nptl/pthread_rwlock_wrlock.c

   1 /* Copyright (C) 2003-2015 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <sysdep.h>
  21 #include <lowlevellock.h>
  22 #include <pthread.h>
  23 #include <pthreadP.h>
  24 #include <stap-probe.h>
  25 #include <elide.h>
  26
  27
  28 /* Acquire write lock for RWLOCK.  */
  29 static int __attribute__((noinline))
  30 __pthread_rwlock_wrlock_slow (pthread_rwlock_t *rwlock)
  31 {
  32   int result = 0;
  33
  34   /* Caller has taken the lock.  */
  35
  36   while (1)
  37     {
  38       /* Make sure we are not holding the rwlock as a writer.  This is
  39          a deadlock situation we recognize and report.  */
  40       if (__builtin_expect (rwlock->__data.__writer
  41                             == THREAD_GETMEM (THREAD_SELF, tid), 0))
  42         {
  43           result = EDEADLK;
  44           break;
  45         }
  46
  47       /* Remember that we are a writer.  */
  48       if (++rwlock->__data.__nr_writers_queued == 0)
  49         {
  50           /* Overflow on number of queued writers.  */
  51           --rwlock->__data.__nr_writers_queued;
  52           result = EAGAIN;
  53           break;
  54         }
  55
  56       int waitval = rwlock->__data.__writer_wakeup;
  57
  58       /* Free the lock.  */
  59       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  60
  61       /* Wait for the writer or reader(s) to finish.  */
  62       lll_futex_wait (&rwlock->__data.__writer_wakeup, waitval,
  63                       rwlock->__data.__shared);
  64
  65       /* Get the lock.  */
  66       lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  67
  68       /* To start over again, remove the thread from the writer list.  */
  69       --rwlock->__data.__nr_writers_queued;
  70
  71       /* Get the rwlock if there is no writer and no reader.  */
  72       if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
  73         {
  74           /* Mark self as writer.  */
  75           rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
  76
  77           LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
  78           break;
  79         }
  80     }
  81
  82   /* We are done, free the lock.  */
  83   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  84
  85   return result;
  86 }
  87
  88 /* Fast path of acquiring write lock for RWLOCK.  */
  89
  90 int
  91 __pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
  92 {
  93   LIBC_PROBE (wrlock_entry, 1, rwlock);
  94
  95   if (ELIDE_LOCK (rwlock->__data.__rwelision,
  96                   rwlock->__data.__lock == 0
  97                   && rwlock->__data.__writer == 0
  98                   && rwlock->__data.__nr_readers == 0))
  99     return 0;
 100
 101   /* Make sure we are alone.  */
 102   lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
 103
 104   /* Get the rwlock if there is no writer and no reader.  */
 105   if (__glibc_likely((rwlock->__data.__writer |
 106         rwlock->__data.__nr_readers) == 0))
 107     {
 108       /* Mark self as writer.  */
 109       rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
 110
 111       LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
 112
 113       /* We are done, free the lock.  */
 114       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 115
 116       return 0;
 117     }
 118
 119   return __pthread_rwlock_wrlock_slow (rwlock);
 120 }
 121
 122
 123 weak_alias (__pthread_rwlock_wrlock, pthread_rwlock_wrlock)
 124 hidden_def (__pthread_rwlock_wrlock)