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/*
* condvar.c
*
* Description:
* This translation unit implements condition variables and their primitives.
*
* Pthreads-win32 - POSIX Threads Library for Win32
* Copyright (C) 1998
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the Free
* Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
* MA 02111-1307, USA
*/
#include "pthread.h"
#include "implement.h"
static int
_cond_check_need_init(pthread_cond_t *cond)
{
int result = 0;
/*
* The following guarded test is specifically for statically
* initialised condition variables (via PTHREAD_OBJECT_INITIALIZER).
*
* Note that by not providing this synchronisation we risk
* introducing race conditions into applications which are
* correctly written.
*
* Approach
* --------
* We know that static condition variables will not be PROCESS_SHARED
* so we can serialise access to internal state using
* Win32 Critical Sections rather than Win32 Mutexes.
*
* If using a single global lock slows applications down too much,
* multiple global locks could be created and hashed on some random
* value associated with each mutex, the pointer perhaps. At a guess,
* a good value for the optimal number of global locks might be
* the number of processors + 1.
*
*/
EnterCriticalSection(&_pthread_cond_test_init_lock);
/*
* We got here possibly under race
* conditions. Check again inside the critical section.
* If a static cv has been destroyed, the application can
* re-initialise it only by calling pthread_cond_init()
* explicitly.
*/
if (*cond == (pthread_cond_t) _PTHREAD_OBJECT_AUTO_INIT)
{
result = pthread_cond_init(cond, NULL);
}
else if (*cond == NULL)
{
/*
* The cv has been destroyed while we were waiting to
* initialise it, so the operation that caused the
* auto-initialisation should fail.
*/
result = EINVAL;
}
LeaveCriticalSection(&_pthread_cond_test_init_lock);
return(result);
}
int
pthread_condattr_init (pthread_condattr_t * attr)
/*
* ------------------------------------------------------
* DOCPUBLIC
* Initializes a condition variable attributes object
* with default attributes.
*
* PARAMETERS
* attr
* pointer to an instance of pthread_condattr_t
*
*
* DESCRIPTION
* Initializes a condition variable attributes object
* with default attributes.
*
* NOTES:
* 1) Use to define condition variable types
* 2) It is up to the application to ensure
* that it doesn't re-init an attribute
* without destroying it first. Otherwise
* a memory leak is created.
*
* RESULTS
* 0 successfully initialized attr,
* ENOMEM insufficient memory for attr.
*
* ------------------------------------------------------
*/
{
pthread_condattr_t attr_result;
int result = 0;
attr_result = (pthread_condattr_t) calloc (1, sizeof (*attr_result));
if (attr_result == NULL)
{
result = ENOMEM;
}
*attr = attr_result;
return (result);
} /* pthread_condattr_init */
int
pthread_condattr_destroy (pthread_condattr_t * attr)
/*
* ------------------------------------------------------
* DOCPUBLIC
* Destroys a condition variable attributes object.
* The object can no longer be used.
*
* PARAMETERS
* attr
* pointer to an instance of pthread_condattr_t
*
*
* DESCRIPTION
* Destroys a condition variable attributes object.
* The object can no longer be used.
*
* NOTES:
* 1) Does not affect condition variables created
* using 'attr'
*
* RESULTS
* 0 successfully released attr,
* EINVAL 'attr' is invalid.
*
* ------------------------------------------------------
*/
{
int result = 0;
if (attr == NULL || *attr == NULL)
{
result = EINVAL;
}
else
{
free (*attr);
*attr = NULL;
result = 0;
}
return (result);
} /* pthread_condattr_destroy */
int
pthread_condattr_getpshared (const pthread_condattr_t * attr, int *pshared)
/*
* ------------------------------------------------------
* DOCPUBLIC
* Determine whether condition variables created with 'attr'
* can be shared between processes.
*
* PARAMETERS
* attr
* pointer to an instance of pthread_condattr_t
*
* pshared
* will be set to one of:
*
* PTHREAD_PROCESS_SHARED
* May be shared if in shared memory
*
* PTHREAD_PROCESS_PRIVATE
* Cannot be shared.
*
*
* DESCRIPTION
* Condition Variables created with 'attr' can be shared
* between processes if pthread_cond_t variable is allocated
* in memory shared by these processes.
* NOTES:
* 1) pshared condition variables MUST be allocated in
* shared memory.
