sysdeps/htl/pt-rwlock-timedrdlock.c

   1 /* Acquire a rwlock for reading.  Generic version.
   2    Copyright (C) 2002-2019 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   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    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <pthread.h>
  20 #include <assert.h>
  21 #include <time.h>
  22
  23 #include <pt-internal.h>
  24
  25 /* Acquire the rwlock *RWLOCK for reading blocking until *ABSTIME if
  26    it is already held.  As a GNU extension, if TIMESPEC is NULL then
  27    wait forever.  */
  28 int
  29 __pthread_rwlock_timedrdlock_internal (struct __pthread_rwlock *rwlock,
  30                                        const struct timespec *abstime)
  31 {
  32   error_t err;
  33   int drain;
  34   struct __pthread *self;
  35
  36   __pthread_spin_lock (&rwlock->__lock);
  37   if (__pthread_spin_trylock (&rwlock->__held) == 0)
  38     /* Successfully acquired the lock.  */
  39     {
  40       assert (rwlock->__readerqueue == 0);
  41       assert (rwlock->__writerqueue == 0);
  42       assert (rwlock->__readers == 0);
  43
  44       rwlock->__readers = 1;
  45       __pthread_spin_unlock (&rwlock->__lock);
  46       return 0;
  47     }
  48   else
  49     /* Lock is held, but is held by a reader?  */
  50   if (rwlock->__readers > 0)
  51     /* Just add ourself to number of readers.  */
  52     {
  53       assert (rwlock->__readerqueue == 0);
  54       rwlock->__readers++;
  55       __pthread_spin_unlock (&rwlock->__lock);
  56       return 0;
  57     }
  58
  59   /* The lock is busy.  */
  60
  61   /* Better be blocked by a writer.  */
  62   assert (rwlock->__readers == 0);
  63
  64   if (abstime != NULL && ! valid_nanoseconds (abstime->tv_nsec))
  65     return EINVAL;
  66
  67   self = _pthread_self ();
  68
  69   /* Add ourself to the queue.  */
  70   __pthread_enqueue (&rwlock->__readerqueue, self);
  71   __pthread_spin_unlock (&rwlock->__lock);
  72
  73   /* Block the thread.  */
  74   if (abstime != NULL)
  75     err = __pthread_timedblock (self, abstime, CLOCK_REALTIME);
  76   else
  77     {
  78       err = 0;
  79       __pthread_block (self);
  80     }
  81
  82   __pthread_spin_lock (&rwlock->__lock);
  83   if (self->prevp == NULL)
  84     /* Another thread removed us from the queue, which means a wakeup message
  85        has been sent.  It was either consumed while we were blocking, or
  86        queued after we timed out and before we acquired the rwlock lock, in
  87        which case the message queue must be drained.  */
  88     drain = err ? 1 : 0;
  89   else
  90     {
  91       /* We're still in the queue.  Noone attempted to wake us up, i.e. we
  92          timed out.  */
  93       __pthread_dequeue (self);
  94       drain = 0;
  95     }
  96   __pthread_spin_unlock (&rwlock->__lock);
  97
  98   if (drain)
  99     __pthread_block (self);
 100
 101   if (err)
 102     {
 103       assert (err == ETIMEDOUT);
 104       return err;
 105     }
 106
 107   /* The reader count has already been increment by whoever woke us
 108      up.  */
 109
 110   assert (rwlock->__readers > 0);
 111
 112   return 0;
 113 }
 114
 115 int
 116 __pthread_rwlock_timedrdlock (struct __pthread_rwlock *rwlock,
 117                               const struct timespec *abstime)
 118 {
 119   return __pthread_rwlock_timedrdlock_internal (rwlock, abstime);
 120 }
 121 weak_alias (__pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock)