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      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 (at) 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 }
    152