nptl/pthread_rwlock_wrlock.c

   1 /* Copyright (C) 2003-2016 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 <futex-internal.h>
  23 #include <pthread.h>
  24 #include <pthreadP.h>
  25 #include <stap-probe.h>
  26 #include <elide.h>
  27
  28
  29 /* Acquire write lock for RWLOCK.  */
  30 static int __attribute__((noinline))
  31 __pthread_rwlock_wrlock_slow (pthread_rwlock_t *rwlock)
  32 {
  33   int result = 0;
  34   int futex_shared =
  35       rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
  36
  37   /* Caller has taken the lock.  */
  38
  39   while (1)
  40     {
  41       /* Make sure we are not holding the rwlock as a writer.  This is
  42          a deadlock situation we recognize and report.  */
  43       if (__builtin_expect (rwlock->__data.__writer
  44                             == THREAD_GETMEM (THREAD_SELF, tid), 0))
  45         {
  46           result = EDEADLK;
  47           break;
  48         }
  49
  50       /* Remember that we are a writer.  */
  51       if (++rwlock->__data.__nr_writers_queued == 0)
  52         {
  53           /* Overflow on number of queued writers.  */
  54           --rwlock->__data.__nr_writers_queued;
  55           result = EAGAIN;
  56           break;
  57         }
  58
  59       int waitval = rwlock->__data.__writer_wakeup;
  60
  61       /* Free the lock.  */
  62       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  63
  64       /* Wait for the writer or reader(s) to finish.  We do not check the
  65          return value because we decide how to continue based on the state of
  66          the rwlock.  */
  67       futex_wait_simple (&rwlock->__data.__writer_wakeup, waitval,
  68                          futex_shared);
  69
  70       /* Get the lock.  */
  71       lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  72
  73       /* To start over again, remove the thread from the writer list.  */
  74       --rwlock->__data.__nr_writers_queued;
  75
  76       /* Get the rwlock if there is no writer and no reader.  */
  77       if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
  78         {
  79           /* Mark self as writer.  */
  80           rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
  81
  82           LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
  83           break;
  84         }
  85     }
  86
  87   /* We are done, free the lock.  */
  88   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  89
  90   return result;
  91 }
  92
  93 /* Fast path of acquiring write lock for RWLOCK.  */
  94
  95 int
  96 __pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
  97 {
  98   LIBC_PROBE (wrlock_entry, 1, rwlock);
  99
 100   if (ELIDE_LOCK (rwlock->__data.__rwelision,
 101                   rwlock->__data.__lock == 0
 102                   && rwlock->__data.__writer == 0
 103                   && rwlock->__data.__nr_readers == 0))
 104     return 0;
 105
 106   /* Make sure we are alone.  */
 107   lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
 108
 109   /* Get the rwlock if there is no writer and no reader.  */
 110   if (__glibc_likely((rwlock->__data.__writer |
 111         rwlock->__data.__nr_readers) == 0))
 112     {
 113       /* Mark self as writer.  */
 114       rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
 115
 116       LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
 117
 118       /* We are done, free the lock.  */
 119       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 120
 121       return 0;
 122     }
 123
 124   return __pthread_rwlock_wrlock_slow (rwlock);
 125 }
 126
 127
 128 weak_alias (__pthread_rwlock_wrlock, pthread_rwlock_wrlock)
 129 hidden_def (__pthread_rwlock_wrlock)