C++ ResetLatch函数代码示例

/*
 * ProcWaitForSignal - wait for a signal from another backend.
 *
 * As this uses the generic process latch the caller has to be robust against
 * unrelated wakeups: Always check that the desired state has occurred, and
 * wait again if not.
 */
void
ProcWaitForSignal(void)
{
	WaitLatch(MyLatch, WL_LATCH_SET, 0);
	ResetLatch(MyLatch);
	CHECK_FOR_INTERRUPTS();
}

/*
 * hello_main
 *
 * Main loop processing.
 */
void
hello_main(Datum main_arg)
{
	/* Set up the sigterm signal before unblocking them */
	pqsignal(SIGTERM, hello_sigterm);

	/* We're now ready to receive signals */
	BackgroundWorkerUnblockSignals();
	while (!got_sigterm)
	{
		int rc;

		/* Wait 10s */
		rc = WaitLatch(&MyProc->procLatch,
					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
					   10000L,
					   PG_WAIT_EXTENSION);
		ResetLatch(&MyProc->procLatch);

		/* Emergency bailout if postmaster has died */
		if (rc & WL_POSTMASTER_DEATH)
			proc_exit(1);

		elog(LOG, "Hello World!"); /* Say Hello to the world */
	}
	proc_exit(0);
}

/*
 * Wait until at least *nbytesp bytes are available to be read from the
 * shared message queue, or until the buffer wraps around.  If the queue is
 * detached, returns SHM_MQ_DETACHED.  If nowait is specified and a wait
 * would be required, returns SHM_MQ_WOULD_BLOCK.  Otherwise, *datap is set
 * to the location at which data bytes can be read, *nbytesp is set to the
 * number of bytes which can be read at that address, and the return value
 * is SHM_MQ_SUCCESS.
 */
static shm_mq_result
shm_mq_receive_bytes(shm_mq *mq, Size bytes_needed, bool nowait,
					 Size *nbytesp, void **datap)
{
	Size		ringsize = mq->mq_ring_size;
	uint64		used;
	uint64		written;

	for (;;)
	{
		Size		offset;
		bool		detached;

		/* Get bytes written, so we can compute what's available to read. */
		written = shm_mq_get_bytes_written(mq, &detached);
		used = written - mq->mq_bytes_read;
		Assert(used <= ringsize);
		offset = mq->mq_bytes_read % (uint64) ringsize;

		/* If we have enough data or buffer has wrapped, we're done. */
		if (used >= bytes_needed || offset + used >= ringsize)
		{
			*nbytesp = Min(used, ringsize - offset);
			*datap = &mq->mq_ring[mq->mq_ring_offset + offset];
			return SHM_MQ_SUCCESS;
		}

		/*
		 * Fall out before waiting if the queue has been detached.
		 *
		 * Note that we don't check for this until *after* considering
		 * whether the data already available is enough, since the
		 * receiver can finish receiving a message stored in the buffer
		 * even after the sender has detached.
		 */
		if (detached)
			return SHM_MQ_DETACHED;

		/* Skip manipulation of our latch if nowait = true. */
		if (nowait)
			return SHM_MQ_WOULD_BLOCK;

		/*
		 * Wait for our latch to be set.  It might already be set for
		 * some unrelated reason, but that'll just result in one extra
		 * trip through the loop.  It's worth it to avoid resetting the
		 * latch at top of loop, because setting an already-set latch is
		 * much cheaper than setting one that has been reset.
		 */
		WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0);

		/* An interrupt may have occurred while we were waiting. */
		CHECK_FOR_INTERRUPTS();

		/* Reset the latch so we don't spin. */
		ResetLatch(&MyProc->procLatch);
	}
}

static void
wait_for_workers_to_become_ready(worker_state *wstate,
								 volatile test_shm_mq_header *hdr)
{
	bool		save_set_latch_on_sigusr1;
	bool		result = false;

	save_set_latch_on_sigusr1 = set_latch_on_sigusr1;
	set_latch_on_sigusr1 = true;

	PG_TRY();
	{
		for (;;)
		{
			int			workers_ready;

			/* If all the workers are ready, we have succeeded. */
			SpinLockAcquire(&hdr->mutex);
			workers_ready = hdr->workers_ready;
			SpinLockRelease(&hdr->mutex);
			if (workers_ready >= wstate->nworkers)
			{
				result = true;
				break;
			}

			/* If any workers (or the postmaster) have died, we have failed. */
			if (!check_worker_status(wstate))
			{
				result = false;
				break;
			}

			/* Wait to be signalled. */
			WaitLatch(MyLatch, WL_LATCH_SET, 0);

			/* An interrupt may have occurred while we were waiting. */
			CHECK_FOR_INTERRUPTS();

			/* Reset the latch so we don't spin. */
			ResetLatch(MyLatch);
		}
	}
	PG_CATCH();
	{
		set_latch_on_sigusr1 = save_set_latch_on_sigusr1;
		PG_RE_THROW();
	}
	PG_END_TRY();

	if (!result)
		ereport(ERROR,
				(errcode(ERRCODE_INSUFFICIENT_RESOURCES),
				 errmsg("one or more background workers failed to start")));
}

/*
 * Wait for a background worker to start up and attach to the shmem context.
 *
 * This is only needed for cleaning up the shared memory in case the worker
 * fails to attach.
 */
static void
WaitForReplicationWorkerAttach(LogicalRepWorker *worker,
							   uint16 generation,
							   BackgroundWorkerHandle *handle)
{
	BgwHandleStatus status;
	int			rc;

	for (;;)
	{
		pid_t		pid;

		CHECK_FOR_INTERRUPTS();

		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);

		/* Worker either died or has started; no need to do anything. */
		if (!worker->in_use || worker->proc)
		{
			LWLockRelease(LogicalRepWorkerLock);
			return;
		}

		LWLockRelease(LogicalRepWorkerLock);

		/* Check if worker has died before attaching, and clean up after it. */
		status = GetBackgroundWorkerPid(handle, &pid);

		if (status == BGWH_STOPPED)
		{
			LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
			/* Ensure that this was indeed the worker we waited for. */
			if (generation == worker->generation)
				logicalrep_worker_cleanup(worker);
			LWLockRelease(LogicalRepWorkerLock);
			return;
		}

		/*
		 * We need timeout because we generally don't get notified via latch
		 * about the worker attach.  But we don't expect to have to wait long.
		 */
		rc = WaitLatch(MyLatch,
					   WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
					   10L, WAIT_EVENT_BGWORKER_STARTUP);

		if (rc & WL_LATCH_SET)
		{
			ResetLatch(MyLatch);
			CHECK_FOR_INTERRUPTS();
		}
	}

	return;
}

/*
 *	Read data from a secure connection.
 */
ssize_t
secure_read(Port *port, void *ptr, size_t len)
{
	ssize_t		n;
	int			waitfor;

retry:
#ifdef USE_SSL
	waitfor = 0;
	if (port->ssl_in_use)
	{
		n = be_tls_read(port, ptr, len, &waitfor);
	}
	else
#endif
	{
		n = secure_raw_read(port, ptr, len);
		waitfor = WL_SOCKET_READABLE;
	}

	/* In blocking mode, wait until the socket is ready */
	if (n < 0 && !port->noblock && (errno == EWOULDBLOCK || errno == EAGAIN))
	{
		int		w;

		Assert(waitfor);

		w = WaitLatchOrSocket(MyLatch,
							  WL_LATCH_SET | waitfor,
							  port->sock, 0);

		/* Handle interrupt. */
		if (w & WL_LATCH_SET)
		{
			ResetLatch(MyLatch);
			ProcessClientReadInterrupt(true);

			/*
			 * We'll retry the read. Most likely it will return immediately
			 * because there's still no data available, and we'll wait
			 * for the socket to become ready again.
			 */
		}
		goto retry;
	}

	/*
	 * Process interrupts that happened while (or before) receiving. Note that
	 * we signal that we're not blocking, which will prevent some types of
	 * interrupts from being processed.
	 */
	ProcessClientReadInterrupt(false);

	return n;
}

/*
 * pg_sleep - delay for N seconds
 */
Datum
pg_sleep(PG_FUNCTION_ARGS)
{
	float8		secs = PG_GETARG_FLOAT8(0);
	float8		endtime;

