/* * Copyright (c) 2000 by Hewlett-Packard Company. All rights reserved. * * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED * OR IMPLIED. ANY USE IS AT YOUR OWN RISK. * * Permission is hereby granted to use or copy this program * for any purpose, provided the above notices are retained on all copies. * Permission to modify the code and to distribute modified code is granted, * provided the above notices are retained, and a notice that the code was * modified is included with the above copyright notice.
*/
#include"private/thread_local_alloc.h" /* To determine type of tsd impl. */ /* Includes private/specific.h */ /* if needed. */
#ifdefined(USE_CUSTOM_SPECIFIC)
staticconst tse invalid_tse = {INVALID_QTID, 0, 0, INVALID_THREADID}; /* A thread-specific data entry which will never */ /* appear valid to a reader. Used to fill in empty */ /* cache entries to avoid a check for 0. */
GC_INNER int GC_key_create_inner(tsd ** key_ptr)
{ int i; int ret;
tsd * result;
GC_ASSERT(I_HOLD_LOCK()); /* A quick alignment check, since we need atomic stores */
GC_ASSERT((word)(&invalid_tse.next) % sizeof(tse *) == 0);
result = (tsd *)MALLOC_CLEAR(sizeof(tsd)); if (NULL == result) return ENOMEM;
ret = pthread_mutex_init(&result->lock, NULL); if (ret != 0) return ret; for (i = 0; i < TS_CACHE_SIZE; ++i) {
result -> cache[i] = (/* no const */ tse *)&invalid_tse;
} # ifdef GC_ASSERTIONS for (i = 0; i < TS_HASH_SIZE; ++i) {
GC_ASSERT(result -> hash[i].p == 0);
} # endif
*key_ptr = result; return 0;
}
pthread_mutex_lock(&(key -> lock)); /* Could easily check for an existing entry here. */
entry -> next = key->hash[hash_val].p;
entry -> thread = self;
entry -> value = TS_HIDE_VALUE(value);
GC_ASSERT(entry -> qtid == INVALID_QTID); /* There can only be one writer at a time, but this needs to be */ /* atomic with respect to concurrent readers. */
AO_store_release(&key->hash[hash_val].ao, (AO_t)entry);
GC_dirty((/* no volatile */ void *)entry);
GC_dirty(key->hash + hash_val); if (pthread_mutex_unlock(&key->lock) != 0)
ABORT("pthread_mutex_unlock failed (setspecific)"); return 0;
}
/* Remove thread-specific data for a given thread. This function is */ /* called at fork from the child process for all threads except for the */ /* survived one. GC_remove_specific() should be called on thread exit. */
GC_INNER void GC_remove_specific_after_fork(tsd * key, pthread_t t)
{ unsigned hash_val = HASH(t);
tse *entry;
tse *prev = NULL;
# ifdef CAN_HANDLE_FORK /* Both GC_setspecific and GC_remove_specific should be called */ /* with the allocation lock held to ensure the consistency of */ /* the hash table in the forked child. */
GC_ASSERT(I_HOLD_LOCK()); # endif
pthread_mutex_lock(&(key -> lock));
entry = key->hash[hash_val].p; while (entry != NULL && !THREAD_EQUAL(entry->thread, t)) {
prev = entry;
entry = entry->next;
} /* Invalidate qtid field, since qtids may be reused, and a later */ /* cache lookup could otherwise find this entry. */ if (entry != NULL) {
entry -> qtid = INVALID_QTID; if (NULL == prev) {
key->hash[hash_val].p = entry->next;
GC_dirty(key->hash + hash_val);
} else {
prev->next = entry->next;
GC_dirty(prev);
} /* Atomic! concurrent accesses still work. */ /* They must, since readers don't lock. */ /* We shouldn't need a volatile access here, */ /* since both this and the preceding write */ /* should become visible no later than */ /* the pthread_mutex_unlock() call. */
} /* If we wanted to deallocate the entry, we'd first have to clear */ /* any cache entries pointing to it. That probably requires */ /* additional synchronization, since we can't prevent a concurrent */ /* cache lookup, which should still be examining deallocated memory.*/ /* This can only happen if the concurrent access is from another */ /* thread, and hence has missed the cache, but still... */ # ifdef LINT2
GC_noop1((word)entry); # endif
/* With GC, we're done, since the pointers from the cache will */ /* be overwritten, all local pointers to the entries will be */ /* dropped, and the entry will then be reclaimed. */ if (pthread_mutex_unlock(&key->lock) != 0)
ABORT("pthread_mutex_unlock failed (remove_specific after fork)");
}
/* Note that even the slow path doesn't lock. */
GC_INNER void * GC_slow_getspecific(tsd * key, word qtid,
tse * volatile * cache_ptr)
{
pthread_t self = pthread_self();
tse *entry = key->hash[HASH(self)].p;
GC_ASSERT(qtid != INVALID_QTID); while (entry != NULL && !THREAD_EQUAL(entry->thread, self)) {
entry = entry -> next;
} if (entry == NULL) return NULL; /* Set cache_entry. */
entry -> qtid = (AO_t)qtid; /* It's safe to do this asynchronously. Either value */ /* is safe, though may produce spurious misses. */ /* We're replacing one qtid with another one for the */ /* same thread. */
*cache_ptr = entry; /* Again this is safe since pointer assignments are */ /* presumed atomic, and either pointer is valid. */ return TS_REVEAL_PTR(entry -> value);
}
#ifdef GC_ASSERTIONS /* Check that that all elements of the data structure associated */ /* with key are marked. */ void GC_check_tsd_marks(tsd *key)
{ int i;
tse *p;
if (!GC_is_marked(GC_base(key))) {
ABORT("Unmarked thread-specific-data table");
} for (i = 0; i < TS_HASH_SIZE; ++i) { for (p = key->hash[i].p; p != 0; p = p -> next) { if (!GC_is_marked(GC_base(p))) {
ABORT_ARG1("Unmarked thread-specific-data entry", " at %p", (void *)p);
}
}
} for (i = 0; i < TS_CACHE_SIZE; ++i) {
p = key -> cache[i]; if (p != &invalid_tse && !GC_is_marked(GC_base(p))) {
ABORT_ARG1("Unmarked cached thread-specific-data entry", " at %p", (void *)p);
}
}
} #endif/* GC_ASSERTIONS */
#endif/* USE_CUSTOM_SPECIFIC */
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