sysdeps/htl/pt-rwlock-timedrdlock.c

   1 /* Acquire a rwlock for reading.  Generic version.
   2    Copyright (C) 2002-2023 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                                        clockid_t clockid,
  31                                        const struct timespec *abstime)
  32 {
  33   error_t err;
  34   int drain;
  35   struct __pthread *self;
  36
  37   __pthread_spin_wait (&rwlock->__lock);
  38   if (__pthread_spin_trylock (&rwlock->__held) == 0)
  39     /* Successfully acquired the lock.  */
  40     {
  41       assert (rwlock->__readerqueue == 0);
  42       assert (rwlock->__writerqueue == 0);
  43       assert (rwlock->__readers == 0);
  44
  45       rwlock->__readers = 1;
  46       __pthread_spin_unlock (&rwlock->__lock);
  47       return 0;
  48     }
  49   else
  50     /* Lock is held, but is held by a reader?  */
  51   if (rwlock->__readers > 0)
  52     /* Just add ourself to number of readers.  */
  53     {
  54       assert (rwlock->__readerqueue == 0);
  55       rwlock->__readers++;
  56       __pthread_spin_unlock (&rwlock->__lock);
  57       return 0;
  58     }
  59
  60   /* The lock is busy.  */
  61
  62   /* Better be blocked by a writer.  */
  63   assert (rwlock->__readers == 0);
  64
  65   if (abstime != NULL && ! valid_nanoseconds (abstime->tv_nsec))
  66     {
  67       __pthread_spin_unlock (&rwlock->__lock);
  68       return EINVAL;
  69     }
  70
  71   self = _pthread_self ();
  72
  73   /* Add ourself to the queue.  */
  74   __pthread_enqueue (&rwlock->__readerqueue, self);
  75   __pthread_spin_unlock (&rwlock->__lock);
  76
  77   /* Block the thread.  */
  78   if (abstime != NULL)
  79     err = __pthread_timedblock (self, abstime, clockid);
  80   else
  81     {
  82       err = 0;
  83       __pthread_block (self);
  84     }
  85
  86   __pthread_spin_wait (&rwlock->__lock);
  87   if (self->prevp == NULL)
  88     /* Another thread removed us from the queue, which means a wakeup message
  89        has been sent.  It was either consumed while we were blocking, or
  90        queued after we timed out and before we acquired the rwlock lock, in
  91        which case the message queue must be drained.  */
  92     drain = err ? 1 : 0;
  93   else
  94     {
  95       /* We're still in the queue.  No one attempted to wake us up, i.e. we
  96          timed out.  */
  97       __pthread_dequeue (self);
  98       drain = 0;
  99     }
 100   __pthread_spin_unlock (&rwlock->__lock);
 101
 102   if (drain)
 103     __pthread_block (self);
 104
 105   if (err)
 106     {
 107       assert (err == ETIMEDOUT);
 108       return err;
 109     }
 110
 111   /* The reader count has already been increment by whoever woke us
 112      up.  */
 113
 114   assert (rwlock->__readers > 0);
 115
 116   return 0;
 117 }
 118
 119 int
 120 __pthread_rwlock_timedrdlock (struct __pthread_rwlock *rwlock,
 121                               const struct timespec *abstime)
 122 {
 123   return __pthread_rwlock_timedrdlock_internal (rwlock, CLOCK_REALTIME, abstime);
 124 }
 125 weak_alias (__pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock)
 126
 127 int
 128 __pthread_rwlock_clockrdlock (struct __pthread_rwlock *rwlock,
 129                               clockid_t clockid,
 130                               const struct timespec *abstime)
 131 {
 132   return __pthread_rwlock_timedrdlock_internal (rwlock, clockid, abstime);
 133 }
 134 weak_alias (__pthread_rwlock_clockrdlock, pthread_rwlock_clockrdlock)