	/*
	 * We sleep using WaitLatch, to ensure that we'll wake up promptly if an
	 * important signal (such as SIGALRM or SIGINT) arrives.  Because
	 * WaitLatch's upper limit of delay is INT_MAX milliseconds, and the user
	 * might ask for more than that, we sleep for at most 10 minutes and then
	 * loop.
	 *
	 * By computing the intended stop time initially, we avoid accumulation of
	 * extra delay across multiple sleeps.  This also ensures we won't delay
	 * less than the specified time when WaitLatch is terminated early by a
	 * non-query-canceling signal such as SIGHUP.
	 */

#ifdef HAVE_INT64_TIMESTAMP
#define GetNowFloat()	((float8) GetCurrentTimestamp() / 1000000.0)
#else
#define GetNowFloat()	GetCurrentTimestamp()
#endif

	endtime = GetNowFloat() + secs;

	for (;;)
	{
		float8		delay;
		long		delay_ms;

		CHECK_FOR_INTERRUPTS();

		delay = endtime - GetNowFloat();
		if (delay >= 600.0)
			delay_ms = 600000;
		else if (delay > 0.0)
			delay_ms = (long) ceil(delay * 1000.0);
		else
			break;

		(void) WaitLatch(MyLatch,
						 WL_LATCH_SET | WL_TIMEOUT,
						 delay_ms,
						 WAIT_EVENT_PG_SLEEP);
		ResetLatch(MyLatch);
	}

	PG_RETURN_VOID();
}

static void
BufferSaverMain(Datum main_arg)
{
	WorkerCommon();

	/*
	 * Main loop: do this until the SIGTERM handler tells us to terminate
	 */
	while (!got_sigterm)
	{
		int	rc;

		ResetLatch(&MyProc->procLatch);

		/*
		 * Wait on the process latch, which sleeps as necessary, but is awakened
		 * if postmaster dies. This way the background process goes away
		 * immediately in case of an emergency.
		 */
		rc = WaitLatch(&MyProc->procLatch,
					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
					   10 * 1000L);

		/* emergency bailout if postmaster has died */
		if (rc & WL_POSTMASTER_DEATH)
			proc_exit(1);

		/*
		 * In case of a SIGHUP, just reload the configuration.
		 */
		if (got_sighup)
		{
			got_sighup = false;
			ProcessConfigFile(PGC_SIGHUP);
		}
	}

	/*
	 * We recieved the SIGTERM; Shutdown is in progress, so save the
	 * shared-buffer contents.
	 */

	/* Save the buffers only if the extension is enabled. */
	if (guc_enabled)
		SaveBuffers();

	/*
	 * The worker exits here. A proc_exit(0) is not necessary, we'll let the
	 * caller do that.
	 */
}

/*
 * This is used when a process is waiting for its counterpart to attach to the
 * queue.  We exit when the other process attaches as expected, or, if
 * handle != NULL, when the referenced background process or the postmaster
 * dies.  Note that if handle == NULL, and the process fails to attach, we'll
 * potentially get stuck here forever waiting for a process that may never
 * start.  We do check for interrupts, though.
 *
 * ptr is a pointer to the memory address that we're expecting to become
 * non-NULL when our counterpart attaches to the queue.
 */
static bool
shm_mq_wait_internal(volatile shm_mq *mq, PGPROC *volatile * ptr,
					 BackgroundWorkerHandle *handle)
{
	bool		result = false;

	for (;;)
	{
		BgwHandleStatus status;
		pid_t		pid;
		bool		detached;

		/* Acquire the lock just long enough to check the pointer. */
		SpinLockAcquire(&mq->mq_mutex);
		detached = mq->mq_detached;
		result = (*ptr != NULL);
		SpinLockRelease(&mq->mq_mutex);

		/* Fail if detached; else succeed if initialized. */
		if (detached)
		{
			result = false;
			break;
		}
		if (result)
			break;

		if (handle != NULL)
		{
			/* Check for unexpected worker death. */
			status = GetBackgroundWorkerPid(handle, &pid);
			if (status != BGWH_STARTED && status != BGWH_NOT_YET_STARTED)
			{
				result = false;
				break;
			}
		}

		/* Wait to be signalled. */
		WaitLatch(MyLatch, WL_LATCH_SET, 0);

		/* An interrupt may have occurred while we were waiting. */
		CHECK_FOR_INTERRUPTS();

