#include <errno.h>
#include <poll.h>
-#include "urcu/wfqueue.h"
+#include "urcu/wfcqueue.h"
+#include "urcu/wfstack.h"
#include "urcu/map/urcu-qsbr.h"
#define BUILD_QSBR_LIB
#include "urcu/static/urcu-qsbr.h"
#include "urcu-pointer.h"
+#include "urcu/tls-compat.h"
+
+#include "urcu-die.h"
/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
#undef _LGPL_SOURCE
static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
-int32_t gp_futex;
+int32_t rcu_gp_futex;
/*
* Global grace period counter.
* Written to only by each individual reader. Read by both the reader and the
* writers.
*/
-struct rcu_reader __thread rcu_reader;
+DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
#ifdef DEBUG_YIELD
-unsigned int yield_active;
-unsigned int __thread rand_yield;
+unsigned int rcu_yield_active;
+DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
#endif
static CDS_LIST_HEAD(registry);
+/*
+ * Number of busy-loop attempts before waiting on futex for grace period
+ * batching.
+ */
+#define RCU_AWAKE_ATTEMPTS 1000
+
+enum adapt_wakeup_state {
+ /* AWAKE_WAITING is compared directly (futex compares it). */
+ AWAKE_WAITING = 0,
+ /* non-zero are used as masks. */
+ AWAKE_WAKEUP = (1 << 0),
+ AWAKE_AWAKENED = (1 << 1),
+ AWAKE_TEARDOWN = (1 << 2),
+};
+
+struct gp_waiters_thread {
+ struct cds_wfs_node node;
+ int32_t wait_futex;
+};
+
+/*
+ * Stack keeping threads awaiting to wait for a grace period. Contains
+ * struct gp_waiters_thread objects.
+ */
+static struct cds_wfs_stack gp_waiters = {
+ .head = CDS_WFS_END,
+ .lock = PTHREAD_MUTEX_INITIALIZER,
+};
+
static void mutex_lock(pthread_mutex_t *mutex)
{
int ret;
#ifndef DISTRUST_SIGNALS_EXTREME
ret = pthread_mutex_lock(mutex);
- if (ret) {
- perror("Error in pthread mutex lock");
- exit(-1);
- }
+ if (ret)
+ urcu_die(ret);
#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
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");
- exit(-1);
- }
+ if (ret != EBUSY && ret != EINTR)
+ urcu_die(ret);
poll(NULL,0,10);
}
#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
int ret;
ret = pthread_mutex_unlock(mutex);
- if (ret) {
- perror("Error in pthread mutex unlock");
- exit(-1);
- }
+ if (ret)
+ urcu_die(ret);
}
/*
{
/* Read reader_gp before read futex */
cmm_smp_rmb();
- if (uatomic_read(&gp_futex) == -1)
- futex_noasync(&gp_futex, FUTEX_WAIT, -1,
+ if (uatomic_read(&rcu_gp_futex) == -1)
+ futex_noasync(&rcu_gp_futex, FUTEX_WAIT, -1,
NULL, NULL, 0);
}
-static void update_counter_and_wait(void)
+/*
+ * Note: urcu_adaptative_wake_up needs "value" to stay allocated
+ * throughout its execution. In this scheme, the waiter owns the futex
+ * memory, and we only allow it to free this memory when it receives the
+ * AWAKE_TEARDOWN flag.
+ */
+static void urcu_adaptative_wake_up(int32_t *value)
{
- CDS_LIST_HEAD(qsreaders);
- int wait_loops = 0;
- struct rcu_reader *index, *tmp;
+ cmm_smp_mb();
+ assert(uatomic_read(value) == AWAKE_WAITING);
+ uatomic_set(value, AWAKE_WAKEUP);
+ if (!(uatomic_read(value) & AWAKE_AWAKENED))
+ futex_noasync(value, FUTEX_WAKE, 1, NULL, NULL, 0);
+ /* Allow teardown of "value" memory. */
+ uatomic_or(value, AWAKE_TEARDOWN);
+}
-#if (CAA_BITS_PER_LONG < 64)
- /* Switch parity: 0 -> 1, 1 -> 0 */
- CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
-#else /* !(CAA_BITS_PER_LONG < 64) */
- /* Increment current G.P. */
- CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
-#endif /* !(CAA_BITS_PER_LONG < 64) */
+/*
+ * Caller must initialize "value" to AWAKE_WAITING before passing its
+ * memory to waker thread.
