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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 */