ceph/src/boost/tools/build/src/engine/boehm_gc/specific.c

   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 #include "private/gc_priv.h"    /* For configuration, pthreads.h. */
  15 #include "private/thread_local_alloc.h"
  16                                 /* To determine type of tsd impl. */
  17                                 /* Includes private/specific.h    */
  18                                 /* if needed.                     */
  19
  20 #if defined(USE_CUSTOM_SPECIFIC)
  21
  22 #include "atomic_ops.h"
  23
  24 static tse invalid_tse = {INVALID_QTID, 0, 0, INVALID_THREADID};
  25                         /* A thread-specific data entry which will never    */
  26                         /* appear valid to a reader.  Used to fill in empty */
  27                         /* cache entries to avoid a check for 0.            */
  28
  29 int PREFIXED(key_create) (tsd ** key_ptr, void (* destructor)(void *)) {
  30     int i;
  31     tsd * result = (tsd *)MALLOC_CLEAR(sizeof (tsd));
  32
  33     /* A quick alignment check, since we need atomic stores */
  34       GC_ASSERT((unsigned long)(&invalid_tse.next) % sizeof(tse *) == 0);
  35     if (0 == result) return ENOMEM;
  36     pthread_mutex_init(&(result -> lock), NULL);
  37     for (i = 0; i < TS_CACHE_SIZE; ++i) {
  38         result -> cache[i] = &invalid_tse;
  39     }
  40 #   ifdef GC_ASSERTIONS
  41       for (i = 0; i < TS_HASH_SIZE; ++i) {
  42         GC_ASSERT(result -> hash[i] == 0);
  43       }
  44 #   endif
  45     *key_ptr = result;
  46     return 0;
  47 }
  48
  49 int PREFIXED(setspecific) (tsd * key, void * value) {
  50     pthread_t self = pthread_self();
  51     int hash_val = HASH(self);
  52     volatile tse * entry = (volatile tse *)MALLOC_CLEAR(sizeof (tse));
  53
  54     GC_ASSERT(self != INVALID_THREADID);
  55     if (0 == entry) return ENOMEM;
  56     pthread_mutex_lock(&(key -> lock));
  57     /* Could easily check for an existing entry here.   */
  58     entry -> next = key -> hash[hash_val];
  59     entry -> thread = self;
  60     entry -> value = value;
  61     GC_ASSERT(entry -> qtid == INVALID_QTID);
  62     /* There can only be one writer at a time, but this needs to be     */
  63     /* atomic with respect to concurrent readers.                       */
  64     AO_store_release((volatile AO_t *)(key -> hash + hash_val), (AO_t)entry);
  65     pthread_mutex_unlock(&(key -> lock));
  66     return 0;
  67 }
  68
  69 /* Remove thread-specific data for this thread.  Should be called on    */
  70 /* thread exit.                                                         */
  71 void PREFIXED(remove_specific) (tsd * key) {
  72     pthread_t self = pthread_self();
  73     unsigned hash_val = HASH(self);
  74     tse *entry;
  75     tse **link = key -> hash + hash_val;
  76
  77     pthread_mutex_lock(&(key -> lock));
  78     entry = *link;
  79     while (entry != NULL && entry -> thread != self) {
  80         link = &(entry -> next);
  81         entry = *link;
  82     }
  83     /* Invalidate qtid field, since qtids may be reused, and a later    */
  84     /* cache lookup could otherwise find this entry.                    */
  85         entry -> qtid = INVALID_QTID;
  86     if (entry != NULL) {
  87         *link = entry -> next;
  88         /* Atomic! concurrent accesses still work.      */
  89         /* They must, since readers don't lock.         */
  90         /* We shouldn't need a volatile access here,    */
  91         /* since both this and the preceding write      */
  92         /* should become visible no later than          */
  93         /* the pthread_mutex_unlock() call.             */
  94     }
  95     /* If we wanted to deallocate the entry, we'd first have to clear   */
  96     /* any cache entries pointing to it.  That probably requires        */
  97     /* additional synchronization, since we can't prevent a concurrent  */
  98     /* cache lookup, which should still be examining deallocated memory.*/
  99     /* This can only happen if the concurrent access is from another    */
 100     /* thread, and hence has missed the cache, but still...             */
 101
 102     /* With GC, we're done, since the pointers from the cache will      */
 103     /* be overwritten, all local pointers to the entries will be        */
 104     /* dropped, and the entry will then be reclaimed.                   */
 105     pthread_mutex_unlock(&(key -> lock));
 106 }
 107
 108 /* Note that even the slow path doesn't lock.   */
 109 void *  PREFIXED(slow_getspecific) (tsd * key, unsigned long qtid,
 110                                     tse * volatile * cache_ptr) {
 111     pthread_t self = pthread_self();
 112     unsigned hash_val = HASH(self);
 113     tse *entry = key -> hash[hash_val];
 114
 115     GC_ASSERT(qtid != INVALID_QTID);
 116     while (entry != NULL && entry -> thread != self) {
 117         entry = entry -> next;
 118     }
 119     if (entry == NULL) return NULL;
 120     /* Set cache_entry.         */
 121         entry -> qtid = qtid;
 122                 /* It's safe to do this asynchronously.  Either value   */
 123                 /* is safe, though may produce spurious misses.         */
 124                 /* We're replacing one qtid with another one for the    */
 125                 /* same thread.                                         */
 126         *cache_ptr = entry;
 127                 /* Again this is safe since pointer assignments are     */
 128                 /* presumed atomic, and either pointer is valid.        */
 129     return entry -> value;
 130 }
 131
 132 #ifdef GC_ASSERTIONS
 133
 134 /* Check that that all elements of the data structure associated        */
 135 /* with key are marked.                                                 */
 136 void PREFIXED(check_tsd_marks) (tsd *key)
 137 {
 138     int i;
 139     tse *p;
 140
 141     if (!GC_is_marked(GC_base(key))) {
 142         ABORT("Unmarked thread-specific-data table");
 143     }
 144     for (i = 0; i < TS_HASH_SIZE; ++i) {
 145         for (p = key -> hash[i]; p != 0; p = p -> next) {
 146             if (!GC_is_marked(GC_base(p))) {
 147                 GC_err_printf(
 148                         "Thread-specific-data entry at %p not marked\n",p);
 149                 ABORT("Unmarked tse");
 150             }
 151         }
 152     }
 153     for (i = 0; i < TS_CACHE_SIZE; ++i) {
 154         p = key -> cache[i];
 155         if (p != &invalid_tse && !GC_is_marked(GC_base(p))) {
 156             GC_err_printf(
 157                 "Cached thread-specific-data entry at %p not marked\n",p);
 158             ABORT("Unmarked cached tse");
 159         }
 160     }
 161 }
 162
 163 #endif
 164
 165 #endif /* USE_CUSTOM_SPECIFIC */