X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=d6adc5bfaafa9d4d851842bad7d398967b081eec;hp=5b341b5cfd6d97034b08ca5ea6df913a0c8a7736;hb=92af1a30ca6a70945b167c31631c8598a626c71a;hpb=708d89f0b396d20522fe87cc80d91072bb9fcb02 diff --git a/urcu-qsbr.c b/urcu-qsbr.c index 5b341b5..d6adc5b 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -43,6 +43,7 @@ #include "urcu/tls-compat.h" #include "urcu-die.h" +#include "urcu-wait.h" /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ #undef _LGPL_SOURCE @@ -52,13 +53,7 @@ void __attribute__((destructor)) rcu_exit(void); static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; - -int32_t rcu_gp_futex; - -/* - * Global grace period counter. - */ -unsigned long rcu_gp_ctr = RCU_GP_ONLINE; +struct rcu_gp rcu_gp = { .ctr = RCU_GP_ONLINE }; /* * Active attempts to check for reader Q.S. before calling futex(). @@ -78,6 +73,12 @@ DEFINE_URCU_TLS(unsigned int, rcu_rand_yield); static CDS_LIST_HEAD(registry); +/* + * Queue keeping threads awaiting to wait for a grace period. Contains + * struct gp_waiters_thread objects. + */ +static DEFINE_URCU_WAIT_QUEUE(gp_waiters); + static void mutex_lock(pthread_mutex_t *mutex) { int ret; @@ -111,8 +112,8 @@ static void wait_gp(void) { /* Read reader_gp before read futex */ cmm_smp_rmb(); - if (uatomic_read(&rcu_gp_futex) == -1) - futex_noasync(&rcu_gp_futex, FUTEX_WAIT, -1, + if (uatomic_read(&rcu_gp.futex) == -1) + futex_noasync(&rcu_gp.futex, FUTEX_WAIT, -1, NULL, NULL, 0); } @@ -126,12 +127,12 @@ static void wait_for_readers(struct cds_list_head *input_readers, /* * Wait for each thread URCU_TLS(rcu_reader).ctr to either * indicate quiescence (offline), or for them to observe the - * current rcu_gp_ctr value. + * current rcu_gp.ctr value. */ for (;;) { wait_loops++; if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { - uatomic_set(&rcu_gp_futex, -1); + uatomic_set(&rcu_gp.futex, -1); /* * Write futex before write waiting (the other side * reads them in the opposite order). @@ -170,7 +171,7 @@ static void wait_for_readers(struct cds_list_head *input_readers, if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ cmm_smp_mb(); - uatomic_set(&rcu_gp_futex, 0); + uatomic_set(&rcu_gp.futex, 0); } break; } else { @@ -198,8 +199,10 @@ void synchronize_rcu(void) CDS_LIST_HEAD(cur_snap_readers); CDS_LIST_HEAD(qsreaders); unsigned long was_online; + DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); + struct urcu_waiters waiters; - was_online = URCU_TLS(rcu_reader).ctr; + was_online = rcu_read_ongoing(); /* All threads should read qparity before accessing data structure * where new ptr points to. In the "then" case, rcu_thread_offline @@ -214,8 +217,26 @@ void synchronize_rcu(void) else cmm_smp_mb(); + /* + * Add ourself to gp_waiters queue of threads awaiting to wait + * for a grace period. Proceed to perform the grace period only + * if we are the first thread added into the queue. + */ + if (urcu_wait_add(&gp_waiters, &wait) != 0) { + /* Not first in queue: will be awakened by another thread. */ + urcu_adaptative_busy_wait(&wait); + goto gp_end; + } + /* We won't need to wake ourself up */ + urcu_wait_set_state(&wait, URCU_WAIT_RUNNING); + mutex_lock(&rcu_gp_lock); + /* + * Move all waiters into our local queue. + */ + urcu_move_waiters(&waiters, &gp_waiters); + if (cds_list_empty(®istry)) goto out; @@ -226,11 +247,11 @@ void synchronize_rcu(void) /* * Must finish waiting for quiescent state for original parity - * before committing next rcu_gp_ctr update to memory. Failure + * before 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 URCU_TLS(rcu_reader).ctr before store - * to rcu_gp_ctr. + * to rcu_gp.ctr. */ cmm_barrier(); @@ -242,13 +263,13 @@ void synchronize_rcu(void) cmm_smp_mb(); /* Switch parity: 0 -> 1, 1 -> 0 */ - CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); + CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR); /* - * Must commit rcu_gp_ctr update to memory before waiting for + * Must commit rcu_gp.ctr update to memory before waiting for * 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 + * (no progress). Enforce compiler-order of store to rcu_gp.ctr * before load URCU_TLS(rcu_reader).ctr. */ cmm_barrier(); @@ -271,7 +292,8 @@ void synchronize_rcu(void) cds_list_splice(&qsreaders, ®istry); out: mutex_unlock(&rcu_gp_lock); - + urcu_wake_all_waiters(&waiters); +gp_end: /* * Finish waiting for reader threads before letting the old ptr being * freed. @@ -286,8 +308,10 @@ void synchronize_rcu(void) { CDS_LIST_HEAD(qsreaders); unsigned long was_online; + DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); + struct urcu_waiters waiters; - was_online = URCU_TLS(rcu_reader).ctr; + was_online = rcu_read_ongoing(); /* * Mark the writer thread offline to make sure we don't wait for @@ -299,18 +323,37 @@ void synchronize_rcu(void) else cmm_smp_mb(); + /* + * Add ourself to gp_waiters queue of threads awaiting to wait + * for a grace period. Proceed to perform the grace period only + * if we are the first thread added into the queue. + */ + if (urcu_wait_add(&gp_waiters, &wait) != 0) { + /* Not first in queue: will be awakened by another thread. */ + urcu_adaptative_busy_wait(&wait); + goto gp_end; + } + /* We won't need to wake ourself up */ + urcu_wait_set_state(&wait, URCU_WAIT_RUNNING); + mutex_lock(&rcu_gp_lock); + + /* + * Move all waiters into our local queue. + */ + urcu_move_waiters(&waiters, &gp_waiters); + if (cds_list_empty(®istry)) goto out; /* Increment current G.P. */ - CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); + CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr + RCU_GP_CTR); /* - * Must commit rcu_gp_ctr update to memory before waiting for + * Must commit rcu_gp.ctr update to memory before waiting for * 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 + * (no progress). Enforce compiler-order of store to rcu_gp.ctr * before load URCU_TLS(rcu_reader).ctr. */ cmm_barrier(); @@ -333,7 +376,8 @@ void synchronize_rcu(void) cds_list_splice(&qsreaders, ®istry); out: mutex_unlock(&rcu_gp_lock); - + urcu_wake_all_waiters(&waiters); +gp_end: if (was_online) rcu_thread_online(); else @@ -355,6 +399,11 @@ void rcu_read_unlock(void) _rcu_read_unlock(); } +int rcu_read_ongoing(void) +{ + return _rcu_read_ongoing(); +} + void rcu_quiescent_state(void) { _rcu_quiescent_state();