X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=f681c05bf0c05d96860e06cbb8771b11c9e3e829;hp=fd0ebf6c4a710ae2bed98e6a919f424eb05bc992;hb=b55487c706982c8190e42545f7f74dfadad59548;hpb=9f1621ca8d6ce9178343ae24aeef406c0ac2564a diff --git a/urcu-qsbr.c b/urcu-qsbr.c index fd0ebf6..f681c05 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -1,7 +1,7 @@ /* - * urcu.c + * urcu-qsbr.c * - * Userspace RCU library + * Userspace RCU QSBR library * * Copyright (c) 2009 Mathieu Desnoyers * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. @@ -32,35 +32,30 @@ #include #include -#include "urcu-static.h" +#define BUILD_QSBR_LIB +#include "urcu-qsbr-static.h" /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ -#include "urcu.h" +#include "urcu-qsbr.h" -void __attribute__((constructor)) urcu_init(void); -void __attribute__((destructor)) urcu_exit(void); - -int init_done; - -pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; +static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; /* * Global grace period counter. */ -long urcu_gp_ctr = 0; +unsigned long urcu_gp_ctr = RCU_GP_ONLINE; /* * Written to only by each individual reader. Read by both the reader and the * writers. */ -long __thread urcu_active_readers; +unsigned long __thread rcu_reader_qs_gp; /* Thread IDs of registered readers */ #define INIT_NUM_THREADS 4 struct reader_registry { pthread_t tid; - long *urcu_active_readers; - char *need_mb; + unsigned long *rcu_reader_qs_gp; }; #ifdef DEBUG_YIELD @@ -69,10 +64,9 @@ unsigned int __thread rand_yield; #endif static struct reader_registry *registry; -static char __thread need_mb; static int num_readers, alloc_readers; -void internal_urcu_lock(void) +static void internal_urcu_lock(void) { int ret; @@ -89,17 +83,12 @@ void internal_urcu_lock(void) perror("Error in pthread mutex lock"); exit(-1); } - if (need_mb) { - smp_mb(); - need_mb = 0; - smp_mb(); - } poll(NULL,0,10); } #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ } -void internal_urcu_unlock(void) +static void internal_urcu_unlock(void) { int ret; @@ -110,127 +99,136 @@ void internal_urcu_unlock(void) } } -#ifdef DEBUG_FULL_MB -#ifdef HAS_INCOHERENT_CACHES -static void force_mb_single_thread(struct reader_registry *index) +static void wait_for_quiescent_state(void) { - smp_mb(); + struct reader_registry *index; + + if (!registry) + return; + /* + * Wait for each thread rcu_reader_qs_gp count to become 0. + */ + for (index = registry; index < registry + num_readers; index++) { +#ifndef HAS_INCOHERENT_CACHES + while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) + cpu_relax(); +#else /* #ifndef HAS_INCOHERENT_CACHES */ + while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) + smp_mb(); +#endif /* #else #ifndef HAS_INCOHERENT_CACHES */ + } } -#endif /* #ifdef HAS_INCOHERENT_CACHES */ -static void force_mb_all_threads(void) +/* + * Using a two-subphases algorithm for architectures with smaller than 64-bit + * long-size to ensure we do not encounter an overflow bug. + */ + +#if (BITS_PER_LONG < 64) +/* + * called with urcu_mutex held. + */ +static void switch_next_urcu_qparity(void) { - smp_mb(); + STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR); } -#else /* #ifdef DEBUG_FULL_MB */ -#ifdef HAS_INCOHERENT_CACHES -static void force_mb_single_thread(struct reader_registry *index) + +void synchronize_rcu(void) { - assert(registry); - /* - * pthread_kill has a 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 smp_mc() to make sure the - * cache flush is enforced. + unsigned long was_online; + + was_online = rcu_reader_qs_gp; + + /* All threads should read qparity before accessing data structure + * where new ptr points to. */ - *index->need_mb = 1; - smp_mc(); /* write ->need_mb before sending the signals */ - pthread_kill(index->tid, SIGURCU); + /* Write new ptr before changing the qparity */ smp_mb(); + /* - * Wait for sighandler (and thus mb()) to execute on every thread. - * BUSY-LOOP. + * 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. */ - while (*index->need_mb) { - poll(NULL, 0, 1); - } - smp_mb(); /* read ->need_mb before ending the barrier */ -} -#endif /* #ifdef HAS_INCOHERENT_CACHES */ + if (was_online) + STORE_SHARED(rcu_reader_qs_gp, 0); + + internal_urcu_lock(); + + switch_next_urcu_qparity(); /* 0 -> 1 */ -static void force_mb_all_threads(void) -{ - struct reader_registry *index; /* - * Ask for each threads to execute a smp_mb() so we can consider the - * compiler barriers around rcu read lock as real memory barriers. + * Must commit qparity update to memory before waiting for parity + * 0 quiescent state. Failure to do so could result in the writer + * waiting forever while new readers are always accessing data (no + * progress). + * Ensured by STORE_SHARED and LOAD_SHARED. */ - if (!registry) - return; + /* - * pthread_kill has a 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 smp_mc() to make sure the - * cache flush is enforced. + * Wait for previous parity to be empty of readers. */ - for (index = registry; index < registry + num_readers; index++) { - *index->need_mb = 1; - smp_mc(); /* write need_mb before sending the signal */ - pthread_kill(index->tid, SIGURCU); - } + wait_for_quiescent_state(); /* Wait readers in parity 0 */ + /* - * 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). + * Must finish waiting for quiescent state for parity 0 before + * committing qparity update to memory. Failure to do so could result in + * the writer waiting forever while new readers are always accessing + * data (no progress). + * Ensured by STORE_SHARED and LOAD_SHARED. */ - for (index = registry; index < registry + num_readers; index++) { - while (*index->need_mb) { - pthread_kill(index->tid, SIGURCU); - poll(NULL, 0, 1); - } - } - smp_mb(); /* read ->need_mb before ending the barrier */ -} -#endif /* #else #ifdef DEBUG_FULL_MB */ -void wait_for_quiescent_state(void) -{ - struct reader_registry *index; + switch_next_urcu_qparity(); /* 1 -> 0 */ - if (!registry) - return; /* - * Wait for each thread urcu_active_readers count to become 0. + * Must commit qparity update to memory before waiting for parity + * 1 quiescent state. Failure to do so could result in the writer + * waiting forever while new readers are always accessing data (no + * progress). + * Ensured by STORE_SHARED and LOAD_SHARED. */ - for (index = registry; index < registry + num_readers; index++) { -#ifndef HAS_INCOHERENT_CACHES - while (rcu_old_gp_ongoing(index->urcu_active_readers)) - cpu_relax(); -#else /* #ifndef HAS_INCOHERENT_CACHES */ - int wait_loops = 0; - /* - * BUSY-LOOP. Force the reader thread to commit its - * urcu_active_readers update to memory if we wait for too long. - */ - while (rcu_old_gp_ongoing(index->urcu_active_readers)) { - if (wait_loops++ == KICK_READER_LOOPS) { - force_mb_single_thread(index); - wait_loops = 0; - } else { - cpu_relax(); - } - } -#endif /* #else #ifndef HAS_INCOHERENT_CACHES */ - } -} + /* + * Wait for previous parity to be empty of readers. + */ + wait_for_quiescent_state(); /* Wait readers in parity 1 */ + + internal_urcu_unlock(); + + /* + * Finish waiting for reader threads before letting the old ptr being + * freed. + */ + if (was_online) + _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr)); + smp_mb(); +} +#else /* !(BITS_PER_LONG < 64) */ void synchronize_rcu(void) { + unsigned long was_online; + + was_online = rcu_reader_qs_gp; + + /* + * 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. + */ + smp_mb(); + if (was_online) + STORE_SHARED(rcu_reader_qs_gp, 0); + internal_urcu_lock(); - force_mb_all_threads(); - urcu_gp_ctr += 2; + STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR); wait_for_quiescent_state(); - force_mb_all_threads(); internal_urcu_unlock(); + + if (was_online) + _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr)); + smp_mb(); } +#endif /* !(BITS_PER_LONG < 64) */ /* * library wrappers to be used by non-LGPL compatible source code. @@ -272,6 +270,21 @@ void *rcu_publish_content_sym(void **p, void *v) return oldptr; } +void rcu_quiescent_state(void) +{ + _rcu_quiescent_state(); +} + +void rcu_thread_offline(void) +{ + _rcu_thread_offline(); +} + +void rcu_thread_online(void) +{ + _rcu_thread_online(); +} + static void rcu_add_reader(pthread_t id) { struct reader_registry *oldarray; @@ -293,8 +306,7 @@ static void rcu_add_reader(pthread_t id) } registry[num_readers].tid = id; /* reference to the TLS of _this_ reader thread. */ - registry[num_readers].urcu_active_readers = &urcu_active_readers; - registry[num_readers].need_mb = &need_mb; + registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp; num_readers++; } @@ -312,7 +324,7 @@ static void rcu_remove_reader(pthread_t id) memcpy(index, ®istry[num_readers - 1], sizeof(struct reader_registry)); registry[num_readers - 1].tid = 0; - registry[num_readers - 1].urcu_active_readers = NULL; + registry[num_readers - 1].rcu_reader_qs_gp = NULL; num_readers--; return; } @@ -324,67 +336,19 @@ static void rcu_remove_reader(pthread_t id) void rcu_register_thread(void) { internal_urcu_lock(); - urcu_init(); /* In case gcc does not support constructor attribute */ rcu_add_reader(pthread_self()); internal_urcu_unlock(); + _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(); internal_urcu_lock(); rcu_remove_reader(pthread_self()); internal_urcu_unlock(); } - -#ifndef DEBUG_FULL_MB -static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) -{ - /* - * Executing this smp_mb() is the only purpose of this signal handler. - * It punctually promotes barrier() into smp_mb() on every thread it is - * executed on. - */ - smp_mb(); - need_mb = 0; - smp_mb(); -} - -/* - * urcu_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 internal_urcu_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 urcu_init(void) -{ - struct sigaction act; - int ret; - - if (init_done) - return; - init_done = 1; - - act.sa_sigaction = sigurcu_handler; - ret = sigaction(SIGURCU, &act, NULL); - if (ret) { - perror("Error in sigaction"); - exit(-1); - } -} - -void urcu_exit(void) -{ - struct sigaction act; - int ret; - - ret = sigaction(SIGURCU, NULL, &act); - if (ret) { - perror("Error in sigaction"); - exit(-1); - } - assert(act.sa_sigaction == sigurcu_handler); - free(registry); -} -#endif /* #ifndef DEBUG_FULL_MB */