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+/*
+ * condvar_destroy.c
+ *
+ * Description:
+ * This translation unit implements condition variables and their primitives.
+ *
+ *
+ * --------------------------------------------------------------------------
+ *
+ *      Pthreads-win32 - POSIX Threads Library for Win32
+ *      Copyright(C) 1998 John E. Bossom
+ *      Copyright(C) 1999,2002 Pthreads-win32 contributors
+ * 
+ *      Contact Email: rpj@ise.canberra.edu.au
+ * 
+ *      The current list of contributors is contained
+ *      in the file CONTRIBUTORS included with the source
+ *      code distribution. The list can also be seen at the
+ *      following World Wide Web location:
+ *      http://sources.redhat.com/pthreads-win32/contributors.html
+ * 
+ *      This library is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU Lesser 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
+ *      Lesser General Public License for more details.
+ * 
+ *      You should have received a copy of the GNU Lesser General Public
+ *      License along with this library in the file COPYING.LIB;
+ *      if not, write to the Free Software Foundation, Inc.,
+ *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+
+#include "pthread.h"
+#include "implement.h"
+
+
+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)      A condition variable can be destroyed
+      *                      immediately after all the threads that
+      *                      are blocked on it are awakened. e.g.
+      *
+      *                      struct list {
+      *                        pthread_mutex_t lm;
+      *                        ...
+      *                      }
+      *
+      *                      struct elt {
+      *                        key k;
+      *                        int busy;
+      *                        pthread_cond_t notbusy;
+      *                        ...
+      *                      }
+      *
+      *                      
+      *                      struct elt *
+      *                      list_find(struct list *lp, key k)
+      *                      {
+      *                        struct elt *ep;
+      *
+      *                        pthread_mutex_lock(&lp->lm);
+      *                        while ((ep = find_elt(l,k) != NULL) && ep->busy)
+      *                          pthread_cond_wait(&ep->notbusy, &lp->lm);
+      *                        if (ep != NULL)
+      *                          ep->busy = 1;
+      *                        pthread_mutex_unlock(&lp->lm);
+      *                        return(ep);
+      *                      }
+      *
+      *                      delete_elt(struct list *lp, struct elt *ep)
+      *                      {
+      *                        pthread_mutex_lock(&lp->lm);
+      *                        assert(ep->busy);
+      *                        ... remove ep from list ...
+      *                        ep->busy = 0;
+      *                    (A) pthread_cond_broadcast(&ep->notbusy);
+      *                        pthread_mutex_unlock(&lp->lm);
+      *                    (B) pthread_cond_destroy(&rp->notbusy);
+      *                        free(ep);
+      *                      }
+      *
+      *                      In this example, the condition variable
+      *                      and its list element may be freed (line B)
+      *                      immediately after all threads waiting for
+      *                      it are awakened (line A), since the mutex
+      *                      and the code ensure that no other thread
+      *                      can touch the element to be deleted.
+      *
+      * RESULTS
+      *              0               successfully released condition variable,
+      *              EINVAL          'cond' is invalid,
+      *              EBUSY           'cond' is in use,
+      *
+      * ------------------------------------------------------
+      */
+{
+  pthread_cond_t cv;
+  int result = 0, result1 = 0, result2 = 0;
+
+  /*
+   * Assuming any race condition here is harmless.
+   */
+  if (cond == NULL
+      || *cond == NULL)
+    {
+      return EINVAL;
+    }
+
+  if (*cond != PTHREAD_COND_INITIALIZER)
+    {
+      cv = *cond;
+
+      /*
+       * Close the gate; this will synchronize this thread with
+       * all already signaled waiters to let them retract their
+       * waiter status - SEE NOTE 1 ABOVE!!!
+       */
+      if (sem_wait(&(cv->semBlockLock)) != 0)
+        {
+          return errno;
+        }
+
+      /*
+       * !TRY! lock mtxUnblockLock; try will detect busy condition
+       * and will not course a deadlock with respect to concurrent
+       * signal/broadcast.
+       */
+      if ((result = pthread_mutex_trylock(&(cv->mtxUnblockLock))) != 0)
+        {
+          (void) sem_post(&(cv->semBlockLock));
+          return result;
+        }
+
+      /*
+       * Check whether cv is still busy (still has waiters)
+       */
+      if (cv->nWaitersBlocked > cv->nWaitersGone)
+        {
+          if (sem_post(&(cv->semBlockLock)) != 0)
+            {
+              result = errno;
+            }
+          result1 = pthread_mutex_unlock(&(cv->mtxUnblockLock));
+          result2 = EBUSY;
+        }
+      else
+        {
+          /*
+           * Now it is safe to destroy
+           */
+          *cond = NULL;
+          if (sem_destroy(&(cv->semBlockLock)) != 0)
+            {
+              result = errno;
+            }
+          if (sem_destroy(&(cv->semBlockQueue)) != 0)
+            {
+              result1 = errno;
+            }
+          if ((result2 = pthread_mutex_unlock(&(cv->mtxUnblockLock))) == 0)
+            {
+              result2 = pthread_mutex_destroy(&(cv->mtxUnblockLock));
+            }
+
+          (void) free(cv);
+        }
+    }
+  else
+    {
+      /*
+       * See notes in ptw32_cond_check_need_init() above also.
+       */
+      EnterCriticalSection(&ptw32_cond_test_init_lock);
+
+      /*
+       * Check again.
+       */
+      if (*cond == PTHREAD_COND_INITIALIZER)
+        {
+          /*
+           * This is all we need to do to destroy a statically
+           * initialised cond that has not yet been used (initialised).
+           * If we get to here, another thread waiting to initialise
+           * this cond will get an EINVAL. That's OK.
+           */
+          *cond = NULL;
+        }
+      else
+        {
+          /*
+           * The cv has been initialised while we were waiting
+           * so assume it's in use.
+           */
+          result = EBUSY;
+        }
+
+      LeaveCriticalSection(&ptw32_cond_test_init_lock);
+    }
+
+    return ((result != 0) ? result : ((result1 != 0) ? result1 : result2));
+
+}