nptl/pthread_rwlock_wrlock.c

   1 /* Copyright (C) 2003-2014 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
  26
  27 /* Acquire write lock for RWLOCK.  */
  28 int
  29 __pthread_rwlock_wrlock (rwlock)
  30      pthread_rwlock_t *rwlock;
  31 {
  32   int result = 0;
  33
  34   LIBC_PROBE (wrlock_entry, 1, rwlock);
  35
  36   /* Make sure we are alone.  */
  37   lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  38
  39   while (1)
  40     {
  41       /* Get the rwlock if there is no writer and no reader.  */
  42       if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
  43         {
  44           /* Mark self as writer.  */
  45           rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
  46
  47           LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
  48           break;
  49         }
  50
  51       /* Make sure we are not holding the rwlock as a writer.  This is
  52          a deadlock situation we recognize and report.  */
  53       if (__builtin_expect (rwlock->__data.__writer
  54                             == THREAD_GETMEM (THREAD_SELF, tid), 0))
  55         {
  56           result = EDEADLK;
  57           break;
  58         }
  59
  60       /* Remember that we are a writer.  */
  61       if (++rwlock->__data.__nr_writers_queued == 0)
  62         {
  63           /* Overflow on number of queued writers.  */
  64           --rwlock->__data.__nr_writers_queued;
  65           result = EAGAIN;
  66           break;
  67         }
  68
  69       int waitval = rwlock->__data.__writer_wakeup;
  70
  71       /* Free the lock.  */
  72       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  73
  74       /* Wait for the writer or reader(s) to finish.  */
  75       lll_futex_wait (&rwlock->__data.__writer_wakeup, waitval,
  76                       rwlock->__data.__shared);
  77
  78       /* Get the lock.  */
  79       lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  80
  81       /* To start over again, remove the thread from the writer list.  */
  82       --rwlock->__data.__nr_writers_queued;
  83     }
  84
  85   /* We are done, free the lock.  */
  86   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  87
  88   return result;
  89 }
  90
  91 weak_alias (__pthread_rwlock_wrlock, pthread_rwlock_wrlock)
  92 hidden_def (__pthread_rwlock_wrlock)