X-Git-Url: http://git.liburcu.org/?p=userspace-rcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=52cb04aee9ff1b1b5a7b2caef45d6d5b5317ba77;hp=5eda71dbf3c1ee454f9b29e19c752ff946f7c9b3;hb=2819ef641bb6e2f7aa60c28f3a8f5ad252aa7d00;hpb=af7c2dbeac32c663b64ad05e4eca70e18784463b diff --git a/urcu-qsbr.c b/urcu-qsbr.c index 5eda71d..52cb04a 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -24,42 +24,70 @@ */ #define _GNU_SOURCE +#define _LGPL_SOURCE #include #include #include #include #include +#include #include #include #include +#include "urcu/wfqueue.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); +/* + * rcu_gp_lock ensures mutual exclusion between threads calling + * synchronize_rcu(). + */ static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; +/* + * rcu_registry_lock ensures mutual exclusion between threads + * registering and unregistering themselves to/from the registry, and + * with threads reading that registry from synchronize_rcu(). However, + * this lock is not held all the way through the completion of awaiting + * for the grace period. It is sporadically released between iterations + * on the registry. + * rcu_registry_lock may nest inside rcu_gp_lock. + */ +static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER; -int gp_futex; +int32_t 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. */ -struct rcu_reader __thread rcu_reader; +__DEFINE_URCU_TLS_GLOBAL(struct rcu_reader, rcu_reader); #ifdef DEBUG_YIELD unsigned int yield_active; -unsigned int __thread rand_yield; +__DEFINE_URCU_TLS_GLOBAL(unsigned int, rand_yield); #endif static CDS_LIST_HEAD(registry); @@ -70,17 +98,12 @@ static void mutex_lock(pthread_mutex_t *mutex) #ifndef DISTRUST_SIGNALS_EXTREME ret = pthread_mutex_lock(mutex); - if (ret) { - perror("Error in pthread mutex lock"); - exit(-1); - } + if (ret) + urcu_die(ret); #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ while ((ret = pthread_mutex_trylock(mutex)) != 0) { - if (ret != EBUSY && ret != EINTR) { - printf("ret = %d, errno = %d\n", ret, errno); - perror("Error in pthread mutex lock"); - exit(-1); - } + if (ret != EBUSY && ret != EINTR) + urcu_die(ret); poll(NULL,0,10); } #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ @@ -91,10 +114,8 @@ static void mutex_unlock(pthread_mutex_t *mutex) int ret; ret = pthread_mutex_unlock(mutex); - if (ret) { - perror("Error in pthread mutex unlock"); - exit(-1); - } + if (ret) + urcu_die(ret); } /* @@ -104,15 +125,32 @@ static void wait_gp(void) { /* Read reader_gp before read futex */ cmm_smp_rmb(); - if (uatomic_read(&gp_futex) == -1) - futex_noasync(&gp_futex, FUTEX_WAIT, -1, - NULL, NULL, 0); + if (uatomic_read(&gp_futex) != -1) + return; + while (futex_noasync(&gp_futex, FUTEX_WAIT, -1, + NULL, NULL, 0)) { + switch (errno) { + case EWOULDBLOCK: + /* Value already changed. */ + return; + case EINTR: + /* Retry if interrupted by signal. */ + break; /* Get out of switch. */ + default: + /* Unexpected error. */ + urcu_die(errno); + } + } } +/* + * Always called with rcu_registry lock held. Releases this lock between + * iterations and grabs it again. Holds the lock when it returns. + */ static void update_counter_and_wait(void) { CDS_LIST_HEAD(qsreaders); - int wait_loops = 0; + unsigned int wait_loops = 0; struct rcu_reader *index, *tmp; #if (CAA_BITS_PER_LONG < 64) @@ -128,7 +166,7 @@ static void update_counter_and_wait(void) * 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 rcu_reader ctr. + * before load URCU_TLS(rcu_reader).ctr. */ cmm_barrier(); @@ -143,27 +181,37 @@ static void update_counter_and_wait(void) * Wait for each thread rcu_reader_qs_gp count to become 0. */ for (;;) { - wait_loops++; - if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { - uatomic_dec(&gp_futex); + if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS) + wait_loops++; + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + