Thu Sep 16 1999 Ross Johnson <rpj@swan.canberra.edu.au>

	* rwlock.c (pthread_rwlock_destroy): Add serialisation.
	(_rwlock_check_need_init): Check for detroyed rwlock.
	* rwlock.c: Check return codes from _rwlock_check_need_init();
	modify comments; serialise access to rwlock objects during
	operations; rename rw_mutex to rw_lock.
	* implement.h: Rename rw_mutex to rw_lock.
        * mutex.c (pthread_mutex_destroy): Add serialisation.
        (_mutex_check_need_init): Check for detroyed mutex.
        * condvar.c (pthread_cond_destroy): Add serialisation.
        (_cond_check_need_init): Check for detroyed condvar.
        * mutex.c: Modify comments.
	* condvar.c: Modify comments.

1 files changed, 557 insertions, 450 deletions

diff --git a/rwlock.c b/rwlock.c
index 499de59..d135c39 100644
--- a/rwlock.c
+++ b/rwlock.c
@@ -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);
+}