/*
* rwlock.c
*
* Description:
* This translation unit implements read/write lock primitives.
*
* Pthreads-win32 - POSIX Threads Library for Win32
* Copyright (C) 1998 Ben Elliston and Ross Johnson
* Copyright (C) 1999,2000,2001 Ross Johnson
*
* Contact Email: rpj@ise.canberra.edu.au
*
* 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 <errno.h>
#include <limits.h>
#include "pthread.h"
#include "implement.h"
static INLINE int
ptw32_rwlock_check_need_init(pthread_rwlock_t *rwlock)
{
int result = 0;
/*
* The following guarded test is specifically for statically
* initialised rwlocks (via PTHREAD_RWLOCK_INITIALIZER).
*
* Note that by not providing this synchronisation we risk
* introducing race conditions into applications which are
* correctly written.
*
* Approach
* --------
* We know that static rwlocks 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(&ptw32_rwlock_test_init_lock);
/*
* We got here possibly under race
* conditions. Check again inside the critical section
* and only initialise if the rwlock is valid (not been destroyed).
* If a static rwlock has been destroyed, the application can
* re-initialise it only by calling pthread_rwlock_init()
* explicitly.
*/
if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
{
result = pthread_rwlock_init(rwlock, NULL);
}
else if (*rwlock == NULL)
{
/*
* The rwlock has been destroyed while we were waiting to
* initialise it, so the operation that caused the
* auto-initialisation should fail.
*/
result = EINVAL;
}
LeaveCriticalSection(&ptw32_rwlock_test_init_lock);
return result;
}
int
pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
{
int result;
pthread_rwlock_t rwl = 0;
if (rwlock == NULL)
{
return EINVAL;
}
if (attr != NULL && *attr != NULL)
{
result = EINVAL; /* Not supported */
goto DONE;
}
rwl = (pthread_rwlock_t) calloc(1, sizeof(*rwl));
if (rwl == NULL)
{
result = ENOMEM;
goto DONE;
}
rwl->nSharedAccessCount = 0;
rwl->nExclusiveAccessCount = 0;
rwl->nCompletedSharedAccessCount = 0;
result = pthread_mutex_init(&rwl->mtxExclusiveAccess, NULL);
if (result != 0)
{
goto FAIL0;
}
result = pthread_mutex_init(&rwl->mtxSharedAccessCompleted, NULL);
if (result != 0)
{
goto FAIL1;
}
result = pthread_cond_init(&rwl->cndSharedAccessCompleted, NULL);
if (result != 0)
{
goto FAIL2;
}
rwl->nMagic = PTW32_RWLOCK_MAGIC;
result = 0;
goto DONE;
FAIL2:
(void) pthread_mutex_destroy(&(rwl->mtxSharedAccessCompleted));
FAIL1:
(void) pthread_mutex_destroy(&(rwl->mtxExclusiveAccess));
FAIL0:
(void) free(rwl);
rwl = NULL;
DONE:
*rwlock = rwl;
return result;
}
int
pthread_rwlock_destroy(pthread_rwlock_t *rwlock)
{
pthread_rwlock_t rwl;
int result = 0, result1 = 0, result2 = 0;
if (rwlock == NULL || *rwlock == NULL)
{
return EINVAL;
}
if (*rwlock != PTHREAD_RWLOCK_INITIALIZER)
{
rwl = *rwlock;
if (rwl->nMagic != PTW32_RWLOCK_MAGIC)
{
return EINVAL;
}
if ((result = pthread_mutex_lock(&(rwl->mtxExclusiveAccess))) != 0)
{
return result;
}
if ((result = pthread_mutex_lock(&(rwl->mtxSharedAccessCompleted))) != 0)
{
(void) pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
return result;
}
/*
* Check whether any threads own/wait for the lock (wait for ex.access);
* report "BUSY" if so.
