/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
#include "urcu-qsbr.h"
-static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
+void __attribute__((destructor)) rcu_exit(void);
+
+static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
+
+int gp_futex;
/*
* Global grace period counter.
*/
-unsigned long urcu_gp_ctr = RCU_GP_ONLINE;
+unsigned long rcu_gp_ctr = RCU_GP_ONLINE;
/*
* Written to only by each individual reader. Read by both the reader and the
* writers.
*/
-unsigned long __thread rcu_reader_qs_gp;
-
-/* Thread IDs of registered readers */
-#define INIT_NUM_THREADS 4
-
-struct reader_registry {
- pthread_t tid;
- unsigned long *rcu_reader_qs_gp;
-};
+struct rcu_reader __thread rcu_reader;
#ifdef DEBUG_YIELD
unsigned int yield_active;
unsigned int __thread rand_yield;
#endif
-static struct reader_registry *registry;
-static int num_readers, alloc_readers;
+static LIST_HEAD(registry);
-static void internal_urcu_lock(void)
+static void mutex_lock(pthread_mutex_t *mutex)
{
int ret;
#ifndef DISTRUST_SIGNALS_EXTREME
- ret = pthread_mutex_lock(&urcu_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(&urcu_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_urcu_unlock(void)
+static void mutex_unlock(pthread_mutex_t *mutex)
{
int ret;
- ret = pthread_mutex_unlock(&urcu_mutex);
+ ret = pthread_mutex_unlock(mutex);
if (ret) {
perror("Error in pthread mutex unlock");
exit(-1);
}
}
-static void wait_for_quiescent_state(void)
+/*
+ * synchronize_rcu() waiting. Single thread.
+ */
+static void wait_gp(void)
+{
+ /* Read reader_gp before read futex */
+ smp_rmb();
+ if (uatomic_read(&gp_futex) == -1)
+ futex_noasync(&gp_futex, FUTEX_WAIT, -1,
+ NULL, NULL, 0);
+}
+
+static void update_counter_and_wait(void)
{
- struct reader_registry *index;
+ LIST_HEAD(qsreaders);
+ int wait_loops = 0;
+ struct rcu_reader *index, *tmp;
+
+#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();
- if (!registry)
- return;
/*
* Wait for each thread rcu_reader_qs_gp count to become 0.
*/
- for (index = registry; index < registry + num_readers; index++) {
+ for (;;) {
+ wait_loops++;
+ if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
+ uatomic_dec(&gp_futex);
+ /* Write futex before read reader_gp */
+ smp_mb();
+ }
+
+ list_for_each_entry_safe(index, tmp, ®istry, node) {
+ if (!rcu_gp_ongoing(&index->ctr))
+ list_move(&index->node, &qsreaders);
+ }
+
+ if (list_empty(®istry)) {
+ if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
+ /* Read reader_gp before write futex */
+ smp_mb();
+ uatomic_set(&gp_futex, 0);
+ }
+ break;
+ } else {
+ if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
+ wait_gp();
+ } else {
#ifndef HAS_INCOHERENT_CACHES
- while (rcu_gp_ongoing(index->rcu_reader_qs_gp))
- cpu_relax();
+ cpu_relax();
#else /* #ifndef HAS_INCOHERENT_CACHES */
- while (rcu_gp_ongoing(index->rcu_reader_qs_gp))
- smp_mb();
+ smp_mb();
#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
+ }
+ }
}
+ /* put back the reader list in the registry */
+ list_splice(&qsreaders, ®istry);
}
/*
*/
#if (BITS_PER_LONG < 64)
-/*
- * called with urcu_mutex held.
- */
-static void switch_next_urcu_qparity(void)
-{
- STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR);
-}
-
void synchronize_rcu(void)
{
unsigned long was_online;
- was_online = rcu_reader_qs_gp;
+ was_online = rcu_reader.ctr;
/* All threads should read qparity before accessing data structure
* where new ptr points to.
* threads registered as readers.
