pthread_cond_wait.c

电驴下载工具eMule0.47aVeryCD的源代码,可作分析测试也可用于P2P软件的开发研究.

/*
 * pthread_cond_wait.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) 1999,2004 Pthreads-win32 contributors
 * 
 *      Contact Email: [e-mail]
 * 
 *      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
 *
 * -------------------------------------------------------------
 * Algorithm:
 * The algorithm used in this implementation is that developed by
 * Alexander Terekhov in colaboration with Louis Thomas. The bulk
 * of the discussion is recorded in the file README.CV, which contains
 * several generations of both colaborators original algorithms. The final
 * algorithm used here is the one referred to as
 *
 *     Algorithm 8a / IMPL_SEM,UNBLOCK_STRATEGY == UNBLOCK_ALL
 * 
 * presented below in pseudo-code as it appeared:
 *
 *
 * given:
 * semBlockLock - bin.semaphore
 * semBlockQueue - semaphore
 * mtxExternal - mutex or CS
 * mtxUnblockLock - mutex or CS
 * nWaitersGone - int
 * nWaitersBlocked - int
 * nWaitersToUnblock - int
 * 
 * wait( timeout ) {
 * 
 *   [auto: register int result          ]     // error checking omitted
 *   [auto: register int nSignalsWasLeft ]
 *   [auto: register int nWaitersWasGone ]
 * 
 *   sem_wait( semBlockLock );
 *   nWaitersBlocked++;
 *   sem_post( semBlockLock );
 * 
 *   unlock( mtxExternal );
 *   bTimedOut = sem_wait( semBlockQueue,timeout );
 * 
 *   lock( mtxUnblockLock );
 *   if ( 0 != (nSignalsWasLeft = nWaitersToUnblock) ) {
 *     if ( bTimeout ) {                       // timeout (or canceled)
 *       if ( 0 != nWaitersBlocked ) {
 *         nWaitersBlocked--;
 *       }
 *       else {
 *         nWaitersGone++;                     // count spurious wakeups.
 *       }
 *     }
 *     if ( 0 == --nWaitersToUnblock ) {
 *       if ( 0 != nWaitersBlocked ) {
 *         sem_post( semBlockLock );           // open the gate.
 *         nSignalsWasLeft = 0;                // do not open the gate
 *                                             // below again.
 *       }
 *       else if ( 0 != (nWaitersWasGone = nWaitersGone) ) {
 *         nWaitersGone = 0;
 *       }
 *     }
 *   }
 *   else if ( INT_MAX/2 == ++nWaitersGone ) { // timeout/canceled or
 *                                             // spurious semaphore :-)
 *     sem_wait( semBlockLock );
 *     nWaitersBlocked -= nWaitersGone;     // something is going on here
 *                                          //  - test of timeouts? :-)
 *     sem_post( semBlockLock );
 *     nWaitersGone = 0;
 *   }
 *   unlock( mtxUnblockLock );
 * 
 *   if ( 1 == nSignalsWasLeft ) {
 *     if ( 0 != nWaitersWasGone ) {
 *       // sem_adjust( semBlockQueue,-nWaitersWasGone );
 *       while ( nWaitersWasGone-- ) {
 *         sem_wait( semBlockQueue );       // better now than spurious later
 *       }
 *     } sem_post( semBlockLock );          // open the gate
 *   }
 * 
 *   lock( mtxExternal );
 * 
 *   return ( bTimedOut ) ? ETIMEOUT : 0;
 * }
 * 
 * signal(bAll) {
 * 
 *   [auto: register int result         ]
 *   [auto: register int nSignalsToIssue]
 * 
 *   lock( mtxUnblockLock );
 * 
 *   if ( 0 != nWaitersToUnblock ) {        // the gate is closed!!!
 *     if ( 0 == nWaitersBlocked ) {        // NO-OP
 *       return unlock( mtxUnblockLock );
 *     }
 *     if (bAll) {
 *       nWaitersToUnblock += nSignalsToIssue=nWaitersBlocked;
 *       nWaitersBlocked = 0;
 *     }
 *     else {
 *       nSignalsToIssue = 1;
 *       nWaitersToUnblock++;
 *       nWaitersBlocked--;
 *     }
 *   }
 *   else if ( nWaitersBlocked > nWaitersGone ) { // HARMLESS RACE CONDITION!
 *     sem_wait( semBlockLock );                  // close the gate
 *     if ( 0 != nWaitersGone ) {
 *       nWaitersBlocked -= nWaitersGone;
 *       nWaitersGone = 0;
 *     }
 *     if (bAll) {
 *       nSignalsToIssue = nWaitersToUnblock = nWaitersBlocked;
 *       nWaitersBlocked = 0;
 *     }
 *     else {
