#define _BSD_SOURCE
#define _GNU_SOURCE
#define _LGPL_SOURCE
+#define _DEFAULT_SOURCE
#include <stdio.h>
#include <pthread.h>
#include <signal.h>
#include <errno.h>
#include <poll.h>
+#include "urcu/arch.h"
#include "urcu/wfcqueue.h"
#include "urcu/map/urcu.h"
#include "urcu/static/urcu.h"
#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
/*
* If a reader is really non-cooperative and refuses to commit its
* rcu_active_readers count to memory (there is no barrier in the reader
- * per-se), kick it after a few loops waiting for it.
+ * per-se), kick it after 10 loops waiting for it.
*/
-#define KICK_READER_LOOPS 10000
+#define KICK_READER_LOOPS 10
/*
* Active attempts to check for reader Q.S. before calling futex().
*/
#define RCU_QS_ACTIVE_ATTEMPTS 100
+/* If the headers do not support membarrier system call, fall back on RCU_MB */
+#ifdef __NR_membarrier
+# define membarrier(...) syscall(__NR_membarrier, __VA_ARGS__)
+#else
+# define membarrier(...) -ENOSYS
+#endif
+
+enum membarrier_cmd {
+ MEMBARRIER_CMD_QUERY = 0,
+ MEMBARRIER_CMD_SHARED = (1 << 0),
+};
+
#ifdef RCU_MEMBARRIER
static int init_done;
int rcu_has_sys_membarrier;
void __attribute__((destructor)) rcu_exit(void);
#endif
+/*
+ * 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.
- * Contains the current RCU_GP_CTR_PHASE.
- * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
- * Written to only by writer with mutex taken. Read by both writer and readers.
+ * 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_COUNT;
+static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
+struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
/*
* Written to only by each individual reader. Read by both the reader and the
*/
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;
_CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
cmm_smp_mb();
}
- poll(NULL,0,10);
+ (void) poll(NULL, 0, 10);
}
#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
}
}
#ifdef RCU_MEMBARRIER
-static void smp_mb_master(int group)
+static void smp_mb_master(void)
{
if (caa_likely(rcu_has_sys_membarrier))
- membarrier(MEMBARRIER_EXPEDITED);
+ (void) membarrier(MEMBARRIER_CMD_SHARED, 0);
else
cmm_smp_mb();
}
#endif
#ifdef RCU_MB
-static void smp_mb_master(int group)
+static void smp_mb_master(void)
{
cmm_smp_mb();
}
cds_list_for_each_entry(index, ®istry, node) {
while (CMM_LOAD_SHARED(index->need_mb)) {
pthread_kill(index->tid, SIGRCU);
- poll(NULL, 0, 1);
+ (void) poll(NULL, 0, 1);
}
}
cmm_smp_mb(); /* read ->need_mb before ending the barrier */
}
-static void smp_mb_master(int group)
+static void smp_mb_master(void)
{
force_mb_all_readers();
}
/*
* synchronize_rcu() waiting. Single thread.
+ * Always called with rcu_registry lock held. Releases this lock and
+ * grabs it again. Holds the lock when it returns.
*/
static void wait_gp(void)
{
- /* Read reader_gp before read futex */
- smp_mb_master(RCU_MB_GROUP);
- if (uatomic_read(&rcu_gp_futex) == -1)
- futex_async(&rcu_gp_futex, FUTEX_WAIT, -1,
- NULL, NULL, 0);
+ /*
+ * Read reader_gp before read futex. smp_mb_master() needs to
+ * be called with the rcu registry lock held in RCU_SIGNAL
+ * flavor.
+ */
+ smp_mb_master();
+ /* Temporarily unlock the registry lock. */
+ mutex_unlock(&rcu_registry_lock);
+ if (uatomic_read(&rcu_gp.futex) != -1)
+ goto end;
+ while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1,
+ NULL, NULL, 0)) {
+ switch (errno) {
+ case EWOULDBLOCK:
+ /* Value already changed. */
+ goto end;
+ case EINTR:
+ /* Retry if interrupted by signal. */
+ break; /* Get out of switch. */
+ default:
+ /* Unexpected error. */
+ urcu_die(errno);
+ }
+ }
+end:
+ /*
+ * Re-lock the registry lock before the next loop.
+ */
+ mutex_lock(&rcu_registry_lock);
}
+/*
+ * 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;
+#ifdef HAS_INCOHERENT_CACHES
+ unsigned int wait_gp_loops = 0;
+#endif /* HAS_INCOHERENT_CACHES */
/*
* Wait for each thread URCU_TLS(rcu_reader).ctr to either
* indicate quiescence (not nested), or observe the current
- * rcu_gp_ctr value.
+ * rcu_gp.ctr value.
*/
for (;;) {
- wait_loops++;
- if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
- uatomic_dec(&rcu_gp_futex);
+ if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
+ wait_loops++;
+ if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+ uatomic_dec(&rcu_gp.futex);
/* Write futex before read reader_gp */
- smp_mb_master(RCU_MB_GROUP);
+ smp_mb_master();
}
cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
#ifndef HAS_INCOHERENT_CACHES
if (cds_list_empty(input_readers)) {
- if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
+ if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
/* Read reader_gp before write futex */
- smp_mb_master(RCU_MB_GROUP);
- uatomic_set(&rcu_gp_futex, 0);
+ smp_mb_master();
+ uatomic_set(&rcu_gp.futex, 0);
}
break;
} else {
- if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
+ if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+ /* wait_gp unlocks/locks registry lock. */
wait_gp();
- else
+ } else {
+ /* Temporarily unlock the registry lock. */
+ mutex_unlock(&rcu_registry_lock);
caa_cpu_relax();
+ /*
+ * Re-lock the registry lock before the
+ * next loop.
