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/*-
* Copyright (c) 2014-2017 MongoDB, Inc.
* Copyright (c) 2008-2014 WiredTiger, Inc.
* All rights reserved.
*
* See the file LICENSE for redistribution information.
*/
#include "wt_internal.h"
/*
* __wt_cond_alloc --
* Allocate and initialize a condition variable.
*/
int
__wt_cond_alloc(WT_SESSION_IMPL *session, const char *name, WT_CONDVAR **condp)
{
WT_CONDVAR *cond;
WT_DECL_RET;
WT_RET(__wt_calloc_one(session, &cond));
WT_ERR(pthread_mutex_init(&cond->mtx, NULL));
#ifdef HAVE_PTHREAD_COND_MONOTONIC
{
pthread_condattr_t condattr;
WT_ERR(pthread_condattr_init(&condattr));
WT_ERR(pthread_condattr_setclock(&condattr, CLOCK_MONOTONIC));
WT_ERR(pthread_cond_init(&cond->cond, &condattr));
}
#else
WT_ERR(pthread_cond_init(&cond->cond, NULL));
#endif
cond->name = name;
cond->waiters = 0;
*condp = cond;
return (0);
err: __wt_free(session, cond);
return (ret);
}
/*
* __wt_cond_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_wait_signal(WT_SESSION_IMPL *session, WT_CONDVAR *cond,
uint64_t usecs, bool (*run_func)(WT_SESSION_IMPL *), bool *signalled)
{
struct timespec ts;
WT_DECL_RET;
bool locked;
locked = false;
/* Fast path if already signalled. */
*signalled = true;
if (__wt_atomic_addi32(&cond->waiters, 1) == 0)
return;
__wt_verbose(session, WT_VERB_MUTEX, "wait %s", cond->name);
WT_STAT_CONN_INCR(session, cond_wait);
WT_ERR(pthread_mutex_lock(&cond->mtx));
locked = true;
/*
* It's possible to race with threads waking us up. That's not a problem
* if there are multiple wakeups because the next wakeup will get us, or
* if we're only pausing for a short period. It's a problem if there's
* only a single wakeup, our waker is likely waiting for us to exit.
* After acquiring the mutex (so we're guaranteed to be awakened by any
* future wakeup call), optionally check if we're OK to keep running.
* This won't ensure our caller won't just loop and call us again, but
* at least it's not our fault.
*
* Assert we're not waiting longer than a second if not checking the
* run status.
*/
WT_ASSERT(session, run_func != NULL || usecs <= WT_MILLION);
if (run_func != NULL && !run_func(session))
goto skipping;
if (usecs > 0) {
/*
* Get the current time as the basis for calculating when the
* wait should end. Prefer a monotonic clock source to avoid
* unexpectedly long sleeps when the system clock is adjusted.
*
* Failing that, query the time directly and don't attempt to
* correct for the clock moving backwards, which would result
* in a sleep that is too long by however much the clock is
* updated. This isn't as good as a monotonic clock source but
* makes the window of vulnerability smaller (i.e., the
* calculated time is only incorrect if the system clock
* changes in between us querying it and waiting).
*/
#ifdef HAVE_PTHREAD_COND_MONOTONIC
WT_SYSCALL_RETRY(clock_gettime(CLOCK_MONOTONIC, &ts), ret);
if (ret != 0)
WT_PANIC_MSG(session, ret, "clock_gettime");
#else
__wt_epoch_raw(session, &ts);
#endif
ts.tv_sec += (time_t)
(((uint64_t)ts.tv_nsec + WT_THOUSAND * usecs) / WT_BILLION);
ts.tv_nsec = (long)
(((uint64_t)ts.tv_nsec + WT_THOUSAND * usecs) % WT_BILLION);
ret = pthread_cond_timedwait(&cond->cond, &cond->mtx, &ts);
} else
ret = pthread_cond_wait(&cond->cond, &cond->mtx);
/*
* Check pthread_cond_wait() return for EINTR, ETIME and
* ETIMEDOUT, some systems return these errors.
*/
if (ret == EINTR ||
#ifdef ETIME
ret == ETIME ||
#endif
ret == ETIMEDOUT) {
skipping: *signalled = false;
ret = 0;
}
err: (void)__wt_atomic_subi32(&cond->waiters, 1);
if (locked)
WT_TRET(pthread_mutex_unlock(&cond->mtx));
if (ret == 0)
return;
WT_PANIC_MSG(session, ret, "pthread_cond_wait: %s", cond->name);
}
/*
* __wt_cond_signal --
* Signal a waiting thread.
*/
void
__wt_cond_signal(WT_SESSION_IMPL *session, WT_CONDVAR *cond)
{
WT_DECL_RET;
__wt_verbose(session, WT_VERB_MUTEX, "signal %s", cond->name);
/*
* Our callers often set flags to cause a thread to exit. Add a barrier
* to ensure exit flags are seen by the sleeping threads, otherwise we
* can wake up a thread, it immediately goes back to sleep, and we'll
* hang. Use a full barrier (we may not write before waiting on thread
* join).
*/
WT_FULL_BARRIER();
/*
* Fast path if we are in (or can enter), a state where the next waiter
* will return immediately as already signaled.
*/
if (cond->waiters == -1 ||
(cond->waiters == 0 && __wt_atomic_casi32(&cond->waiters, 0, -1)))
return;
WT_ERR(pthread_mutex_lock(&cond->mtx));
ret = pthread_cond_broadcast(&cond->cond);
WT_TRET(pthread_mutex_unlock(&cond->mtx));
if (ret == 0)
return;
err:
WT_PANIC_MSG(session, ret, "pthread_cond_broadcast: %s", cond->name);
}
/*
* __wt_cond_destroy --
* Destroy a condition variable.
*/
void
__wt_cond_destroy(WT_SESSION_IMPL *session, WT_CONDVAR **condp)
{
WT_CONDVAR *cond;
WT_DECL_RET;
cond = *condp;
if (cond == NULL)
return;
if ((ret = pthread_cond_destroy(&cond->cond)) != 0)
WT_PANIC_MSG(
session, ret, "pthread_cond_destroy: %s", cond->name);
if ((ret = pthread_mutex_destroy(&cond->mtx)) != 0)
WT_PANIC_MSG(
session, ret, "pthread_mutex_destroy: %s", cond->name);
__wt_free(session, *condp);
}
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