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84 lines
3.0 KiB
C
84 lines
3.0 KiB
C
/*
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* This is a reimplementation of a subset of the pthread_getspecific/setspecific
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* interface. This appears to outperform the standard linuxthreads one
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* by a significant margin.
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* The major restriction is that each thread may only make a single
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* pthread_setspecific call on a single key. (The current data structure
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* doesn't really require that. The restriction should be easily removable.)
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* We don't currently support the destruction functions, though that
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* could be done.
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* We also currently assume that only one pthread_setspecific call
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* can be executed at a time, though that assumption would be easy to remove
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* by adding a lock.
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*/
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#include <errno.h>
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/* Called during key creation or setspecific. */
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/* For the GC we already hold lock. */
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/* Currently allocated objects leak on thread exit. */
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/* That's hard to fix, but OK if we allocate garbage */
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/* collected memory. */
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#define MALLOC_CLEAR(n) GC_INTERNAL_MALLOC(n, NORMAL)
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#define PREFIXED(name) GC_##name
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#define TS_CACHE_SIZE 1024
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#define CACHE_HASH(n) (((((long)n) >> 8) ^ (long)n) & (TS_CACHE_SIZE - 1))
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#define TS_HASH_SIZE 1024
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#define HASH(n) (((((long)n) >> 8) ^ (long)n) & (TS_HASH_SIZE - 1))
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typedef struct thread_specific_entry {
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unsigned long qtid; /* quick thread id, only for cache */
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void * value;
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pthread_t thread;
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struct thread_specific_entry *next;
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} tse;
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/* We represent each thread-specific datum as two tables. The first is */
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/* a cache, index by a "quick thread identifier". The "quick" thread */
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/* identifier is an easy to compute value, which is guaranteed to */
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/* determine the thread, though a thread may correspond to more than */
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/* one value. We typically use the address of a page in the stack. */
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/* The second is a hash table, indexed by pthread_self(). It is used */
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/* only as a backup. */
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/* Return the "quick thread id". Default version. Assumes page size, */
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/* or at least thread stack separation, is at least 4K. */
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static __inline__ long quick_thread_id() {
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int dummy;
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return (long)(&dummy) >> 12;
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}
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#define INVALID_QTID ((unsigned long)(-1))
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typedef struct thread_specific_data {
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tse * volatile cache[TS_CACHE_SIZE];
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/* A faster index to the hash table */
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tse * hash[TS_HASH_SIZE];
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pthread_mutex_t lock;
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} tsd;
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typedef tsd * PREFIXED(key_t);
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extern int PREFIXED(key_create) (tsd ** key_ptr, void (* destructor)(void *));
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extern int PREFIXED(setspecific) (tsd * key, void * value);
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extern void PREFIXED(remove_specific) (tsd * key);
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/* An internal version of getspecific that assumes a cache miss. */
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void * PREFIXED(slow_getspecific) (tsd * key, unsigned long qtid,
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tse * volatile * cache_entry);
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static __inline__ void * PREFIXED(getspecific) (tsd * key) {
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long qtid = quick_thread_id();
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unsigned hash_val = CACHE_HASH(qtid);
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tse * volatile * entry_ptr = key -> cache + hash_val;
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tse * entry = *entry_ptr; /* Must be loaded only once. */
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if (entry -> qtid == qtid) return entry -> value;
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return PREFIXED(slow_getspecific) (key, qtid, entry_ptr);
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}
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