Adding upstream version 14.5.upstream/14.5upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 779 insertions, 0 deletions

diff --git a/src/backend/utils/misc/timeout.c b/src/backend/utils/misc/timeout.c
new file mode 100644
index 0000000..b79df17
--- /dev/null
+++ b/src/backend/utils/misc/timeout.c
@@ -0,0 +1,779 @@
+/*-------------------------------------------------------------------------
+ *
+ * timeout.c
+ *	  Routines to multiplex SIGALRM interrupts for multiple timeout reasons.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/misc/timeout.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <sys/time.h>
+
+#include "miscadmin.h"
+#include "storage/proc.h"
+#include "utils/timeout.h"
+#include "utils/timestamp.h"
+
+
+/* Data about any one timeout reason */
+typedef struct timeout_params
+{
+	TimeoutId	index;			/* identifier of timeout reason */
+
+	/* volatile because these may be changed from the signal handler */
+	volatile bool active;		/* true if timeout is in active_timeouts[] */
+	volatile bool indicator;	/* true if timeout has occurred */
+
+	/* callback function for timeout, or NULL if timeout not registered */
+	timeout_handler_proc timeout_handler;
+
+	TimestampTz start_time;		/* time that timeout was last activated */
+	TimestampTz fin_time;		/* time it is, or was last, due to fire */
+} timeout_params;
+
+/*
+ * List of possible timeout reasons in the order of enum TimeoutId.
+ */
+static timeout_params all_timeouts[MAX_TIMEOUTS];
+static bool all_timeouts_initialized = false;
+
+/*
+ * List of active timeouts ordered by their fin_time and priority.
+ * This list is subject to change by the interrupt handler, so it's volatile.
+ */
+static volatile int num_active_timeouts = 0;
+static timeout_params *volatile active_timeouts[MAX_TIMEOUTS];
+
+/*
+ * Flag controlling whether the signal handler is allowed to do anything.
+ * This is useful to avoid race conditions with the handler.  Note in
+ * particular that this lets us make changes in the data structures without
+ * tediously disabling and re-enabling the timer signal.  Most of the time,
+ * no interrupt would happen anyway during such critical sections, but if
+ * one does, this rule ensures it's safe.  Leaving the signal enabled across
+ * multiple operations can greatly reduce the number of kernel calls we make,
+ * too.  See comments in schedule_alarm() about that.
+ *
+ * We leave this "false" when we're not expecting interrupts, just in case.
+ */
+static volatile sig_atomic_t alarm_enabled = false;
+
+#define disable_alarm() (alarm_enabled = false)
+#define enable_alarm()	(alarm_enabled = true)
+
+/*
+ * State recording if and when we next expect the interrupt to fire.
+ * (signal_due_at is valid only when signal_pending is true.)
+ * Note that the signal handler will unconditionally reset signal_pending to
+ * false, so that can change asynchronously even when alarm_enabled is false.
+ */
+static volatile sig_atomic_t signal_pending = false;
+static volatile TimestampTz signal_due_at = 0;
+
+
+/*****************************************************************************
+ * Internal helper functions
+ *
+ * For all of these, it is caller's responsibility to protect them from
+ * interruption by the signal handler.  Generally, call disable_alarm()
+ * first to prevent interruption, then update state, and last call
+ * schedule_alarm(), which will re-enable the signal handler if needed.
+ *****************************************************************************/
+
+/*
+ * Find the index of a given timeout reason in the active array.
+ * If it's not there, return -1.
+ */
+static int
+find_active_timeout(TimeoutId id)
+{
+	int			i;
+
+	for (i = 0; i < num_active_timeouts; i++)
+	{
+		if (active_timeouts[i]->index == id)
+			return i;
+	}
+
+	return -1;
+}
+
+/*
+ * Insert specified timeout reason into the list of active timeouts
+ * at the given index.
+ */
+static void
+insert_timeout(TimeoutId id, int index)
+{
+	int			i;
+
+	if (index < 0 || index > num_active_timeouts)
+		elog(FATAL, "timeout index %d out of range 0..%d", index,
+			 num_active_timeouts);
+
+	Assert(!all_timeouts[id].active);
+	all_timeouts[id].active = true;
+
+	for (i = num_active_timeouts - 1; i >= index; i--)
+		active_timeouts[i + 1] = active_timeouts[i];
+
+	active_timeouts[index] = &all_timeouts[id];
+
+	num_active_timeouts++;
+}
+
+/*
+ * Remove the index'th element from the timeout list.