*
* 2) The following macro is defined if shared mutexes
* are supported:
* _POSIX_THREAD_PROCESS_SHARED
*
* RESULTS
* 0 successfully retrieved attribute,
* EINVAL 'attr' is invalid,
*
* ------------------------------------------------------
*/
{
int result;
if ((attr != NULL && *attr != NULL) &&
(pshared != NULL))
{
*pshared = (*attr)->pshared;
result = 0;
}
else
{
*pshared = PTHREAD_PROCESS_PRIVATE;
result = EINVAL;
}
return (result);
} /* pthread_condattr_getpshared */
int
pthread_condattr_setpshared (pthread_condattr_t * attr, int pshared)
/*
* ------------------------------------------------------
* DOCPUBLIC
* Mutexes created with 'attr' can be shared between
* processes if pthread_mutex_t variable is allocated
* in memory shared by these processes.
*
* PARAMETERS
* attr
* pointer to an instance of pthread_mutexattr_t
*
* pshared
* must be one of:
*
* PTHREAD_PROCESS_SHARED
* May be shared if in shared memory
*
* PTHREAD_PROCESS_PRIVATE
* Cannot be shared.
*
* DESCRIPTION
* Mutexes creatd with 'attr' can be shared between
* processes if pthread_mutex_t variable is allocated
* in memory shared by these processes.
*
* NOTES:
* 1) pshared mutexes MUST be allocated in shared
* memory.
*
* 2) The following macro is defined if shared mutexes
* are supported:
* _POSIX_THREAD_PROCESS_SHARED
*
* RESULTS
* 0 successfully set attribute,
* EINVAL 'attr' or pshared is invalid,
* ENOSYS PTHREAD_PROCESS_SHARED not supported,
*
* ------------------------------------------------------
*/
{
int result;
if ((attr != NULL && *attr != NULL) &&
((pshared == PTHREAD_PROCESS_SHARED) ||
(pshared == PTHREAD_PROCESS_PRIVATE)))
{
if (pshared == PTHREAD_PROCESS_SHARED)
{
#if !defined( _POSIX_THREAD_PROCESS_SHARED )
result = ENOSYS;
pshared = PTHREAD_PROCESS_PRIVATE;
#else
result = 0;
#endif /* _POSIX_THREAD_PROCESS_SHARED */
}
else
{
result = 0;
}
(*attr)->pshared = pshared;
}
else
{
result = EINVAL;
}
return (result);
} /* pthread_condattr_setpshared */
int
pthread_cond_init (pthread_cond_t * cond, const pthread_condattr_t * attr)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function initializes a condition variable.
*
* PARAMETERS
* cond
* pointer to an instance of pthread_cond_t
*
* attr
* specifies optional creation attributes.
*
*
* DESCRIPTION
* This function initializes a condition variable.
*
* RESULTS
* 0 successfully created condition variable,
* EINVAL 'attr' is invalid,
* EAGAIN insufficient resources (other than
* memory,
* ENOMEM insufficient memory,
* EBUSY 'cond' is already initialized,
*
* ------------------------------------------------------
*/
{
int result = EAGAIN;
pthread_cond_t cv = NULL;
if (cond == NULL)
{
return EINVAL;
}
if ((attr != NULL && *attr != NULL) &&
((*attr)->pshared == PTHREAD_PROCESS_SHARED))
{
/*
* Creating condition variable that can be shared between
* processes.
*/
result = ENOSYS;
goto FAIL0;
}
cv = (pthread_cond_t) calloc (1, sizeof (*cv));
if (cv == NULL)
{
result = ENOMEM;
goto FAIL0;
}
cv->waiters = 0;
cv->wasBroadcast = FALSE;
if (sem_init (&(cv->sema), 0, 0) != 0)
{
goto FAIL0;
}
if (pthread_mutex_init (&(cv->waitersLock), NULL) != 0)
{
goto FAIL1;
}
cv->waitersDone = CreateEvent (
0,
(int) FALSE, /* manualReset */
(int) FALSE, /* setSignaled */
NULL);
if (cv->waitersDone == NULL)
{
goto FAIL2;
}
result = 0;
goto DONE;
/*
* -------------
* Failure Code
* -------------
*/
FAIL2:
(void) pthread_mutex_destroy (&(cv->waitersLock));
FAIL1:
(void) sem_destroy (&(cv->sema));
FAIL0:
DONE:
*cond = cv;
return (result);
} /* pthread_cond_init */
int
pthread_cond_destroy (pthread_cond_t * cond)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function destroys a condition variable
*
*
* PARAMETERS
* cond
* pointer to an instance of pthread_cond_t
*
*
* DESCRIPTION
* This function destroys a condition variable.
