/*
* Copyright (c) 2000 by Hewlett-Packard Company. All rights reserved.
*
* THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
* OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
*
* Permission is hereby granted to use or copy this program
* for any purpose, provided the above notices are retained on all copies.
* Permission to modify the code and to distribute modified code is granted,
* provided the above notices are retained, and a notice that the code was
* modified is included with the above copyright notice.
*/
#include "private/thread_local_alloc.h"
/* To determine type of tsd impl. */
/* Includes private/specific.h */
/* if needed. */
#if defined(USE_CUSTOM_SPECIFIC)
static const tse invalid_tse = {INVALID_QTID, 0, 0, INVALID_THREADID};
/* A thread-specific data entry which will never */
/* appear valid to a reader. Used to fill in empty */
/* cache entries to avoid a check for 0. */
GC_INNER int GC_key_create_inner(tsd ** key_ptr)
{
int i;
int ret;
tsd * result;
GC_ASSERT(I_HOLD_LOCK());
/* A quick alignment check, since we need atomic stores */
GC_ASSERT((word)(&invalid_tse.next) % sizeof(tse *) == 0);
result = (tsd *)MALLOC_CLEAR(sizeof(tsd));
if (NULL == result) return ENOMEM;
ret = pthread_mutex_init(&result->lock, NULL);
if (ret != 0) return ret;
for (i = 0; i < TS_CACHE_SIZE; ++i) {
result -> cache[i] = (/* no const */ tse *)&invalid_tse;
}
# ifdef GC_ASSERTIONS
for (i = 0; i < TS_HASH_SIZE; ++i) {
GC_ASSERT(result -> hash[i].p == 0);
}
# endif
*key_ptr = result;
return 0;
}
pthread_mutex_lock(&(key -> lock));
/* Could easily check for an existing entry here. */
entry -> next = key->hash[hash_val].p;
entry -> thread = self;
entry -> value = TS_HIDE_VALUE(value);
GC_ASSERT(entry -> qtid == INVALID_QTID);
/* There can only be one writer at a time, but this needs to be */
/* atomic with respect to concurrent readers. */
AO_store_release(&key->hash[hash_val].ao, (AO_t)entry);
GC_dirty((/* no volatile */ void *)entry);
GC_dirty(key->hash + hash_val);
if (pthread_mutex_unlock(&key->lock) != 0)
ABORT("pthread_mutex_unlock failed (setspecific)");
return 0;
}
/* Remove thread-specific data for a given thread. This function is */
/* called at fork from the child process for all threads except for the */
/* survived one. GC_remove_specific() should be called on thread exit. */
GC_INNER void GC_remove_specific_after_fork(tsd * key, pthread_t t)
{
unsigned hash_val = HASH(t);
tse *entry;
tse *prev = NULL;
# ifdef CAN_HANDLE_FORK
/* Both GC_setspecific and GC_remove_specific should be called */
/* with the allocation lock held to ensure the consistency of */
/* the hash table in the forked child. */
GC_ASSERT(I_HOLD_LOCK());
# endif
pthread_mutex_lock(&(key -> lock));
entry = key->hash[hash_val].p;
while (entry != NULL && !THREAD_EQUAL(entry->thread, t)) {
prev = entry;
entry = entry->next;
}
/* Invalidate qtid field, since qtids may be reused, and a later */
/* cache lookup could otherwise find this entry. */
if (entry != NULL) {
entry -> qtid = INVALID_QTID;
if (NULL == prev) {
key->hash[hash_val].p = entry->next;
GC_dirty(key->hash + hash_val);
} else {
prev->next = entry->next;
GC_dirty(prev);
}
/* Atomic! concurrent accesses still work. */
/* They must, since readers don't lock. */
/* We shouldn't need a volatile access here, */
/* since both this and the preceding write */
/* should become visible no later than */
/* the pthread_mutex_unlock() call. */
}
/* If we wanted to deallocate the entry, we'd first have to clear */
/* any cache entries pointing to it. That probably requires */
/* additional synchronization, since we can't prevent a concurrent */
/* cache lookup, which should still be examining deallocated memory.*/
/* This can only happen if the concurrent access is from another */
/* thread, and hence has missed the cache, but still... */
# ifdef LINT2
GC_noop1((word)entry);
# endif
/* With GC, we're done, since the pointers from the cache will */
/* be overwritten, all local pointers to the entries will be */
/* dropped, and the entry will then be reclaimed. */
if (pthread_mutex_unlock(&key->lock) != 0)
ABORT("pthread_mutex_unlock failed (remove_specific after fork)");
}
/* Note that even the slow path doesn't lock. */
GC_INNER void * GC_slow_getspecific(tsd * key, word qtid,
tse * volatile * cache_ptr)
{
pthread_t self = pthread_self();
tse *entry = key->hash[HASH(self)].p;
GC_ASSERT(qtid != INVALID_QTID);
while (entry != NULL && !THREAD_EQUAL(entry->thread, self)) {
entry = entry -> next;
}
if (entry == NULL) return NULL;
/* Set cache_entry. */
AO_store(&(entry -> qtid), qtid);
/* It's safe to do this asynchronously. Either value */
/* is safe, though may produce spurious misses. */
/* We're replacing one qtid with another one for the */
/* same thread. */
AO_store((volatile AO_t *)cache_ptr, (AO_t)entry);
return TS_REVEAL_PTR(entry -> value);
}
#ifdef GC_ASSERTIONS
/* Check that that all elements of the data structure associated */
/* with key are marked. */
void GC_check_tsd_marks(tsd *key)
{
int i;
tse *p;
if (!GC_is_marked(GC_base(key))) {
ABORT("Unmarked thread-specific-data table");
}
for (i = 0; i < TS_HASH_SIZE; ++i) {
for (p = key->hash[i].p; p != 0; p = p -> next) {
if (!GC_is_marked(GC_base(p))) {
ABORT_ARG1("Unmarked thread-specific-data entry",
" at %p", (void *)p);
}
}
}
for (i = 0; i < TS_CACHE_SIZE; ++i) {
p = key -> cache[i];
if (p != &invalid_tse && !GC_is_marked(GC_base(p))) {
ABORT_ARG1("Unmarked cached thread-specific-data entry",
" at %p", (void *)p);
}
}
}
#endif /* GC_ASSERTIONS */
