--- /dev/null
+/*
+ * urcu.c
+ *
+ * Userspace RCU library
+ *
+ * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * IBM's contributions to this file may be relicensed under LGPLv2 or later.
+ */
+
+#define _BSD_SOURCE
+#define _LGPL_SOURCE
+#define _DEFAULT_SOURCE
+#include <stdio.h>
+#include <pthread.h>
+#include <signal.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.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-pointer.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
+#include "urcu.h"
+#define _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 10 loops waiting for it.
+ */
+#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__((constructor)) rcu_init(void);
+#endif
+
+#ifdef RCU_MB
+void rcu_init(void)
+{
+}
+#endif
+
+#ifdef RCU_SIGNAL
+static int init_done;
+
+void __attribute__((constructor)) rcu_init(void);
+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;
+/*
+ * 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
+ * writers.
+ */
+DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
+
+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;
+
+#ifndef DISTRUST_SIGNALS_EXTREME
+ ret = pthread_mutex_lock(mutex);
+ if (ret)
+ urcu_die(ret);
+#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
+ while ((ret = pthread_mutex_trylock(mutex)) != 0) {
+ if (ret != EBUSY && ret != EINTR)
+ urcu_die(ret);
+ if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) {
+ cmm_smp_mb();
+ _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
+ cmm_smp_mb();
+ }
+ (void) poll(NULL, 0, 10);
+ }
+#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
+}
+
+static void mutex_unlock(pthread_mutex_t *mutex)
+{
+ int ret;
+
+ ret = pthread_mutex_unlock(mutex);
+ if (ret)
+ urcu_die(ret);
+}
+
+#ifdef RCU_MEMBARRIER
+static void smp_mb_master(void)
+{
+ if (caa_likely(rcu_has_sys_membarrier))
+ (void) membarrier(MEMBARRIER_CMD_SHARED, 0);
+ else
+ cmm_smp_mb();
+}
+#endif
+
+#ifdef RCU_MB
+static void smp_mb_master(void)
+{
+ cmm_smp_mb();
+}
+#endif
+
+#ifdef RCU_SIGNAL
+static void force_mb_all_readers(void)
+{
+ struct rcu_reader *index;
+
+ /*
+ * Ask for each threads to execute a cmm_smp_mb() so we can consider the
+ * compiler barriers around rcu read lock as real memory barriers.
+ */
+ if (cds_list_empty(®istry))
+ return;
+ /*
+ * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
+ * a cache flush on architectures with non-coherent cache. Let's play
+ * safe and don't assume anything : we use cmm_smp_mc() to make sure the
+ * cache flush is enforced.
+ */
+ cds_list_for_each_entry(index, ®istry, node) {
+ CMM_STORE_SHARED(index->need_mb, 1);
+ pthread_kill(index->tid, SIGRCU);
+ }
+ /*
+ * Wait for sighandler (and thus mb()) to execute on every thread.
+ *
+ * Note that the pthread_kill() will never be executed on systems
+ * that correctly deliver signals in a timely manner. However, it
+ * is not uncommon for kernels to have bugs that can result in
+ * lost or unduly delayed signals.
+ *
+ * If you are seeing the below pthread_kill() executing much at
+ * all, we suggest testing the underlying kernel and filing the
+ * relevant bug report. For Linux kernels, we recommend getting
+ * the Linux Test Project (LTP).
+ */
+ cds_list_for_each_entry(index, ®istry, node) {
+ while (CMM_LOAD_SHARED(index->need_mb)) {
+ pthread_kill(index->tid, SIGRCU);
+ (void) poll(NULL, 0, 1);
+ }
+ }
+ cmm_smp_mb(); /* read ->need_mb before ending the barrier */
+}
+
+static void smp_mb_master(void)
+{
+ force_mb_all_readers();
+}
+#endif /* #ifdef RCU_SIGNAL */
+
+/*
+ * 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() 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)
+{
+ 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.
+ */
+ for (;;) {
+ 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();
+ }
+
+ 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(input_readers)) {
+ if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+ /* Read reader_gp before write futex */
+ smp_mb_master();
+ uatomic_set(&rcu_gp.futex, 0);
+ }
+ break;
+ } else {
+ if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+ /* wait_gp unlocks/locks registry lock. */
+ wait_gp();
+ } 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 */
+ /*
+ * BUSY-LOOP. Force the reader thread to commit its
+ * URCU_TLS(rcu_reader).ctr update to memory if we wait
+ * for too long.
+ */
+ if (cds_list_empty(input_readers)) {
+ if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+ /* Read reader_gp before write futex */
+ smp_mb_master();
+ uatomic_set(&rcu_gp.futex, 0);
+ }
+ break;
+ } else {
+ 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();
+ 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 */
+ }
+}
+
+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);
+
+ 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_registry_lock
+ * because it iterates on reader threads.
+ */
+ /* Write new ptr before changing the qparity */
+ 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
+ * 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.
+ */
+ 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_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() can release and grab again rcu_registry_lock
+ * interally.
+ */
+ wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
+
+ /*
+ * Put quiescent reader list back into registry.
+ */
+ cds_list_splice(&qsreaders, ®istry);
+
+ /*
+ * 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);
+}
+
+/*
+ * library wrappers to be used by non-LGPL compatible source code.
+ */
+
+void rcu_read_lock(void)
+{
+ _rcu_read_lock();
+}
+
+void rcu_read_unlock(void)
+{
+ _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_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_registry_lock);
+}
+
+void rcu_unregister_thread(void)
+{
+ 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_registry_lock);
+}
+
+#ifdef RCU_MEMBARRIER
+void rcu_init(void)
+{
+ int ret;
+
+ if (init_done)
+ return;
+ init_done = 1;
+ ret = membarrier(MEMBARRIER_CMD_QUERY, 0);
+ if (ret >= 0 && (ret & MEMBARRIER_CMD_SHARED)) {
+ rcu_has_sys_membarrier = 1;
+ }
+}
+#endif
+
+#ifdef RCU_SIGNAL
+static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
+{
+ /*
+ * Executing this cmm_smp_mb() is the only purpose of this signal handler.
+ * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
+ * executed on.
+ */
+ cmm_smp_mb();
+ _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
+ cmm_smp_mb();
+}
+
+/*
+ * 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_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)
+{
+ struct sigaction act;
+ int ret;
+
+ if (init_done)
+ return;
+ init_done = 1;
+
+ act.sa_sigaction = sigrcu_handler;
+ act.sa_flags = SA_SIGINFO | SA_RESTART;
+ sigemptyset(&act.sa_mask);
+ ret = sigaction(SIGRCU, &act, NULL);
+ if (ret)
+ urcu_die(errno);
+}
+
+void rcu_exit(void)
+{
+ /*
+ * 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 */
+
+DEFINE_RCU_FLAVOR(rcu_flavor);
+
+#include "urcu-call-rcu-impl.h"
+#include "urcu-defer-impl.h"
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