*
* NOTES:
* 1) Safest after wakeup from 'cond', when
* no other threads will wait.
*
* RESULTS
* 0 successfully released condition variable,
* EINVAL 'cond' is invalid,
* EBUSY 'cond' is in use,
*
* ------------------------------------------------------
*/
{
int result = 0;
pthread_cond_t cv;
/*
* Assuming any race condition here is harmless.
*/
if (cond == NULL
|| *cond == NULL)
{
return EINVAL;
}
if (*cond != (pthread_cond_t) _PTHREAD_OBJECT_AUTO_INIT)
{
cv = *cond;
if (pthread_mutex_lock(&(cv->waitersLock)) != 0)
{
return EINVAL;
}
if (cv->waiters > 0)
{
(void) pthread_mutex_unlock(&(cv->waitersLock));
return EBUSY;
}
(void) sem_destroy (&(cv->sema));
(void) CloseHandle (cv->waitersDone);
(void) pthread_mutex_unlock(&(cv->waitersLock));
(void) pthread_mutex_destroy (&(cv->waitersLock));
free(cv);
*cond = NULL;
}
else
{
/*
* See notes in _cond_check_need_init() above also.
*/
EnterCriticalSection(&_pthread_cond_test_init_lock);
/*
* Check again.
*/
if (*cond == (pthread_cond_t) _PTHREAD_OBJECT_AUTO_INIT)
{
/*
* This is all we need to do to destroy a statically
* initialised cond that has not yet been used (initialised).
* If we get to here, another thread
* waiting to initialise this cond will get an EINVAL.
*/
*cond = NULL;
}
else
{
/*
* The cv has been initialised while we were waiting
* so assume it's in use.
*/
result = EBUSY;
}
LeaveCriticalSection(&_pthread_cond_test_init_lock);
}
return (result);
}
/*
* Arguments for cond_wait_cleanup, since we can only pass a
* single void * to it.
*/
typedef struct {
pthread_mutex_t * mutexPtr;
pthread_cond_t cv;
int * resultPtr;
} cond_wait_cleanup_args_t;
static void
cond_wait_cleanup(void * args)
{
cond_wait_cleanup_args_t * cleanup_args = (cond_wait_cleanup_args_t *) args;
pthread_mutex_t * mutexPtr = cleanup_args->mutexPtr;
pthread_cond_t cv = cleanup_args->cv;
int * resultPtr = cleanup_args->resultPtr;
int lock_result;
int lastWaiter = FALSE;
if ((lock_result = pthread_mutex_lock (&(cv->waitersLock))) == 0)
{
/*
* The waiter is responsible for decrementing
* its count, protected by an internal mutex.
*/
cv->waiters--;
lastWaiter = cv->wasBroadcast && (cv->waiters == 0);
if (lastWaiter)
{
cv->wasBroadcast = FALSE;
}
lock_result = pthread_mutex_unlock (&(cv->waitersLock));
}
if ((*resultPtr == 0 || *resultPtr == ETIMEDOUT) && lock_result == 0)
{
if (lastWaiter)
{
/*
* If we are the last waiter on this broadcast
* let the thread doing the broadcast proceed
*/
if (!SetEvent (cv->waitersDone))
{
*resultPtr = EINVAL;
}
}
}
/*
* We must always regain the external mutex, even when
* errors occur, because that's the guarantee that we give
* to our callers
*/
(void) pthread_mutex_lock (mutexPtr);
}
static int
cond_timedwait (pthread_cond_t * cond,
pthread_mutex_t * mutex,
const struct timespec *abstime)
{
int result = 0;
pthread_cond_t cv;
cond_wait_cleanup_args_t cleanup_args;
if (cond == NULL || *cond == NULL)
{
return EINVAL;
}
/*
* We do a quick check to see if we need to do more work
* to initialise a static condition variable. We check
* again inside the guarded section of _cond_check_need_init()
* to avoid race conditions.