*/
if (was_online)
- STORE_SHARED(rcu_reader_qs_gp, 0);
-
- internal_urcu_lock();
+ STORE_SHARED(rcu_reader.ctr, 0);
- switch_next_urcu_qparity(); /* 0 -> 1 */
+ mutex_lock(&rcu_gp_lock);
- /*
- * 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_urcu_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_urcu_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
* freed.
*/
if (was_online)
- _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
+ _STORE_SHARED(rcu_reader.ctr, LOAD_SHARED(rcu_gp_ctr));
smp_mb();
}
#else /* !(BITS_PER_LONG < 64) */
{
unsigned long was_online;
- was_online = rcu_reader_qs_gp;
+ was_online = rcu_reader.ctr;
/*
* Mark the writer thread offline to make sure we don't wait for
*/
smp_mb();
if (was_online)
- STORE_SHARED(rcu_reader_qs_gp, 0);
+ STORE_SHARED(rcu_reader.ctr, 0);
- internal_urcu_lock();
- STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR);
- wait_for_quiescent_state();
- internal_urcu_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_qs_gp, LOAD_SHARED(urcu_gp_ctr));
+ _STORE_SHARED(rcu_reader.ctr, LOAD_SHARED(rcu_gp_ctr));
smp_mb();
}
#endif /* !(BITS_PER_LONG < 64) */
_rcu_read_unlock();
}
-void *rcu_dereference(void *p)
-{
- return _rcu_dereference(p);
-}
-
-void *rcu_assign_pointer_sym(void **p, void *v)
-{
- wmb();
- return STORE_SHARED(p, v);
-}
-
-void *rcu_xchg_pointer_sym(void **p, void *v)
-{
- wmb();
- return xchg(p, v);
-}
-
-void *rcu_publish_content_sym(void **p, void *v)
-{
- void *oldptr;
-
- oldptr = _rcu_xchg_pointer(p, v);
- synchronize_rcu();
- return oldptr;
-}
-
void rcu_quiescent_state(void)
{
_rcu_quiescent_state();
_rcu_thread_online();
}
-static void rcu_add_reader(pthread_t id)
-{
- struct reader_registry *oldarray;
-
- if (!registry) {
- alloc_readers = INIT_NUM_THREADS;
- num_readers = 0;
- registry =
- malloc(sizeof(struct reader_registry) * alloc_readers);
- }
- if (alloc_readers < num_readers + 1) {
- oldarray = registry;
- registry = malloc(sizeof(struct reader_registry)
- * (alloc_readers << 1));
- memcpy(registry, oldarray,
- sizeof(struct reader_registry) * alloc_readers);
- alloc_readers <<= 1;
- free(oldarray);
- }
- registry[num_readers].tid = id;
- /* reference to the TLS of _this_ reader thread. */
- registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp;
- num_readers++;
-}
-
-/*
- * Never shrink (implementation limitation).
- * This is O(nb threads). Eventually use a hash table.
- */
-static void rcu_remove_reader(pthread_t id)
-{
- struct reader_registry *index;
-
- assert(registry != NULL);
- for (index = registry; index < registry + num_readers; index++) {
- if (pthread_equal(index->tid, id)) {
- memcpy(index, ®istry[num_readers - 1],
- sizeof(struct reader_registry));
- registry[num_readers - 1].tid = 0;
- registry[num_readers - 1].rcu_reader_qs_gp = NULL;
- num_readers--;
- return;
- }
- }
- /* Hrm not found, forgot to register ? */
- assert(0);
-}
-
void rcu_register_thread(void)
{
- internal_urcu_lock();
- rcu_add_reader(pthread_self());
- internal_urcu_unlock();
+ rcu_reader.tid = pthread_self();
+ assert(rcu_reader.ctr == 0);
+
+ 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_urcu_lock();
- rcu_remove_reader(pthread_self());
- internal_urcu_unlock();
+ mutex_lock(&rcu_gp_lock);
+ list_del(&rcu_reader.node);
+ mutex_unlock(&rcu_gp_lock);
+}
+
+void rcu_exit(void)
+{
+ assert(list_empty(®istry));
}
projects / urcu.git / blobdiff