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