boehm-gc/include/private/specific.h

   1 /*
   2  * This is a reimplementation of a subset of the pthread_getspecific/setspecific
   3  * interface. This appears to outperform the standard linuxthreads one
   4  * by a significant margin.
   5  * The major restriction is that each thread may only make a single
   6  * pthread_setspecific call on a single key.  (The current data structure
   7  * doesn't really require that.  The restriction should be easily removable.)
   8  * We don't currently support the destruction functions, though that
   9  * could be done.
  10  * We also currently assume that only one pthread_setspecific call
  11  * can be executed at a time, though that assumption would be easy to remove
  12  * by adding a lock.
  13  */
  14
  15 #include <errno.h>
  16
  17 /* Called during key creation or setspecific.           */
  18 /* For the GC we already hold lock.                     */
  19 /* Currently allocated objects leak on thread exit.     */
  20 /* That's hard to fix, but OK if we allocate garbage    */
  21 /* collected memory.                                    */
  22 #define MALLOC_CLEAR(n) GC_INTERNAL_MALLOC(n, NORMAL)
  23 #define PREFIXED(name) GC_##name
  24
  25 #define TS_CACHE_SIZE 1024
  26 #define CACHE_HASH(n) (((((long)n) >> 8) ^ (long)n) & (TS_CACHE_SIZE - 1))
  27 #define TS_HASH_SIZE 1024
  28 #define HASH(n) (((((long)n) >> 8) ^ (long)n) & (TS_HASH_SIZE - 1))
  29
  30 /* An entry describing a thread-specific value for a given thread.      */
  31 /* All such accessible structures preserve the invariant that if either */
  32 /* thread is a valid pthread id or qtid is a valid "quick tread id"     */
  33 /* for a thread, then value holds the corresponding thread specific     */
  34 /* value.  This invariant must be preserved at ALL times, since         */
  35 /* asynchronous reads are allowed.                                      */
  36 typedef struct thread_specific_entry {
  37         unsigned long qtid;     /* quick thread id, only for cache */
  38         void * value;
  39         struct thread_specific_entry *next;
  40         pthread_t thread;
  41 } tse;
  42
  43
  44 /* We represent each thread-specific datum as two tables.  The first is */
  45 /* a cache, indexed by a "quick thread identifier".  The "quick" thread */
  46 /* identifier is an easy to compute value, which is guaranteed to       */
  47 /* determine the thread, though a thread may correspond to more than    */
  48 /* one value.  We typically use the address of a page in the stack.     */
  49 /* The second is a hash table, indexed by pthread_self().  It is used   */
  50 /* only as a backup.                                                    */
  51
  52 /* Return the "quick thread id".  Default version.  Assumes page size,  */
  53 /* or at least thread stack separation, is at least 4K.                 */
  54 /* Must be defined so that it never returns 0.  (Page 0 can't really    */
  55 /* be part of any stack, since that would make 0 a valid stack pointer.)*/
  56 static __inline__ unsigned long quick_thread_id() {
  57     int dummy;
  58     return (unsigned long)(&dummy) >> 12;
  59 }
  60
  61 #define INVALID_QTID ((unsigned long)0)
  62 #define INVALID_THREADID ((pthread_t)0)
  63
  64 typedef struct thread_specific_data {
  65     tse * volatile cache[TS_CACHE_SIZE];
  66                         /* A faster index to the hash table */
  67     tse * hash[TS_HASH_SIZE];
  68     pthread_mutex_t lock;
  69 } tsd;
  70
  71 typedef tsd * PREFIXED(key_t);
  72
  73 extern int PREFIXED(key_create) (tsd ** key_ptr, void (* destructor)(void *));
  74
  75 extern int PREFIXED(setspecific) (tsd * key, void * value);
  76
  77 extern void PREFIXED(remove_specific) (tsd * key);
  78
  79 /* An internal version of getspecific that assumes a cache miss.        */
  80 void * PREFIXED(slow_getspecific) (tsd * key, unsigned long qtid,
  81                                    tse * volatile * cache_entry);
  82
  83 static __inline__ void * PREFIXED(getspecific) (tsd * key) {
  84     long qtid = quick_thread_id();
  85     unsigned hash_val = CACHE_HASH(qtid);
  86     tse * volatile * entry_ptr = key -> cache + hash_val;
  87     tse * entry = *entry_ptr;   /* Must be loaded only once.    */
  88     if (EXPECT(entry -> qtid == qtid, 1)) {
  89       GC_ASSERT(entry -> thread == pthread_self());
  90       return entry -> value;
  91     }
  92     return PREFIXED(slow_getspecific) (key, qtid, entry_ptr);
  93 }
  94
  95