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/*
* condvar.c
*
* Description:
* This translation unit implements condition variables and their primitives.
*/
/*
* Code contributed by John E. Bossom <JEB>.
*/
#include <string.h>
#include "pthread.h"
#include "implement.h"
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 = 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;
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, 1) != 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));
free (cv);
cv = NULL;
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;
if (cond != NULL && *cond != NULL)
{
cv = *cond;
(void) sem_destroy (&(cv->sema));
(void) pthread_mutex_destroy (&(cv->waitersLock));
(void) CloseHandle (cv->waitersDone);
free (cv);
*cond = NULL;
}
return (result);
}
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,
*
* ------------------------------------------------------
*/
{
int result = 0;
pthread_cond_t cv;
int lastWaiter;
cv = *cond;
/*
* OK to increment cv->waiters because the caller locked 'mutex'
*
* FIXME: This is true. However, it is technically possible to call cond_wait
* on this cv with a different mutex. The standard leaves the result of such an
* action as undefined. (RPJ)
*/
cv->waiters++;
/*
* 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
*/
if ((result = pthread_mutex_unlock (mutex)) == 0)
{
/*
* Wait to be awakened by
* pthread_cond_signal, or
* pthread_cond_broadcast
*
* Note:
* sem_wait is a cancellation point, hence providing the
* mechanism for making pthread_cond_wait a cancellation
* point. We use the cleanup mechanism to ensure we
* re-lock the mutex if we are cancelled.
*/
pthread_cleanup_push (pthread_mutex_lock, mutex);
result = sem_wait (&(cv->sema));
pthread_cleanup_pop (0);
}
if ((result = pthread_mutex_lock (&(cv->waitersLock))) == 0)
{
/*
* By making the waiter responsible for decrementing
* its count we don't have to worry about having an internal
* mutex.
*/
cv->waiters--;
lastWaiter = cv->wasBroadcast && (cv->waiters == 0);
result = pthread_mutex_unlock (&(cv->waitersLock));
}
if (result == 0)
{
if (lastWaiter)
{
/*
* If we are the last waiter on this broadcast
* let the thread doing the broadcast proceed
*/
if (!SetEvent (cv->waitersDone))
{
result = 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 (mutex);
return (result);
} /* pthread_cond_wait */
int
pthread_cond_timedwait (pthread_cond_t * cond,
pthread_mutex_t * mutex,
const struct timespec *abstime)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function initializes an unnamed semaphore. the
* initial value of the semaphore is 'value'
*
* PARAMETERS
* sem
* pointer to an instance of sem_t
*
*
* DESCRIPTION
* This function initializes an unnamed semaphore. The
* initial value of the semaphore is set to 'value'.
*
* RESULTS
* 0 successfully created semaphore,
* EINVAL 'sem' is not a valid semaphore,
* ENOSPC a required resource has been exhausted,
* ENOSYS semaphores are not supported,
* EPERM the process lacks appropriate privilege
*
* ------------------------------------------------------
*/
{
int result = 0;
/*
* NOT IMPLEMENTED YET!!!
*/
return (result);
}
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 = *cond;
/*
* If there aren't any waiters, then this is a no-op.
*/
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
* sem
* pointer to an instance of pthread_cond_t
*
*
* DESCRIPTION
* This function initializes an unnamed semaphore. The
* initial value of the semaphore is set to 'value'.
*
* 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 created semaphore,
* EINVAL 'cond' is invalid
* ENOSPC a required resource has been exhausted,
*
* ------------------------------------------------------
*/
{
int result = 0;
pthread_cond_t cv = *cond;
int i;
cv->wasBroadcast = TRUE;
/*
* Wake up all waiters
*/
for (i = cv->waiters; i > 0 && result == 0; i--)
{
result = sem_post (&(cv->sema));
}
if (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);
}
/* </JEB> */

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