diff options
Diffstat (limited to 'rwlock.c')
| -rw-r--r-- | rwlock.c | 1007 |
1 files changed, 557 insertions, 450 deletions
@@ -1,450 +1,557 @@ -/*
- * rwlock.c
- *
- * Description:
- * This translation unit implements read/write lock 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 <errno.h>
-
-#include "pthread.h"
-#include "implement.h"
-
-static int
-_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(&_pthread_rwlock_test_init_lock);
-
- /*
- * We got here possibly under race
- * conditions. Check again inside the critical section
- * and only initialise if the mutex is valid (not been destroyed).
- * If a static mutex has been destroyed, the application can
- * re-initialise it only by calling pthread_mutex_init()
- * explicitly.
- */
- if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT)
- {
- result = pthread_rwlock_init(rwlock, NULL);
- }
-
- LeaveCriticalSection(&_pthread_rwlock_test_init_lock);
-
- return(result);
-}
-
-int pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
-{
- int result = 0;
- pthread_rwlock_t rw;
-
- if (rwlock == NULL)
- {
- return EINVAL;
- }
-
- rw = *rwlock;
-
- rw = (pthread_rwlock_t) calloc(1, sizeof(*rw));
-
- if (rw == NULL)
- {
- result = ENOMEM;
- goto fail0;
- }
-
- if (attr != NULL
- && *attr != NULL)
- {
- result = EINVAL; /* Not supported */
- goto fail0;
- }
-
- if ((result = pthread_mutex_init(&rw->rw_mutex, NULL)) != 0)
- {
- goto fail1;
- }
-
- if ((result = pthread_cond_init(&rw->rw_condreaders, NULL)) != 0)
- {
- goto fail2;
- }
-
- if ((result = pthread_cond_init(&rw->rw_condwriters, NULL)) != 0)
- {
- goto fail3;
- }
-
- rw->rw_nwaitreaders = 0;
- rw->rw_nwaitwriters = 0;
- rw->rw_refcount = 0;
- rw->rw_magic = RW_MAGIC;
-
- result = 0;
- goto fail0;
-
-fail3:
- pthread_cond_destroy(&rw->rw_condreaders);
-
-fail2:
- pthread_mutex_destroy(&rw->rw_mutex);
-
-fail1:
-fail0:
- *rwlock = rw;
-
- return(result); /* an errno value */
-}
-
-int pthread_rwlock_destroy(pthread_rwlock_t *rwlock)
-{
- pthread_rwlock_t rw;
-
- if (rwlock == NULL || *rwlock == NULL || (*rwlock)->rw_magic != RW_MAGIC)
- {
- return(EINVAL);
- }
-
- if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT)
- {
- /*
- * Destroy a static declared R/W lock that has never been
- * initialised.
- */
- *rwlock = NULL;
- return(0);
- }
-
- rw = *rwlock;
-
- if (rw->rw_refcount != 0
- || rw->rw_nwaitreaders != 0
- || rw->rw_nwaitwriters != 0)
- {
- return(EBUSY);
- }
-
- pthread_mutex_destroy(&rw->rw_mutex);
- pthread_cond_destroy(&rw->rw_condreaders);
- pthread_cond_destroy(&rw->rw_condwriters);
- rw->rw_magic = 0;
- free(rw);
- *rwlock = NULL;
-
- return(0);
-}
-
-static void _rwlock_cancelrdwait(void *arg)
-{
- pthread_rwlock_t rw;
-
- rw = arg;
- rw->rw_nwaitreaders--;
- pthread_mutex_unlock(&rw->rw_mutex);
-}
-
-int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock)
-{
- int result = 0;
- pthread_rwlock_t rw;
-
- 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 _rwlock_check_need_init()
- * to avoid race conditions.
- */
- if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT)
- {
- result = _rwlock_check_need_init(rwlock);
- }
-
- rw = *rwlock;
-
- if (rw->rw_magic != RW_MAGIC)
- {
- return(EINVAL);
- }
-
- if ((result = pthread_mutex_lock(&rw->rw_mutex)) != 0)
- {
- return(result);
- }
-
- /* give preference to waiting writers */
- while (rw->rw_refcount < 0 || rw->rw_nwaitwriters > 0)
- {
- rw->rw_nwaitreaders++;
- pthread_cleanup_push(_rwlock_cancelrdwait, rw);
- result = pthread_cond_wait(&rw->rw_condreaders, &rw->rw_mutex);
- pthread_cleanup_pop(0);
- rw->rw_nwaitreaders--;
-
- if (result != 0)
- {
- break;
- }
- }
-
- if (result == 0)
- {
- rw->rw_refcount++; /* another reader has a read lock */
- }
-
- pthread_mutex_unlock(&rw->rw_mutex);
-
- return(result);
-}
-
-static void _rwlock_cancelwrwait(void *arg)
-{
- pthread_rwlock_t rw;
-
- rw = arg;
- rw->rw_nwaitwriters--;
- pthread_mutex_unlock(&rw->rw_mutex);
-}
-
-int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock)
-{
- int result;
- pthread_rwlock_t rw;
-
- 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 _rwlock_check_need_init()
- * to avoid race conditions.
