X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=337f7640b44d208855277f6fc53d9322f212d638;hp=9542b264a6dbf53d36d2fb63e7578b4e7ff2b2f5;hb=ad7de003b45b3a7339b90208c321517c2dcbdc3e;hpb=9598a4814c854780e9ca9bb2cfff8d77442c3db6 diff --git a/urcu.c b/urcu.c index 9542b26..337f764 100644 --- a/urcu.c +++ b/urcu.c @@ -6,6 +6,8 @@ * Copyright February 2009 - Mathieu Desnoyers * * Distributed under GPLv2 + * + * IBM's contributions to this file may be relicensed under LGPLv2 or later. */ #include @@ -14,6 +16,8 @@ #include #include #include +#include +#include #include "urcu.h" @@ -23,17 +27,23 @@ pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; * Global grace period counter. * Contains the current RCU_GP_CTR_BIT. * Also has a RCU_GP_CTR_BIT of 1, to accelerate the reader fast path. + * Written to only by writer with mutex taken. Read by both writer and readers. */ long urcu_gp_ctr = RCU_GP_COUNT; +/* + * Written to only by each individual reader. Read by both the reader and the + * writers. + */ long __thread urcu_active_readers; /* Thread IDs of registered readers */ #define INIT_NUM_THREADS 4 -struct reader_data { +struct reader_registry { pthread_t tid; long *urcu_active_readers; + char *need_mb; }; #ifdef DEBUG_YIELD @@ -41,18 +51,35 @@ unsigned int yield_active; unsigned int __thread rand_yield; #endif -static struct reader_data *reader_data; +static struct reader_registry *registry; +static char __thread need_mb; static int num_readers, alloc_readers; -static int sig_done; void internal_urcu_lock(void) { int ret; + +#ifndef DISTRUST_SIGNALS_EXTREME ret = pthread_mutex_lock(&urcu_mutex); if (ret) { perror("Error in pthread mutex lock"); exit(-1); } +#else /* #ifndef DISTRUST_SIGNALS_EXTREME */ + while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) { + if (ret != EBUSY && ret != EINTR) { + printf("ret = %d, errno = %d\n", ret, errno); + 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) @@ -71,148 +98,200 @@ void internal_urcu_unlock(void) */ static void switch_next_urcu_qparity(void) { - urcu_gp_ctr ^= RCU_GP_CTR_BIT; + STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR_BIT); } #ifdef DEBUG_FULL_MB +#ifdef HAS_INCOHERENT_CACHES +static void force_mb_single_thread(struct reader_registry *index) +{ + smp_mb(); +} +#endif /* #ifdef HAS_INCOHERENT_CACHES */ + static void force_mb_all_threads(void) { - mb(); + smp_mb(); } -#else +#else /* #ifdef DEBUG_FULL_MB */ +#ifdef HAS_INCOHERENT_CACHES +static void force_mb_single_thread(struct reader_registry *index) +{ + 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. + */ + *index->need_mb = 1; + smp_mc(); /* write ->need_mb before sending the signals */ + pthread_kill(index->tid, SIGURCU); + smp_mb(); + /* + * Wait for sighandler (and thus mb()) to execute on every thread. + * BUSY-LOOP. + */ + while (*index->need_mb) { + poll(NULL, 0, 1); + } + smp_mb(); /* read ->need_mb before ending the barrier */ +} +#endif /* #ifdef HAS_INCOHERENT_CACHES */ + static void force_mb_all_threads(void) { - struct reader_data *index; + struct reader_registry *index; /* - * Ask for each threads to execute a mb() so we can consider the + * Ask for each threads to execute a smp_mb() so we can consider the * compiler barriers around rcu read lock as real memory barriers. */ - if (!reader_data) + if (!registry) return; - debug_yield_write(); - sig_done = 0; - debug_yield_write(); - mb(); /* write sig_done before sending the signals */ - debug_yield_write(); - for (index = reader_data; index < reader_data + num_readers; index++) { + /* + * 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. + */ + 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); - debug_yield_write(); } /* * Wait for sighandler (and thus mb()) to execute on every thread. - * BUSY-LOOP. + * + * 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). */ - while (sig_done < num_readers) - barrier(); - debug_yield_write(); - mb(); /* read sig_done before ending the barrier */ - debug_yield_write(); + 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 +#endif /* #else #ifdef DEBUG_FULL_MB */ void wait_for_quiescent_state(void) { - struct reader_data *index; + struct reader_registry *index; - if (!reader_data) + if (!registry) return; - /* Wait for each thread urcu_active_readers count to become 0. + /* + * Wait for each thread urcu_active_readers count to become 0. */ - for (index = reader_data; index < reader_data + num_readers; index++) { + 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. + * 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)) - barrier(); + 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 */ } } void synchronize_rcu(void) { + internal_urcu_lock(); + /* All threads should read qparity before accessing data structure - * where new ptr points to. */ + * where new ptr points to. Must be done within internal_urcu_lock + * because it iterates on reader threads.*/ /* Write new ptr before changing the qparity */ force_mb_all_threads(); - debug_yield_write(); - - internal_urcu_lock(); - debug_yield_write(); switch_next_urcu_qparity(); /* 0 -> 1 */ - debug_yield_write(); /* * 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. */ - mb(); /* * Wait for previous parity to be empty of readers. */ wait_for_quiescent_state(); /* Wait readers in parity 0 */ - debug_yield_write(); /* * 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. */ - mb(); switch_next_urcu_qparity(); /* 1 -> 0 */ - debug_yield_write(); /* * 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. */ - mb(); /* * Wait for previous parity to be empty of readers. */ wait_for_quiescent_state(); /* Wait readers in parity 1 */ - debug_yield_write(); - - internal_urcu_unlock(); - debug_yield_write(); - /* All threads should finish using the data referred to by old ptr - * before decrementing their urcu_active_readers count */ /* Finish waiting for reader threads before letting the old ptr being - * freed. */ + * freed. Must be done within internal_urcu_lock because it iterates on + * reader threads. */ force_mb_all_threads(); - debug_yield_write(); + + internal_urcu_unlock(); } void urcu_add_reader(pthread_t id) { - struct reader_data *oldarray; + struct reader_registry *oldarray; - if (!reader_data) { + if (!registry) { alloc_readers = INIT_NUM_THREADS; num_readers = 0; - reader_data = - malloc(sizeof(struct reader_data) * alloc_readers); + registry = + malloc(sizeof(struct reader_registry) * alloc_readers); } if (alloc_readers < num_readers + 1) { - oldarray = reader_data; - reader_data = malloc(sizeof(struct reader_data) + oldarray = registry; + registry = malloc(sizeof(struct reader_registry) * (alloc_readers << 1)); - memcpy(reader_data, oldarray, - sizeof(struct reader_data) * alloc_readers); + memcpy(registry, oldarray, + sizeof(struct reader_registry) * alloc_readers); alloc_readers <<= 1; free(oldarray); } - reader_data[num_readers].tid = id; + registry[num_readers].tid = id; /* reference to the TLS of _this_ reader thread. */ - reader_data[num_readers].urcu_active_readers = &urcu_active_readers; + registry[num_readers].urcu_active_readers = &urcu_active_readers; + registry[num_readers].need_mb = &need_mb; num_readers++; } @@ -222,15 +301,15 @@ void urcu_add_reader(pthread_t id) */ void urcu_remove_reader(pthread_t id) { - struct reader_data *index; + struct reader_registry *index; - assert(reader_data != NULL); - for (index = reader_data; index < reader_data + num_readers; index++) { + assert(registry != NULL); + for (index = registry; index < registry + num_readers; index++) { if (pthread_equal(index->tid, id)) { - memcpy(index, &reader_data[num_readers - 1], - sizeof(struct reader_data)); - reader_data[num_readers - 1].tid = 0; - reader_data[num_readers - 1].urcu_active_readers = NULL; + memcpy(index, ®istry[num_readers - 1], + sizeof(struct reader_registry)); + registry[num_readers - 1].tid = 0; + registry[num_readers - 1].urcu_active_readers = NULL; num_readers--; return; } @@ -256,8 +335,14 @@ void urcu_unregister_thread(void) #ifndef DEBUG_FULL_MB void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) { - mb(); - atomic_inc(&sig_done); + /* + * 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(); } void __attribute__((constructor)) urcu_init(void) @@ -284,6 +369,6 @@ void __attribute__((destructor)) urcu_exit(void) exit(-1); } assert(act.sa_sigaction == sigurcu_handler); - free(reader_data); + free(registry); } -#endif +#endif /* #ifndef DEBUG_FULL_MB */