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/*
* 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/gc_priv.h" /* For GC_compare_and_exchange, GC_memory_barrier */
#if defined(GC_LINUX_THREADS)
#include "private/specific.h"
static 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. */
int PREFIXED(key_create) (tsd ** key_ptr, void (* destructor)(void *)) {
int i;
tsd * result = (tsd *)MALLOC_CLEAR(sizeof (tsd));
/* A quick alignment check, since we need atomic stores */
GC_ASSERT((unsigned long)(&invalid_tse.next) % sizeof(tse *) == 0);
if (0 == result) return ENOMEM;
pthread_mutex_init(&(result -> lock), NULL);
for (i = 0; i < TS_CACHE_SIZE; ++i) {
result -> cache[i] = &invalid_tse;
}
# ifdef GC_ASSERTIONS
for (i = 0; i < TS_HASH_SIZE; ++i) {
GC_ASSERT(result -> hash[i] == 0);
}
# endif
*key_ptr = result;
return 0;
}
int PREFIXED(setspecific) (tsd * key, void * value) {
pthread_t self = pthread_self();
int hash_val = HASH(self);
volatile tse * entry = (volatile tse *)MALLOC_CLEAR(sizeof (tse));
GC_ASSERT(self != INVALID_THREADID);
if (0 == entry) return ENOMEM;
pthread_mutex_lock(&(key -> lock));
/* Could easily check for an existing entry here. */
entry -> next = key -> hash[hash_val];
entry -> thread = self;
entry -> 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. */
*(volatile tse **)(key -> hash + hash_val) = entry;
pthread_mutex_unlock(&(key -> lock));
return 0;
}
/* Remove thread-specific data for this thread. Should be called on */
/* thread exit. */
void PREFIXED(remove_specific) (tsd * key) {
pthread_t self = pthread_self();
unsigned hash_val = HASH(self);
tse *entry;
tse **link = key -> hash + hash_val;
pthread_mutex_lock(&(key -> lock));
entry = *link;
while (entry != NULL && entry -> thread != self) {
link = &(entry -> next);
entry = *link;
}
/* Invalidate qtid field, since qtids may be reused, and a later */
/* cache lookup could otherwise find this entry. */
entry -> qtid = INVALID_QTID;
if (entry != NULL) {
*link = entry -> next;
/* 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... */
/* 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. */
pthread_mutex_unlock(&(key -> lock));
}
/* Note that even the slow path doesn't lock. */
void * PREFIXED(slow_getspecific) (tsd * key, unsigned long qtid,
tse * volatile * cache_ptr) {
pthread_t self = pthread_self();
unsigned hash_val = HASH(self);
tse *entry = key -> hash[hash_val];
GC_ASSERT(qtid != INVALID_QTID);
while (entry != NULL && entry -> thread != self) {
entry = entry -> next;
}
if (entry == NULL) return NULL;
/* Set cache_entry. */
entry -> qtid = 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 entry -> value;
}
#endif /* GC_LINUX_THREADS */
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