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/* Linuxthreads - a simple clone()-based implementation of Posix */
/* threads for Linux. */
/* Copyright (C) 1998 Xavier Leroy (Xavier.Leroy@inria.fr) */
/* */
/* This program is free software; you can redistribute it and/or */
/* modify it under the terms of the GNU Library General Public License */
/* as published by the Free Software Foundation; either version 2 */
/* of the License, or (at your option) any later version. */
/* */
/* This program 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 Library General Public License for more details. */
#include <bits/initspin.h>
/* There are 2 compare and swap synchronization primitives with
different semantics:
1. compare_and_swap, which has acquire semantics (i.e. it
completes befor subsequent writes.)
2. compare_and_swap_with_release_semantics, which has release
semantics (it completes after previous writes.)
For those platforms on which they are the same. HAS_COMPARE_AND_SWAP
should be defined. For those platforms on which they are different,
HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS has to be defined. */
#ifndef HAS_COMPARE_AND_SWAP
#ifdef HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS
#define HAS_COMPARE_AND_SWAP
#endif
#endif
#if defined(TEST_FOR_COMPARE_AND_SWAP)
extern int __pthread_has_cas;
extern int __pthread_compare_and_swap(long * ptr, long oldval, long newval,
int * spinlock);
static inline int compare_and_swap(long * ptr, long oldval, long newval,
int * spinlock)
{
if (__builtin_expect (__pthread_has_cas, 1))
return __compare_and_swap(ptr, oldval, newval);
else
return __pthread_compare_and_swap(ptr, oldval, newval, spinlock);
}
#elif defined(HAS_COMPARE_AND_SWAP)
#ifdef IMPLEMENT_TAS_WITH_CAS
#define testandset(p) !__compare_and_swap((long int *) p, 0, 1)
#endif
#ifdef HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS
static inline int
compare_and_swap_with_release_semantics (long * ptr, long oldval,
long newval, int * spinlock)
{
return __compare_and_swap_with_release_semantics (ptr, oldval,
newval);
}
#endif
static inline int compare_and_swap(long * ptr, long oldval, long newval,
int * spinlock)
{
return __compare_and_swap(ptr, oldval, newval);
}
#else
extern int __pthread_compare_and_swap(long * ptr, long oldval, long newval,
int * spinlock);
static inline int compare_and_swap(long * ptr, long oldval, long newval,
int * spinlock)
{
return __pthread_compare_and_swap(ptr, oldval, newval, spinlock);
}
#endif
#ifndef HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS
#define compare_and_swap_with_release_semantics compare_and_swap
#define __compare_and_swap_with_release_semantics __compare_and_swap
#endif
/* Internal locks */
extern void internal_function __pthread_lock(struct _pthread_fastlock * lock,
pthread_descr self);
extern int __pthread_unlock(struct _pthread_fastlock *lock);
static inline void __pthread_init_lock(struct _pthread_fastlock * lock)
{
lock->__status = 0;
lock->__spinlock = __LT_SPINLOCK_INIT;
}
static inline int __pthread_trylock (struct _pthread_fastlock * lock)
{
#if defined TEST_FOR_COMPARE_AND_SWAP
if (!__pthread_has_cas)
#endif
#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
{
return (testandset(&lock->__spinlock) ? EBUSY : 0);
}
#endif
#if defined HAS_COMPARE_AND_SWAP
do {
if (lock->__status != 0) return EBUSY;
} while(! __compare_and_swap(&lock->__status, 0, 1));
return 0;
#endif
}
/* Variation of internal lock used for pthread_mutex_t, supporting
timed-out waits. Warning: do not mix these operations with the above ones
over the same lock object! */
extern void __pthread_alt_lock(struct _pthread_fastlock * lock,
pthread_descr self);
extern int __pthread_alt_timedlock(struct _pthread_fastlock * lock,
pthread_descr self, const struct timespec *abstime);
extern void __pthread_alt_unlock(struct _pthread_fastlock *lock);
static inline void __pthread_alt_init_lock(struct _pthread_fastlock * lock)
{
lock->__status = 0;
lock->__spinlock = __LT_SPINLOCK_INIT;
}
static inline int __pthread_alt_trylock (struct _pthread_fastlock * lock)
{
#if defined TEST_FOR_COMPARE_AND_SWAP
if (!__pthread_has_cas)
#endif
#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
{
int res = EBUSY;
if (testandset(&lock->__spinlock) == 0)
{
if (lock->__status == 0)
{
lock->__status = 1;
WRITE_MEMORY_BARRIER();
res = 0;
}
lock->__spinlock = __LT_SPINLOCK_INIT;
}
return res;
}
#endif
#if defined HAS_COMPARE_AND_SWAP
do {
if (lock->__status != 0) return EBUSY;
} while(! compare_and_swap(&lock->__status, 0, 1, &lock->__spinlock));
return 0;
#endif
}
/* Operations on pthread_atomic, which is defined in internals.h */
static inline long atomic_increment(struct pthread_atomic *pa)
{
long oldval;
do {
oldval = pa->p_count;
} while (!compare_and_swap(&pa->p_count, oldval, oldval + 1, &pa->p_spinlock));
return oldval;
}
static inline long atomic_decrement(struct pthread_atomic *pa)
{
long oldval;
do {
oldval = pa->p_count;
} while (!compare_and_swap(&pa->p_count, oldval, oldval - 1, &pa->p_spinlock));
return oldval;
}
static inline void
__pthread_set_own_extricate_if (pthread_descr self, pthread_extricate_if *peif)
{
/* Only store a non-null peif if the thread has cancellation enabled.
Otherwise pthread_cancel will unconditionally call the extricate handler,
and restart the thread giving rise to forbidden spurious wakeups. */
if (peif == NULL
|| THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE)
{
/* If we are removing the extricate interface, we need to synchronize
against pthread_cancel so that it does not continue with a pointer
to a deallocated pthread_extricate_if struct! The thread lock
is (ab)used for this synchronization purpose. */
if (peif == NULL)
__pthread_lock (THREAD_GETMEM(self, p_lock), self);
THREAD_SETMEM(self, p_extricate, peif);
if (peif == NULL)
__pthread_unlock (THREAD_GETMEM(self, p_lock));
}
}
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