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.
16 #if defined(GC_LINUX_THREADS)
18 #include "private/gc_priv.h" /* For GC_compare_and_exchange, GC_memory_barrier */
19 #include "private/specific.h"
21 static tse invalid_tse = {INVALID_QTID, 0, 0, INVALID_THREADID};
22 /* A thread-specific data entry which will never */
23 /* appear valid to a reader. Used to fill in empty */
24 /* cache entries to avoid a check for 0. */
26 int PREFIXED(key_create) (tsd ** key_ptr, void (* destructor)(void *)) {
28 tsd * result = (tsd *)MALLOC_CLEAR(sizeof (tsd));
30 /* A quick alignment check, since we need atomic stores */
31 GC_ASSERT((unsigned long)(&invalid_tse.next) % sizeof(tse *) == 0);
32 if (0 == result) return ENOMEM;
33 pthread_mutex_init(&(result -> lock), NULL);
34 for (i = 0; i < TS_CACHE_SIZE; ++i) {
35 result -> cache[i] = &invalid_tse;
38 for (i = 0; i < TS_HASH_SIZE; ++i) {
39 GC_ASSERT(result -> hash[i] == 0);
46 int PREFIXED(setspecific) (tsd * key, void * value) {
47 pthread_t self = pthread_self();
48 int hash_val = HASH(self);
49 volatile tse * entry = (volatile tse *)MALLOC_CLEAR(sizeof (tse));
51 GC_ASSERT(self != INVALID_THREADID);
52 if (0 == entry) return ENOMEM;
53 pthread_mutex_lock(&(key -> lock));
54 /* Could easily check for an existing entry here. */
55 entry -> next = key -> hash[hash_val];
56 entry -> thread = self;
57 entry -> value = value;
58 GC_ASSERT(entry -> qtid == INVALID_QTID);
59 /* There can only be one writer at a time, but this needs to be */
60 /* atomic with respect to concurrent readers. */
61 *(volatile tse **)(key -> hash + hash_val) = entry;
62 pthread_mutex_unlock(&(key -> lock));
66 /* Remove thread-specific data for this thread. Should be called on */
68 void PREFIXED(remove_specific) (tsd * key) {
69 pthread_t self = pthread_self();
70 unsigned hash_val = HASH(self);
72 tse **link = key -> hash + hash_val;
74 pthread_mutex_lock(&(key -> lock));
76 while (entry != NULL && entry -> thread != self) {
77 link = &(entry -> next);
80 /* Invalidate qtid field, since qtids may be reused, and a later */
81 /* cache lookup could otherwise find this entry. */
82 entry -> qtid = INVALID_QTID;
84 *link = entry -> next;
85 /* Atomic! concurrent accesses still work. */
86 /* They must, since readers don't lock. */
87 /* We shouldn't need a volatile access here, */
88 /* since both this and the preceding write */
89 /* should become visible no later than */
90 /* the pthread_mutex_unlock() call. */
92 /* If we wanted to deallocate the entry, we'd first have to clear */
93 /* any cache entries pointing to it. That probably requires */
94 /* additional synchronization, since we can't prevent a concurrent */
95 /* cache lookup, which should still be examining deallocated memory.*/
96 /* This can only happen if the concurrent access is from another */
97 /* thread, and hence has missed the cache, but still... */
99 /* With GC, we're done, since the pointers from the cache will */
100 /* be overwritten, all local pointers to the entries will be */
101 /* dropped, and the entry will then be reclaimed. */
102 pthread_mutex_unlock(&(key -> lock));
105 /* Note that even the slow path doesn't lock. */
106 void * PREFIXED(slow_getspecific) (tsd * key, unsigned long qtid,
107 tse * volatile * cache_ptr) {
108 pthread_t self = pthread_self();
109 unsigned hash_val = HASH(self);
110 tse *entry = key -> hash[hash_val];
112 GC_ASSERT(qtid != INVALID_QTID);
113 while (entry != NULL && entry -> thread != self) {
114 entry = entry -> next;
116 if (entry == NULL) return NULL;
117 /* Set cache_entry. */
118 entry -> qtid = qtid;
119 /* It's safe to do this asynchronously. Either value */
120 /* is safe, though may produce spurious misses. */
121 /* We're replacing one qtid with another one for the */
124 /* Again this is safe since pointer assignments are */
125 /* presumed atomic, and either pointer is valid. */
126 return entry -> value;
129 #endif /* GC_LINUX_THREADS */