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/*
* %CopyrightBegin%
*
* Copyright Ericsson AB 2005-2009. All Rights Reserved.
*
* The contents of this file are subject to the Erlang Public License,
* Version 1.1, (the "License"); you may not use this file except in
* compliance with the License. You should have received a copy of the
* Erlang Public License along with this software. If not, it can be
* retrieved online at http://www.erlang.org/.
*
* Software distributed under the License is distributed on an "AS IS"
* basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
* the License for the specific language governing rights and limitations
* under the License.
*
* %CopyrightEnd%
*/
/*
* Native ethread rwlocks on x86/x86-64.
* Author: Mikael Pettersson.
*
* This code requires a 486 or newer processor.
*/
#ifndef ETHREAD_I386_RWLOCK_H
#define ETHREAD_I386_RWLOCK_H
/* XXX: describe the algorithm */
typedef struct {
volatile int lock;
} ethr_native_rwlock_t;
#ifdef ETHR_TRY_INLINE_FUNCS
#define ETHR_RWLOCK_OFFSET (1<<24)
static ETHR_INLINE void
ethr_native_rwlock_init(ethr_native_rwlock_t *lock)
{
lock->lock = 0;
}
static ETHR_INLINE void
ethr_native_read_unlock(ethr_native_rwlock_t *lock)
{
__asm__ __volatile__(
"lock; decl %0"
: "=m"(lock->lock)
: "m"(lock->lock));
}
static ETHR_INLINE int
ethr_native_read_trylock(ethr_native_rwlock_t *lock)
{
int tmp;
tmp = 1;
__asm__ __volatile__(
"lock; xaddl %0, %1"
: "=r"(tmp)
: "m"(lock->lock), "0"(tmp));
/* tmp is now the lock's previous value */
if (__builtin_expect(tmp >= 0, 1))
return 1;
ethr_native_read_unlock(lock);
return 0;
}
static ETHR_INLINE int
ethr_native_read_is_locked(ethr_native_rwlock_t *lock)
{
return lock->lock < 0;
}
static ETHR_INLINE void
ethr_native_read_lock(ethr_native_rwlock_t *lock)
{
for(;;) {
if (__builtin_expect(ethr_native_read_trylock(lock) != 0, 1))
break;
do {
__asm__ __volatile__("rep;nop" : "=m"(lock->lock) : : "memory");
} while (ethr_native_read_is_locked(lock));
}
}
static ETHR_INLINE void
ethr_native_write_unlock(ethr_native_rwlock_t *lock)
{
__asm__ __volatile__(
"lock; addl %2,%0"
: "=m"(lock->lock)
: "m"(lock->lock), "i"(ETHR_RWLOCK_OFFSET));
}
static ETHR_INLINE int
ethr_native_write_trylock(ethr_native_rwlock_t *lock)
{
int tmp;
tmp = -ETHR_RWLOCK_OFFSET;
__asm__ __volatile__(
"lock; xaddl %0, %1"
: "=r"(tmp)
: "m"(lock->lock), "0"(tmp));
/* tmp is now the lock's previous value */
if (__builtin_expect(tmp == 0, 1))
return 1;
ethr_native_write_unlock(lock);
return 0;
}
static ETHR_INLINE int
ethr_native_write_is_locked(ethr_native_rwlock_t *lock)
{
return lock->lock != 0;
}
static ETHR_INLINE void
ethr_native_write_lock(ethr_native_rwlock_t *lock)
{
for(;;) {
if (__builtin_expect(ethr_native_write_trylock(lock) != 0, 1))
break;
do {
__asm__ __volatile__("rep;nop" : "=m"(lock->lock) : : "memory");
} while (ethr_native_write_is_locked(lock));
}
}
#endif /* ETHR_TRY_INLINE_FUNCS */
#endif /* ETHREAD_I386_RWLOCK_H */
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