X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-bp.c;h=93d781fcf44e5f2c9ee89928631a9d0d6cbb3e21;hp=b07a1bbed912a5998c1089a2237825d2801f7032;hb=5c02e37d09b7b89f68429751344d2af00c89f4fd;hpb=1de4df4b770e5e90440008becc5e14a15c75c6e0 diff --git a/urcu-bp.c b/urcu-bp.c index b07a1bb..93d781f 100644 --- a/urcu-bp.c +++ b/urcu-bp.c @@ -109,13 +109,7 @@ unsigned int rcu_yield_active; DEFINE_URCU_TLS(unsigned int, rcu_rand_yield); #endif -/* - * Global grace period counter. - * Contains the current RCU_GP_CTR_PHASE. - * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path. - * Written to only by writer with mutex taken. Read by both writer and readers. - */ -long rcu_gp_ctr = RCU_GP_COUNT; +struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT }; /* * Pointer to registry elements. Written to only by each individual reader. Read @@ -164,40 +158,44 @@ static void mutex_unlock(pthread_mutex_t *mutex) urcu_die(ret); } -static void update_counter_and_wait(void) +static void wait_for_readers(struct cds_list_head *input_readers, + struct cds_list_head *cur_snap_readers, + struct cds_list_head *qsreaders) { - CDS_LIST_HEAD(qsreaders); int wait_loops = 0; struct rcu_reader *index, *tmp; - /* Switch parity: 0 -> 1, 1 -> 0 */ - CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE); - - /* - * Must commit qparity update to memory before waiting for other parity - * quiescent state. Failure to do so could result in the writer waiting - * forever while new readers are always accessing data (no progress). - * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED. - */ - /* - * Adding a cmm_smp_mb() which is _not_ formally required, but makes the - * model easier to understand. It does not have a big performance impact - * anyway, given this is the write-side. - */ - cmm_smp_mb(); - - /* - * Wait for each thread rcu_reader.ctr count to become 0. + * Wait for each thread URCU_TLS(rcu_reader).ctr to either + * indicate quiescence (not nested), or observe the current + * rcu_gp.ctr value. */ for (;;) { wait_loops++; - cds_list_for_each_entry_safe(index, tmp, ®istry, node) { - if (!rcu_old_gp_ongoing(&index->ctr)) - cds_list_move(&index->node, &qsreaders); + cds_list_for_each_entry_safe(index, tmp, input_readers, node) { + switch (rcu_reader_state(&index->ctr)) { + case RCU_READER_ACTIVE_CURRENT: + if (cur_snap_readers) { + cds_list_move(&index->node, + cur_snap_readers); + break; + } + /* Fall-through */ + case RCU_READER_INACTIVE: + cds_list_move(&index->node, qsreaders); + break; + case RCU_READER_ACTIVE_OLD: + /* + * Old snapshot. Leaving node in + * input_readers will make us busy-loop + * until the snapshot becomes current or + * the reader becomes inactive. + */ + break; + } } - if (cds_list_empty(®istry)) { + if (cds_list_empty(input_readers)) { break; } else { if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) @@ -206,18 +204,18 @@ static void update_counter_and_wait(void) caa_cpu_relax(); } } - /* put back the reader list in the registry */ - cds_list_splice(&qsreaders, ®istry); } void synchronize_rcu(void) { + CDS_LIST_HEAD(cur_snap_readers); + CDS_LIST_HEAD(qsreaders); sigset_t newmask, oldmask; int ret; - ret = sigemptyset(&newmask); + ret = sigfillset(&newmask); assert(!ret); - ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask); + ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask); assert(!ret); mutex_lock(&rcu_gp_lock); @@ -234,9 +232,26 @@ void synchronize_rcu(void) rcu_gc_registry(); /* - * Wait for previous parity to be empty of readers. + * Wait for readers to observe original parity or be quiescent. + */ + wait_for_readers(®istry, &cur_snap_readers, &qsreaders); + + /* + * Adding a cmm_smp_mb() which is _not_ formally required, but makes the + * model easier to understand. It does not have a big performance impact + * anyway, given this is the write-side. + */ + cmm_smp_mb(); + + /* Switch parity: 0 -> 1, 1 -> 0 */ + CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE); + + /* + * Must commit qparity update to memory before waiting for other parity + * quiescent state. Failure to do so could result in the writer waiting + * forever while new readers are always accessing data (no progress). + * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED. */ - update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */ /* * Adding a cmm_smp_mb() which is _not_ formally required, but makes the @@ -246,9 +261,14 @@ void synchronize_rcu(void) cmm_smp_mb(); /* - * Wait for previous parity to be empty of readers. + * Wait for readers to observe new parity or be quiescent. + */ + wait_for_readers(&cur_snap_readers, NULL, &qsreaders); + + /* + * Put quiescent reader list back into registry. */ - update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ + cds_list_splice(&qsreaders, ®istry); /* * Finish waiting for reader threads before letting the old ptr being @@ -275,31 +295,47 @@ void rcu_read_unlock(void) _rcu_read_unlock(); } +int rcu_read_ongoing(void) +{ + return _rcu_read_ongoing(); +} + /* * only grow for now. */ static void resize_arena(struct registry_arena *arena, size_t len) { - void *new_arena; + void *new_p; + size_t old_len; + + old_len = arena->len; if (!arena->p) - new_arena = mmap(arena->p, len, - PROT_READ | PROT_WRITE, - MAP_ANONYMOUS | MAP_PRIVATE, - -1, 0); + new_p = mmap(arena->p, len, + PROT_READ | PROT_WRITE, + MAP_ANONYMOUS | MAP_PRIVATE, + -1, 0); else - new_arena = mremap_wrapper(arena->p, arena->len, - len, MREMAP_MAYMOVE); - assert(new_arena != MAP_FAILED); + new_p = mremap_wrapper(arena->p, old_len, + len, MREMAP_MAYMOVE); + assert(new_p != MAP_FAILED); + + /* + * Zero the newly allocated memory. Since mmap() does not + * clearly specify if memory is zeroed or not (although it is + * very likely that it is), be extra careful by not expecting + * the new range to be zeroed by mremap. + */ + bzero(new_p + old_len, len - old_len); /* - * re-used the same region ? + * If we did not re-use the same region, we need to update the + * arena pointer. */ - if (new_arena == arena->p) - return; + if (new_p != arena->p) + arena->p = new_p; - bzero(new_arena + arena->len, len - arena->len); - arena->p = new_arena; + arena->len = len; } /* Called with signals off and mutex locked */ @@ -360,9 +396,9 @@ void rcu_bp_register(void) sigset_t newmask, oldmask; int ret; - ret = sigemptyset(&newmask); + ret = sigfillset(&newmask); assert(!ret); - ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask); + ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask); assert(!ret); /* @@ -395,9 +431,9 @@ void rcu_bp_before_fork(void) sigset_t newmask, oldmask; int ret; - ret = sigemptyset(&newmask); + ret = sigfillset(&newmask); assert(!ret); - ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask); + ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask); assert(!ret); mutex_lock(&rcu_gp_lock); saved_fork_signal_mask = oldmask;