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glibc  2.9
Functions
pthread_rwlock_timedrdlock.c File Reference
#include <errno.h>
#include <sysdep.h>
#include <lowlevellock.h>
#include <pthread.h>
#include <pthreadP.h>

Go to the source code of this file.

Functions

int pthread_rwlock_timedrdlock (pthread_rwlock_t *rwlock, const struct timespec *abstime)

Function Documentation

int pthread_rwlock_timedrdlock ( pthread_rwlock_t *  rwlock,
const struct timespec abstime 
)

Definition at line 29 of file pthread_rwlock_timedrdlock.c.

{
  int result = 0;

  /* Make sure we are along.  */
  lll_lock(rwlock->__data.__lock, rwlock->__data.__shared);

  while (1)
    {
      int err;

      /* Get the rwlock if there is no writer...  */
      if (rwlock->__data.__writer == 0
         /* ...and if either no writer is waiting or we prefer readers.  */
         && (!rwlock->__data.__nr_writers_queued
             || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
       {
         /* Increment the reader counter.  Avoid overflow.  */
         if (++rwlock->__data.__nr_readers == 0)
           {
             /* Overflow on number of readers.    */
             --rwlock->__data.__nr_readers;
             result = EAGAIN;
           }

         break;
       }

      /* Make sure we are not holding the rwlock as a writer.  This is
        a deadlock situation we recognize and report.  */
      if (__builtin_expect (rwlock->__data.__writer
                         == THREAD_GETMEM (THREAD_SELF, tid), 0))
       {
         result = EDEADLK;
         break;
       }

      /* Make sure the passed in timeout value is valid.  Ideally this
        test would be executed once.  But since it must not be
        performed if we would not block at all simply moving the test
        to the front is no option.  Replicating all the code is
        costly while this test is not.  */
      if (__builtin_expect (abstime->tv_nsec >= 1000000000
                            || abstime->tv_nsec < 0, 0))
       {
         result = EINVAL;
         break;
       }

      /* Get the current time.  So far we support only one clock.  */
      struct timeval tv;
      (void) gettimeofday (&tv, NULL);

      /* Convert the absolute timeout value to a relative timeout.  */
      struct timespec rt;
      rt.tv_sec = abstime->tv_sec - tv.tv_sec;
      rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
      if (rt.tv_nsec < 0)
       {
         rt.tv_nsec += 1000000000;
         --rt.tv_sec;
       }
      /* Did we already time out?  */
      if (rt.tv_sec < 0)
       {
         /* Yep, return with an appropriate error.  */
         result = ETIMEDOUT;
         break;
       }

      /* Remember that we are a reader.  */
      if (++rwlock->__data.__nr_readers_queued == 0)
       {
         /* Overflow on number of queued readers.  */
         --rwlock->__data.__nr_readers_queued;
         result = EAGAIN;
         break;
       }

      int waitval = rwlock->__data.__readers_wakeup;

      /* Free the lock.  */
      lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);

      /* Wait for the writer to finish.  */
      err = lll_futex_timed_wait (&rwlock->__data.__readers_wakeup,
                              waitval, &rt, rwlock->__data.__shared);

      /* Get the lock.  */
      lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);

      --rwlock->__data.__nr_readers_queued;

      /* Did the futex call time out?  */
      if (err == -ETIMEDOUT)
       {
         /* Yep, report it.  */
         result = ETIMEDOUT;
         break;
       }
    }

  /* We are done, free the lock.  */
  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);

  return result;
}

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