*/
if (*cond == (pthread_cond_t) _PTHREAD_OBJECT_AUTO_INIT)
{
result = _cond_check_need_init(cond);
}
if (result != 0 && result != EBUSY)
{
return result;
}
cv = *cond;
/*
* It's not OK to increment cond->waiters while the caller locked 'mutex',
* there may be other threads just waking up (with 'mutex' unlocked)
* and cv->... data is not protected.
*/
if (pthread_mutex_lock(&(cv->waitersLock)) != 0)
{
return EINVAL;
}
cv->waiters++;
if (pthread_mutex_unlock(&(cv->waitersLock)) != 0)
{
return EINVAL;
}
/*
* We keep the lock held just long enough to increment the count of
* waiters by one (above).
* Note that we can't keep it held across the
* call to sem_wait since that will deadlock other calls
* to pthread_cond_signal
*/
cleanup_args.mutexPtr = mutex;
cleanup_args.cv = cv;
cleanup_args.resultPtr = &result;
pthread_cleanup_push (cond_wait_cleanup, (void *) &cleanup_args);
if ((result = pthread_mutex_unlock (mutex)) == 0)
{
/*
* Wait to be awakened by
* pthread_cond_signal, or
* pthread_cond_broadcast
* timeout
*
* Note:
* _pthread_sem_timedwait is a cancelation point,
* hence providing the
* mechanism for making pthread_cond_wait a cancelation
* point. We use the cleanup mechanism to ensure we
* re-lock the mutex and decrement the waiters count
* if we are canceled.
*/
if (_pthread_sem_timedwait (&(cv->sema), abstime) == -1)
{
result = errno;
}
}
pthread_cleanup_pop (1);
/*
* "result" can be modified by the cleanup handler.
* Specifically, if we are the last waiting thread and failed
* to notify the broadcast thread to proceed.
*/
return (result);
} /* cond_timedwait */
int
pthread_cond_wait (pthread_cond_t * cond,
pthread_mutex_t * mutex)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function waits on a condition variable until
* awakened by a signal or broadcast.
*
* Caller MUST be holding the mutex lock; the
* lock is released and the caller is blocked waiting
* on 'cond'. When 'cond' is signaled, the mutex
* is re-acquired before returning to the caller.
*
* PARAMETERS
* cond
* pointer to an instance of pthread_cond_t
*
* mutex
* pointer to an instance of pthread_mutex_t
*
*
* DESCRIPTION
* This function waits on a condition variable until
* awakened by a signal or broadcast.
*
* NOTES:
* 1) The function must be called with 'mutex' LOCKED
* by the calling thread, or undefined behaviour
* will result.
*
* 2) This routine atomically releases 'mutex' and causes
* the calling thread to block on the condition variable.
* The blocked thread may be awakened by
* pthread_cond_signal or
* pthread_cond_broadcast.
*
* Upon successful completion, the 'mutex' has been locked and
* is owned by the calling thread.
*
*
* RESULTS
* 0 caught condition; mutex released,
* EINVAL 'cond' or 'mutex' is invalid,
* EINVAL different mutexes for concurrent waits,
* EINVAL mutex is not held by the calling thread,
*
* ------------------------------------------------------
*/
{
/* The NULL abstime arg means INFINITE waiting. */
return(cond_timedwait(cond, mutex, NULL));
} /* pthread_cond_wait */
int
pthread_cond_timedwait (pthread_cond_t * cond,
pthread_mutex_t * mutex,
const struct timespec *abstime)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function waits on a condition variable either until
* awakened by a signal or broadcast; or until the time
* specified by abstime passes.
*
* PARAMETERS
* cond
* pointer to an instance of pthread_cond_t
*
* mutex
* pointer to an instance of pthread_mutex_t
*
* abstime
* pointer to an instance of (const struct timespec)
*
*
* DESCRIPTION
* This function waits on a condition variable either until
* awakened by a signal or broadcast; or until the time
* specified by abstime passes.
*
* NOTES:
* 1) The function must be called with 'mutex' LOCKED
* by the calling thread, or undefined behaviour
* will result.
*
* 2) This routine atomically releases 'mutex' and causes
* the calling thread to block on the condition variable.
* The blocked thread may be awakened by
* pthread_cond_signal or
* pthread_cond_broadcast.
*
*
* RESULTS
* 0 caught condition; mutex released,
* EINVAL 'cond', 'mutex', or abstime is invalid,
* EINVAL different mutexes for concurrent waits,
* EINVAL mutex is not held by the calling thread,
* ETIMEDOUT abstime ellapsed before cond was signaled.
