void __attribute__((destructor)) rcu_exit(void);
-static pthread_mutex_t rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
+static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
int gp_futex;
static LIST_HEAD(registry);
-static void internal_rcu_lock(void)
+static void mutex_lock(pthread_mutex_t *mutex)
{
int ret;
#ifndef DISTRUST_SIGNALS_EXTREME
- ret = pthread_mutex_lock(&rcu_mutex);
+ ret = pthread_mutex_lock(mutex);
if (ret) {
perror("Error in pthread mutex lock");
exit(-1);
}
#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
- while ((ret = pthread_mutex_trylock(&rcu_mutex)) != 0) {
+ while ((ret = pthread_mutex_trylock(mutex)) != 0) {
if (ret != EBUSY && ret != EINTR) {
printf("ret = %d, errno = %d\n", ret, errno);
perror("Error in pthread mutex lock");
#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
}
-static void internal_rcu_unlock(void)
+static void mutex_unlock(pthread_mutex_t *mutex)
{
int ret;
- ret = pthread_mutex_unlock(&rcu_mutex);
+ ret = pthread_mutex_unlock(mutex);
if (ret) {
perror("Error in pthread mutex unlock");
exit(-1);
NULL, NULL, 0);
}
-static void wait_for_quiescent_state(void)
+static void update_counter_and_wait(void)
{
LIST_HEAD(qsreaders);
int wait_loops = 0;
struct rcu_reader *index, *tmp;
- if (list_empty(®istry))
- return;
+#if (BITS_PER_LONG < 64)
+ /* Switch parity: 0 -> 1, 1 -> 0 */
+ STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
+#else /* !(BITS_PER_LONG < 64) */
+ /* Increment current G.P. */
+ STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
+#endif /* !(BITS_PER_LONG < 64) */
+
+ /*
+ * Must commit rcu_gp_ctr update to memory before waiting for quiescent
+ * state. Failure to do so could result in the writer waiting forever
+ * while new readers are always accessing data (no progress). Enforce
+ * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr.
+ */
+ barrier();
+
+ /*
+ * Adding a smp_mb() which is _not_ formally required, but makes the
+ * model easier to understand. It does not have a big performance impact
+ * anyway, given this is the write-side.
+ */
+ smp_mb();
+
/*
* Wait for each thread rcu_reader_qs_gp count to become 0.
*/
smp_mb();
}
- list_for_each_entry_safe(index, tmp, ®istry, head) {
+ list_for_each_entry_safe(index, tmp, ®istry, node) {
if (!rcu_gp_ongoing(&index->ctr))
- list_move(&index->head, &qsreaders);
+ list_move(&index->node, &qsreaders);
}
if (list_empty(®istry)) {
*/
#if (BITS_PER_LONG < 64)
-/*
- * called with rcu_mutex held.
- */
-static void switch_next_rcu_qparity(void)
-{
- STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
-}
-
void synchronize_rcu(void)
{
unsigned long was_online;
if (was_online)
STORE_SHARED(rcu_reader.ctr, 0);
- internal_rcu_lock();
+ mutex_lock(&rcu_gp_lock);
- switch_next_rcu_qparity(); /* 0 -> 1 */
-
- /*
- * Must commit qparity update to memory before waiting for parity
- * 0 quiescent state. Failure to do so could result in the writer
- * waiting forever while new readers are always accessing data (no
- * progress).
- * Ensured by STORE_SHARED and LOAD_SHARED.
- */
+ if (list_empty(®istry))
+ goto out;
/*
* Wait for previous parity to be empty of readers.
*/
- wait_for_quiescent_state(); /* Wait readers in parity 0 */
+ update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
/*
* Must finish waiting for quiescent state for parity 0 before
- * committing qparity update to memory. Failure to do so could result in
- * the writer waiting forever while new readers are always accessing
- * data (no progress).
- * Ensured by STORE_SHARED and LOAD_SHARED.
+ * committing next rcu_gp_ctr update to memory. Failure to do so could
+ * result in the writer waiting forever while new readers are always
+ * accessing data (no progress). Enforce compiler-order of load
+ * rcu_reader ctr before store to rcu_gp_ctr.
*/
-
- switch_next_rcu_qparity(); /* 1 -> 0 */
+ barrier();
/*
- * Must commit qparity update to memory before waiting for parity
- * 1 quiescent state. Failure to do so could result in the writer
- * waiting forever while new readers are always accessing data (no
- * progress).
- * Ensured by STORE_SHARED and LOAD_SHARED.
+ * Adding a smp_mb() which is _not_ formally required, but makes the
+ * model easier to understand. It does not have a big performance impact
+ * anyway, given this is the write-side.
*/
+ smp_mb();
/*
* Wait for previous parity to be empty of readers.
*/
- wait_for_quiescent_state(); /* Wait readers in parity 1 */
-
- internal_rcu_unlock();
+ update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
+out:
+ mutex_unlock(&rcu_gp_lock);
/*
* Finish waiting for reader threads before letting the old ptr being
if (was_online)
STORE_SHARED(rcu_reader.ctr, 0);
- internal_rcu_lock();
- STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
- wait_for_quiescent_state();
- internal_rcu_unlock();
+ mutex_lock(&rcu_gp_lock);
+ if (list_empty(®istry))
+ goto out;
+ update_counter_and_wait();
+out:
+ mutex_unlock(&rcu_gp_lock);
if (was_online)
_STORE_SHARED(rcu_reader.ctr, LOAD_SHARED(rcu_gp_ctr));
rcu_reader.tid = pthread_self();
assert(rcu_reader.ctr == 0);
- internal_rcu_lock();
- list_add(&rcu_reader.head, ®istry);
- internal_rcu_unlock();
+ mutex_lock(&rcu_gp_lock);
+ list_add(&rcu_reader.node, ®istry);
+ mutex_unlock(&rcu_gp_lock);
_rcu_thread_online();
}
* with a waiting writer.
*/
_rcu_thread_offline();
- internal_rcu_lock();
- list_del(&rcu_reader.head);
- internal_rcu_unlock();
+ mutex_lock(&rcu_gp_lock);
+ list_del(&rcu_reader.node);
+ mutex_unlock(&rcu_gp_lock);
}
void rcu_exit(void)
projects / urcu.git / blobdiff