nptl/pthread_rwlock_timedwrlock.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 <kernel-features.h>
  25
  26
  27 /* Try to acquire write lock for RWLOCK or return after specfied time.  */
  28 int
  29 pthread_rwlock_timedwrlock (rwlock, abstime)
  30      pthread_rwlock_t *rwlock;
  31      const struct timespec *abstime;
  32 {
  33   int result = 0;
  34
  35   /* Make sure we are alone.  */
  36   lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  37
  38   while (1)
  39     {
  40       int err;
  41
  42       /* Get the rwlock if there is no writer and no reader.  */
  43       if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
  44         {
  45           /* Mark self as writer.  */
  46           rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
  47           break;
  48         }
  49
  50       /* Make sure we are not holding the rwlock as a writer.  This is
  51          a deadlock situation we recognize and report.  */
  52       if (__builtin_expect (rwlock->__data.__writer
  53                             == THREAD_GETMEM (THREAD_SELF, tid), 0))
  54         {
  55           result = EDEADLK;
  56           break;
  57         }
  58
  59       /* Make sure the passed in timeout value is valid.  Ideally this
  60          test would be executed once.  But since it must not be
  61          performed if we would not block at all simply moving the test
  62          to the front is no option.  Replicating all the code is
  63          costly while this test is not.  */
  64       if (__builtin_expect (abstime->tv_nsec >= 1000000000
  65                             || abstime->tv_nsec < 0, 0))
  66         {
  67           result = EINVAL;
  68           break;
  69         }
  70
  71       /* Work around the fact that the kernel rejects negative timeout values
  72          despite them being valid.  */
  73       if (__glibc_unlikely (abstime->tv_sec < 0))
  74         {
  75           result = ETIMEDOUT;
  76           break;
  77         }
  78
  79 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
  80      || !defined lll_futex_timed_wait_bitset)
  81       /* Get the current time.  So far we support only one clock.  */
  82       struct timeval tv;
  83       (void) gettimeofday (&tv, NULL);
  84
  85       /* Convert the absolute timeout value to a relative timeout.  */
  86       struct timespec rt;
  87       rt.tv_sec = abstime->tv_sec - tv.tv_sec;
  88       rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
  89       if (rt.tv_nsec < 0)
  90         {
  91           rt.tv_nsec += 1000000000;
  92           --rt.tv_sec;
  93         }
  94       /* Did we already time out?  */
  95       if (rt.tv_sec < 0)
  96         {
  97           result = ETIMEDOUT;
  98           break;
  99         }
 100 #endif
 101
 102       /* Remember that we are a writer.  */
 103       if (++rwlock->__data.__nr_writers_queued == 0)
 104         {
 105           /* Overflow on number of queued writers.  */
 106           --rwlock->__data.__nr_writers_queued;
 107           result = EAGAIN;
 108           break;
 109         }
 110
 111       int waitval = rwlock->__data.__writer_wakeup;
 112
 113       /* Free the lock.  */
 114       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 115
 116       /* Wait for the writer or reader(s) to finish.  */
 117 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
 118      || !defined lll_futex_timed_wait_bitset)
 119       err = lll_futex_timed_wait (&rwlock->__data.__writer_wakeup,
 120                                   waitval, &rt, rwlock->__data.__shared);
 121 #else
 122       err = lll_futex_timed_wait_bitset (&rwlock->__data.__writer_wakeup,
 123                                          waitval, abstime,
 124                                          FUTEX_CLOCK_REALTIME,
 125                                          rwlock->__data.__shared);
 126 #endif
 127
 128       /* Get the lock.  */
 129       lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
 130
 131       /* To start over again, remove the thread from the writer list.  */
 132       --rwlock->__data.__nr_writers_queued;
 133
 134       /* Did the futex call time out?  */
 135       if (err == -ETIMEDOUT)
 136         {
 137           result = ETIMEDOUT;
 138           break;
 139         }
 140     }
 141
 142   /* We are done, free the lock.  */
 143   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 144
 145   return result;
 146 }