- */
- if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT)
- {
- result = _rwlock_check_need_init(rwlock);
- }
-
- rw = *rwlock;
-
- if (rw->rw_magic != RW_MAGIC)
- return(EINVAL);
-
- if ( (result = pthread_mutex_lock(&rw->rw_mutex)) != 0)
- return(result);
-
- while (rw->rw_refcount != 0) {
- rw->rw_nwaitwriters++;
- pthread_cleanup_push(_rwlock_cancelwrwait, rw);
- result = pthread_cond_wait(&rw->rw_condwriters, &rw->rw_mutex);
- pthread_cleanup_pop(0);
- rw->rw_nwaitwriters--;
- if (result != 0)
- break;
- }
- if (result == 0)
- rw->rw_refcount = -1;
-
- pthread_mutex_unlock(&rw->rw_mutex);
- return(result);
-}
-
-int pthread_rwlock_unlock(pthread_rwlock_t *rwlock)
-{
- int result = 0;
- pthread_rwlock_t rw;
-
- if (rwlock == NULL || *rwlock == NULL)
- {
- return(EINVAL);
- }
-
- if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT)
- {
- return(0);
- }
-
- rw = *rwlock;
-
- if (rw->rw_magic != RW_MAGIC)
- {
- return(EINVAL);
- }
-
- if ( (result = pthread_mutex_lock(&rw->rw_mutex)) != 0)
- {
- return(result);
- }
-
- if (rw->rw_refcount > 0)
- {
- rw->rw_refcount--; /* releasing a reader */
- }
- else if (rw->rw_refcount == -1)
- {
- rw->rw_refcount = 0; /* releasing a writer */
- }
- else
- {
- return(EINVAL);
- }
-
- result = 0;
-
- /*
- * Give preference to waiting writers over waiting readers
- */
- if (rw->rw_nwaitwriters > 0)
- {
- if (rw->rw_refcount == 0)
- {
- result = pthread_cond_signal(&rw->rw_condwriters);
- }
- }
- else if (rw->rw_nwaitreaders > 0)
- {
- result = pthread_cond_broadcast(&rw->rw_condreaders);
- }
-
- pthread_mutex_unlock(&rw->rw_mutex);
- return(result);
-}
-
-int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock)
-{
- int result = 0;
- pthread_rwlock_t rw;
-
- 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 _rwlock_check_need_init()
- * to avoid race conditions.
- */
- if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT)
- {
- result = _rwlock_check_need_init(rwlock);
- }
-
- rw = *rwlock;
-
- if (rw->rw_magic != RW_MAGIC)
- {
- return(EINVAL);
- }
-
- if ( (result = pthread_mutex_lock(&rw->rw_mutex)) != 0)
- {
- return(result);
- }
-
- if (rw->rw_refcount == -1 || rw->rw_nwaitwriters > 0)
- {
- result = EBUSY; /* held by a writer or waiting writers */
- }
- else
- {
- rw->rw_refcount++; /* increment count of reader locks */
- }
-
- pthread_mutex_unlock(&rw->rw_mutex);
- return(result);
-}
-
-int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock)
-{
- int result = 0;
- pthread_rwlock_t rw;
-
- 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 _rwlock_check_need_init()
- * to avoid race conditions.