*/
if (rwl->nExclusiveAccessCount > 0
|| rwl->nSharedAccessCount > rwl->nCompletedSharedAccessCount)
{
result = pthread_mutex_unlock(&(rwl->mtxSharedAccessCompleted));
result1 = pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
result2 = EBUSY;
}
else
{
rwl->nMagic = 0;
if ((result = pthread_mutex_unlock(&(rwl->mtxSharedAccessCompleted))) != 0)
{
pthread_mutex_unlock(&rwl->mtxExclusiveAccess);
return result;
}
if ((result = pthread_mutex_unlock(&(rwl->mtxExclusiveAccess))) != 0)
{
return result;
}
*rwlock = NULL; /* Invalidate rwlock before anything else */
result = pthread_cond_destroy(&(rwl->cndSharedAccessCompleted));
result1 = pthread_mutex_destroy(&(rwl->mtxSharedAccessCompleted));
result2 = pthread_mutex_destroy(&(rwl->mtxExclusiveAccess));
(void) free(rwl);
}
}
else
{
/*
* See notes in ptw32_rwlock_check_need_init() above also.
*/
EnterCriticalSection(&ptw32_rwlock_test_init_lock);
/*
* Check again.
*/
if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
{
/*
* This is all we need to do to destroy a statically
* initialised rwlock that has not yet been used (initialised).
* If we get to here, another thread
* waiting to initialise this rwlock will get an EINVAL.
*/
*rwlock = NULL;
}
else
{
/*
* The rwlock has been initialised while we were waiting
* so assume it's in use.
*/
result = EBUSY;
}
LeaveCriticalSection(&ptw32_rwlock_test_init_lock);
}
return ((result != 0) ? result : ((result1 != 0) ? result1 : result2));
}
int
pthread_rwlockattr_init (pthread_rwlockattr_t * attr)
/*
* ------------------------------------------------------
* DOCPUBLIC
* Initializes a rwlock attributes object with default
* attributes.
*
* PARAMETERS
* attr
* pointer to an instance of pthread_rwlockattr_t
*
*
* DESCRIPTION
* Initializes a rwlock attributes object with default
* attributes.
*
* RESULTS
* 0 successfully initialized attr,
* ENOMEM insufficient memory for attr.
*
* ------------------------------------------------------
*/
{
int result = 0;
pthread_rwlockattr_t rwa;
rwa = (pthread_rwlockattr_t) calloc (1, sizeof (*rwa));
if (rwa == NULL)
{
result = ENOMEM;
}
else
{
rwa->pshared = PTHREAD_PROCESS_PRIVATE;
}
*attr = rwa;
return(result);
} /* pthread_rwlockattr_init */
int
pthread_rwlockattr_destroy (pthread_rwlockattr_t * attr)
/*
* ------------------------------------------------------
* DOCPUBLIC
* Destroys a rwlock attributes object. The object can
* no longer be used.
*
* PARAMETERS
* attr
* pointer to an instance of pthread_rwlockattr_t
*
*
* DESCRIPTION
* Destroys a rwlock attributes object. The object can
* no longer be used.
*
* NOTES:
* 1) Does not affect rwlockss created using 'attr'
*
* RESULTS
* 0 successfully released attr,
* EINVAL 'attr' is invalid.
*
* ------------------------------------------------------
*/
{
int result = 0;
if (attr == NULL || *attr == NULL)
{
result = EINVAL;
}
else
{
pthread_rwlockattr_t rwa = *attr;
*attr = NULL;
free (rwa);
}
return(result);
} /* pthread_rwlockattr_destroy */
int
pthread_rwlockattr_getpshared (const pthread_rwlockattr_t * attr,
int *pshared)
/*
* ------------------------------------------------------
* DOCPUBLIC
* Determine whether rwlocks created with 'attr' can be
* shared between processes.
*
* PARAMETERS
* attr
* pointer to an instance of pthread_rwlockattr_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
* Rwlocks creatd with 'attr' can be shared between
* processes if pthread_rwlock_t variable is allocated
* in memory shared by these processes.
* NOTES:
* 1) pshared rwlocks MUST be allocated in shared
* memory.
* 2) The following macro is defined if shared rwlocks
* 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
{
result = EINVAL;
}
return (result);
} /* pthread_rwlockattr_getpshared */
int
pthread_rwlockattr_setpshared (pthread_rwlockattr_t * attr,
int pshared)
/*
* ------------------------------------------------------
* DOCPUBLIC
* Rwlocks created with 'attr' can be shared between
* processes if pthread_rwlock_t variable is allocated
* in memory shared by these processes.
*
* PARAMETERS
* attr
* pointer to an instance of pthread_rwlockattr_t
*
* pshared
* must be one of:
*
* PTHREAD_PROCESS_SHARED
* May be shared if in shared memory
*
* PTHREAD_PROCESS_PRIVATE
* Cannot be shared.
