw_type, BGW_MAXLEN, "parallel worker");
	worker.bgw_flags =
		BGWORKER_SHMEM_ACCESS | BGWORKER_BACKEND_DATABASE_CONNECTION
		| BGWORKER_CLASS_PARALLEL;
	worker.bgw_start_time = BgWorkerStart_ConsistentState;
	worker.bgw_restart_time = BGW_NEVER_RESTART;
	sprintf(worker.bgw_library_name, "postgres");
	sprintf(worker.bgw_function_name, "ParallelWorkerMain");
	worker.bgw_main_arg = UInt32GetDatum(dsm_segment_handle(pcxt->seg));
	worker.bgw_notify_pid = MyProcPid;

	/*
	 * Start workers.
	 *
	 * The caller must be able to tolerate ending up with fewer workers than
	 * expected, so there is no need to throw an error here if registration
	 * fails.  It wouldn't help much anyway, because registering the worker in
	 * no way guarantees that it will start up and initialize successfully.
	 */
	for (i = 0; i < pcxt->nworkers_to_launch; ++i)
	{
		memcpy(worker.bgw_extra, &i, sizeof(int));
		if (!any_registrations_failed &&
			RegisterDynamicBackgroundWorker(&worker,
											&pcxt->worker[i].bgwhandle))
		{
			shm_mq_set_handle(pcxt->worker[i].error_mqh,
							  pcxt->worker[i].bgwhandle);
			pcxt->nworkers_launched++;
		}
		else
		{
			/*