+ */
+static void
+remove_timeout_index(int index)
+{
+	int			i;
+
+	if (index < 0 || index >= num_active_timeouts)
+		elog(FATAL, "timeout index %d out of range 0..%d", index,
+			 num_active_timeouts - 1);
+
+	Assert(active_timeouts[index]->active);
+	active_timeouts[index]->active = false;
+
+	for (i = index + 1; i < num_active_timeouts; i++)
+		active_timeouts[i - 1] = active_timeouts[i];
+
+	num_active_timeouts--;
+}
+
+/*
+ * Enable the specified timeout reason
+ */
+static void
+enable_timeout(TimeoutId id, TimestampTz now, TimestampTz fin_time)
+{
+	int			i;
+
+	/* Assert request is sane */
+	Assert(all_timeouts_initialized);
+	Assert(all_timeouts[id].timeout_handler != NULL);
+
+	/*
+	 * If this timeout was already active, momentarily disable it.  We
+	 * interpret the call as a directive to reschedule the timeout.
+	 */
+	if (all_timeouts[id].active)
+		remove_timeout_index(find_active_timeout(id));
+
+	/*
+	 * Find out the index where to insert the new timeout.  We sort by
+	 * fin_time, and for equal fin_time by priority.
+	 */
+	for (i = 0; i < num_active_timeouts; i++)
+	{
+		timeout_params *old_timeout = active_timeouts[i];
+
+		if (fin_time < old_timeout->fin_time)
+			break;
+		if (fin_time == old_timeout->fin_time && id < old_timeout->index)
+			break;
+	}
+
+	/*
+	 * Mark the timeout active, and insert it into the active list.
+	 */
+	all_timeouts[id].indicator = false;
+	all_timeouts[id].start_time = now;
+	all_timeouts[id].fin_time = fin_time;
+
+	insert_timeout(id, i);
+}
+
+/*
+ * Schedule alarm for the next active timeout, if any
+ *
+ * We assume the caller has obtained the current time, or a close-enough
+ * approximation.  (It's okay if a tick or two has passed since "now", or
+ * if a little more time elapses before we reach the kernel call; that will
+ * cause us to ask for an interrupt a tick or two later than the nearest
+ * timeout, which is no big deal.  Passing a "now" value that's in the future
+ * would be bad though.)
+ */
+static void
+schedule_alarm(TimestampTz now)
+{
+	if (num_active_timeouts > 0)
+	{
+		struct itimerval timeval;
+		TimestampTz nearest_timeout;
+		long		secs;
+		int			usecs;
+
+		MemSet(&timeval, 0, sizeof(struct itimerval));
+
+		/*
+		 * If we think there's a signal pending, but current time is more than
+		 * 10ms past when the signal was due, then assume that the timeout
+		 * request got lost somehow; clear signal_pending so that we'll reset
+		 * the interrupt request below.  (10ms corresponds to the worst-case
+		 * timeout granularity on modern systems.)  It won't hurt us if the
+		 * interrupt does manage to fire between now and when we reach the
+		 * setitimer() call.
+		 */
+		if (signal_pending && now > signal_due_at + 10 * 1000)
+			signal_pending = false;
+
+		/*
+		 * Get the time remaining till the nearest pending timeout.  If it is
+		 * negative, assume that we somehow missed an interrupt, and clear
+		 * signal_pending.  This gives us another chance to recover if the
+		 * kernel drops a timeout request for some reason.
+		 */
+		nearest_timeout = active_timeouts[0]->fin_time;
+		if (now > nearest_timeout)
+		{
+			signal_pending = false;
+			/* force an interrupt as soon as possible */
+			secs = 0;
+			usecs = 1;
+		}
+		else
+		{
+			TimestampDifference(now, nearest_timeout,
+								&secs, &usecs);
+
+			/*
+			 * It's possible that the difference is less than a microsecond;
+			 * ensure we don't cancel, rather than set, the interrupt.