+ */
+static void urcu_adaptative_busy_wait(int32_t *value)
+{
+ unsigned int i;
- /*
- * 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();
+ /* Load and test condition before read futex */
+ cmm_smp_rmb();
+ for (i = 0; i < RCU_AWAKE_ATTEMPTS; i++) {
+ if (uatomic_read(value) != AWAKE_WAITING)
+ goto skip_futex_wait;
+ caa_cpu_relax();
+ }
+ futex_noasync(value, FUTEX_WAIT, AWAKE_WAITING, NULL, NULL, 0);
+skip_futex_wait:
+
+ /* Tell waker thread than we are awakened. */
+ uatomic_or(value, AWAKE_AWAKENED);
/*
- * 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.
+ * Wait until waker thread lets us know it's ok to tear down
+ * memory allocated for value.
*/
- cmm_smp_mb();
+ for (i = 0; i < RCU_AWAKE_ATTEMPTS; i++) {
+ if (uatomic_read(value) & AWAKE_TEARDOWN)
+ break;
+ caa_cpu_relax();
+ }
+ while (!(uatomic_read(value) & AWAKE_TEARDOWN))
+ poll(NULL, 0, 10);
+ assert(uatomic_read(value) & AWAKE_TEARDOWN);
+}
+
+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;
+ struct rcu_reader *index, *tmp;
/*
- * Wait for each thread rcu_reader_qs_gp count to become 0.
+ * 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.
*/
for (;;) {
wait_loops++;
if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
- uatomic_set(&gp_futex, -1);
+ uatomic_set(&rcu_gp_futex, -1);
/*
* Write futex before write waiting (the other side
* reads them in the opposite order).
*/
cmm_smp_wmb();
- cds_list_for_each_entry(index, ®istry, node) {
+ cds_list_for_each_entry(index, input_readers, node) {
_CMM_STORE_SHARED(index->waiting, 1);
}
/* Write futex before read reader_gp */
cmm_smp_mb();
}
- 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;
+ }
}
- if (cds_list_empty(®istry)) {
+ if (cds_list_empty(input_readers)) {
if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
/* Read reader_gp before write futex */
cmm_smp_mb();
- uatomic_set(&gp_futex, 0);
+ uatomic_set(&rcu_gp_futex, 0);
}
break;
} else {
}
}
}
- /* put back the reader list in the registry */
- cds_list_splice(&qsreaders, ®istry);
}
/*
#if (CAA_BITS_PER_LONG < 64)
void synchronize_rcu(void)
{
+ CDS_LIST_HEAD(cur_snap_readers);
+ CDS_LIST_HEAD(qsreaders);
unsigned long was_online;
+ struct gp_waiters_thread gp_waiters_thread;
+ struct cds_wfs_head *gp_waiters_head;
+ struct cds_wfs_node *waiters_iter, *waiters_iter_n;
- was_online = rcu_reader.ctr;
+ was_online = URCU_TLS(rcu_reader).ctr;
/* 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 stack 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 stack.
+ */
+ cds_wfs_node_init(&gp_waiters_thread.node);
+ gp_waiters_thread.wait_futex = AWAKE_WAITING;
+ if (cds_wfs_push(&gp_waiters, &gp_waiters_node) != 0) {
+ /* Not first in stack: will be awakened by another thread. */
+ urcu_adaptative_busy_wait(&gp_waiters_thread.wait_futex);
+ goto gp_end;
+ }
+
mutex_lock(&rcu_gp_lock);
+ /*
+ * Pop all waiters into our local stack head.
+ */
+ gp_waiters_head = __cds_wfs_pop_all(&gp_waiters);
+
if (cds_list_empty(®istry))
goto out;
/*
- * 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
- * committing next rcu_gp_ctr update to memory. Failure to
- * do so could result in the writer waiting forever while new
+ * 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 rcu_reader ctr before store to
- * rcu_gp_ctr.
+ * compiler-order of load URCU_TLS(rcu_reader).ctr before store
+ * to rcu_gp_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();
+
+ /* Switch parity: 0 -> 1, 1 -> 0 */
+ CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
+
+ /*
+ * 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 URCU_TLS(rcu_reader).ctr.