uatomic_set(&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) { + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ cmm_smp_mb(); uatomic_set(&gp_futex, 0); } break; } else { - if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + /* Temporarily unlock the registry lock. */ + mutex_unlock(&rcu_registry_lock); + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { wait_gp(); } else { #ifndef HAS_INCOHERENT_CACHES @@ -172,6 +220,8 @@ static void update_counter_and_wait(void) cmm_smp_mb(); #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } + /* Re-lock the registry lock before the next loop. */ + mutex_lock(&rcu_registry_lock); } } /* put back the reader list in the registry */ @@ -188,29 +238,31 @@ void synchronize_rcu(void) { unsigned long was_online; - was_online = rcu_reader.ctr; + was_online = URCU_TLS(rcu_reader).ctr; /* All threads should read qparity before accessing data structure - * where new ptr points to. - */ - /* Write new ptr before changing the qparity */ - cmm_smp_mb(); - - /* + * 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) - CMM_STORE_SHARED(rcu_reader.ctr, 0); + rcu_thread_offline(); + else + cmm_smp_mb(); mutex_lock(&rcu_gp_lock); + mutex_lock(&rcu_registry_lock); if (cds_list_empty(®istry)) goto out; /* * Wait for previous parity to be empty of readers. + * update_counter_and_wait() can release and grab again + * rcu_registry_lock interally. */ update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */ @@ -219,7 +271,7 @@ void synchronize_rcu(void) * 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 rcu_reader ctr before store to + * compiler-order of load URCU_TLS(rcu_reader).ctr before store to * rcu_gp_ctr. */ cmm_barrier(); @@ -233,9 +285,12 @@ void synchronize_rcu(void) /* * Wait for previous parity to be empty of readers. + * update_counter_and_wait() can release and grab again + * rcu_registry_lock interally. */ update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ out: + mutex_unlock(&rcu_registry_lock); mutex_unlock(&rcu_gp_lock); /* @@ -243,37 +298,44 @@ out: * freed. */ if (was_online) - _CMM_STORE_SHARED(rcu_reader.ctr, - CMM_LOAD_SHARED(rcu_gp_ctr)); - cmm_smp_mb(); + rcu_thread_online(); + else + cmm_smp_mb(); } #else /* !(CAA_BITS_PER_LONG < 64) */ void synchronize_rcu(void) { unsigned long was_online; - was_online = rcu_reader.ctr; + 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. */ - cmm_smp_mb(); if (was_online) - CMM_STORE_SHARED(rcu_reader.ctr, 0); + rcu_thread_offline(); + else + cmm_smp_mb(); mutex_lock(&rcu_gp_lock); + mutex_lock(&rcu_registry_lock); if (cds_list_empty(®istry)) goto out; + /* + * update_counter_and_wait() can release and grab again + * rcu_registry_lock interally. + */ update_counter_and_wait(); out: + mutex_unlock(&rcu_registry_lock); mutex_unlock(&rcu_gp_lock); if (was_online) - _CMM_STORE_SHARED(rcu_reader.ctr, - CMM_LOAD_SHARED(rcu_gp_ctr)); - cmm_smp_mb(); + rcu_thread_online(); + else + cmm_smp_mb(); } #endif /* !(CAA_BITS_PER_LONG < 64) */ @@ -308,12 +370,12 @@ void rcu_thread_online(void) void rcu_register_thread(void) { - rcu_reader.tid = pthread_self(); - assert(rcu_reader.ctr == 0); + URCU_TLS(rcu_reader).tid = pthread_self(); + assert(URCU_TLS(rcu_reader).ctr == 0); - mutex_lock(&rcu_gp_lock); - cds_list_add(&rcu_reader.node, ®istry); - mutex_unlock(&rcu_gp_lock); + mutex_lock(&rcu_registry_lock); + cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); + mutex_unlock(&rcu_registry_lock); _rcu_thread_online(); } @@ -324,15 +386,21 @@ void rcu_unregister_thread(void) * with a waiting writer. */ _rcu_thread_offline(); - mutex_lock(&rcu_gp_lock); - cds_list_del(&rcu_reader.node); - mutex_unlock(&rcu_gp_lock); + mutex_lock(&rcu_registry_lock); + cds_list_del(&URCU_TLS(rcu_reader).node); + mutex_unlock(&rcu_registry_lock); } void rcu_exit(void) { - assert(cds_list_empty(®istry)); + /* + * 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"