#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
void __attribute__((destructor)) rcu_exit(void);
+/*
+ * rcu_gp_lock ensures mutual exclusion between threads calling
+ * synchronize_rcu().
+ */
static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
-
-int32_t rcu_gp_futex;
-
/*
- * Global grace period counter.
+ * rcu_registry_lock ensures mutual exclusion between threads
+ * registering and unregistering themselves to/from the registry, and
+ * with threads reading that registry from synchronize_rcu(). However,
+ * this lock is not held all the way through the completion of awaiting
+ * for the grace period. It is sporadically released between iterations
+ * on the registry.
+ * rcu_registry_lock may nest inside rcu_gp_lock.
*/
-unsigned long rcu_gp_ctr = RCU_GP_ONLINE;
+static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
+struct rcu_gp rcu_gp = { .ctr = RCU_GP_ONLINE };
/*
* Active attempts to check for reader Q.S. before calling futex().
*/
DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
-#ifdef DEBUG_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;
{
/* Read reader_gp before read futex */
cmm_smp_rmb();
- if (uatomic_read(&rcu_gp_futex) == -1)
- futex_noasync(&rcu_gp_futex, FUTEX_WAIT, -1,
- NULL, NULL, 0);
+ if (uatomic_read(&rcu_gp.futex) != -1)
+ return;
+ while (futex_noasync(&rcu_gp.futex, FUTEX_WAIT, -1,
+ NULL, NULL, 0)) {
+ switch (errno) {
+ case EWOULDBLOCK:
+ /* Value already changed. */
+ return;
+ case EINTR:
+ /* Retry if interrupted by signal. */
+ break; /* Get out of switch. */
+ default:
+ /* Unexpected error. */
+ urcu_die(errno);
+ }
+ }
}
+/*
+ * Always called with rcu_registry lock held. Releases this lock between
+ * iterations and grabs it again. Holds the lock when it returns.
+ */
static void wait_for_readers(struct cds_list_head *input_readers,
struct cds_list_head *cur_snap_readers,
struct cds_list_head *qsreaders)
{
- int wait_loops = 0;
+ unsigned int wait_loops = 0;
struct rcu_reader *index, *tmp;
/*
* Wait for each thread URCU_TLS(rcu_reader).ctr to either
* indicate quiescence (offline), or for them to observe the
- * current rcu_gp_ctr value.
+ * current rcu_gp.ctr value.
*/
for (;;) {
- wait_loops++;
+ if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
+ wait_loops++;
if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
- uatomic_set(&rcu_gp_futex, -1);
+ uatomic_set(&rcu_gp.futex, -1);
/*
* Write futex before write waiting (the other side
* reads them in the opposite order).
if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
/* Read reader_gp before write futex */
cmm_smp_mb();
- uatomic_set(&rcu_gp_futex, 0);
+ uatomic_set(&rcu_gp.futex, 0);
}
break;
} else {
+ /* Temporarily unlock the registry lock. */
+ mutex_unlock(&rcu_registry_lock);
if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
wait_gp();
} else {
cmm_smp_mb();
#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
}
+ /* Re-lock the registry lock before the next loop. */
+ mutex_lock(&rcu_registry_lock);
}
}
}
CDS_LIST_HEAD(cur_snap_readers);
CDS_LIST_HEAD(qsreaders);
unsigned long was_online;
+ DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
+ struct urcu_waiters waiters;
- was_online = URCU_TLS(rcu_reader).ctr;
+ was_online = rcu_read_ongoing();
/* All threads should read qparity before accessing data structure
* where new ptr points to. In the "then" case, rcu_thread_offline
else
cmm_smp_mb();
+ /*
+ * 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.
+ */
+ if (urcu_wait_add(&gp_waiters, &wait) != 0) {
+ /* Not first in queue: will be awakened by another thread. */
+ urcu_adaptative_busy_wait(&wait);
+ goto gp_end;
+ }
+ /* 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);
+
+ mutex_lock(&rcu_registry_lock);
+
if (cds_list_empty(®istry))
goto out;
/*
* Wait for readers to observe original parity or be quiescent.
+ * wait_for_readers() can release and grab again rcu_registry_lock
+ * interally.
