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jlechner |
/*
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* Copyright (c) 2000 by Hewlett-Packard Company. All rights reserved.
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*
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* THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
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* OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
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*
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* Permission is hereby granted to use or copy this program
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* for any purpose, provided the above notices are retained on all copies.
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* Permission to modify the code and to distribute modified code is granted,
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* provided the above notices are retained, and a notice that the code was
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* modified is included with the above copyright notice.
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*/
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#include "private/gc_priv.h" /* For GC_compare_and_exchange, GC_memory_barrier */
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#if defined(GC_LINUX_THREADS)
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#include "private/specific.h"
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static tse invalid_tse = {INVALID_QTID, 0, 0, INVALID_THREADID};
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/* A thread-specific data entry which will never */
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/* appear valid to a reader. Used to fill in empty */
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/* cache entries to avoid a check for 0. */
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int PREFIXED(key_create) (tsd ** key_ptr, void (* destructor)(void *)) {
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int i;
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tsd * result = (tsd *)MALLOC_CLEAR(sizeof (tsd));
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/* A quick alignment check, since we need atomic stores */
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GC_ASSERT((unsigned long)(&invalid_tse.next) % sizeof(tse *) == 0);
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if (0 == result) return ENOMEM;
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pthread_mutex_init(&(result -> lock), NULL);
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for (i = 0; i < TS_CACHE_SIZE; ++i) {
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result -> cache[i] = &invalid_tse;
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}
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# ifdef GC_ASSERTIONS
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for (i = 0; i < TS_HASH_SIZE; ++i) {
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GC_ASSERT(result -> hash[i] == 0);
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}
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# endif
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*key_ptr = result;
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return 0;
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}
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int PREFIXED(setspecific) (tsd * key, void * value) {
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pthread_t self = pthread_self();
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int hash_val = HASH(self);
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volatile tse * entry = (volatile tse *)MALLOC_CLEAR(sizeof (tse));
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GC_ASSERT(self != INVALID_THREADID);
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if (0 == entry) return ENOMEM;
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pthread_mutex_lock(&(key -> lock));
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/* Could easily check for an existing entry here. */
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entry -> next = key -> hash[hash_val];
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entry -> thread = self;
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entry -> value = value;
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GC_ASSERT(entry -> qtid == INVALID_QTID);
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/* There can only be one writer at a time, but this needs to be */
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/* atomic with respect to concurrent readers. */
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*(volatile tse **)(key -> hash + hash_val) = entry;
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pthread_mutex_unlock(&(key -> lock));
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return 0;
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}
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/* Remove thread-specific data for this thread. Should be called on */
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/* thread exit. */
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void PREFIXED(remove_specific) (tsd * key) {
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pthread_t self = pthread_self();
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unsigned hash_val = HASH(self);
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tse *entry;
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tse **link = key -> hash + hash_val;
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pthread_mutex_lock(&(key -> lock));
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entry = *link;
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while (entry != NULL && entry -> thread != self) {
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link = &(entry -> next);
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entry = *link;
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}
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/* Invalidate qtid field, since qtids may be reused, and a later */
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/* cache lookup could otherwise find this entry. */
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entry -> qtid = INVALID_QTID;
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if (entry != NULL) {
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*link = entry -> next;
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/* Atomic! concurrent accesses still work. */
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/* They must, since readers don't lock. */
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/* We shouldn't need a volatile access here, */
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/* since both this and the preceding write */
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/* should become visible no later than */
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/* the pthread_mutex_unlock() call. */
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}
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/* If we wanted to deallocate the entry, we'd first have to clear */
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/* any cache entries pointing to it. That probably requires */
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/* additional synchronization, since we can't prevent a concurrent */
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/* cache lookup, which should still be examining deallocated memory.*/
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/* This can only happen if the concurrent access is from another */
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/* thread, and hence has missed the cache, but still... */
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/* With GC, we're done, since the pointers from the cache will */
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/* be overwritten, all local pointers to the entries will be */
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/* dropped, and the entry will then be reclaimed. */
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pthread_mutex_unlock(&(key -> lock));
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}
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/* Note that even the slow path doesn't lock. */
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void * PREFIXED(slow_getspecific) (tsd * key, unsigned long qtid,
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tse * volatile * cache_ptr) {
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pthread_t self = pthread_self();
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unsigned hash_val = HASH(self);
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tse *entry = key -> hash[hash_val];
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GC_ASSERT(qtid != INVALID_QTID);
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while (entry != NULL && entry -> thread != self) {
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entry = entry -> next;
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}
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if (entry == NULL) return NULL;
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/* Set cache_entry. */
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entry -> qtid = qtid;
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/* It's safe to do this asynchronously. Either value */
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/* is safe, though may produce spurious misses. */
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/* We're replacing one qtid with another one for the */
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/* same thread. */
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*cache_ptr = entry;
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/* Again this is safe since pointer assignments are */
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/* presumed atomic, and either pointer is valid. */
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return entry -> value;
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}
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#endif /* GC_LINUX_THREADS */
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