		/* Reset the latch so we don't spin. */
		ResetLatch(MyLatch);
	}

	return result;
}

/*
 * Prepare to wait on a given condition variable.
 *
 * This can optionally be called before entering a test/sleep loop.
 * Doing so is more efficient if we'll need to sleep at least once.
 * However, if the first test of the exit condition is likely to succeed,
 * it's more efficient to omit the ConditionVariablePrepareToSleep call.
 * See comments in ConditionVariableSleep for more detail.
 *
 * Caution: "before entering the loop" means you *must* test the exit
 * condition between calling ConditionVariablePrepareToSleep and calling
 * ConditionVariableSleep.  If that is inconvenient, omit calling
 * ConditionVariablePrepareToSleep.
 */
void
ConditionVariablePrepareToSleep(ConditionVariable *cv)
{
	int			pgprocno = MyProc->pgprocno;

	/*
	 * If first time through in this process, create a WaitEventSet, which
	 * we'll reuse for all condition variable sleeps.
	 */
	if (cv_wait_event_set == NULL)
	{
		WaitEventSet *new_event_set;

		new_event_set = CreateWaitEventSet(TopMemoryContext, 2);
		AddWaitEventToSet(new_event_set, WL_LATCH_SET, PGINVALID_SOCKET,
						  MyLatch, NULL);
		AddWaitEventToSet(new_event_set, WL_EXIT_ON_PM_DEATH, PGINVALID_SOCKET,
						  NULL, NULL);
		/* Don't set cv_wait_event_set until we have a correct WES. */
		cv_wait_event_set = new_event_set;
	}

	/*
	 * If some other sleep is already prepared, cancel it; this is necessary
	 * because we have just one static variable tracking the prepared sleep,
	 * and also only one cvWaitLink in our PGPROC.  It's okay to do this
	 * because whenever control does return to the other test-and-sleep loop,
	 * its ConditionVariableSleep call will just re-establish that sleep as
	 * the prepared one.
	 */
	if (cv_sleep_target != NULL)
		ConditionVariableCancelSleep();

	/* Record the condition variable on which we will sleep. */
	cv_sleep_target = cv;

	/*
	 * Reset my latch before adding myself to the queue, to ensure that we
	 * don't miss a wakeup that occurs immediately.
	 */
	ResetLatch(MyLatch);

	/* Add myself to the wait queue. */
	SpinLockAcquire(&cv->mutex);
	proclist_push_tail(&cv->wakeup, pgprocno, cvWaitLink);
	SpinLockRelease(&cv->mutex);
}

/*
 * Wait until the apply worker changes the state of our synchronization
 * worker to the expected one.
 *
 * Used when transitioning from SYNCWAIT state to CATCHUP.
 *
 * Returns false if the apply worker has disappeared.
 */
static bool
wait_for_worker_state_change(char expected_state)
{
	int			rc;

	for (;;)
	{
		LogicalRepWorker *worker;

		CHECK_FOR_INTERRUPTS();

		/*
		 * Done if already in correct state.  (We assume this fetch is atomic
		 * enough to not give a misleading answer if we do it with no lock.)
		 */
		if (MyLogicalRepWorker->relstate == expected_state)
			return true;

		/*
		 * Bail out if the apply worker has died, else signal it we're
		 * waiting.
		 */
		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
		worker = logicalrep_worker_find(MyLogicalRepWorker->subid,
										InvalidOid, false);
		if (worker && worker->proc)
			logicalrep_worker_wakeup_ptr(worker);
		LWLockRelease(LogicalRepWorkerLock);
		if (!worker)
			break;

		/*
		 * Wait.  We expect to get a latch signal back from the apply worker,
		 * but use a timeout in case it dies without sending one.
		 */
		rc = WaitLatch(MyLatch,
					   WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
					   1000L, WAIT_EVENT_LOGICAL_SYNC_STATE_CHANGE);

		if (rc & WL_LATCH_SET)
			ResetLatch(MyLatch);
	}

	return false;
}

/*
 * Wait until the relation synchronization state is set in the catalog to the
 * expected one.
 *
 * Used when transitioning from CATCHUP state to SYNCDONE.
 *
 * Returns false if the synchronization worker has disappeared or the table state
 * has been reset.
 */
static bool
wait_for_relation_state_change(Oid relid, char expected_state)
{
	char		state;

	for (;;)
	{
		LogicalRepWorker *worker;
		XLogRecPtr	statelsn;

		CHECK_FOR_INTERRUPTS();

