X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=337f7640b44d208855277f6fc53d9322f212d638;hp=b04b121344c5e0d425c0d2cfaee34a662ecb8cbf;hb=ad7de003b45b3a7339b90208c321517c2dcbdc3e;hpb=3b55dbf4ce37054fa097a827a0e4ab322cf18ca0 diff --git a/urcu.c b/urcu.c index b04b121..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 @@ -41,20 +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; -#ifndef DEBUG_FULL_MB -static int sig_done; -#endif 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) @@ -73,83 +98,104 @@ 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 -static void force_mb_single_thread(pthread_t tid) +#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) { smp_mb(); } -#else - -static void force_mb_single_thread(pthread_t tid) +#else /* #ifdef DEBUG_FULL_MB */ +#ifdef HAS_INCOHERENT_CACHES +static void force_mb_single_thread(struct reader_registry *index) { - assert(reader_data); - sig_done = 0; + 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. - * smp_mb(); write sig_done before sending the signals */ - smp_mc(); /* write sig_done before sending the signals */ - pthread_kill(tid, SIGURCU); + *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 (LOAD_REMOTE(sig_done) < 1) - cpu_relax(); - smp_mb(); /* read sig_done before ending the barrier */ + 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 smp_mb() so we can consider the * compiler barriers around rcu read lock as real memory barriers. */ - if (!reader_data) + if (!registry) return; - sig_done = 0; /* * 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. - * smp_mb(); write sig_done before sending the signals */ - smp_mc(); /* write sig_done before sending the signals */ - for (index = reader_data; index < reader_data + num_readers; index++) + 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 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 (LOAD_REMOTE(sig_done) < num_readers) - cpu_relax(); - smp_mb(); /* read sig_done before ending the barrier */ + 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. */ - 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. Force the reader thread to commit its @@ -157,12 +203,13 @@ void wait_for_quiescent_state(void) */ while (rcu_old_gp_ongoing(index->urcu_active_readers)) { if (wait_loops++ == KICK_READER_LOOPS) { - force_mb_single_thread(index->tid); + force_mb_single_thread(index); wait_loops = 0; } else { cpu_relax(); } } +#endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } } @@ -183,8 +230,8 @@ void synchronize_rcu(void) * 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. */ - smp_mc(); /* * Wait for previous parity to be empty of readers. @@ -196,8 +243,8 @@ void synchronize_rcu(void) * 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. */ - smp_mc(); switch_next_urcu_qparity(); /* 1 -> 0 */ @@ -206,8 +253,8 @@ void synchronize_rcu(void) * 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. */ - smp_mc(); /* * Wait for previous parity to be empty of readers. @@ -224,26 +271,27 @@ void synchronize_rcu(void) 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++; } @@ -253,15 +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; } @@ -293,7 +341,8 @@ void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) * executed on. */ smp_mb(); - atomic_inc(&sig_done); + need_mb = 0; + smp_mb(); } void __attribute__((constructor)) urcu_init(void) @@ -320,6 +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 */