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 HAS_COMPARE_AND_SWAP
111 #if defined TEST_FOR_COMPARE_AND_SWAP
112 if (!__pthread_has_cas
)
114 #if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
116 return (testandset(&lock
->__spinlock
) ? EBUSY
: 0);
120 #if defined HAS_COMPARE_AND_SWAP
122 oldstatus
= lock
->__status
;
123 if (oldstatus
!= 0) return EBUSY
;
124 } while(! __compare_and_swap(&lock
->__status
, 0, 1));
129 /* Variation of internal lock used for pthread_mutex_t, supporting
130 timed-out waits. Warning: do not mix these operations with the above ones
131 over the same lock object! */
133 extern void __pthread_alt_lock(struct _pthread_fastlock
* lock
,
136 extern int __pthread_alt_timedlock(struct _pthread_fastlock
* lock
,
137 pthread_descr self
, const struct timespec
*abstime
);
139 extern void __pthread_alt_unlock(struct _pthread_fastlock
*lock
);
141 static inline void __pthread_alt_init_lock(struct _pthread_fastlock
* lock
)
144 lock
->__spinlock
= __LT_SPINLOCK_INIT
;
147 static inline int __pthread_alt_trylock (struct _pthread_fastlock
* lock
)
149 #if defined HAS_COMPARE_AND_SWAP
153 #if defined TEST_FOR_COMPARE_AND_SWAP
154 if (!__pthread_has_cas
)
156 #if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
160 if (testandset(&lock
->__spinlock
) == 0)
162 if (lock
->__status
== 0)
165 WRITE_MEMORY_BARRIER();
168 lock
->__spinlock
= __LT_SPINLOCK_INIT
;
174 #if defined HAS_COMPARE_AND_SWAP
176 oldstatus
= lock
->__status
;
177 if (oldstatus
!= 0) return EBUSY
;
178 } while(! compare_and_swap(&lock
->__status
, 0, 1, &lock
->__spinlock
));
183 /* Operations on pthread_atomic, which is defined in internals.h */
185 static inline long atomic_increment(struct pthread_atomic
*pa
)
190 oldval
= pa
->p_count
;
191 } while (!compare_and_swap(&pa
->p_count
, oldval
, oldval
+ 1, &pa
->p_spinlock
));
197 static inline long atomic_decrement(struct pthread_atomic
*pa
)
202 oldval
= pa
->p_count
;
203 } while (!compare_and_swap(&pa
->p_count
, oldval
, oldval
- 1, &pa
->p_spinlock
));
210 __pthread_set_own_extricate_if (pthread_descr self
, pthread_extricate_if
*peif
)
212 /* Only store a non-null peif if the thread has cancellation enabled.
213 Otherwise pthread_cancel will unconditionally call the extricate handler,
214 and restart the thread giving rise to forbidden spurious wakeups. */
216 || THREAD_GETMEM(self
, p_cancelstate
) == PTHREAD_CANCEL_ENABLE
)
218 /* If we are removing the extricate interface, we need to synchronize
219 against pthread_cancel so that it does not continue with a pointer
220 to a deallocated pthread_extricate_if struct! The thread lock
221 is (ab)used for this synchronization purpose. */
223 __pthread_lock (THREAD_GETMEM(self
, p_lock
), self
);
224 THREAD_SETMEM(self
, p_extricate
, peif
);
226 __pthread_unlock (THREAD_GETMEM(self
, p_lock
));