Function BackendStartup

src/backend/postmaster/postmaster.c:4732–4840

* BackendStartup -- start backend process * * returns: STATUS_ERROR if the fork failed, STATUS_OK otherwise. * * Note: if you change this code, also consider StartAutovacuumWorker. */

 * Note: if you change this code, also consider StartAutovacuumWorker.
 */
static int
BackendStartup(Port *port)
{
	Backend    *bn;				/* for backend cleanup */
	pid_t		pid;

	/*
	 * Create backend data structure.  Better before the fork() so we can
	 * handle failure cleanly.
	 */
	bn = (Backend *) malloc(sizeof(Backend));
	if (!bn)
	{
		ereport(LOG,
				(errcode(ERRCODE_OUT_OF_MEMORY),
				 errmsg("out of memory")));
		return STATUS_ERROR;
	}

	/*
	 * Compute the cancel key that will be assigned to this backend. The
	 * backend will have its own copy in the forked-off process' value of
	 * MyCancelKey, so that it can transmit the key to the frontend.
	 */
	if (!RandomCancelKey(&MyCancelKey))
	{
		free(bn);
		ereport(LOG,
				(errcode(ERRCODE_INTERNAL_ERROR),
				 errmsg("could not generate random cancel key")));
		return STATUS_ERROR;
	}

	bn->cancel_key = MyCancelKey;

	/* Pass down canAcceptConnections state */
	port->canAcceptConnections = canAcceptConnections(BACKEND_TYPE_NORMAL);
	bn->dead_end = (port->canAcceptConnections != CAC_OK &&
					port->canAcceptConnections != CAC_SUPERUSER &&
					port->canAcceptConnections != CAC_MIRROR_READY);

	/*
	 * Unless it's a dead_end child, assign it a child slot number
	 */
	if (!bn->dead_end)
		bn->child_slot = MyPMChildSlot = AssignPostmasterChildSlot();
	else
		bn->child_slot = 0;

	/* Hasn't asked to be notified about any bgworkers yet */
	bn->bgworker_notify = false;

#ifdef EXEC_BACKEND
	pid = backend_forkexec(port);
#else							/* !EXEC_BACKEND */
	pid = fork_process();
	if (pid == 0)				/* child */
	{