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 configuration, pthreads.h. */
15 #include "private/thread_local_alloc.h"
16 /* To determine type of tsd impl. */
17 /* Includes private/specific.h */
20 #if defined(USE_CUSTOM_SPECIFIC)
22 #include "atomic_ops.h"
24 static tse invalid_tse = {INVALID_QTID, 0, 0, INVALID_THREADID};
25 /* A thread-specific data entry which will never */
26 /* appear valid to a reader. Used to fill in empty */
27 /* cache entries to avoid a check for 0. */
29 int PREFIXED(key_create) (tsd ** key_ptr, void (* destructor)(void *)) {
31 tsd * result = (tsd *)MALLOC_CLEAR(sizeof(tsd));
33 /* A quick alignment check, since we need atomic stores */
34 GC_ASSERT((unsigned long)(&invalid_tse.next) % sizeof(tse *) == 0);
35 if (0 == result) return ENOMEM;
36 pthread_mutex_init(&(result -> lock), NULL);
37 for (i = 0; i < TS_CACHE_SIZE; ++i) {
38 result -> cache[i] = &invalid_tse;
41 for (i = 0; i < TS_HASH_SIZE; ++i) {
42 GC_ASSERT(result -> hash[i] == 0);
49 int PREFIXED(setspecific) (tsd * key, void * value) {
50 pthread_t self = pthread_self();
51 int hash_val = HASH(self);
52 volatile tse * entry = (volatile tse *)MALLOC_CLEAR(sizeof (tse));
54 GC_ASSERT(self != INVALID_THREADID);
55 if (0 == entry) return ENOMEM;
56 pthread_mutex_lock(&(key -> lock));
57 /* Could easily check for an existing entry here. */
58 entry -> next = key -> hash[hash_val];
59 entry -> thread = self;
60 entry -> value = value;
61 GC_ASSERT(entry -> qtid == INVALID_QTID);
62 /* There can only be one writer at a time, but this needs to be */
63 /* atomic with respect to concurrent readers. */
64 AO_store_release((volatile AO_t *)(key -> hash + hash_val), (AO_t)entry);
65 pthread_mutex_unlock(&(key -> lock));
69 /* Remove thread-specific data for this thread. Should be called on */
71 void PREFIXED(remove_specific) (tsd * key) {
72 pthread_t self = pthread_self();
73 unsigned hash_val = HASH(self);
75 tse **link = key -> hash + hash_val;
77 pthread_mutex_lock(&(key -> lock));
79 while (entry != NULL && entry -> thread != self) {
80 link = &(entry -> next);
83 /* Invalidate qtid field, since qtids may be reused, and a later */
84 /* cache lookup could otherwise find this entry. */
86 entry -> qtid = INVALID_QTID;
87 *link = entry -> next;
88 /* Atomic! concurrent accesses still work. */
89 /* They must, since readers don't lock. */
90 /* We shouldn't need a volatile access here, */
91 /* since both this and the preceding write */
92 /* should become visible no later than */
93 /* the pthread_mutex_unlock() call. */
95 /* If we wanted to deallocate the entry, we'd first have to clear */
96 /* any cache entries pointing to it. That probably requires */
97 /* additional synchronization, since we can't prevent a concurrent */
98 /* cache lookup, which should still be examining deallocated memory.*/
99 /* This can only happen if the concurrent access is from another */
100 /* thread, and hence has missed the cache, but still... */
102 /* With GC, we're done, since the pointers from the cache will */
103 /* be overwritten, all local pointers to the entries will be */
104 /* dropped, and the entry will then be reclaimed. */
105 pthread_mutex_unlock(&(key -> lock));
108 /* Note that even the slow path doesn't lock. */
109 void * PREFIXED(slow_getspecific) (tsd * key, unsigned long qtid,
110 tse * volatile * cache_ptr) {
111 pthread_t self = pthread_self();
112 unsigned hash_val = HASH(self);
113 tse *entry = key -> hash[hash_val];
115 GC_ASSERT(qtid != INVALID_QTID);
116 while (entry != NULL && entry -> thread != self) {
117 entry = entry -> next;
119 if (entry == NULL) return NULL;
120 /* Set cache_entry. */
121 entry -> qtid = (AO_t)qtid;
122 /* It's safe to do this asynchronously. Either value */
123 /* is safe, though may produce spurious misses. */
124 /* We're replacing one qtid with another one for the */
127 /* Again this is safe since pointer assignments are */
128 /* presumed atomic, and either pointer is valid. */
129 return entry -> value;
133 /* Check that that all elements of the data structure associated */
134 /* with key are marked. */
135 void PREFIXED(check_tsd_marks) (tsd *key)
140 if (!GC_is_marked(GC_base(key))) {
141 ABORT("Unmarked thread-specific-data table");
143 for (i = 0; i < TS_HASH_SIZE; ++i) {
144 for (p = key -> hash[i]; p != 0; p = p -> next) {
145 if (!GC_is_marked(GC_base(p))) {
146 GC_err_printf("Thread-specific-data entry at %p not marked\n", p);
147 ABORT("Unmarked tse");
151 for (i = 0; i < TS_CACHE_SIZE; ++i) {
153 if (p != &invalid_tse && !GC_is_marked(GC_base(p))) {
154 GC_err_printf("Cached thread-specific-data entry at %p not marked\n",
156 ABORT("Unmarked cached tse");
160 #endif /* GC_ASSERTIONS */
162 #endif /* USE_CUSTOM_SPECIFIC */