*/
cmm_barrier();
cmm_smp_mb();
/*
- * Wait for previous parity to be empty of readers.
+ * Wait for readers to observe new parity or be quiescent.
*/
- update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
+ wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
+
+ /*
+ * Put quiescent reader list back into registry.
+ */
+ cds_list_splice(&qsreaders, ®istry);
out:
mutex_unlock(&rcu_gp_lock);
+ /* Wake all waiters in our stack head, excluding ourself. */
+ cds_wfs_for_each_blocking_safe(gp_waiters_head, waiters_iter,
+ waiters_iter_n) {
+ struct gp_waiters_thread *wt;
+
+ wt = caa_container_of(waiters_iter,
+ struct gp_waiters_thread, node);
+ if (wt == &gp_waiters_thread)
+ continue;
+ urcu_adaptative_wake_up(&wt->wait_futex);
+ }
+
+gp_end:
/*
* Finish waiting for reader threads before letting the old ptr being
* freed.
#else /* !(CAA_BITS_PER_LONG < 64) */
void synchronize_rcu(void)
{
+ CDS_LIST_HEAD(qsreaders);
unsigned long was_online;
+ struct gp_waiters_thread gp_waiters_thread;
+ struct cds_wfs_head *gp_waiters_head;
+ struct cds_wfs_node *waiters_iter, *waiters_iter_n;
- was_online = rcu_reader.ctr;
+ was_online = URCU_TLS(rcu_reader).ctr;
/*
* Mark the writer thread offline to make sure we don't wait for
else
cmm_smp_mb();
+ /*
+ * Add ourself to gp_waiters stack 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 stack.
+ */
+ cds_wfs_node_init(&gp_waiters_thread.node);
+ gp_waiters_thread.wait_futex = AWAKE_WAITING;
+ if (cds_wfs_push(&gp_waiters, &gp_waiters_thread.node) != 0) {
+ /* Not first in stack: will be awakened by another thread. */
+ urcu_adaptative_busy_wait(&gp_waiters_thread.wait_futex);
+ goto gp_end;
+ }
+
mutex_lock(&rcu_gp_lock);
+
+ /*
+ * Pop all waiters into our local stack head.
+ */
+ gp_waiters_head = __cds_wfs_pop_all(&gp_waiters);
+
if (cds_list_empty(®istry))
goto out;
- update_counter_and_wait();
+
+ /* Increment current G.P. */
+ CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
+
+ /*
+ * 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 URCU_TLS(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 count of be quiescent.
+ */
+ wait_for_readers(®istry, NULL, &qsreaders);
+
+ /*
+ * Put quiescent reader list back into registry.
+ */
+ cds_list_splice(&qsreaders, ®istry);
out:
mutex_unlock(&rcu_gp_lock);
+ /* Wake all waiters in our stack head, excluding ourself. */
+ cds_wfs_for_each_blocking_safe(gp_waiters_head, waiters_iter,
+ waiters_iter_n) {
+ struct gp_waiters_thread *wt;
+
+ wt = caa_container_of(waiters_iter,
+ struct gp_waiters_thread, node);
+ if (wt == &gp_waiters_thread)
+ continue;
+ urcu_adaptative_wake_up(&wt->wait_futex);
+ }
+
+gp_end:
if (was_online)
rcu_thread_online();
else
void rcu_register_thread(void)
{
- rcu_reader.tid = pthread_self();
- assert(rcu_reader.ctr == 0);
+ URCU_TLS(rcu_reader).tid = pthread_self();
+ assert(URCU_TLS(rcu_reader).ctr == 0);
mutex_lock(&rcu_gp_lock);
- cds_list_add(&rcu_reader.node, ®istry);
+ cds_list_add(&URCU_TLS(rcu_reader).node, ®istry);
mutex_unlock(&rcu_gp_lock);
_rcu_thread_online();
}
*/
_rcu_thread_offline();
mutex_lock(&rcu_gp_lock);
- cds_list_del(&rcu_reader.node);
+ cds_list_del(&URCU_TLS(rcu_reader).node);
mutex_unlock(&rcu_gp_lock);
}