diff options
Diffstat (limited to 'gc/include/private/specific.h')
| -rw-r--r-- | gc/include/private/specific.h | 24 |
1 files changed, 18 insertions, 6 deletions
diff --git a/gc/include/private/specific.h b/gc/include/private/specific.h index 60c152c..399f84f 100644 --- a/gc/include/private/specific.h +++ b/gc/include/private/specific.h @@ -27,16 +27,22 @@ #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; - pthread_t thread; struct thread_specific_entry *next; + pthread_t thread; } tse; /* We represent each thread-specific datum as two tables. The first is */ -/* a cache, index by a "quick thread identifier". The "quick" thread */ +/* 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. */ @@ -45,12 +51,15 @@ typedef struct thread_specific_entry { /* Return the "quick thread id". Default version. Assumes page size, */ /* or at least thread stack separation, is at least 4K. */ -static __inline__ long quick_thread_id() { +/* 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 (long)(&dummy) >> 12; + return (unsigned long)(&dummy) >> 12; } -#define INVALID_QTID ((unsigned long)(-1)) +#define INVALID_QTID ((unsigned long)0) +#define INVALID_THREADID ((pthread_t)0) typedef struct thread_specific_data { tse * volatile cache[TS_CACHE_SIZE]; @@ -76,7 +85,10 @@ static __inline__ void * PREFIXED(getspecific) (tsd * key) { unsigned hash_val = CACHE_HASH(qtid); tse * volatile * entry_ptr = key -> cache + hash_val; tse * entry = *entry_ptr; /* Must be loaded only once. */ - if (entry -> qtid == qtid) return entry -> value; + if (entry -> qtid == qtid) { + GC_ASSERT(entry -> thread == pthread_self()); + return entry -> value; + } return PREFIXED(slow_getspecific) (key, qtid, entry_ptr); } |