* BackendStartup -- start backend process * * returns: STATUS_ERROR if the fork failed, STATUS_OK otherwise. * * Note: if you change this code, also consider StartAutovacuumWorker. */static intBackendStartup(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.     */    MyCancelKey = PostmasterRandom();    bn->cancel_key = MyCancelKey;    /* Pass down canAcceptConnections state */    port->canAcceptConnections = canAcceptConnections();    bn->dead_end = (port->canAcceptConnections != CAC_OK &&                    port->canAcceptConnections != CAC_WAITBACKUP);    /*     * 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;#ifdef EXEC_BACKEND    pid = backend_forkexec(port);#else                            /* !EXEC_BACKEND */    pid = fork_process();    if (pid == 0)                /* child */    {        free(bn);        /*         * Let's clean up ourselves as the postmaster child, and close the         * postmaster's listen sockets.  (In EXEC_BACKEND case this is all         * done in SubPostmasterMain.)         */        IsUnderPostmaster = true;        /* we are a postmaster subprocess now */        MyProcPid = getpid();    /* reset MyProcPid */        MyStartTime = time(NULL);        /* We don't want the postmaster's proc_exit() handlers */        on_exit_reset();        /* Close the postmaster's sockets */        ClosePostmasterPorts(false);        /* Perform additional initialization and collect startup packet */        BackendInitialize(port);        /* And run the backend */        proc_exit(BackendRun(port));    }#endif   /* EXEC_BACKEND */    if (pid < 0)    {        /* in parent, fork failed */        int            save_errno = errno;        if (!bn->dead_end)            (void) ReleasePostmasterChildSlot(bn->child_slot);        free(bn);        errno = save_errno;        ereport(LOG,                (errmsg("could not fork new process for connection: %m")));        report_fork_failure_to_client(port, save_errno);        return STATUS_ERROR;    }    /* in parent, successful fork */    ereport(DEBUG2,            (errmsg_internal("forked new backend, pid=%d socket=%d",                             (int) pid, (int) port->sock)));    /*     * Everything's been successful, it's safe to add this backend to our list     * of backends.     */    bn->pid = pid;    bn->is_autovacuum = false;    DLInitElem(&bn->elem, bn);    DLAddHead(BackendList, &bn->elem);#ifdef EXEC_BACKEND    if (!bn->dead_end)        ShmemBackendArrayAdd(bn);#endif    return STATUS_OK;}