*/
wait_for_readers(®istry, &cur_snap_readers, &qsreaders);
/*
* Must finish waiting for quiescent state for original parity
- * before committing next rcu_gp_ctr update to memory. Failure
+ * 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 URCU_TLS(rcu_reader).ctr before store
- * to rcu_gp_ctr.
+ * to rcu_gp.ctr.
*/
cmm_barrier();
cmm_smp_mb();
/* Switch parity: 0 -> 1, 1 -> 0 */
- CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
+ CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR);
/*
- * Must commit rcu_gp_ctr update to memory before waiting for
+ * 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
+ * (no progress). Enforce compiler-order of store to rcu_gp.ctr
* before load URCU_TLS(rcu_reader).ctr.
*/
cmm_barrier();
/*
* Wait for readers to observe new parity or be quiescent.
+ * wait_for_readers() can release and grab again rcu_registry_lock
+ * interally.
*/
wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
*/
cds_list_splice(&qsreaders, ®istry);
out:
+ mutex_unlock(&rcu_registry_lock);
mutex_unlock(&rcu_gp_lock);
-
+ urcu_wake_all_waiters(&waiters);
+gp_end:
/*
* Finish waiting for reader threads before letting the old ptr being
* freed.
{
CDS_LIST_HEAD(qsreaders);
unsigned long was_online;
+ DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
+ struct urcu_waiters waiters;
- was_online = URCU_TLS(rcu_reader).ctr;
+ was_online = rcu_read_ongoing();
/*
* Mark the writer thread offline to make sure we don't wait for
else
cmm_smp_mb();
+ /*
+ * 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.
+ */
+ if (urcu_wait_add(&gp_waiters, &wait) != 0) {
+ /* Not first in queue: will be awakened by another thread. */
+ urcu_adaptative_busy_wait(&wait);
+ goto gp_end;
+ }
+ /* 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);
+
+ mutex_lock(&rcu_registry_lock);
+
if (cds_list_empty(®istry))
goto out;
/* Increment current G.P. */
- CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
+ CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr + RCU_GP_CTR);
/*
- * Must commit rcu_gp_ctr update to memory before waiting for
+ * 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
+ * (no progress). Enforce compiler-order of store to rcu_gp.ctr
* before load URCU_TLS(rcu_reader).ctr.
*/
cmm_barrier();
/*
* Wait for readers to observe new count of be quiescent.
+ * wait_for_readers() can release and grab again rcu_registry_lock
+ * interally.
*/
wait_for_readers(®istry, NULL, &qsreaders);
*/
cds_list_splice(&qsreaders, ®istry);
out:
+ mutex_unlock(&rcu_registry_lock);
mutex_unlock(&rcu_gp_lock);
-
+ urcu_wake_all_waiters(&waiters);
+gp_end:
if (was_online)
rcu_thread_online();
else
_rcu_read_unlock();
}
+int rcu_read_ongoing(void)
+{
+ return _rcu_read_ongoing();
+}
+
void rcu_quiescent_state(void)
{
_rcu_quiescent_state();
URCU_TLS(rcu_reader).tid = pthread_self();
assert(URCU_TLS(rcu_reader).ctr == 0);
- mutex_lock(&rcu_gp_lock);
+ mutex_lock(&rcu_registry_lock);
+ assert(!URCU_TLS(rcu_reader).registered);
+ URCU_TLS(rcu_reader).registered = 1;
cds_list_add(&URCU_TLS(rcu_reader).node, ®istry);
- mutex_unlock(&rcu_gp_lock);
+ mutex_unlock(&rcu_registry_lock);
_rcu_thread_online();
}
* with a waiting writer.
*/
_rcu_thread_offline();
- mutex_lock(&rcu_gp_lock);
+ assert(URCU_TLS(rcu_reader).registered);
+ URCU_TLS(rcu_reader).registered = 0;
+ mutex_lock(&rcu_registry_lock);
cds_list_del(&URCU_TLS(rcu_reader).node);
- mutex_unlock(&rcu_gp_lock);
+ mutex_unlock(&rcu_registry_lock);
}
void rcu_exit(void)
projects / urcu.git / blobdiff