+ */
+ mutex_lock(&rcu_registry_lock);
+ }
}
#else /* #ifndef HAS_INCOHERENT_CACHES */
/*
* for too long.
*/
if (cds_list_empty(input_readers)) {
- if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
+ if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
/* Read reader_gp before write futex */
- smp_mb_master(RCU_MB_GROUP);
- uatomic_set(&rcu_gp_futex, 0);
+ smp_mb_master();
+ uatomic_set(&rcu_gp.futex, 0);
}
break;
} else {
- switch (wait_loops) {
- case RCU_QS_ACTIVE_ATTEMPTS:
+ if (wait_gp_loops == KICK_READER_LOOPS) {
+ smp_mb_master();
+ wait_gp_loops = 0;
+ }
+ if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+ /* wait_gp unlocks/locks registry lock. */
wait_gp();
- break; /* only escape switch */
- case KICK_READER_LOOPS:
- smp_mb_master(RCU_MB_GROUP);
- wait_loops = 0;
- break; /* only escape switch */
- default:
+ wait_gp_loops++;
+ } else {
+ /* Temporarily unlock the registry lock. */
+ mutex_unlock(&rcu_registry_lock);
caa_cpu_relax();
+ /*
+ * Re-lock the registry lock before the
+ * next loop.
+ */
+ mutex_lock(&rcu_registry_lock);
}
}
#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
{
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);
+
+ mutex_lock(&rcu_registry_lock);
+
if (cds_list_empty(®istry))
goto out;
- /* All threads should read qparity before accessing data structure
- * where new ptr points to. Must be done within rcu_gp_lock because it
- * iterates on reader threads.*/
+ /*
+ * All threads should read qparity before accessing data structure
+ * where new ptr points to. Must be done within rcu_registry_lock
+ * because it iterates on reader threads.
+ */
/* Write new ptr before changing the qparity */
- smp_mb_master(RCU_MB_GROUP);
+ smp_mb_master();
/*
* 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 to do so could
+ * 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.
+ * URCU_TLS(rcu_reader).ctr before store 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_PHASE);
+ 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
+ * 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.
+ * compiler-order of store to rcu_gp.ctr before load 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);
- /* Finish waiting for reader threads before letting the old ptr being
- * freed. Must be done within rcu_gp_lock because it iterates on reader
- * threads. */
- smp_mb_master(RCU_MB_GROUP);
+ /*
+ * Finish waiting for reader threads before letting the old ptr
+ * being freed. Must be done within rcu_registry_lock because it
+ * iterates on reader threads.
+ */
+ smp_mb_master();
out:
+ mutex_unlock(&rcu_registry_lock);
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();
assert(URCU_TLS(rcu_reader).need_mb == 0);
assert(!(URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK));
- mutex_lock(&rcu_gp_lock);
+ mutex_lock(&rcu_registry_lock);
+ assert(!URCU_TLS(rcu_reader).registered);
+ URCU_TLS(rcu_reader).registered = 1;
rcu_init(); /* In case gcc does not support constructor attribute */
cds_list_add(&URCU_TLS(rcu_reader).node, ®istry);
- mutex_unlock(&rcu_gp_lock);
+ mutex_unlock(&rcu_registry_lock);
}
void rcu_unregister_thread(void)
{
- mutex_lock(&rcu_gp_lock);
+ mutex_lock(&rcu_registry_lock);
+ assert(URCU_TLS(rcu_reader).registered);
+ URCU_TLS(rcu_reader).registered = 0;
cds_list_del(&URCU_TLS(rcu_reader).node);
- mutex_unlock(&rcu_gp_lock);
+ mutex_unlock(&rcu_registry_lock);
}
#ifdef RCU_MEMBARRIER
void rcu_init(void)
{
+ int ret;
+
if (init_done)
return;
init_done = 1;
- if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY))
+ ret = membarrier(MEMBARRIER_CMD_QUERY, 0);
+ if (ret >= 0 && (ret & MEMBARRIER_CMD_SHARED)) {
rcu_has_sys_membarrier = 1;
+ }
}
#endif
* rcu_init constructor. Called when the library is linked, but also when
* reader threads are calling rcu_register_thread().
* Should only be called by a single thread at a given time. This is ensured by
- * holing the rcu_gp_lock from rcu_register_thread() or by running at library
- * load time, which should not be executed by multiple threads nor concurrently
- * with rcu_register_thread() anyway.
+ * holing the rcu_registry_lock from rcu_register_thread() or by running
+ * at library load time, which should not be executed by multiple
+ * threads nor concurrently with rcu_register_thread() anyway.
*/
void rcu_init(void)
{
void rcu_exit(void)
{
- struct sigaction act;
- int ret;
-
- ret = sigaction(SIGRCU, NULL, &act);
- if (ret)
- urcu_die(errno);
- assert(act.sa_sigaction == sigrcu_handler);
- assert(cds_list_empty(®istry));
+ /*
+ * Don't unregister the SIGRCU signal handler anymore, because
+ * call_rcu threads could still be using it shortly before the
+ * application exits.
+ * Assertion disabled because call_rcu threads are now rcu
+ * readers, and left running at exit.
+ * assert(cds_list_empty(®istry));
+ */
}
#endif /* #ifdef RCU_SIGNAL */
projects / urcu.git / blobdiff