glibc/nptl/lowlevellock.c

/* low level locking for pthread library.  Generic futex-using version.
   Copyright (C) 2003-2015 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <errno.h>
#include <sysdep.h>
#include <lowlevellock.h>
#include <sys/time.h>
#include <atomic.h>

void
__lll_lock_wait_private (int *futex)
{
  if (*futex == 2)
    lll_futex_wait (futex, 2, LLL_PRIVATE); /* Wait if *futex == 2.  */

  while (atomic_exchange_acq (futex, 2) != 0)
    lll_futex_wait (futex, 2, LLL_PRIVATE); /* Wait if *futex == 2.  */
}


/* These functions don't get included in libc.so  */
#if IS_IN (libpthread)
void
__lll_lock_wait (int *futex, int private)
{
  if (*futex == 2)
    lll_futex_wait (futex, 2, private); /* Wait if *futex == 2.  */

  while (atomic_exchange_acq (futex, 2) != 0)
    lll_futex_wait (futex, 2, private); /* Wait if *futex == 2.  */
}


int
__lll_timedlock_wait (int *futex, const struct timespec *abstime, int private)
{
  /* Reject invalid timeouts.  */
  if (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000)
    return EINVAL;

  /* Try locking.  */
  while (atomic_exchange_acq (futex, 2) != 0)
    {
      struct timeval tv;

      /* Get the current time.  */
      (void) __gettimeofday (&tv, NULL);

      /* Compute 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;
	}

      if (rt.tv_sec < 0)
	return ETIMEDOUT;

      /* If *futex == 2, wait until woken or timeout.  */
      lll_futex_timed_wait (futex, 2, &rt, private);
    }

  return 0;
}


/* The kernel notifies a process which uses CLONE_CHILD_CLEARTID via futex
   wake-up when the clone terminates.  The memory location contains the
   thread ID while the clone is running and is reset to zero by the kernel
   afterwards.  The kernel up to version 3.16.3 does not use the private futex
   operations for futex wake-up when the clone terminates.  */
int
__lll_timedwait_tid (int *tidp, const struct timespec *abstime)
{
  int tid;

  if (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000)
    return EINVAL;

  /* Repeat until thread terminated.  */
  while ((tid = *tidp) != 0)
    {
      struct timeval tv;
      struct timespec rt;

      /* Get the current time.  */
      (void) __gettimeofday (&tv, NULL);

      /* Compute relative timeout.  */
      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;
	}

      /* Already timed out?  */
      if (rt.tv_sec < 0)
	return ETIMEDOUT;

      /* If *tidp == tid, wait until thread terminates or the wait times out.
         The kernel up to version 3.16.3 does not use the private futex
         operations for futex wake-up when the clone terminates.
      */
      if (lll_futex_timed_wait (tidp, tid, &rt, LLL_SHARED) == -ETIMEDOUT)
	return ETIMEDOUT;
    }

  return 0;
}
#endif