Return to specific.c CVS log

Up to [local] / OpenXM_contrib2 / asir2000 / gc

Annotation of OpenXM_contrib2/asir2000/gc/specific.c, Revision 1.1

1.1     ! noro        1: /*
        !             2:  * Copyright (c) 2000 by Hewlett-Packard Company.  All rights reserved.
        !             3:  *
        !             4:  * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
        !             5:  * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
        !             6:  *
        !             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.
        !            12:  */
        !            13:
        !            14: #if defined(GC_LINUX_THREADS)
        !            15:
        !            16: #include "private/gc_priv.h" /* For GC_compare_and_exchange, GC_memory_barrier */
        !            17: #include "private/specific.h"
        !            18:
        !            19: static tse invalid_tse = {INVALID_QTID, 0, 0, INVALID_THREADID};
        !            20:                        /* A thread-specific data entry which will never        */
        !            21:                        /* appear valid to a reader.  Used to fill in empty     */
        !            22:                        /* cache entries to avoid a check for 0.                */
        !            23:
        !            24: int PREFIXED(key_create) (tsd ** key_ptr, void (* destructor)(void *)) {
        !            25:     int i;
        !            26:     tsd * result = (tsd *)MALLOC_CLEAR(sizeof (tsd));
        !            27:
        !            28:     /* A quick alignment check, since we need atomic stores */
        !            29:       GC_ASSERT((unsigned long)(&invalid_tse.next) % sizeof(tse *) == 0);
        !            30:     if (0 == result) return ENOMEM;
        !            31:     pthread_mutex_init(&(result -> lock), NULL);
        !            32:     for (i = 0; i < TS_CACHE_SIZE; ++i) {
        !            33:        result -> cache[i] = &invalid_tse;
        !            34:     }
        !            35: #   ifdef GC_ASSERTIONS
        !            36:       for (i = 0; i < TS_HASH_SIZE; ++i) {
        !            37:        GC_ASSERT(result -> hash[i] == 0);
        !            38:       }
        !            39: #   endif
        !            40:     *key_ptr = result;
        !            41:     return 0;
        !            42: }
        !            43:
        !            44: int PREFIXED(setspecific) (tsd * key, void * value) {
        !            45:     pthread_t self = pthread_self();
        !            46:     int hash_val = HASH(self);
        !            47:     volatile tse * entry = (volatile tse *)MALLOC_CLEAR(sizeof (tse));
        !            48:
        !            49:     GC_ASSERT(self != INVALID_THREADID);
        !            50:     if (0 == entry) return ENOMEM;
        !            51:     pthread_mutex_lock(&(key -> lock));
        !            52:     /* Could easily check for an existing entry here.  */
        !            53:     entry -> next = key -> hash[hash_val];
        !            54:     entry -> thread = self;
        !            55:     entry -> value = value;
        !            56:     GC_ASSERT(entry -> qtid == INVALID_QTID);
        !            57:     /* There can only be one writer at a time, but this needs to be    */
        !            58:     /* atomic with respect to concurrent readers.                      */
        !            59:     *(volatile tse **)(key -> hash + hash_val) = entry;
        !            60:     pthread_mutex_unlock(&(key -> lock));
        !            61:     return 0;
        !            62: }
        !            63:
        !            64: /* Remove thread-specific data for this thread.  Should be called on   */
        !            65: /* thread exit.                                                                */
        !            66: void PREFIXED(remove_specific) (tsd * key) {
        !            67:     pthread_t self = pthread_self();
        !            68:     unsigned hash_val = HASH(self);
        !            69:     tse *entry;
        !            70:     tse **link = key -> hash + hash_val;
        !            71:
        !            72:     pthread_mutex_lock(&(key -> lock));
        !            73:     entry = *link;
        !            74:     while (entry != NULL && entry -> thread != self) {
        !            75:        link = &(entry -> next);
        !            76:         entry = *link;
        !            77:     }
        !            78:     /* Invalidate qtid field, since qtids may be reused, and a later   */
        !            79:     /* cache lookup could otherwise find this entry.                   */
        !            80:         entry -> qtid = INVALID_QTID;
        !            81:     if (entry != NULL) {
        !            82:        *link = entry -> next;
        !            83:        /* Atomic! concurrent accesses still work.      */
        !            84:        /* They must, since readers don't lock.         */
        !            85:        /* We shouldn't need a volatile access here,    */
        !            86:        /* since both this and the preceding write      */
        !            87:        /* should become visible no later than          */
        !            88:        /* the pthread_mutex_unlock() call.             */
        !            89:     }
        !            90:     /* If we wanted to deallocate the entry, we'd first have to clear  */
        !            91:     /* any cache entries pointing to it.  That probably requires       */
        !            92:     /* additional synchronization, since we can't prevent a concurrent         */
        !            93:     /* cache lookup, which should still be examining deallocated memory.*/
        !            94:     /* This can only happen if the concurrent access is from another   */
        !            95:     /* thread, and hence has missed the cache, but still...            */
        !            96:
        !            97:     /* With GC, we're done, since the pointers from the cache will     */
        !            98:     /* be overwritten, all local pointers to the entries will be       */
        !            99:     /* dropped, and the entry will then be reclaimed.                  */
        !           100:     pthread_mutex_unlock(&(key -> lock));
        !           101: }
        !           102:
        !           103: /* Note that even the slow path doesn't lock.  */
        !           104: void *  PREFIXED(slow_getspecific) (tsd * key, unsigned long qtid,
        !           105:                                    tse * volatile * cache_ptr) {
        !           106:     pthread_t self = pthread_self();
        !           107:     unsigned hash_val = HASH(self);
        !           108:     tse *entry = key -> hash[hash_val];
        !           109:
        !           110:     GC_ASSERT(qtid != INVALID_QTID);
        !           111:     while (entry != NULL && entry -> thread != self) {
        !           112:        entry = entry -> next;
        !           113:     }
        !           114:     if (entry == NULL) return NULL;
        !           115:     /* Set cache_entry.                */
        !           116:         entry -> qtid = qtid;
        !           117:                /* It's safe to do this asynchronously.  Either value   */
        !           118:                /* is safe, though may produce spurious misses.         */
        !           119:                /* We're replacing one qtid with another one for the    */
        !           120:                /* same thread.                                         */
        !           121:        *cache_ptr = entry;
        !           122:                /* Again this is safe since pointer assignments are     */
        !           123:                /* presumed atomic, and either pointer is valid.        */
        !           124:     return entry -> value;
        !           125: }
        !           126:
        !           127: #endif /* GC_LINUX_THREADS */