native_client_sdk/src/libraries/third_party/pthreads-win32/ptw32_reuse.c

   1 /*
   2  * ptw32_threadReuse.c
   3  *
   4  * Description:
   5  * This translation unit implements miscellaneous thread functions.
   6  *
   7  * --------------------------------------------------------------------------
   8  *
   9  *      Pthreads-win32 - POSIX Threads Library for Win32
  10  *      Copyright(C) 1998 John E. Bossom
  11  *      Copyright(C) 1999,2005 Pthreads-win32 contributors
  12  *
  13  *      Contact Email: rpj@callisto.canberra.edu.au
  14  *
  15  *      The current list of contributors is contained
  16  *      in the file CONTRIBUTORS included with the source
  17  *      code distribution. The list can also be seen at the
  18  *      following World Wide Web location:
  19  *      http://sources.redhat.com/pthreads-win32/contributors.html
  20  *
  21  *      This library is free software; you can redistribute it and/or
  22  *      modify it under the terms of the GNU Lesser General Public
  23  *      License as published by the Free Software Foundation; either
  24  *      version 2 of the License, or (at your option) any later version.
  25  *
  26  *      This library is distributed in the hope that it will be useful,
  27  *      but WITHOUT ANY WARRANTY; without even the implied warranty of
  28  *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  29  *      Lesser General Public License for more details.
  30  *
  31  *      You should have received a copy of the GNU Lesser General Public
  32  *      License along with this library in the file COPYING.LIB;
  33  *      if not, write to the Free Software Foundation, Inc.,
  34  *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  35  */
  36
  37 #include "pthread.h"
  38 #include "implement.h"
  39
  40
  41 /*
  42  * How it works:
  43  * A pthread_t is a struct (2x32 bit scalar types on IA-32, 2x64 bit on IA-64)
  44  * which is normally passed/returned by value to/from pthreads routines.
  45  * Applications are therefore storing a copy of the struct as it is at that
  46  * time.
  47  *
  48  * The original pthread_t struct plus all copies of it contain the address of
  49  * the thread state struct ptw32_thread_t_ (p), plus a reuse counter (x). Each
  50  * ptw32_thread_t contains the original copy of it's pthread_t.
  51  * Once malloced, a ptw32_thread_t_ struct is not freed until the process exits.
  52  *
  53  * The thread reuse stack is a simple LILO stack managed through a singly
  54  * linked list element in the ptw32_thread_t.
  55  *
  56  * Each time a thread is destroyed, the ptw32_thread_t address is pushed onto the
  57  * reuse stack after it's ptHandle's reuse counter has been incremented.
  58  *
  59  * The following can now be said from this:
  60  * - two pthread_t's are identical if their ptw32_thread_t reference pointers
  61  * are equal and their reuse counters are equal. That is,
  62  *
  63  *   equal = (a.p == b.p && a.x == b.x)
  64  *
  65  * - a pthread_t copy refers to a destroyed thread if the reuse counter in
  66  * the copy is not equal to the reuse counter in the original.
  67  *
  68  *   threadDestroyed = (copy.x != ((ptw32_thread_t *)copy.p)->ptHandle.x)
  69  *
  70  */
  71
  72 /*
  73  * Pop a clean pthread_t struct off the reuse stack.
  74  */
  75 pthread_t
  76 ptw32_threadReusePop (void)
  77 {
  78   pthread_t t = {NULL, 0};
  79   ptw32_mcs_local_node_t node;
  80
  81   ptw32_mcs_lock_acquire(&ptw32_thread_reuse_lock, &node);
  82
  83   if (PTW32_THREAD_REUSE_EMPTY != ptw32_threadReuseTop)
  84     {
  85       ptw32_thread_t * tp;
  86
  87       tp = ptw32_threadReuseTop;
  88
  89       ptw32_threadReuseTop = tp->prevReuse;
  90
  91       if (PTW32_THREAD_REUSE_EMPTY == ptw32_threadReuseTop)
  92         {
  93           ptw32_threadReuseBottom = PTW32_THREAD_REUSE_EMPTY;
  94         }
  95
  96       tp->prevReuse = NULL;
  97
  98       t = tp->ptHandle;
  99     }
 100
 101   ptw32_mcs_lock_release(&node);
 102
 103   return t;
 104
 105 }
 106
 107 /*
 108  * Push a clean pthread_t struct onto the reuse stack.
 109  * Must be re-initialised when reused.
 110  * All object elements (mutexes, events etc) must have been either
 111  * detroyed before this, or never initialised.
 112  */
 113 void
 114 ptw32_threadReusePush (pthread_t thread)
 115 {
 116   ptw32_thread_t * tp = (ptw32_thread_t *) thread.p;
 117   pthread_t t;
 118   ptw32_mcs_local_node_t node;
 119
 120   ptw32_mcs_lock_acquire(&ptw32_thread_reuse_lock, &node);
 121
 122   t = tp->ptHandle;
 123   memset(tp, 0, sizeof(ptw32_thread_t));
 124
 125   /* Must restore the original POSIX handle that we just wiped. */
 126   tp->ptHandle = t;
 127
 128   /* Bump the reuse counter now */
 129 #if defined(PTW32_THREAD_ID_REUSE_INCREMENT)
 130   tp->ptHandle.x += PTW32_THREAD_ID_REUSE_INCREMENT;
 131 #else
 132   tp->ptHandle.x++;
 133 #endif
 134
 135   tp->state = PThreadStateReuse;
 136
 137   tp->prevReuse = PTW32_THREAD_REUSE_EMPTY;
 138
 139   if (PTW32_THREAD_REUSE_EMPTY != ptw32_threadReuseBottom)
 140     {
 141       ptw32_threadReuseBottom->prevReuse = tp;
 142     }
 143   else
 144     {
 145       ptw32_threadReuseTop = tp;
 146     }
 147
 148   ptw32_threadReuseBottom = tp;
 149
 150   ptw32_mcs_lock_release(&node);
 151 }