PR tree-optimization/51865

[pf3gnuchains/gcc-fork.git] / boehm-gc / specific.c

diff --git a/boehm-gc/specific.c b/boehm-gc/specific.c
index 5afd10b..7d5d889 100644 (file)
--- a/boehm-gc/specific.c
+++ b/boehm-gc/specific.c
@@ -11,22 +11,33 @@
  * modified is included with the above copyright notice.
  */
 
-#if defined(LINUX_THREADS) || defined(GC_LINUX_THREADS)
-
 #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;        /* 0 qtid is guaranteed to be invalid   */
+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;
 }
@@ -36,12 +47,14 @@ int PREFIXED(setspecific) (tsd * key, void * value) {
     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;
@@ -70,6 +83,10 @@ void PREFIXED(remove_specific) (tsd * key) {
        *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       */
@@ -91,6 +108,7 @@ void *  PREFIXED(slow_getspecific) (tsd * key, unsigned long qtid,
     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;
     } 
@@ -99,10 +117,12 @@ void *  PREFIXED(slow_getspecific) (tsd * key, unsigned long qtid,
         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 /* LINUX_THREADS */
+#endif /* GC_LINUX_THREADS */