+			 */
+			if (secs == 0 && usecs == 0)
+				usecs = 1;
+		}
+
+		timeval.it_value.tv_sec = secs;
+		timeval.it_value.tv_usec = usecs;
+
+		/*
+		 * We must enable the signal handler before calling setitimer(); if we
+		 * did it in the other order, we'd have a race condition wherein the
+		 * interrupt could occur before we can set alarm_enabled, so that the
+		 * signal handler would fail to do anything.
+		 *
+		 * Because we didn't bother to disable the timer in disable_alarm(),
+		 * it's possible that a previously-set interrupt will fire between
+		 * enable_alarm() and setitimer().  This is safe, however.  There are
+		 * two possible outcomes:
+		 *
+		 * 1. The signal handler finds nothing to do (because the nearest
+		 * timeout event is still in the future).  It will re-set the timer
+		 * and return.  Then we'll overwrite the timer value with a new one.
+		 * This will mean that the timer fires a little later than we
+		 * intended, but only by the amount of time it takes for the signal
+		 * handler to do nothing useful, which shouldn't be much.
+		 *
+		 * 2. The signal handler executes and removes one or more timeout
+		 * events.  When it returns, either the queue is now empty or the
+		 * frontmost event is later than the one we looked at above.  So we'll
+		 * overwrite the timer value with one that is too soon (plus or minus
+		 * the signal handler's execution time), causing a useless interrupt
+		 * to occur.  But the handler will then re-set the timer and
+		 * everything will still work as expected.
+		 *
+		 * Since these cases are of very low probability (the window here
+		 * being quite narrow), it's not worth adding cycles to the mainline
+		 * code to prevent occasional wasted interrupts.
+		 */
+		enable_alarm();
+
+		/*
+		 * If there is already an interrupt pending that's at or before the
+		 * needed time, we need not do anything more.  The signal handler will
+		 * do the right thing in the first case, and re-schedule the interrupt
+		 * for later in the second case.  It might seem that the extra
+		 * interrupt is wasted work, but it's not terribly much work, and this
+		 * method has very significant advantages in the common use-case where
+		 * we repeatedly set a timeout that we don't expect to reach and then
+		 * cancel it.  Instead of invoking setitimer() every time the timeout
+		 * is set or canceled, we perform one interrupt and a re-scheduling
+		 * setitimer() call at intervals roughly equal to the timeout delay.
+		 * For example, with statement_timeout = 1s and a throughput of
+		 * thousands of queries per second, this method requires an interrupt
+		 * and setitimer() call roughly once a second, rather than thousands
+		 * of setitimer() calls per second.
+		 *
+		 * Because of the possible passage of time between when we obtained
+		 * "now" and when we reach setitimer(), the kernel's opinion of when
+		 * to trigger the interrupt is likely to be a bit later than
+		 * signal_due_at.  That's fine, for the same reasons described above.
+		 */
+		if (signal_pending && nearest_timeout >= signal_due_at)
+			return;
+
+		/*
+		 * As with calling enable_alarm(), we must set signal_pending *before*
+		 * calling setitimer(); if we did it after, the signal handler could
+		 * trigger before we set it, leaving us with a false opinion that a
+		 * signal is still coming.
+		 *
+		 * Other race conditions involved with setting/checking signal_pending
+		 * are okay, for the reasons described above.  One additional point is
+		 * that the signal handler could fire after we set signal_due_at, but
+		 * still before the setitimer() call.  Then the handler could
+		 * overwrite signal_due_at with a value it computes, which will be the
+		 * same as or perhaps later than what we just computed.  After we
+		 * perform setitimer(), the net effect would be that signal_due_at
+		 * gives a time later than when the interrupt will really happen;
+		 * which is a safe situation.
+		 */
+		signal_due_at = nearest_timeout;
+		signal_pending = true;
+
+		/* Set the alarm timer */
+		if (setitimer(ITIMER_REAL, &timeval, NULL) != 0)
+		{
+			/*
+			 * Clearing signal_pending here is a bit pro forma, but not
+			 * entirely so, since something in the FATAL exit path could try
+			 * to use timeout facilities.
+			 */
+			signal_pending = false;
+			elog(FATAL, "could not enable SIGALRM timer: %m");
+		}
+	}
+}
+
+
+/*****************************************************************************
+ * Signal handler
+ *****************************************************************************/
+
+/*
+ * Signal handler for SIGALRM
+ *
+ * Process any active timeout reasons and then reschedule the interrupt
+ * as needed.
