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Allow discovery of whether a dynamic background worker is running.

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Using the infrastructure provided by this patch, it's possible either
to wait for the startup of a dynamically-registered background worker,
or to poll the status of such a worker without waiting.  In either
case, the current PID of the worker process can also be obtained.
As usual, worker_spi is updated to demonstrate the new functionality.

Patch by me.  Review by Andres Freund.
This commit is contained in:
Robert Haas
2013-08-28 14:08:13 -04:00
parent c9e2e2db5c
commit 090d0f2050
12 changed files with 367 additions and 12 deletions
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24
contrib/worker_spi/worker_spi.c
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@ -365,6 +365,9 @@ worker_spi_launch(PG_FUNCTION_ARGS)
{
int32 i = PG_GETARG_INT32(0);
BackgroundWorker worker;
BackgroundWorkerHandle *handle;
BgwHandleStatus status;
pid_t pid;
worker.bgw_flags = BGWORKER_SHMEM_ACCESS |
BGWORKER_BACKEND_DATABASE_CONNECTION;
@ -375,6 +378,25 @@ worker_spi_launch(PG_FUNCTION_ARGS)
sprintf(worker.bgw_function_name, "worker_spi_main");
snprintf(worker.bgw_name, BGW_MAXLEN, "worker %d", i);
worker.bgw_main_arg = Int32GetDatum(i);
/* set bgw_notify_pid so that we can use WaitForBackgroundWorkerStartup */
worker.bgw_notify_pid = MyProcPid;
PG_RETURN_BOOL(RegisterDynamicBackgroundWorker(&worker));
if (!RegisterDynamicBackgroundWorker(&worker, &handle))
PG_RETURN_NULL();
status = WaitForBackgroundWorkerStartup(handle, &pid);
if (status == BGWH_STOPPED)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_RESOURCES),
errmsg("could not start background process"),
errhint("More details may be available in the server log.")));
if (status == BGWH_POSTMASTER_DIED)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_RESOURCES),
errmsg("cannot start background processes without postmaster"),
errhint("Kill all remaining database processes and restart the database.")));
Assert(status == BGWH_STARTED);
PG_RETURN_INT32(pid);
}