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/* Copyright (C) 2002 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#include <atomic.h>
/* Implement generic mutex. Basic futex syscall support is required:
lll_futex_wait(futex, value) - call sys_futex with FUTEX_WAIT
and third parameter VALUE
lll_futex_wake(futex, value) - call sys_futex with FUTEX_WAKE
and third parameter VALUE
*/
/* Mutex lock counter:
bit 31 clear means unlocked;
bit 31 set means locked.
All code that looks at bit 31 first increases the 'number of
interested threads' usage counter, which is in bits 0-30.
All negative mutex values indicate that the mutex is still locked. */
static inline void
__generic_mutex_lock (int *mutex)
{
unsigned int v;
/* Bit 31 was clear, we got the mutex. (this is the fastpath). */
if (atomic_bit_test_set (mutex, 31) == 0)
return;
atomic_increment (mutex);
while (1)
{
if (atomic_bit_test_set (mutex, 31) == 0)
{
atomic_decrement (mutex);
return;
}
/* We have to wait now. First make sure the futex value we are
monitoring is truly negative (i.e. locked). */
v = *mutex;
if (v >= 0)
continue;
lll_futex_wait (mutex, v);
}
}
static inline void
__generic_mutex_unlock (int *mutex)
{
/* Adding 0x80000000 to the counter results in 0 if and only if
there are not other interested threads - we can return (this is
the fastpath). */
if (atomic_add_zero (mutex, 0x80000000))
return;
/* There are other threads waiting for this mutex, wake one of them
up. */
lll_futex_wake (mutex, 1);
}
#define lll_mutex_lock(futex) __generic_mutex_lock (&(futex))
#define lll_mutex_unlock(futex) __generic_mutex_unlock (&(futex))
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