diff options
Diffstat (limited to 'rwlock.c')
| -rw-r--r-- | rwlock.c | 450 |
1 files changed, 450 insertions, 0 deletions
diff --git a/rwlock.c b/rwlock.c new file mode 100644 index 0000000..499de59 --- /dev/null +++ b/rwlock.c @@ -0,0 +1,450 @@ +/*
+ * 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);
+}
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