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/thread_local_alloc.h"
  15                 /* To determine type of tsd impl.       */
  16                 /* Includes private/specific.h          */
  17                 /* if needed.                           */
  18
  19 #if defined(USE_CUSTOM_SPECIFIC)
  20
  21 static const tse invalid_tse = {INVALID_QTID, 0, 0, INVALID_THREADID};
  22             /* A thread-specific data entry which will never    */
  23             /* appear valid to a reader.  Used to fill in empty */
  24             /* cache entries to avoid a check for 0.            */
  25
  26 GC_INNER int GC_key_create_inner(tsd ** key_ptr)
  27 {
  28     int i;
  29     tsd * result = (tsd *)MALLOC_CLEAR(sizeof(tsd));
  30
  31     /* A quick alignment check, since we need atomic stores */
  32     GC_ASSERT((word)(&invalid_tse.next) % sizeof(tse *) == 0);
  33     if (0 == result) return ENOMEM;
  34     pthread_mutex_init(&(result -> lock), NULL);
  35     for (i = 0; i < TS_CACHE_SIZE; ++i) {
  36       result -> cache[i] = (/* no const */ tse *)&invalid_tse;
  37     }
  38 #   ifdef GC_ASSERTIONS
  39       for (i = 0; i < TS_HASH_SIZE; ++i) {
  40         GC_ASSERT(result -> hash[i].p == 0);
  41       }
  42 #   endif
  43     *key_ptr = result;
  44     return 0;
  45 }
  46
  47 /* Called with the lock held.   */
  48 GC_INNER int GC_setspecific(tsd * key, void * value)
  49 {
  50     pthread_t self = pthread_self();
  51     int hash_val = HASH(self);
  52     volatile tse * entry;
  53
  54     GC_ASSERT(self != INVALID_THREADID);
  55     GC_dont_gc++; /* disable GC */
  56     entry = (volatile tse *)MALLOC_CLEAR(sizeof(tse));
  57     GC_dont_gc--;
  58     if (0 == entry) return ENOMEM;
  59
  60     pthread_mutex_lock(&(key -> lock));
  61     /* Could easily check for an existing entry here.   */
  62     entry -> next = key->hash[hash_val].p;
  63     entry -> thread = self;
  64     entry -> value = value;
  65     GC_ASSERT(entry -> qtid == INVALID_QTID);
  66     /* There can only be one writer at a time, but this needs to be     */
  67     /* atomic with respect to concurrent readers.                       */
  68     AO_store_release(&key->hash[hash_val].ao, (AO_t)entry);
  69     pthread_mutex_unlock(&(key -> lock));
  70     return 0;
  71 }
  72
  73 /* Remove thread-specific data for this thread.  Should be called on    */
  74 /* thread exit.                                                         */
  75 GC_INNER void GC_remove_specific(tsd * key)
  76 {
  77     pthread_t self = pthread_self();
  78     unsigned hash_val = HASH(self);
  79     tse *entry;
  80     tse **link = &key->hash[hash_val].p;
  81
  82     pthread_mutex_lock(&(key -> lock));
  83     entry = *link;
  84     while (entry != NULL && entry -> thread != self) {
  85       link = &(entry -> next);
  86       entry = *link;
  87     }
  88     /* Invalidate qtid field, since qtids may be reused, and a later    */
  89     /* cache lookup could otherwise find this entry.                    */
  90     if (entry != NULL) {
  91       entry -> qtid = INVALID_QTID;
  92       *link = entry -> next;
  93       /* Atomic! concurrent accesses still work.        */
  94       /* They must, since readers don't lock.           */
  95       /* We shouldn't need a volatile access here,      */
  96       /* since both this and the preceding write        */
  97       /* should become visible no later than            */
  98       /* the pthread_mutex_unlock() call.               */
  99     }
 100     /* If we wanted to deallocate the entry, we'd first have to clear   */
 101     /* any cache entries pointing to it.  That probably requires        */
 102     /* additional synchronization, since we can't prevent a concurrent  */
 103     /* cache lookup, which should still be examining deallocated memory.*/
 104     /* This can only happen if the concurrent access is from another    */
 105     /* thread, and hence has missed the cache, but still...             */
 106
 107     /* With GC, we're done, since the pointers from the cache will      */
 108     /* be overwritten, all local pointers to the entries will be        */
 109     /* dropped, and the entry will then be reclaimed.                   */
 110     pthread_mutex_unlock(&(key -> lock));
 111 }
 112
 113 /* Note that even the slow path doesn't lock.   */
 114 GC_INNER void * GC_slow_getspecific(tsd * key, word qtid,
 115                                     tse * volatile * cache_ptr)
 116 {
 117     pthread_t self = pthread_self();
 118     unsigned hash_val = HASH(self);
 119     tse *entry = key->hash[hash_val].p;
 120
 121     GC_ASSERT(qtid != INVALID_QTID);
 122     while (entry != NULL && entry -> thread != self) {
 123       entry = entry -> next;
 124     }
 125     if (entry == NULL) return NULL;
 126     /* Set cache_entry. */
 127     entry -> qtid = (AO_t)qtid;
 128         /* It's safe to do this asynchronously.  Either value   */
 129         /* is safe, though may produce spurious misses.         */
 130         /* We're replacing one qtid with another one for the    */
 131         /* same thread.                                         */
 132     *cache_ptr = entry;
 133         /* Again this is safe since pointer assignments are     */
 134         /* presumed atomic, and either pointer is valid.        */
 135     return entry -> value;
 136 }
 137
 138 #ifdef GC_ASSERTIONS
 139   /* Check that that all elements of the data structure associated  */
 140   /* with key are marked.                                           */
 141   void GC_check_tsd_marks(tsd *key)
 142   {
 143     int i;
 144     tse *p;
 145
 146     if (!GC_is_marked(GC_base(key))) {
 147       ABORT("Unmarked thread-specific-data table");
 148     }
 149     for (i = 0; i < TS_HASH_SIZE; ++i) {
 150       for (p = key->hash[i].p; p != 0; p = p -> next) {
 151         if (!GC_is_marked(GC_base(p))) {
 152           GC_err_printf("Thread-specific-data entry at %p not marked\n", p);
 153           ABORT("Unmarked tse");
 154         }
 155       }
 156     }
 157     for (i = 0; i < TS_CACHE_SIZE; ++i) {
 158       p = key -> cache[i];
 159       if (p != &invalid_tse && !GC_is_marked(GC_base(p))) {
 160         GC_err_printf("Cached thread-specific-data entry at %p not marked\n",
 161                       p);
 162         ABORT("Unmarked cached tse");
 163       }
 164     }
 165   }
 166 #endif /* GC_ASSERTIONS */
 167
 168 #endif /* USE_CUSTOM_SPECIFIC */