+ */
+static void
+handle_sig_alarm(SIGNAL_ARGS)
+{
+	int			save_errno = errno;
+
+	/*
+	 * Bump the holdoff counter, to make sure nothing we call will process
+	 * interrupts directly. No timeout handler should do that, but these
+	 * failures are hard to debug, so better be sure.
+	 */
+	HOLD_INTERRUPTS();
+
+	/*
+	 * SIGALRM is always cause for waking anything waiting on the process
+	 * latch.
+	 */
+	SetLatch(MyLatch);
+
+	/*
+	 * Always reset signal_pending, even if !alarm_enabled, since indeed no
+	 * signal is now pending.
+	 */
+	signal_pending = false;
+
+	/*
+	 * Fire any pending timeouts, but only if we're enabled to do so.
+	 */
+	if (alarm_enabled)
+	{
+		/*
+		 * Disable alarms, just in case this platform allows signal handlers
+		 * to interrupt themselves.  schedule_alarm() will re-enable if
+		 * appropriate.
+		 */
+		disable_alarm();
+
+		if (num_active_timeouts > 0)
+		{
+			TimestampTz now = GetCurrentTimestamp();
+
+			/* While the first pending timeout has been reached ... */
+			while (num_active_timeouts > 0 &&
+				   now >= active_timeouts[0]->fin_time)
+			{
+				timeout_params *this_timeout = active_timeouts[0];
+
+				/* Remove it from the active list */
+				remove_timeout_index(0);
+
+				/* Mark it as fired */
+				this_timeout->indicator = true;
+
+				/* And call its handler function */
+				this_timeout->timeout_handler();
+
+				/*
+				 * The handler might not take negligible time (CheckDeadLock
+				 * for instance isn't too cheap), so let's update our idea of
+				 * "now" after each one.
+				 */
+				now = GetCurrentTimestamp();
+			}
+
+			/* Done firing timeouts, so reschedule next interrupt if any */
+			schedule_alarm(now);
+		}
+	}
+
+	RESUME_INTERRUPTS();
+
+	errno = save_errno;
+}
+
+
+/*****************************************************************************
+ * Public API
+ *****************************************************************************/
+
+/*
+ * Initialize timeout module.
+ *
+ * This must be called in every process that wants to use timeouts.
+ *
+ * If the process was forked from another one that was also using this
+ * module, be sure to call this before re-enabling signals; else handlers
+ * meant to run in the parent process might get invoked in this one.
+ */
+void
+InitializeTimeouts(void)
+{
+	int			i;
+
+	/* Initialize, or re-initialize, all local state */
+	disable_alarm();
+
+	num_active_timeouts = 0;
+
+	for (i = 0; i < MAX_TIMEOUTS; i++)
+	{
+		all_timeouts[i].index = i;
+		all_timeouts[i].active = false;
+		all_timeouts[i].indicator = false;
+		all_timeouts[i].timeout_handler = NULL;
+		all_timeouts[i].start_time = 0;
+		all_timeouts[i].fin_time = 0;
+	}
+
+	all_timeouts_initialized = true;
+
+	/* Now establish the signal handler */
+	pqsignal(SIGALRM, handle_sig_alarm);
+}
+
+/*
+ * Register a timeout reason
+ *
+ * For predefined timeouts, this just registers the callback function.
+ *
+ * For user-defined timeouts, pass id == USER_TIMEOUT; we then allocate and
+ * return a timeout ID.
+ */
+TimeoutId
+RegisterTimeout(TimeoutId id, timeout_handler_proc handler)
+{
+	Assert(all_timeouts_initialized);
+
+	/* There's no need to disable the signal handler here. */
+
+	if (id >= USER_TIMEOUT)
+	{
+		/* Allocate a user-defined timeout reason */
+		for (id = USER_TIMEOUT; id < MAX_TIMEOUTS; id++)
+			if (all_timeouts[id].timeout_handler == NULL)
+				break;
+		if (id >= MAX_TIMEOUTS)
+			ereport(FATAL,
+					(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
+					 errmsg("cannot add more timeout reasons")));
+	}
+
+	Assert(all_timeouts[id].timeout_handler == NULL);
+
+	all_timeouts[id].timeout_handler = handler;
+
+	return id;
+}
+
+/*
+ * Reschedule any pending SIGALRM interrupt.