- */
- if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT)
- {
- result = _rwlock_check_need_init(rwlock);
- }
-
- rw = *rwlock;
-
- if (rw->rw_magic != RW_MAGIC)
- {
- return(EINVAL);
- }
-
- if ( (result = pthread_mutex_lock(&rw->rw_mutex)) != 0)
- {
- return(result);
- }
-
- if (rw->rw_refcount != 0)
- {
- result = EBUSY; /* held by either writer or reader(s) */
- }
- else
- {
- rw->rw_refcount = -1; /* available, indicate a writer has it */
- }
-
- pthread_mutex_unlock(&rw->rw_mutex);
- return(result);
-}
+/* + * rwlock.c + * + * Description: + * This translation unit implements read/write lock 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 <errno.h> + +#include "pthread.h" +#include "implement.h" + +static int +_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(&_pthread_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_t) _PTHREAD_OBJECT_AUTO_INIT) + { + 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(&_pthread_rwlock_test_init_lock); + + return(result); +} + +int +pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr) +{ + int result = 0; + pthread_rwlock_t rw; + + if (rwlock == NULL) + { + return EINVAL; + } + + rw = *rwlock; + + rw = (pthread_rwlock_t) calloc(1, sizeof(*rw)); + + if (rw == NULL) + { + result = ENOMEM; + goto FAIL0; + } + + if (attr != NULL + && *attr != NULL) + { + result = EINVAL; /* Not supported */ + goto FAIL0; + } + + if ((result = pthread_mutex_init(&(rw->rw_lock), NULL)) != 0) + { + goto FAIL1; + } + + if ((result = pthread_cond_init(&(rw->rw_condreaders), NULL)) != 0) + { + goto FAIL2; + } + + if ((result = pthread_cond_init(&(rw->rw_condwriters), NULL)) != 0) + { + goto FAIL3; + } + + rw->rw_nwaitreaders = 0; + rw->rw_nwaitwriters = 0; + rw->rw_refcount = 0; + rw->rw_magic = RW_MAGIC; + + result = 0; + goto FAIL0; + +FAIL3: + (void) pthread_cond_destroy(&(rw->rw_condreaders)); + +FAIL2: + (void) pthread_mutex_destroy(&(rw->rw_lock)); + +FAIL1: +FAIL0: + *rwlock = rw; + + return(result); +} + +int +pthread_rwlock_destroy(pthread_rwlock_t *rwlock) +{ + pthread_rwlock_t rw; + int result = 0; + + if (rwlock == NULL || *rwlock == NULL) + { + return(EINVAL); + } + + if (*rwlock != (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT) + { + rw = *rwlock; + + if (pthread_mutex_lock(&(rw->rw_lock)) != 0) + { + return(EINVAL); + } + + if (rw->rw_magic != RW_MAGIC) + { + (void) pthread_mutex_unlock(&(rw->rw_lock)); + return(EINVAL); + } + + if (rw->rw_refcount != 0 + || rw->rw_nwaitreaders != 0 + || rw->rw_nwaitwriters != 0) + { + (void) pthread_mutex_unlock(&(rw->rw_lock)); + result = EBUSY; + } + else + { + rw->rw_magic = NULL; + (void) pthread_mutex_unlock(&(rw->rw_lock)); + (void) pthread_cond_destroy(&(rw->rw_condreaders)); + (void) pthread_cond_destroy(&(rw->rw_condwriters)); + (void) pthread_mutex_destroy(&(rw->rw_lock)); + + free(rw); + *rwlock = NULL; + } + } + else + { + /* + * See notes in _rwlock_check_need_init() above also. + */ + EnterCriticalSection(&_pthread_rwlock_test_init_lock); + + /* + * Check again. + */ + if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT) + { + /* + * 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(&_pthread_rwlock_test_init_lock); + } + + return(result); +} + +static void +_rwlock_cancelrdwait(void * arg) +{ + pthread_rwlock_t rw; + + rw = (pthread_rwlock_t) arg; + rw->rw_nwaitreaders--; + pthread_mutex_unlock(&(rw->rw_lock)); +} + +int +pthread_rwlock_rdlock(pthread_rwlock_t *rwlock) +{ + int result = 0; + pthread_rwlock_t rw; + + 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 _rwlock_check_need_init() + * to avoid race conditions. + */ + if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT) + { + result = _rwlock_check_need_init(rwlock); + + if (result != 0 && result != EBUSY) + { + return(result); + } + } + + rw = *rwlock; + + if ((result = pthread_mutex_lock(&(rw->rw_lock))) != 0) + { + return(result); + } + + if (rw->rw_magic != RW_MAGIC) + { + result = EINVAL; + goto FAIL1; + } + + /* + * Give preference to waiting writers + */ + while (rw->rw_refcount < 0 || rw->rw_nwaitwriters > 0) + { + rw->rw_nwaitreaders++; + pthread_cleanup_push(_rwlock_cancelrdwait, rw); + result = pthread_cond_wait(&(rw->rw_condreaders), &(rw->rw_lock)); + pthread_cleanup_pop(0); + rw->rw_nwaitreaders--; + + if (result != 0) + { + break; + } + } + + if (result == 0) + { + rw->rw_refcount++; /* another reader has a read lock */ + } + +FAIL1: + (void) pthread_mutex_unlock(&(rw->rw_lock)); + + return(result); +} + +static void +_rwlock_cancelwrwait(void * arg) +{ + pthread_rwlock_t rw; + + rw = (pthread_rwlock_t) arg; + rw->rw_nwaitwriters--; + (void) pthread_mutex_unlock(&(rw->rw_lock)); +} + +int +pthread_rwlock_wrlock(pthread_rwlock_t * rwlock) +{ + int result; + pthread_rwlock_t rw; + + 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 _rwlock_check_need_init() + * to avoid race conditions. + */ + if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT) + { + result = _rwlock_check_need_init(rwlock); + + if (result != 0 && result != EBUSY) + { + return(result); + } + } + + rw = *rwlock; + + if (rw->rw_magic != RW_MAGIC) + { + return(EINVAL); + } + + if ((result = pthread_mutex_lock(&(rw->rw_lock))) != 0) + { + return(result); + } + + while (rw->rw_refcount != 0) + { + rw->rw_nwaitwriters++; + pthread_cleanup_push(_rwlock_cancelwrwait, rw); + result = pthread_cond_wait(&(rw->rw_condwriters), &(rw->rw_lock)); + pthread_cleanup_pop(0); + rw->rw_nwaitwriters--; + + if (result != 0) + { + break; + } + } + + if (result == 0) + { + rw->rw_refcount = -1; + } + + (void) pthread_mutex_unlock(&(rw->rw_lock)); + + return(result); +} + +int +pthread_rwlock_unlock(pthread_rwlock_t * rwlock) +{ + int result = 0; + pthread_rwlock_t rw; + + if (rwlock == NULL || *rwlock == NULL) + { + return(EINVAL); + } + + if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT) + { + /* + * Assume any race condition here is harmless. + */ + return(0); + } + + rw = *rwlock; + + if ((result = pthread_mutex_lock(&(rw->rw_lock))) != 0) + { + return(result); + } + + if (rw->rw_magic != RW_MAGIC) + { + result = EINVAL; + goto FAIL1; + } + + if (rw->rw_refcount > 0) + { + rw->rw_refcount--; /* releasing a reader */ + } + else if (rw->rw_refcount == -1) + { + rw->rw_refcount = 0; /* releasing a writer */ + } + else + { + return(EINVAL); + } + + result = 0; + + /* + * Give preference to waiting writers over waiting readers + */ + if (rw->rw_nwaitwriters > 0) + { + if (rw->rw_refcount == 0) + { + result = pthread_cond_signal(&(rw->rw_condwriters)); + } + } + else if (rw->rw_nwaitreaders > 0) + { + result = pthread_cond_broadcast(&(rw->rw_condreaders)); + } + +FAIL1: + (void) pthread_mutex_unlock(&(rw->rw_lock)); + + return(result); +} + +int +pthread_rwlock_tryrdlock(pthread_rwlock_t * rwlock) +{ + int result = 0; + pthread_rwlock_t rw; + + 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 _rwlock_check_need_init() + * to avoid race conditions. + */ + if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT) + { + result = _rwlock_check_need_init(rwlock); + + if (result != 0 && result != EBUSY) + { + return(result); + } + } + + rw = *rwlock; + + if ((result = pthread_mutex_lock(&(rw->rw_lock))) != 0) + { + return(result); + } + + if (rw->rw_magic != RW_MAGIC) + { + result = EINVAL; + goto FAIL1; + } + + if (rw->rw_refcount == -1 || rw->rw_nwaitwriters > 0) + { + result = EBUSY; /* held by a writer or waiting writers */ + } + else + { + rw->rw_refcount++; /* increment count of reader locks */ + } + +FAIL1: + (void) pthread_mutex_unlock(&(rw->rw_lock)); + + return(result); +} + +int +pthread_rwlock_trywrlock(pthread_rwlock_t * rwlock) +{ + int result = 0; + pthread_rwlock_t rw; + + 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 _rwlock_check_need_init() + * to avoid race conditions. + */ + if (*rwlock == (pthread_rwlock_t) _PTHREAD_OBJECT_AUTO_INIT) + { + result = _rwlock_check_need_init(rwlock); + + if (result != 0 && result != EBUSY) + { + return(result); + } + } + + rw = *rwlock; + + if ((result = pthread_mutex_lock(&(rw->rw_lock))) != 0) + { + return(result); + } + + if (rw->rw_magic != RW_MAGIC) + { + result = EINVAL; + goto FAIL1; + } + + if (rw->rw_refcount != 0) + { + result = EBUSY; /* held by either writer or reader(s) */ + } + else + { + rw->rw_refcount = -1; /* available, indicate a writer has it */ + } + +FAIL1: + (void) pthread_mutex_unlock(&(rw->rw_lock)); + + return(result); +} |