/libs/headers/gc/private/specific.h
http://github.com/nddrylliog/ooc · C++ Header · 96 lines · 42 code · 17 blank · 37 comment · 3 complexity · 050b80fa85106917c5109c61fbe18c36 MD5 · raw file
- /*
- * This is a reimplementation of a subset of the pthread_getspecific/setspecific
- * interface. This appears to outperform the standard linuxthreads one
- * by a significant margin.
- * The major restriction is that each thread may only make a single
- * pthread_setspecific call on a single key. (The current data structure
- * doesn't really require that. The restriction should be easily removable.)
- * We don't currently support the destruction functions, though that
- * could be done.
- * We also currently assume that only one pthread_setspecific call
- * can be executed at a time, though that assumption would be easy to remove
- * by adding a lock.
- */
- #include <errno.h>
- #include "atomic_ops.h"
- /* Called during key creation or setspecific. */
- /* For the GC we already hold lock. */
- /* Currently allocated objects leak on thread exit. */
- /* That's hard to fix, but OK if we allocate garbage */
- /* collected memory. */
- #define MALLOC_CLEAR(n) GC_INTERNAL_MALLOC(n, NORMAL)
- #define PREFIXED(name) GC_##name
- #define TS_CACHE_SIZE 1024
- #define CACHE_HASH(n) (((((long)n) >> 8) ^ (long)n) & (TS_CACHE_SIZE - 1))
- #define TS_HASH_SIZE 1024
- #define HASH(n) (((((long)n) >> 8) ^ (long)n) & (TS_HASH_SIZE - 1))
- /* An entry describing a thread-specific value for a given thread. */
- /* All such accessible structures preserve the invariant that if either */
- /* thread is a valid pthread id or qtid is a valid "quick tread id" */
- /* for a thread, then value holds the corresponding thread specific */
- /* value. This invariant must be preserved at ALL times, since */
- /* asynchronous reads are allowed. */
- typedef struct thread_specific_entry {
- volatile AO_t qtid; /* quick thread id, only for cache */
- void * value;
- struct thread_specific_entry *next;
- pthread_t thread;
- } tse;
- /* We represent each thread-specific datum as two tables. The first is */
- /* a cache, indexed by a "quick thread identifier". The "quick" thread */
- /* identifier is an easy to compute value, which is guaranteed to */
- /* determine the thread, though a thread may correspond to more than */
- /* one value. We typically use the address of a page in the stack. */
- /* The second is a hash table, indexed by pthread_self(). It is used */
- /* only as a backup. */
- /* Return the "quick thread id". Default version. Assumes page size, */
- /* or at least thread stack separation, is at least 4K. */
- /* Must be defined so that it never returns 0. (Page 0 can't really */
- /* be part of any stack, since that would make 0 a valid stack pointer.)*/
- static __inline__ unsigned long quick_thread_id() {
- int dummy;
- return (unsigned long)(&dummy) >> 12;
- }
- #define INVALID_QTID ((unsigned long)0)
- #define INVALID_THREADID ((pthread_t)0)
- typedef struct thread_specific_data {
- tse * volatile cache[TS_CACHE_SIZE];
- /* A faster index to the hash table */
- tse * hash[TS_HASH_SIZE];
- pthread_mutex_t lock;
- } tsd;
- typedef tsd * PREFIXED(key_t);
- extern int PREFIXED(key_create) (tsd ** key_ptr, void (* destructor)(void *));
- extern int PREFIXED(setspecific) (tsd * key, void * value);
- extern void PREFIXED(remove_specific) (tsd * key);
- /* An internal version of getspecific that assumes a cache miss. */
- void * PREFIXED(slow_getspecific) (tsd * key, unsigned long qtid,
- tse * volatile * cache_entry);
- static __inline__ void * PREFIXED(getspecific) (tsd * key) {
- long qtid = quick_thread_id();
- unsigned hash_val = CACHE_HASH(qtid);
- tse * volatile * entry_ptr = key -> cache + hash_val;
- tse * entry = *entry_ptr; /* Must be loaded only once. */
- if (EXPECT(entry -> qtid == qtid, 1)) {
- GC_ASSERT(entry -> thread == pthread_self());
- return entry -> value;
- }
- return PREFIXED(slow_getspecific) (key, qtid, entry_ptr);
- }