| /* |
| * 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) || defined(GC_GNU_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 */ |