1 /* Linuxthreads - a simple clone()-based implementation of Posix */
2 /* threads for Linux. */
3 /* Copyright (C) 1998 Xavier Leroy (Xavier.Leroy@inria.fr) */
5 /* This program is free software; you can redistribute it and/or */
6 /* modify it under the terms of the GNU Library General Public License */
7 /* as published by the Free Software Foundation; either version 2 */
8 /* of the License, or (at your option) any later version. */
10 /* This program is distributed in the hope that it will be useful, */
11 /* but WITHOUT ANY WARRANTY; without even the implied warranty of */
12 /* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the */
13 /* GNU Library General Public License for more details. */
15 #include <bits/initspin.h>
18 /* There are 2 compare and swap synchronization primitives with
21 1. compare_and_swap, which has acquire semantics (i.e. it
22 completes befor subsequent writes.)
23 2. compare_and_swap_with_release_semantics, which has release
24 semantics (it completes after previous writes.)
26 For those platforms on which they are the same. HAS_COMPARE_AND_SWAP
27 should be defined. For those platforms on which they are different,
28 HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS has to be defined. */
30 #ifndef HAS_COMPARE_AND_SWAP
31 #ifdef HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS
32 #define HAS_COMPARE_AND_SWAP
36 #if defined(TEST_FOR_COMPARE_AND_SWAP)
38 extern int __pthread_has_cas;
39 extern int __pthread_compare_and_swap(long * ptr, long oldval, long newval,
42 static __inline__ int compare_and_swap(long * ptr, long oldval, long newval,
45 if (__builtin_expect (__pthread_has_cas, 1))
46 return __compare_and_swap(ptr, oldval, newval);
48 return __pthread_compare_and_swap(ptr, oldval, newval, spinlock);
51 #elif defined(HAS_COMPARE_AND_SWAP)
53 #ifdef IMPLEMENT_TAS_WITH_CAS
54 #define testandset(p) !__compare_and_swap((long int *) p, 0, 1)
57 #ifdef HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS
60 compare_and_swap_with_release_semantics (long * ptr, long oldval,
61 long newval, int * spinlock)
63 return __compare_and_swap_with_release_semantics (ptr, oldval,
69 static __inline__ int compare_and_swap(long * ptr, long oldval, long newval,
72 return __compare_and_swap(ptr, oldval, newval);
77 extern int __pthread_compare_and_swap(long * ptr, long oldval, long newval,
80 static __inline__ int compare_and_swap(long * ptr, long oldval, long newval,
83 return __pthread_compare_and_swap(ptr, oldval, newval, spinlock);
88 #ifndef HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS
89 #define compare_and_swap_with_release_semantics compare_and_swap
90 #define __compare_and_swap_with_release_semantics __compare_and_swap
95 extern void internal_function __pthread_lock(struct _pthread_fastlock * lock,
97 extern int __pthread_unlock(struct _pthread_fastlock *lock);
99 static __inline__ void __pthread_init_lock(struct _pthread_fastlock * lock)
102 lock->__spinlock = __LT_SPINLOCK_INIT;
105 static __inline__ int __pthread_trylock (struct _pthread_fastlock * lock)
107 #if defined TEST_FOR_COMPARE_AND_SWAP
108 if (!__pthread_has_cas)
110 #if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
112 return (testandset(&lock->__spinlock) ? EBUSY : 0);
116 #if defined HAS_COMPARE_AND_SWAP
118 if (lock->__status != 0) return EBUSY;
119 } while(! __compare_and_swap(&lock->__status, 0, 1));
124 /* Variation of internal lock used for pthread_mutex_t, supporting
125 timed-out waits. Warning: do not mix these operations with the above ones
126 over the same lock object! */
128 extern void __pthread_alt_lock(struct _pthread_fastlock * lock,
131 extern int __pthread_alt_timedlock(struct _pthread_fastlock * lock,
132 pthread_descr self, const struct timespec *abstime);
134 extern void __pthread_alt_unlock(struct _pthread_fastlock *lock);
136 static __inline__ void __pthread_alt_init_lock(struct _pthread_fastlock * lock)
139 lock->__spinlock = __LT_SPINLOCK_INIT;
142 static __inline__ int __pthread_alt_trylock (struct _pthread_fastlock * lock)
144 #if defined TEST_FOR_COMPARE_AND_SWAP
145 if (!__pthread_has_cas)
147 #if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
151 if (testandset(&lock->__spinlock) == 0)
153 if (lock->__status == 0)
156 WRITE_MEMORY_BARRIER();
159 lock->__spinlock = __LT_SPINLOCK_INIT;
165 #if defined HAS_COMPARE_AND_SWAP
167 if (lock->__status != 0) return EBUSY;
168 } while(! compare_and_swap(&lock->__status, 0, 1, &lock->__spinlock));
173 /* Operations on pthread_atomic, which is defined in internals.h */
175 static __inline__ long
176 pthread_atomic_increment (struct pthread_atomic *pa)
181 oldval = pa->p_count;
182 } while (!compare_and_swap(&pa->p_count, oldval, oldval + 1, &pa->p_spinlock));
188 static __inline__ long
189 pthread_atomic_decrement (struct pthread_atomic *pa)
194 oldval = pa->p_count;
195 } while (!compare_and_swap(&pa->p_count, oldval, oldval - 1, &pa->p_spinlock));
201 static __inline__ __attribute__((always_inline)) void
202 __pthread_set_own_extricate_if (pthread_descr self, pthread_extricate_if *peif)
204 /* Only store a non-null peif if the thread has cancellation enabled.
205 Otherwise pthread_cancel will unconditionally call the extricate handler,
206 and restart the thread giving rise to forbidden spurious wakeups. */
208 || THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE)
210 /* If we are removing the extricate interface, we need to synchronize
211 against pthread_cancel so that it does not continue with a pointer
212 to a deallocated pthread_extricate_if struct! The thread lock
213 is (ab)used for this synchronization purpose. */
215 __pthread_lock (THREAD_GETMEM(self, p_lock), self);
216 THREAD_SETMEM(self, p_extricate, peif);
218 __pthread_unlock (THREAD_GETMEM(self, p_lock));