*
* ------------------------------------------------------
*/
{
int result = 0;
if (abstime == NULL)
{
result = EINVAL;
}
else
{
result = cond_timedwait(cond, mutex, abstime);
}
return(result);
} /* pthread_cond_timedwait */
int
pthread_cond_signal (pthread_cond_t * cond)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function signals a condition variable, waking
* one waiting thread.
* If SCHED_FIFO or SCHED_RR policy threads are waiting
* the highest priority waiter is awakened; otherwise,
* an unspecified waiter is awakened.
*
* PARAMETERS
* cond
* pointer to an instance of pthread_cond_t
*
*
* DESCRIPTION
* This function signals a condition variable, waking
* one waiting thread.
* If SCHED_FIFO or SCHED_RR policy threads are waiting
* the highest priority waiter is awakened; otherwise,
* an unspecified waiter is awakened.
*
* NOTES:
* 1) Use when any waiter can respond and only one need
* respond (all waiters being equal).
*
* 2) This function MUST be called under the protection
* of the SAME mutex that is used with the condition
* variable being signaled; OTHERWISE, the condition
* variable may be signaled between the test of the
* associated condition and the blocking
* pthread_cond_signal.
* This can cause an infinite wait.
*
* RESULTS
* 0 successfully signaled condition,
* EINVAL 'cond' is invalid,
*
* ------------------------------------------------------
*/
{
int result = 0;
pthread_cond_t cv;
if (cond == NULL || *cond == NULL)
{
return EINVAL;
}
cv = *cond;
/*
* No-op if the CV is static and hasn't been initialised yet.
* Assuming that race conditions are harmless.
*/
if (cv == (pthread_cond_t) _PTHREAD_OBJECT_AUTO_INIT)
{
return 0;
}
/*
* If there aren't any waiters, then this is a no-op.
* Assuming that race conditions are harmless.
*/
if (cv->waiters > 0)
{
result = sem_post (&(cv->sema));
}
return (result);
} /* pthread_cond_signal */
int
pthread_cond_broadcast (pthread_cond_t * cond)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function broadcasts the condition variable,
* waking all current waiters.
*
* PARAMETERS
* cond
* pointer to an instance of pthread_cond_t
*
*
* DESCRIPTION
* This function signals a condition variable, waking
* all waiting threads.
*
* NOTES:
* 1) This function MUST be called under the protection
* of the SAME mutex that is used with the condition
* variable being signaled; OTHERWISE, the condition
* variable may be signaled between the test of the
* associated condition and the blocking pthread_cond_wait.
* This can cause an infinite wait.
*
* 2) Use when more than one waiter may respond to
* predicate change or if any waiting thread may
* not be able to respond
*
* RESULTS
* 0 successfully signalled condition to all
* waiting threads,
* EINVAL 'cond' is invalid
* ENOSPC a required resource has been exhausted,
*
* ------------------------------------------------------
*/
{
int result = 0;
int wereWaiters = FALSE;
pthread_cond_t cv;
if (cond == NULL || *cond == NULL)
{
return EINVAL;
}
cv = *cond;
/*
* No-op if the CV is static and hasn't been initialised yet.
* Assuming that any race condition is harmless.
*/
if (cv == (pthread_cond_t) _PTHREAD_OBJECT_AUTO_INIT)
{
return 0;
}
if (pthread_mutex_lock(&(cv->waitersLock)) == EINVAL)
{
return EINVAL;
}
cv->wasBroadcast = TRUE;
wereWaiters = (cv->waiters > 0);
if (wereWaiters)
{
/*
* Wake up all waiters
*/
#ifdef NEED_SEM
result = (_pthread_increase_semaphore( &cv->sema, cv->waiters )
? 0
: EINVAL);
#else /* NEED_SEM */
result = (ReleaseSemaphore( cv->sema, cv->waiters, NULL )
? 0
: EINVAL);
#endif /* NEED_SEM */
}
(void) pthread_mutex_unlock(&(cv->waitersLock));
if (wereWaiters && result == 0)
{
/*
* Wait for all the awakened threads to acquire their part of
* the counting semaphore
*/
if (WaitForSingleObject (cv->waitersDone, INFINITE)
== WAIT_OBJECT_0)
{
result = 0;
}
else
{
result = EINVAL;
}
}
return (result);
}