#define _BSD_SOURCE
#define _GNU_SOURCE
#define _LGPL_SOURCE
+#define _DEFAULT_SOURCE
#include <stdio.h>
#include <pthread.h>
#include <signal.h>
/*
* 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
+/*
+ * RCU_MEMBARRIER is only possibly available on Linux.
+ */
+#if defined(RCU_MEMBARRIER) && defined(__linux__)
+#include <urcu/syscall-compat.h>
+#endif
+
+/* If the headers do not support SYS_membarrier, fall back on RCU_MB */
+#ifdef SYS_membarrier
+# define membarrier(...) syscall(SYS_membarrier, __VA_ARGS__)
+#else
+# define membarrier(...) -ENOSYS
+#endif
+
+#define MEMBARRIER_EXPEDITED (1 << 0)
+#define MEMBARRIER_DELAYED (1 << 1)
+#define MEMBARRIER_QUERY (1 << 16)
+
#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;
-struct urcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
+/*
+ * 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.
+ */
+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);
/*
_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 */
}
static void smp_mb_master(int group)
{
if (caa_likely(rcu_has_sys_membarrier))
- membarrier(MEMBARRIER_EXPEDITED);
+ (void) membarrier(MEMBARRIER_EXPEDITED);
else
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 */
NULL, NULL, 0);
}
+/*
+ * 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
* rcu_gp.ctr value.
*/
for (;;) {
- wait_loops++;
- if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
+ 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);
#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);
}
break;
} else {
- if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
+ /* Temporarily unlock the registry lock. */
+ mutex_unlock(&rcu_registry_lock);
+ if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
wait_gp();
else
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);
}
break;
} else {
- switch (wait_loops) {
- case RCU_QS_ACTIVE_ATTEMPTS:
- wait_gp();
- break; /* only escape switch */
- case KICK_READER_LOOPS:
+ if (wait_gp_loops == KICK_READER_LOOPS) {
smp_mb_master(RCU_MB_GROUP);
- wait_loops = 0;
- break; /* only escape switch */
- default:
+ wait_gp_loops = 0;
+ }
+ /* Temporarily unlock the registry lock. */
+ mutex_unlock(&rcu_registry_lock);
+ if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+ wait_gp();
+ wait_gp_loops++;
+ } else {
caa_cpu_relax();
}
+ /* Re-lock the registry lock before the next loop. */
+ mutex_lock(&rcu_registry_lock);
}
#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
}
*/
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);
/*
* 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);
/*
* 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. */
+ /*
+ * 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(RCU_MB_GROUP);
out:
+ mutex_unlock(&rcu_registry_lock);
mutex_unlock(&rcu_gp_lock);
/*
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);
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);
cds_list_del(&URCU_TLS(rcu_reader).node);
- mutex_unlock(&rcu_gp_lock);
+ mutex_unlock(&rcu_registry_lock);
}
#ifdef RCU_MEMBARRIER
* 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