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/*-
* Copyright (c) 2014-2020 MongoDB, Inc.
* Copyright (c) 2008-2014 WiredTiger, Inc.
* All rights reserved.
*
* See the file LICENSE for redistribution information.
*/
#include "wt_internal.h"
/*
* This is an implementation of condition variables that automatically adjust the wait time
* depending on whether the wake is resulting in useful work.
*/
/*
* __wt_cond_auto_alloc --
* Allocate and initialize an automatically adjusting condition variable.
*/
int
__wt_cond_auto_alloc(
WT_SESSION_IMPL *session, const char *name, uint64_t min, uint64_t max, WT_CONDVAR **condp)
{
WT_CONDVAR *cond;
WT_RET(__wt_cond_alloc(session, name, condp));
cond = *condp;
cond->min_wait = min;
cond->max_wait = max;
cond->prev_wait = min;
return (0);
}
/*
* __wt_cond_auto_wait_signal --
* Wait on a mutex, optionally timing out. If we get it before the time out period expires, let
* the caller know.
*/
void
__wt_cond_auto_wait_signal(WT_SESSION_IMPL *session, WT_CONDVAR *cond, bool progress,
bool (*run_func)(WT_SESSION_IMPL *), bool *signalled)
{
uint64_t delta, saved_prev_wait;
/*
* Catch cases where this function is called with a condition variable that wasn't initialized
* to do automatic adjustments.
*/
WT_ASSERT(session, cond->min_wait != 0);
WT_STAT_CONN_INCR(session, cond_auto_wait);
if (progress)
cond->prev_wait = cond->min_wait;
else {
delta = WT_MAX(1, (cond->max_wait - cond->min_wait) / 10);
/*
* Try to update the previous wait value for the condition variable. There can be multiple
* threads doing this concurrently, so use atomic operations to make sure the value remains
* within the bounds of the maximum configured. Don't retry if our update didn't make it in
* - it's not necessary for the previous wait time to be updated every time.
*/
WT_ORDERED_READ(saved_prev_wait, cond->prev_wait);
__wt_atomic_cas64(
&cond->prev_wait, saved_prev_wait, WT_MIN(cond->max_wait, saved_prev_wait + delta));
}
__wt_cond_wait_signal(session, cond, cond->prev_wait, run_func, signalled);
if (progress || *signalled)
WT_STAT_CONN_INCR(session, cond_auto_wait_reset);
if (*signalled)
cond->prev_wait = cond->min_wait;
}
/*
* __wt_cond_auto_wait --
* Wait on a mutex, optionally timing out. If we get it before the time out period expires, let
* the caller know.
*/
void
__wt_cond_auto_wait(
WT_SESSION_IMPL *session, WT_CONDVAR *cond, bool progress, bool (*run_func)(WT_SESSION_IMPL *))
{
bool notused;
__wt_cond_auto_wait_signal(session, cond, progress, run_func, ¬used);
}
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