+ *
+ * This can be used during error recovery in case query cancel resulted in loss
+ * of a SIGALRM event (due to longjmp'ing out of handle_sig_alarm before it
+ * could do anything).  But note it's not necessary if any of the public
+ * enable_ or disable_timeout functions are called in the same area, since
+ * those all do schedule_alarm() internally if needed.
+ */
+void
+reschedule_timeouts(void)
+{
+	/* For flexibility, allow this to be called before we're initialized. */
+	if (!all_timeouts_initialized)
+		return;
+
+	/* Disable timeout interrupts for safety. */
+	disable_alarm();
+
+	/* Reschedule the interrupt, if any timeouts remain active. */
+	if (num_active_timeouts > 0)
+		schedule_alarm(GetCurrentTimestamp());
+}
+
+/*
+ * Enable the specified timeout to fire after the specified delay.
+ *
+ * Delay is given in milliseconds.
+ */
+void
+enable_timeout_after(TimeoutId id, int delay_ms)
+{
+	TimestampTz now;
+	TimestampTz fin_time;
+
+	/* Disable timeout interrupts for safety. */
+	disable_alarm();
+
+	/* Queue the timeout at the appropriate time. */
+	now = GetCurrentTimestamp();
+	fin_time = TimestampTzPlusMilliseconds(now, delay_ms);
+	enable_timeout(id, now, fin_time);
+
+	/* Set the timer interrupt. */
+	schedule_alarm(now);
+}
+
+/*
+ * Enable the specified timeout to fire at the specified time.
+ *
+ * This is provided to support cases where there's a reason to calculate
+ * the timeout by reference to some point other than "now".  If there isn't,
+ * use enable_timeout_after(), to avoid calling GetCurrentTimestamp() twice.
+ */
+void
+enable_timeout_at(TimeoutId id, TimestampTz fin_time)
+{
+	TimestampTz now;
+
+	/* Disable timeout interrupts for safety. */
+	disable_alarm();
+
+	/* Queue the timeout at the appropriate time. */
+	now = GetCurrentTimestamp();
+	enable_timeout(id, now, fin_time);
+
+	/* Set the timer interrupt. */
+	schedule_alarm(now);
+}
+
+/*
+ * Enable multiple timeouts at once.
+ *
+ * This works like calling enable_timeout_after() and/or enable_timeout_at()
+ * multiple times.  Use this to reduce the number of GetCurrentTimestamp()
+ * and setitimer() calls needed to establish multiple timeouts.
+ */
+void
+enable_timeouts(const EnableTimeoutParams *timeouts, int count)
+{
+	TimestampTz now;
+	int			i;
+
+	/* Disable timeout interrupts for safety. */
+	disable_alarm();
+
+	/* Queue the timeout(s) at the appropriate times. */
+	now = GetCurrentTimestamp();
+
+	for (i = 0; i < count; i++)
+	{
+		TimeoutId	id = timeouts[i].id;
+		TimestampTz fin_time;
+
+		switch (timeouts[i].type)
+		{
+			case TMPARAM_AFTER:
+				fin_time = TimestampTzPlusMilliseconds(now,
+													   timeouts[i].delay_ms);
+				enable_timeout(id, now, fin_time);
+				break;
+
+			case TMPARAM_AT:
+				enable_timeout(id, now, timeouts[i].fin_time);
+				break;
+
+			default:
+				elog(ERROR, "unrecognized timeout type %d",
+					 (int) timeouts[i].type);
+				break;
+		}
+	}
+
+	/* Set the timer interrupt. */
+	schedule_alarm(now);
+}
+
+/*
+ * Cancel the specified timeout.
+ *
+ * The timeout's I've-been-fired indicator is reset,
+ * unless keep_indicator is true.
+ *
+ * When a timeout is canceled, any other active timeout remains in force.
+ * It's not an error to disable a timeout that is not enabled.
