Function throttle

src/backend/replication/basebackup.c:2094–2161

* Increment the network transfer counter by the given number of bytes, * and sleep if necessary to comply with the requested network transfer * rate. */

 * rate.
 */
static void
throttle(size_t increment)
{
	TimeOffset	elapsed_min;

	if (throttling_counter < 0)
		return;

	throttling_counter += increment;
	if (throttling_counter < throttling_sample)
		return;

	/* How much time should have elapsed at minimum? */
	elapsed_min = elapsed_min_unit *
		(throttling_counter / throttling_sample);

	/*
	 * Since the latch could be set repeatedly because of concurrently WAL
	 * activity, sleep in a loop to ensure enough time has passed.
	 */
	for (;;)
	{
		TimeOffset	elapsed,
					sleep;
		int			wait_result;

		/* Time elapsed since the last measurement (and possible wake up). */
		elapsed = GetCurrentTimestamp() - throttled_last;

		/* sleep if the transfer is faster than it should be */
		sleep = elapsed_min - elapsed;
		if (sleep <= 0)
			break;

		ResetLatch(MyLatch);

		/* We're eating a potentially set latch, so check for interrupts */
		CHECK_FOR_INTERRUPTS();

		/*
		 * (TAR_SEND_SIZE / throttling_sample * elapsed_min_unit) should be
		 * the maximum time to sleep. Thus the cast to long is safe.
		 */
		wait_result = WaitLatch(MyLatch,
								WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
								(long) (sleep / 1000),
								WAIT_EVENT_BASE_BACKUP_THROTTLE);

		if (wait_result & WL_LATCH_SET)
			CHECK_FOR_INTERRUPTS();

		/* Done waiting? */
		if (wait_result & WL_TIMEOUT)
			break;
	}

	/*
	 * As we work with integers, only whole multiple of throttling_sample was