		/* XXX use cache invalidation here to improve performance? */
		PushActiveSnapshot(GetLatestSnapshot());
		state = GetSubscriptionRelState(MyLogicalRepWorker->subid,
										relid, &statelsn, true);
		PopActiveSnapshot();

		if (state == SUBREL_STATE_UNKNOWN)
			return false;

		if (state == expected_state)
			return true;

		/* Check if the sync worker is still running and bail if not. */
		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);

		/* Check if the opposite worker is still running and bail if not. */
		worker = logicalrep_worker_find(MyLogicalRepWorker->subid,
										am_tablesync_worker() ? InvalidOid : relid,
										false);
		LWLockRelease(LogicalRepWorkerLock);
		if (!worker)
			return false;

		(void) WaitLatch(MyLatch,
						 WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
						 1000L, WAIT_EVENT_LOGICAL_SYNC_STATE_CHANGE);

		ResetLatch(MyLatch);
	}

	return false;
}

static void
config_log_main(Datum main_arg)
{
	config_log_objects	   *objects;

	pqsignal(SIGTERM, config_log_sigterm);
	pqsignal(SIGHUP,  config_log_sighup);

	/* We're now ready to receive signals */
	BackgroundWorkerUnblockSignals();

	/* Connect to database */
	BackgroundWorkerInitializeConnection(config_log_database, NULL);

	/* Verify expected objects exist */
	objects = initialize_objects();

	while (!got_sigterm)
	{
		int		rc;

		rc = WaitLatch(&MyProc->procLatch,
					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
					   100000L);
		ResetLatch(&MyProc->procLatch);

		/* emergency bailout if postmaster has died */
		if (rc & WL_POSTMASTER_DEATH)
			proc_exit(1);

		/*
		 * In case of a SIGHUP, just reload the configuration.
		 */
		if (got_sighup)
		{
              got_sighup = false;
              ProcessConfigFile(PGC_SIGHUP);
              execute_pg_settings_logger(objects);
		}
    }

	proc_exit(0);
}

/**
 * Main loop of the sender process. It wakes up every
 * gp_perfmon_segment_interval ms to send segment
 * information to perfmon
 */
static void
SegmentInfoSenderLoop(void)
{
	int rc;
	int counter;

	for (counter = 0;; counter += SEGMENT_INFO_LOOP_SLEEP_MS)
	{
		CHECK_FOR_INTERRUPTS();

		if (senderShutdownRequested)
		{
			break;
		}

		/* no need to live on if postmaster has died */
		if (!PostmasterIsAlive())
			exit(1);

		if (cluster_state_collect_hook)
			cluster_state_collect_hook();

		if (gp_enable_gpperfmon && counter >= gp_perfmon_segment_interval)
		{
			SegmentInfoSender();
			counter = 0;
		}

		/* Sleep a while. */
		rc = WaitLatch(&MyProc->procLatch,
				WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
				SEGMENT_INFO_LOOP_SLEEP_MS);
		ResetLatch(&MyProc->procLatch);

		/* emergency bailout if postmaster has died */
		if (rc & WL_POSTMASTER_DEATH)
			proc_exit(1);
	} /* end server loop */

	return;
}

/*
 * Wait for the result from a prior asynchronous execution function call.
 *
 * This function offers quick responsiveness by checking for any interruptions.
 *
 * This function emulates the PQexec()'s behavior of returning the last result
 * when there are many.
 *
 * Caller is responsible for the error handling on the result.
 */
PGresult *
pgfdw_get_result(PGconn *conn, const char *query)
{
	PGresult   *last_res = NULL;

	for (;;)
	{
		PGresult   *res;

		while (PQisBusy(conn))
		{
			int			wc;

			/* Sleep until there's something to do */
			wc = WaitLatchOrSocket(MyLatch,
								   WL_LATCH_SET | WL_SOCKET_READABLE,
								   PQsocket(conn),
								   -1L, PG_WAIT_EXTENSION);
			ResetLatch(MyLatch);

			CHECK_FOR_INTERRUPTS();

			/* Data available in socket */
			if (wc & WL_SOCKET_READABLE)
			{
				if (!PQconsumeInput(conn))
					pgfdw_report_error(ERROR, NULL, conn, false, query);
			}
		}

		res = PQgetResult(conn);
		if (res == NULL)
			break;				/* query is complete */

		PQclear(last_res);
		last_res = res;
	}

	return last_res;
}