X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=f681c05bf0c05d96860e06cbb8771b11c9e3e829;hp=300eb970e17f5031be51d4421a1e4a3a0080cd38;hb=b55487c706982c8190e42545f7f74dfadad59548;hpb=7ac06cef7a7d9394332837edc5c0e9595286a5fc diff --git a/urcu-qsbr.c b/urcu-qsbr.c index 300eb97..f681c05 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -32,30 +32,30 @@ #include #include +#define BUILD_QSBR_LIB #include "urcu-qsbr-static.h" /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ #include "urcu-qsbr.h" -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 rcu_reader_qs_gp; +unsigned long __thread rcu_reader_qs_gp; /* Thread IDs of registered readers */ #define INIT_NUM_THREADS 4 struct reader_registry { pthread_t tid; - long *rcu_reader_qs_gp; - char *need_mb; + unsigned long *rcu_reader_qs_gp; }; #ifdef DEBUG_YIELD @@ -64,10 +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; @@ -84,17 +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; @@ -105,19 +99,7 @@ void internal_urcu_unlock(void) } } -#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(); -} - -void wait_for_quiescent_state(void) +static void wait_for_quiescent_state(void) { struct reader_registry *index; @@ -128,37 +110,125 @@ void wait_for_quiescent_state(void) */ for (index = registry; index < registry + num_readers; index++) { #ifndef HAS_INCOHERENT_CACHES - while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && - (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) + while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) cpu_relax(); #else /* #ifndef HAS_INCOHERENT_CACHES */ - int wait_loops = 0; - /* - * BUSY-LOOP. Force the reader thread to commit its - * rcu_reader_qs_gp update to memory if we wait for too long. - */ - while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && - (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) { - if (wait_loops++ == KICK_READER_LOOPS) { - force_mb_single_thread(index); - wait_loops = 0; - } else { - cpu_relax(); - } - } + while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) + smp_mb(); #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } } +/* + * 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) +{ + STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR); +} + +void synchronize_rcu(void) +{ + unsigned long was_online; + + was_online = rcu_reader_qs_gp; + + /* All threads should read qparity before accessing data structure + * where new ptr points to. + */ + /* Write new ptr before changing the qparity */ + smp_mb(); + + /* + * 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) + STORE_SHARED(rcu_reader_qs_gp, 0); + + internal_urcu_lock(); + + switch_next_urcu_qparity(); /* 0 -> 1 */ + + /* + * 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. + */ + + /* + * Wait for previous parity to be empty of readers. + */ + wait_for_quiescent_state(); /* Wait readers in parity 0 */ + + /* + * 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. + */ + + switch_next_urcu_qparity(); /* 1 -> 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. + */ + + /* + * 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. @@ -237,7 +307,6 @@ static void rcu_add_reader(pthread_t id) registry[num_readers].tid = id; /* reference to the TLS of _this_ reader thread. */ registry[num_readers].rcu_reader_qs_gp = &rcu_reader_qs_gp; - registry[num_readers].need_mb = &need_mb; num_readers++; }