+ */
+void
+disable_timeout(TimeoutId id, bool keep_indicator)
+{
+	/* Assert request is sane */
+	Assert(all_timeouts_initialized);
+	Assert(all_timeouts[id].timeout_handler != NULL);
+
+	/* Disable timeout interrupts for safety. */
+	disable_alarm();
+
+	/* Find the timeout and remove it from the active list. */
+	if (all_timeouts[id].active)
+		remove_timeout_index(find_active_timeout(id));
+
+	/* Mark it inactive, whether it was active or not. */
+	if (!keep_indicator)
+		all_timeouts[id].indicator = false;
+
+	/* Reschedule the interrupt, if any timeouts remain active. */
+	if (num_active_timeouts > 0)
+		schedule_alarm(GetCurrentTimestamp());
+}
+
+/*
+ * Cancel multiple timeouts at once.
+ *
+ * The timeouts' I've-been-fired indicators are reset,
+ * unless timeouts[i].keep_indicator is true.
+ *
+ * This works like calling disable_timeout() multiple times.
+ * Use this to reduce the number of GetCurrentTimestamp()
+ * and setitimer() calls needed to cancel multiple timeouts.
+ */
+void
+disable_timeouts(const DisableTimeoutParams *timeouts, int count)
+{
+	int			i;
+
+	Assert(all_timeouts_initialized);
+
+	/* Disable timeout interrupts for safety. */
+	disable_alarm();
+
+	/* Cancel the timeout(s). */
+	for (i = 0; i < count; i++)
+	{
+		TimeoutId	id = timeouts[i].id;
+
+		Assert(all_timeouts[id].timeout_handler != NULL);
+
+		if (all_timeouts[id].active)
+			remove_timeout_index(find_active_timeout(id));
+
+		if (!timeouts[i].keep_indicator)
+			all_timeouts[id].indicator = false;
+	}
+
+	/* Reschedule the interrupt, if any timeouts remain active. */
+	if (num_active_timeouts > 0)
+		schedule_alarm(GetCurrentTimestamp());
+}
+
+/*
+ * Disable the signal handler, remove all timeouts from the active list,
+ * and optionally reset their timeout indicators.
+ */
+void
+disable_all_timeouts(bool keep_indicators)
+{
+	int			i;
+
+	disable_alarm();
+
+	/*
+	 * We used to disable the timer interrupt here, but in common usage
+	 * patterns it's cheaper to leave it enabled; that may save us from having
+	 * to enable it again shortly.  See comments in schedule_alarm().
+	 */
+
+	num_active_timeouts = 0;
+
+	for (i = 0; i < MAX_TIMEOUTS; i++)
+	{
+		all_timeouts[i].active = false;
+		if (!keep_indicators)
+			all_timeouts[i].indicator = false;
+	}
+}
+
+/*
+ * Return true if the timeout is active (enabled and not yet fired)
+ *
+ * This is, of course, subject to race conditions, as the timeout could fire
+ * immediately after we look.
+ */
+bool
+get_timeout_active(TimeoutId id)
+{
+	return all_timeouts[id].active;
+}
+
+/*
+ * Return the timeout's I've-been-fired indicator
+ *
+ * If reset_indicator is true, reset the indicator when returning true.
+ * To avoid missing timeouts due to race conditions, we are careful not to
+ * reset the indicator when returning false.
+ */
+bool
+get_timeout_indicator(TimeoutId id, bool reset_indicator)
+{
+	if (all_timeouts[id].indicator)
+	{
+		if (reset_indicator)
+			all_timeouts[id].indicator = false;
+		return true;
+	}
+	return false;
+}
+
+/*
+ * Return the time when the timeout was most recently activated
+ *
+ * Note: will return 0 if timeout has never been activated in this process.
+ * However, we do *not* reset the start_time when a timeout occurs, so as
+ * not to create a race condition if SIGALRM fires just as some code is
+ * about to fetch the value.
+ */
+TimestampTz
+get_timeout_start_time(TimeoutId id)
+{
+	return all_timeouts[id].start_time;
+}
+
+/*
+ * Return the time when the timeout is, or most recently was, due to fire
+ *
+ * Note: will return 0 if timeout has never been activated in this process.
+ * However, we do *not* reset the fin_time when a timeout occurs, so as
+ * not to create a race condition if SIGALRM fires just as some code is
+ * about to fetch the value.
+ */
+TimestampTz
+get_timeout_finish_time(TimeoutId id)
+{
+	return all_timeouts[id].fin_time;
+}