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urcu-qsbr.c
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urcu-qsbr.c
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/*
* urcu-qsbr.c
*
* Userspace RCU QSBR library
*
* Copyright (c) 2009 Mathieu Desnoyers <[email protected]>
* 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 _GNU_SOURCE
#define _LGPL_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/wfcqueue.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
#include "urcu-qsbr.h"
#define _LGPL_SOURCE
void __attribute__((destructor)) rcu_exit(void);
static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
int32_t rcu_gp_futex;
/*
* Global grace period counter.
*/
unsigned long rcu_gp_ctr = RCU_GP_ONLINE;
/*
* Active attempts to check for reader Q.S. before calling futex().
*/
#define RCU_QS_ACTIVE_ATTEMPTS 100
/*
* Written to only by each individual reader. Read by both the reader and the
* writers.
*/
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);
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);
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);
}
/*
* synchronize_rcu() waiting. Single thread.
*/
static void wait_gp(void)
{
/* 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);
}
static void update_counter_and_wait(void)
{
CDS_LIST_HEAD(qsreaders);
int wait_loops = 0;
struct rcu_reader *index, *tmp;
#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) */
/*
* 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 each thread rcu_reader_qs_gp count to become 0.
*/
for (;;) {
wait_loops++;
if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
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) {
_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);
}
if (cds_list_empty(®istry)) {
if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
/* Read reader_gp before write futex */
cmm_smp_mb();
uatomic_set(&rcu_gp_futex, 0);
}
break;
} else {
if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
wait_gp();
} else {
#ifndef HAS_INCOHERENT_CACHES
caa_cpu_relax();
#else /* #ifndef HAS_INCOHERENT_CACHES */
cmm_smp_mb();
#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
}
}
}
/* put back the reader list in the registry */
cds_list_splice(&qsreaders, ®istry);
}
/*
* Using a two-subphases algorithm for architectures with smaller than 64-bit
* long-size to ensure we do not encounter an overflow bug.
*/
#if (CAA_BITS_PER_LONG < 64)
void synchronize_rcu(void)
{
unsigned long was_online;
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
* includes a memory barrier.
*
* Mark the writer thread offline to make sure we don't wait for
* our own quiescent state. This allows using synchronize_rcu()
* in threads registered as readers.
*/
if (was_online)
rcu_thread_offline();
else
cmm_smp_mb();
mutex_lock(&rcu_gp_lock);
if (cds_list_empty(®istry))
goto out;
/*
* Wait for previous parity to be empty of readers.
*/
update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
/*
* 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
* 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();
/*
* Wait for previous parity to be empty of readers.
*/
update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
out:
mutex_unlock(&rcu_gp_lock);
/*
* Finish waiting for reader threads before letting the old ptr being
* freed.
*/
if (was_online)
rcu_thread_online();
else
cmm_smp_mb();
}
#else /* !(CAA_BITS_PER_LONG < 64) */
void synchronize_rcu(void)
{
unsigned long was_online;
was_online = URCU_TLS(rcu_reader).ctr;
/*
* Mark the writer thread offline to make sure we don't wait for
* our own quiescent state. This allows using synchronize_rcu()
* in threads registered as readers.
*/
if (was_online)
rcu_thread_offline();
else
cmm_smp_mb();
mutex_lock(&rcu_gp_lock);
if (cds_list_empty(®istry))
goto out;
update_counter_and_wait();
out:
mutex_unlock(&rcu_gp_lock);
if (was_online)
rcu_thread_online();
else
cmm_smp_mb();
}
#endif /* !(CAA_BITS_PER_LONG < 64) */
/*
* 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();
}
void rcu_quiescent_state(void)
{
_rcu_quiescent_state();
}
void rcu_thread_offline(void)
{
_rcu_thread_offline();
}
void rcu_thread_online(void)
{
_rcu_thread_online();
}
void rcu_register_thread(void)
{
URCU_TLS(rcu_reader).tid = pthread_self();
assert(URCU_TLS(rcu_reader).ctr == 0);
mutex_lock(&rcu_gp_lock);
cds_list_add(&URCU_TLS(rcu_reader).node, ®istry);
mutex_unlock(&rcu_gp_lock);
_rcu_thread_online();
}
void rcu_unregister_thread(void)
{
/*
* We have to make the thread offline otherwise we end up dealocking
* with a waiting writer.
*/
_rcu_thread_offline();
mutex_lock(&rcu_gp_lock);
cds_list_del(&URCU_TLS(rcu_reader).node);
mutex_unlock(&rcu_gp_lock);
}
void rcu_exit(void)
{
/*
* Assertion disabled because call_rcu threads are now rcu
* readers, and left running at exit.
* assert(cds_list_empty(®istry));
*/
}
DEFINE_RCU_FLAVOR(rcu_flavor);
#include "urcu-call-rcu-impl.h"
#include "urcu-defer-impl.h"