#include "urcu/tls-compat.h"
#include "urcu-die.h"
+#include "urcu-wait.h"
/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
#undef _LGPL_SOURCE
#ifdef RCU_MEMBARRIER
static int init_done;
-int has_sys_membarrier;
+int rcu_has_sys_membarrier;
void __attribute__((constructor)) rcu_init(void);
#endif
static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
-int32_t gp_futex;
+int32_t rcu_gp_futex;
/*
* Global grace period counter.
DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
#ifdef DEBUG_YIELD
-unsigned int yield_active;
-DEFINE_URCU_TLS(unsigned int, rand_yield);
+unsigned int rcu_yield_active;
+DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
#endif
static CDS_LIST_HEAD(registry);
+/*
+ * Queue keeping threads awaiting to wait for a grace period. Contains
+ * struct gp_waiters_thread objects.
+ */
+static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
+
static void mutex_lock(pthread_mutex_t *mutex)
{
int ret;
#ifdef RCU_MEMBARRIER
static void smp_mb_master(int group)
{
- if (caa_likely(has_sys_membarrier))
+ if (caa_likely(rcu_has_sys_membarrier))
membarrier(MEMBARRIER_EXPEDITED);
else
cmm_smp_mb();
{
/* Read reader_gp before read futex */
smp_mb_master(RCU_MB_GROUP);
- if (uatomic_read(&gp_futex) == -1)
- futex_async(&gp_futex, FUTEX_WAIT, -1,
+ if (uatomic_read(&rcu_gp_futex) == -1)
+ futex_async(&rcu_gp_futex, FUTEX_WAIT, -1,
NULL, NULL, 0);
}
-void update_counter_and_wait(void)
+static void wait_for_readers(struct cds_list_head *input_readers,
+ struct cds_list_head *cur_snap_readers,
+ struct cds_list_head *qsreaders)
{
- CDS_LIST_HEAD(qsreaders);
int wait_loops = 0;
struct rcu_reader *index, *tmp;
- /* Switch parity: 0 -> 1, 1 -> 0 */
- CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
-
/*
- * 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.
- */
- cmm_barrier();
-
- /*
- *
- * Adding a cmm_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.
- */
- cmm_smp_mb();
-
- /*
- * Wait for each thread URCU_TLS(rcu_reader).ctr count to become 0.
+ * Wait for each thread URCU_TLS(rcu_reader).ctr to either
+ * indicate quiescence (not nested), or observe the current
+ * rcu_gp_ctr value.
*/
for (;;) {
wait_loops++;
if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
- uatomic_dec(&gp_futex);
+ uatomic_dec(&rcu_gp_futex);
/* Write futex before read reader_gp */
smp_mb_master(RCU_MB_GROUP);
}
- cds_list_for_each_entry_safe(index, tmp, ®istry, node) {
- if (!rcu_gp_ongoing(&index->ctr))
- cds_list_move(&index->node, &qsreaders);
+ cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
+ switch (rcu_reader_state(&index->ctr)) {
+ case RCU_READER_ACTIVE_CURRENT:
+ if (cur_snap_readers) {
+ cds_list_move(&index->node,
+ cur_snap_readers);
+ break;
+ }
+ /* Fall-through */
+ case RCU_READER_INACTIVE:
+ cds_list_move(&index->node, qsreaders);
+ break;
+ case RCU_READER_ACTIVE_OLD:
+ /*
+ * Old snapshot. Leaving node in
+ * input_readers will make us busy-loop
+ * until the snapshot becomes current or
+ * the reader becomes inactive.
+ */
+ break;
+ }
}
#ifndef HAS_INCOHERENT_CACHES
- if (cds_list_empty(®istry)) {
+ if (cds_list_empty(input_readers)) {
if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
/* Read reader_gp before write futex */
smp_mb_master(RCU_MB_GROUP);
- uatomic_set(&gp_futex, 0);
+ uatomic_set(&rcu_gp_futex, 0);
}
break;
} else {
* URCU_TLS(rcu_reader).ctr update to memory if we wait
* for too long.
*/
- if (cds_list_empty(®istry)) {
+ if (cds_list_empty(input_readers)) {
if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
/* Read reader_gp before write futex */
smp_mb_master(RCU_MB_GROUP);
- uatomic_set(&gp_futex, 0);
+ uatomic_set(&rcu_gp_futex, 0);
}
break;
} else {
}
#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
}
- /* put back the reader list in the registry */
- cds_list_splice(&qsreaders, ®istry);
}
void synchronize_rcu(void)
{
+ CDS_LIST_HEAD(cur_snap_readers);
+ CDS_LIST_HEAD(qsreaders);
+ DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
+ struct urcu_waiters waiters;
+
+ /*
+ * Add ourself to gp_waiters queue of threads awaiting to wait
+ * for a grace period. Proceed to perform the grace period only
+ * if we are the first thread added into the queue.
+ * The implicit memory barrier before urcu_wait_add()
+ * orders prior memory accesses of threads put into the wait
+ * queue before their insertion into the wait queue.
+ */
+ if (urcu_wait_add(&gp_waiters, &wait) != 0) {
+ /* Not first in queue: will be awakened by another thread. */
+ urcu_adaptative_busy_wait(&wait);
+ /* Order following memory accesses after grace period. */
+ cmm_smp_mb();
+ return;
+ }
+ /* We won't need to wake ourself up */
+ urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
+
mutex_lock(&rcu_gp_lock);
+ /*
+ * Move all waiters into our local queue.
+ */
+ urcu_move_waiters(&waiters, &gp_waiters);
+
if (cds_list_empty(®istry))
goto out;
smp_mb_master(RCU_MB_GROUP);
/*
- * Wait for previous parity to be empty of readers.
+ * Wait for readers to observe original parity or be quiescent.
*/
- update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
+ wait_for_readers(®istry, &cur_snap_readers, &qsreaders);
/*
- * Must finish waiting for quiescent state for parity 0 before
+ * Must finish waiting for quiescent state for original parity before
* 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
*/
cmm_smp_mb();
+ /* Switch parity: 0 -> 1, 1 -> 0 */
+ CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
+
+ /*
+ * 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.
+ */
+ cmm_barrier();
+
+ /*
+ *
+ * Adding a cmm_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.
+ */
+ cmm_smp_mb();
+
+ /*
+ * Wait for readers to observe new parity or be quiescent.
+ */
+ wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
+
/*
- * Wait for previous parity to be empty of readers.
+ * Put quiescent reader list back into registry.
*/
- update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
+ cds_list_splice(&qsreaders, ®istry);
/* Finish waiting for reader threads before letting the old ptr being
* freed. Must be done within rcu_gp_lock because it iterates on reader
smp_mb_master(RCU_MB_GROUP);
out:
mutex_unlock(&rcu_gp_lock);
+
+ /*
+ * Wakeup waiters only after we have completed the grace period
+ * and have ensured the memory barriers at the end of the grace
+ * period have been issued.
+ */
+ urcu_wake_all_waiters(&waiters);
}
/*
_rcu_read_unlock();
}
+int rcu_read_ongoing(void)
+{
+ return _rcu_read_ongoing();
+}
+
void rcu_register_thread(void)
{
URCU_TLS(rcu_reader).tid = pthread_self();
return;
init_done = 1;
if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY))
- has_sys_membarrier = 1;
+ rcu_has_sys_membarrier = 1;
}
#endif
projects / urcu.git / blobdiff