*
* DESCRIPTION
* Rwlocks creatd with 'attr' can be shared between
* processes if pthread_rwlock_t variable is allocated
* in memory shared by these processes.
*
* NOTES:
* 1) pshared rwlocks MUST be allocated in shared
* memory.
*
* 2) The following macro is defined if shared rwlocks
* 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_rwlockattr_setpshared */
int
pthread_rwlock_rdlock(pthread_rwlock_t *rwlock)
{
int result;
pthread_rwlock_t rwl;
if (rwlock == NULL || *rwlock == NULL)
{
return EINVAL;
}
/*
* We do a quick check to see if we need to do more work
* to initialise a static rwlock. We check
* again inside the guarded section of ptw32_rwlock_check_need_init()
* to avoid race conditions.
*/
if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
{
result = ptw32_rwlock_check_need_init(rwlock);
if (result != 0 && result != EBUSY)
{
return result;
}
}
rwl = *rwlock;
if (rwl->nMagic != PTW32_RWLOCK_MAGIC)
{
return EINVAL;
}
if ((result = pthread_mutex_lock(&(rwl->mtxExclusiveAccess))) != 0)
{
return result;
}
if (++rwl->nSharedAccessCount == INT_MAX)
{
if ((result = pthread_mutex_lock(&(rwl->mtxSharedAccessCompleted))) != 0)
{
(void) pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
return result;
}
rwl->nSharedAccessCount -= rwl->nCompletedSharedAccessCount;
rwl->nCompletedSharedAccessCount = 0;
if ((result = pthread_mutex_unlock(&(rwl->mtxSharedAccessCompleted))) != 0)
{
(void) pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
return result;
}
}
return (pthread_mutex_unlock(&(rwl->mtxExclusiveAccess)));
}
static void
ptw32_rwlock_cancelwrwait(void * arg)
{
pthread_rwlock_t rwl = (pthread_rwlock_t) arg;
rwl->nSharedAccessCount = -rwl->nCompletedSharedAccessCount;
rwl->nCompletedSharedAccessCount = 0;
(void) pthread_mutex_unlock(&(rwl->mtxSharedAccessCompleted));
(void) pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
}
int
pthread_rwlock_wrlock(pthread_rwlock_t * rwlock)
{
int result;
pthread_rwlock_t rwl;
if (rwlock == NULL || *rwlock == NULL)
{
return EINVAL;
}
/*
* We do a quick check to see if we need to do more work
* to initialise a static rwlock. We check
* again inside the guarded section of ptw32_rwlock_check_need_init()
* to avoid race conditions.
*/
if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
{
result = ptw32_rwlock_check_need_init(rwlock);
if (result != 0 && result != EBUSY)
{
return result;
}
}
rwl = *rwlock;
if (rwl->nMagic != PTW32_RWLOCK_MAGIC)
{
return EINVAL;
}
if ((result = pthread_mutex_lock(&(rwl->mtxExclusiveAccess))) != 0)
{
return result;
}
if ((result = pthread_mutex_lock(&(rwl->mtxSharedAccessCompleted))) != 0)
{
(void) pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
return result;
}
if (rwl->nExclusiveAccessCount == 0)
{
if (rwl->nCompletedSharedAccessCount > 0)
{
rwl->nSharedAccessCount -= rwl->nCompletedSharedAccessCount;
rwl->nCompletedSharedAccessCount = 0;
}
if (rwl->nSharedAccessCount > 0)
{
rwl->nCompletedSharedAccessCount = -rwl->nSharedAccessCount;
/*
* This routine may be a cancelation point
* according to POSIX 1003.1j section 18.1.2.
*/
pthread_cleanup_push(ptw32_rwlock_cancelwrwait, (void*)rwl);
do
{
result = pthread_cond_wait(&(rwl->cndSharedAccessCompleted),
&(rwl->mtxSharedAccessCompleted));
}
while (result == 0 && rwl->nCompletedSharedAccessCount < 0);
pthread_cleanup_pop ((result != 0) ? 1 : 0);
if (result == 0)
{
rwl->nSharedAccessCount = 0;
}
}
}
if (result == 0)
{
rwl->nExclusiveAccessCount++;
}
return result;
}
int
pthread_rwlock_unlock(pthread_rwlock_t * rwlock)
{
int result, result1;
pthread_rwlock_t rwl;
if (rwlock == NULL || *rwlock == NULL)
{
return(EINVAL);
}
if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
{
/*
* Assume any race condition here is harmless.
