Daily bump.
[official-gcc.git] / boehm-gc / specific.c
blob7d5d8894d81039f43bc4cfffdefe09df275d91ce
1 /*
2 * Copyright (c) 2000 by Hewlett-Packard Company. All rights reserved.
4 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
5 * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
7 * Permission is hereby granted to use or copy this program
8 * for any purpose, provided the above notices are retained on all copies.
9 * Permission to modify the code and to distribute modified code is granted,
10 * provided the above notices are retained, and a notice that the code was
11 * modified is included with the above copyright notice.
14 #include "private/gc_priv.h" /* For GC_compare_and_exchange, GC_memory_barrier */
16 #if defined(GC_LINUX_THREADS)
18 #include "private/specific.h"
20 static tse invalid_tse = {INVALID_QTID, 0, 0, INVALID_THREADID};
21 /* A thread-specific data entry which will never */
22 /* appear valid to a reader. Used to fill in empty */
23 /* cache entries to avoid a check for 0. */
25 int PREFIXED(key_create) (tsd ** key_ptr, void (* destructor)(void *)) {
26 int i;
27 tsd * result = (tsd *)MALLOC_CLEAR(sizeof (tsd));
29 /* A quick alignment check, since we need atomic stores */
30 GC_ASSERT((unsigned long)(&invalid_tse.next) % sizeof(tse *) == 0);
31 if (0 == result) return ENOMEM;
32 pthread_mutex_init(&(result -> lock), NULL);
33 for (i = 0; i < TS_CACHE_SIZE; ++i) {
34 result -> cache[i] = &invalid_tse;
36 # ifdef GC_ASSERTIONS
37 for (i = 0; i < TS_HASH_SIZE; ++i) {
38 GC_ASSERT(result -> hash[i] == 0);
40 # endif
41 *key_ptr = result;
42 return 0;
45 int PREFIXED(setspecific) (tsd * key, void * value) {
46 pthread_t self = pthread_self();
47 int hash_val = HASH(self);
48 volatile tse * entry = (volatile tse *)MALLOC_CLEAR(sizeof (tse));
50 GC_ASSERT(self != INVALID_THREADID);
51 if (0 == entry) return ENOMEM;
52 pthread_mutex_lock(&(key -> lock));
53 /* Could easily check for an existing entry here. */
54 entry -> next = key -> hash[hash_val];
55 entry -> thread = self;
56 entry -> value = value;
57 GC_ASSERT(entry -> qtid == INVALID_QTID);
58 /* There can only be one writer at a time, but this needs to be */
59 /* atomic with respect to concurrent readers. */
60 *(volatile tse **)(key -> hash + hash_val) = entry;
61 pthread_mutex_unlock(&(key -> lock));
62 return 0;
65 /* Remove thread-specific data for this thread. Should be called on */
66 /* thread exit. */
67 void PREFIXED(remove_specific) (tsd * key) {
68 pthread_t self = pthread_self();
69 unsigned hash_val = HASH(self);
70 tse *entry;
71 tse **link = key -> hash + hash_val;
73 pthread_mutex_lock(&(key -> lock));
74 entry = *link;
75 while (entry != NULL && entry -> thread != self) {
76 link = &(entry -> next);
77 entry = *link;
79 /* Invalidate qtid field, since qtids may be reused, and a later */
80 /* cache lookup could otherwise find this entry. */
81 entry -> qtid = INVALID_QTID;
82 if (entry != NULL) {
83 *link = entry -> next;
84 /* Atomic! concurrent accesses still work. */
85 /* They must, since readers don't lock. */
86 /* We shouldn't need a volatile access here, */
87 /* since both this and the preceding write */
88 /* should become visible no later than */
89 /* the pthread_mutex_unlock() call. */
91 /* If we wanted to deallocate the entry, we'd first have to clear */
92 /* any cache entries pointing to it. That probably requires */
93 /* additional synchronization, since we can't prevent a concurrent */
94 /* cache lookup, which should still be examining deallocated memory.*/
95 /* This can only happen if the concurrent access is from another */
96 /* thread, and hence has missed the cache, but still... */
98 /* With GC, we're done, since the pointers from the cache will */
99 /* be overwritten, all local pointers to the entries will be */
100 /* dropped, and the entry will then be reclaimed. */
101 pthread_mutex_unlock(&(key -> lock));
104 /* Note that even the slow path doesn't lock. */
105 void * PREFIXED(slow_getspecific) (tsd * key, unsigned long qtid,
106 tse * volatile * cache_ptr) {
107 pthread_t self = pthread_self();
108 unsigned hash_val = HASH(self);
109 tse *entry = key -> hash[hash_val];
111 GC_ASSERT(qtid != INVALID_QTID);
112 while (entry != NULL && entry -> thread != self) {
113 entry = entry -> next;
115 if (entry == NULL) return NULL;
116 /* Set cache_entry. */
117 entry -> qtid = qtid;
118 /* It's safe to do this asynchronously. Either value */
119 /* is safe, though may produce spurious misses. */
120 /* We're replacing one qtid with another one for the */
121 /* same thread. */
122 *cache_ptr = entry;
123 /* Again this is safe since pointer assignments are */
124 /* presumed atomic, and either pointer is valid. */
125 return entry -> value;
128 #endif /* GC_LINUX_THREADS */