 *       nSignalsToIssue = nWaitersToUnblock = 1;
 *       nWaitersBlocked--;
 *     }
 *   }
 *   else { // NO-OP
 *     return unlock( mtxUnblockLock );
 *   }
 * 
 *   unlock( mtxUnblockLock );
 *   sem_post( semBlockQueue,nSignalsToIssue );
 *   return result;
 * }
 * -------------------------------------------------------------
 *
 *     Algorithm 9 / IMPL_SEM,UNBLOCK_STRATEGY == UNBLOCK_ALL
 * 
 * presented below in pseudo-code; basically 8a...
 *                                      ...BUT W/O "spurious wakes" prevention:
 *
 *
 * given:
 * semBlockLock - bin.semaphore
 * semBlockQueue - semaphore
 * mtxExternal - mutex or CS
 * mtxUnblockLock - mutex or CS
 * nWaitersGone - int
 * nWaitersBlocked - int
 * nWaitersToUnblock - int
 * 
 * wait( timeout ) {
 * 
 *   [auto: register int result          ]     // error checking omitted
 *   [auto: register int nSignalsWasLeft ]
 * 
 *   sem_wait( semBlockLock );
 *   ++nWaitersBlocked;
 *   sem_post( semBlockLock );
 * 
 *   unlock( mtxExternal );
 *   bTimedOut = sem_wait( semBlockQueue,timeout );
 * 
 *   lock( mtxUnblockLock );
 *   if ( 0 != (nSignalsWasLeft = nWaitersToUnblock) ) {
 *     --nWaitersToUnblock;
 *   }
 *   else if ( INT_MAX/2 == ++nWaitersGone ) { // timeout/canceled or
 *                                             // spurious semaphore :-)
 *     sem_wait( semBlockLock );
 *     nWaitersBlocked -= nWaitersGone;        // something is going on here
 *                                             //  - test of timeouts? :-)
 *     sem_post( semBlockLock );
 *     nWaitersGone = 0;
 *   }
 *   unlock( mtxUnblockLock );
 * 
 *   if ( 1 == nSignalsWasLeft ) {
 *     sem_post( semBlockLock );               // open the gate
 *   }
 * 
 *   lock( mtxExternal );
 * 
 *   return ( bTimedOut ) ? ETIMEOUT : 0;
 * }
 * 
 * signal(bAll) {
 * 
 *   [auto: register int result         ]
 *   [auto: register int nSignalsToIssue]
 * 
 *   lock( mtxUnblockLock );
 * 
 *   if ( 0 != nWaitersToUnblock ) {        // the gate is closed!!!
 *     if ( 0 == nWaitersBlocked ) {        // NO-OP
 *       return unlock( mtxUnblockLock );
 *     }
 *     if (bAll) {
 *       nWaitersToUnblock += nSignalsToIssue=nWaitersBlocked;
 *       nWaitersBlocked = 0;
 *     }
 *     else {
 *       nSignalsToIssue = 1;
 *       ++nWaitersToUnblock;
 *       --nWaitersBlocked;
 *     }
 *   }
 *   else if ( nWaitersBlocked > nWaitersGone ) { // HARMLESS RACE CONDITION!
 *     sem_wait( semBlockLock );                  // close the gate
 *     if ( 0 != nWaitersGone ) {
 *       nWaitersBlocked -= nWaitersGone;
 *       nWaitersGone = 0;
 *     }
 *     if (bAll) {
 *       nSignalsToIssue = nWaitersToUnblock = nWaitersBlocked;
 *       nWaitersBlocked = 0;
 *     }
 *     else {
 *       nSignalsToIssue = nWaitersToUnblock = 1;
 *       --nWaitersBlocked;
 *     }
 *   }
 *   else { // NO-OP
 *     return unlock( mtxUnblockLock );
 *   }
 *
 *   unlock( mtxUnblockLock );
 *   sem_post( semBlockQueue,nSignalsToIssue );
 *   return result;
 * }
 * -------------------------------------------------------------
 *
 */

#include "pthread.h"
#include "implement.h"

/*
 * Arguments for cond_wait_cleanup, since we can only pass a
 * single void * to it.
 */
typedef struct
{
  pthread_mutex_t *mutexPtr;
  pthread_cond_t cv;
  int *resultPtr;
  int signaled;
} ptw32_cond_wait_cleanup_args_t;

static void PTW32_CDECL
ptw32_cond_wait_cleanup (void *args)
{
  ptw32_cond_wait_cleanup_args_t *cleanup_args =
    (ptw32_cond_wait_cleanup_args_t *) args;
  pthread_cond_t cv = cleanup_args->cv;
  int *resultPtr = cleanup_args->resultPtr;
  int nSignalsWasLeft;
  int result;

  /*
   * Whether we got here as a result of signal/broadcast or because of
   * timeout on wait or thread cancellation we indicate that we are no
   * longer waiting. The waiter is responsible for adjusting waiters
   * (to)unblock(ed) counts (protected by unblock lock).