*/
return 0;
}
rwl = *rwlock;
if (rwl->nMagic != PTW32_RWLOCK_MAGIC)
{
return EINVAL;
}
if (rwl->nExclusiveAccessCount == 0)
{
if ((result = pthread_mutex_lock(&(rwl->mtxSharedAccessCompleted))) != 0)
{
return result;
}
if (++rwl->nCompletedSharedAccessCount == 0)
{
result = pthread_cond_signal(&(rwl->cndSharedAccessCompleted));
}
result1 = pthread_mutex_unlock(&(rwl->mtxSharedAccessCompleted));
}
else
{
rwl->nExclusiveAccessCount--;
result = pthread_mutex_unlock(&(rwl->mtxSharedAccessCompleted));
result1 = pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
}
return ((result != 0) ? result : result1);
}
int
pthread_rwlock_tryrdlock(pthread_rwlock_t * rwlock)
{
int result;
pthread_rwlock_t rwl;
if (rwlock == NULL || *rwlock == NULL)
{
return EINVAL;
}
/*
* We do a quick check to see if we need to do more work
* to initialise a static rwlock. We check
* again inside the guarded section of ptw32_rwlock_check_need_init()
* to avoid race conditions.
*/
if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
{
result = ptw32_rwlock_check_need_init(rwlock);
if (result != 0 && result != EBUSY)
{
return result;
}
}
rwl = *rwlock;
if (rwl->nMagic != PTW32_RWLOCK_MAGIC)
{
return EINVAL;
}
if ((result = pthread_mutex_trylock(&(rwl->mtxExclusiveAccess))) != 0)
{
return result;
}
if (++rwl->nSharedAccessCount == INT_MAX)
{
if ((result = pthread_mutex_lock(&(rwl->mtxSharedAccessCompleted))) != 0)
{
(void) pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
return result;
}
rwl->nSharedAccessCount -= rwl->nCompletedSharedAccessCount;
rwl->nCompletedSharedAccessCount = 0;
if ((result = pthread_mutex_unlock(&(rwl->mtxSharedAccessCompleted))) != 0)
{
(void) pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
return result;
}
}
return (pthread_mutex_unlock(&rwl->mtxExclusiveAccess));
}
int
pthread_rwlock_trywrlock(pthread_rwlock_t * rwlock)
{
int result, result1;
pthread_rwlock_t rwl;
if (rwlock == NULL || *rwlock == NULL)
{
return EINVAL;
}
/*
* We do a quick check to see if we need to do more work
* to initialise a static rwlock. We check
* again inside the guarded section of ptw32_rwlock_check_need_init()
* to avoid race conditions.
*/
if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
{
result = ptw32_rwlock_check_need_init(rwlock);
if (result != 0 && result != EBUSY)
{
return result;
}
}
rwl = *rwlock;
if (rwl->nMagic != PTW32_RWLOCK_MAGIC)
{
return EINVAL;
}
if ((result = pthread_mutex_trylock(&(rwl->mtxExclusiveAccess))) != 0)
{
return result;
}
if ((result = pthread_mutex_trylock(&(rwl->mtxSharedAccessCompleted))) != 0)
{
result1 = pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
return ((result1 != 0) ? result1 : result);
}
if (rwl->nExclusiveAccessCount == 0)
{
if (rwl->nCompletedSharedAccessCount > 0)
{
rwl->nSharedAccessCount -= rwl->nCompletedSharedAccessCount;
rwl->nCompletedSharedAccessCount = 0;
}
if (rwl->nSharedAccessCount > 0)
{
if ((result = pthread_mutex_unlock(&(rwl->mtxSharedAccessCompleted))) != 0)
{
(void) pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
return result;
}
if ((result = pthread_mutex_unlock(&(rwl->mtxExclusiveAccess))) == 0)
{
result = EBUSY;
}
}
else
{
rwl->nExclusiveAccessCount = 1;
}
}
else
{
result = EBUSY;
}
return result;
}