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/*
* 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>
/* 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 {
unsigned long 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);
}
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