[GENERAL] Background worker with Listen

[Ihnat Peter | TSS Group a . s .]

I am trying to create background worker which listens to notifications and do 
some work after receiving one.
I got 2 problems:

-          Worker is receiving notifications from every channel not only the 
registered channel (in my case "foo")

-          Notifications are not logged in the server log - I cannot store the 
payloads for further work
Any help is welcomed.

Here is the code:

PG_MODULE_MAGIC;

void _PG_init(void);
void _PG_fini(void);

static volatile sig_atomic_t got_sigterm = false;
static volatile sig_atomic_t got_sigusr1 = false;
static char *notify_database = NULL;
static emit_log_hook_type prev_log_hook = NULL;

static void
bgw_sigterm(SIGNAL_ARGS)
{
                int save_errno = errno;
                got_sigterm = true;
                if (MyProc)
                                SetLatch(&MyProc->procLatch);
                errno = save_errno;
}

static void
bgw_sigusr1(SIGNAL_ARGS)
{
                int save_errno = errno;
                got_sigusr1 = true;
                if (MyProc)
                                SetLatch(&MyProc->procLatch);
               errno = save_errno;
}

static void
notify_main(Datum main_arg)
{
                pqsignal(SIGTERM, bgw_sigterm);
                pqsignal(SIGUSR1, bgw_sigusr1);

                BackgroundWorkerUnblockSignals();
                BackgroundWorkerInitializeConnection(notify_database, NULL);
                 EnableNotifyInterrupt();

                pgstat_report_activity(STATE_RUNNING, "background_worker");
                StartTransactionCommand();
                Async_Listen("foo");
                CommitTransactionCommand();
                pgstat_report_activity(STATE_IDLE, NULL);

                while (!got_sigterm)
                {
                                int           rc;

                                rc = WaitLatch(&MyProc->procLatch, WL_LATCH_SET 
| WL_TIMEOUT | WL_POSTMASTER_DEATH, 10000L);
                                ResetLatch(&MyProc->procLatch);

                                if (rc & WL_POSTMASTER_DEATH)
                                                proc_exit(1);

                                if (got_sigusr1)
                                {
                                                got_sigusr1 = false;
                                                elog(INFO, " background_worker: 
notification received");
                                                // DO SOME WORK WITH STORED 
NOTIFICATIONS
                                }

                }

                elog(LOG, "background_worker: finished");
                proc_exit(0);
}

static void
store_notification(ErrorData *edata)
{
                // HERE STORE THE NOTIFICATION FROM SERVER LOG

                if (prev_log_hook)
                                (*prev_log_hook) (edata);
}

void
_PG_init(void)
{
                BackgroundWorker worker;
                DefineCustomStringVariable("postgres", NULL, NULL, 
&notify_database,
                                           "postgres",
                                           PGC_POSTMASTER, 0, NULL, NULL, NULL);

                MemSet(&worker, 0, sizeof(BackgroundWorker));
                snprintf(worker.bgw_name, BGW_MAXLEN, "background_worker");
                worker.bgw_flags = BGWORKER_SHMEM_ACCESS | 
BGWORKER_BACKEND_DATABASE_CONNECTION;
                worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
                worker.bgw_main = notify_main;
                worker.bgw_restart_time = 10;
                worker.bgw_main_arg = (Datum) 0;
                worker.bgw_notify_pid = 0;
                RegisterBackgroundWorker(&worker);

                prev_log_hook = emit_log_hook;
                emit_log_hook = store_notification;
}

void
_PG_fini(void)
{
                emit_log_hook = prev_log_hook;
}