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/*-
* Copyright (c) 2014-2016 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_RET(__wt_calloc_one(session, &cond));
InitializeCriticalSection(&cond->mtx);
/* Initialize the condition variable to permit self-blocking. */
InitializeConditionVariable(&cond->cond);
cond->name = name;
cond->waiters = 0;
*condp = cond;
return (0);
}
/*
* __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)
{
BOOL sleepret;
DWORD milliseconds, windows_error;
bool locked;
uint64_t milliseconds64;
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);
EnterCriticalSection(&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) {
milliseconds64 = usecs / WT_THOUSAND;
/*
* Check for 32-bit unsigned integer overflow
* INFINITE is max unsigned int on Windows
*/
if (milliseconds64 >= INFINITE)
milliseconds64 = INFINITE - 1;
milliseconds = (DWORD)milliseconds64;
/*
* 0 would mean the CV sleep becomes a TryCV which we do not
* want
*/
if (milliseconds == 0)
milliseconds = 1;
sleepret = SleepConditionVariableCS(
&cond->cond, &cond->mtx, milliseconds);
} else
sleepret = SleepConditionVariableCS(
&cond->cond, &cond->mtx, INFINITE);
/*
* SleepConditionVariableCS returns non-zero on success, 0 on timeout
* or failure.
*/
if (sleepret == 0) {
windows_error = __wt_getlasterror();
if (windows_error == ERROR_TIMEOUT) {
skipping: *signalled = false;
sleepret = 1;
}
}
(void)__wt_atomic_subi32(&cond->waiters, 1);
if (locked)
LeaveCriticalSection(&cond->mtx);
if (sleepret != 0)
return;
__wt_errx(session, "SleepConditionVariableCS: %s: %s",
cond->name, __wt_formatmessage(session, windows_error));
WT_PANIC_MSG(session, __wt_map_windows_error(windows_error),
"SleepConditionVariableCS: %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;
EnterCriticalSection(&cond->mtx);
WakeAllConditionVariable(&cond->cond);
LeaveCriticalSection(&cond->mtx);
}
/*
* __wt_cond_destroy --
* Destroy a condition variable.
*/
void
__wt_cond_destroy(WT_SESSION_IMPL *session, WT_CONDVAR **condp)
{
WT_CONDVAR *cond;
cond = *condp;
if (cond == NULL)
return;
/* Do nothing to delete Condition Variable */
DeleteCriticalSection(&cond->mtx);
__wt_free(session, *condp);
}
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