X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=a5568bdbd075ed1edc4539dec460c7cce40ee590;hp=e6ff0f349e9e4fef17d6d366b5e7197acb841b84;hb=2af1c19e6a553878fcb2a5106f050d5ed7ac0f54;hpb=fd189fa57fa46b28d59275476993f6a730cde086 diff --git a/urcu.c b/urcu.c index e6ff0f3..a5568bd 100644 --- a/urcu.c +++ b/urcu.c @@ -26,6 +26,7 @@ #define _BSD_SOURCE #define _GNU_SOURCE #define _LGPL_SOURCE +#define _DEFAULT_SOURCE #include #include #include @@ -36,6 +37,7 @@ #include #include +#include "urcu/arch.h" #include "urcu/wfcqueue.h" #include "urcu/map/urcu.h" #include "urcu/static/urcu.h" @@ -43,6 +45,7 @@ #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 @@ -52,15 +55,27 @@ /* * If a reader is really non-cooperative and refuses to commit its * rcu_active_readers count to memory (there is no barrier in the reader - * per-se), kick it after a few loops waiting for it. + * per-se), kick it after 10 loops waiting for it. */ -#define KICK_READER_LOOPS 10000 +#define KICK_READER_LOOPS 10 /* * Active attempts to check for reader Q.S. before calling futex(). */ #define RCU_QS_ACTIVE_ATTEMPTS 100 +/* If the headers do not support membarrier system call, fall back on RCU_MB */ +#ifdef __NR_membarrier +# define membarrier(...) syscall(__NR_membarrier, __VA_ARGS__) +#else +# define membarrier(...) -ENOSYS +#endif + +enum membarrier_cmd { + MEMBARRIER_CMD_QUERY = 0, + MEMBARRIER_CMD_SHARED = (1 << 0), +}; + #ifdef RCU_MEMBARRIER static int init_done; int rcu_has_sys_membarrier; @@ -81,17 +96,22 @@ void __attribute__((constructor)) rcu_init(void); void __attribute__((destructor)) rcu_exit(void); #endif +/* + * rcu_gp_lock ensures mutual exclusion between threads calling + * synchronize_rcu(). + */ static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; - -int32_t rcu_gp_futex; - /* - * 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. + * 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. */ -unsigned long rcu_gp_ctr = RCU_GP_COUNT; +static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER; +struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT }; /* * Written to only by each individual reader. Read by both the reader and the @@ -99,13 +119,14 @@ unsigned long rcu_gp_ctr = RCU_GP_COUNT; */ DEFINE_URCU_TLS(struct rcu_reader, rcu_reader); -#ifdef DEBUG_YIELD -unsigned int rcu_yield_active; -DEFINE_URCU_TLS(unsigned int, rcu_rand_yield); -#endif - 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; @@ -123,7 +144,7 @@ static void mutex_lock(pthread_mutex_t *mutex) _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0); cmm_smp_mb(); } - poll(NULL,0,10); + (void) poll(NULL, 0, 10); } #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ } @@ -138,17 +159,17 @@ static void mutex_unlock(pthread_mutex_t *mutex) } #ifdef RCU_MEMBARRIER -static void smp_mb_master(int group) +static void smp_mb_master(void) { if (caa_likely(rcu_has_sys_membarrier)) - membarrier(MEMBARRIER_EXPEDITED); + (void) membarrier(MEMBARRIER_CMD_SHARED, 0); else cmm_smp_mb(); } #endif #ifdef RCU_MB -static void smp_mb_master(int group) +static void smp_mb_master(void) { cmm_smp_mb(); } @@ -191,13 +212,13 @@ static void force_mb_all_readers(void) cds_list_for_each_entry(index, ®istry, node) { while (CMM_LOAD_SHARED(index->need_mb)) { pthread_kill(index->tid, SIGRCU); - poll(NULL, 0, 1); + (void) poll(NULL, 0, 1); } } cmm_smp_mb(); /* read ->need_mb before ending the barrier */ } -static void smp_mb_master(int group) +static void smp_mb_master(void) { force_mb_all_readers(); } @@ -205,34 +226,68 @@ static void smp_mb_master(int group) /* * synchronize_rcu() waiting. Single thread. + * Always called with rcu_registry lock held. Releases this lock and + * grabs it again. Holds the lock when it returns. */ static void wait_gp(void) { - /* Read reader_gp before read futex */ - smp_mb_master(RCU_MB_GROUP); - if (uatomic_read(&rcu_gp_futex) == -1) - futex_async(&rcu_gp_futex, FUTEX_WAIT, -1, - NULL, NULL, 0); + /* + * Read reader_gp before read futex. smp_mb_master() needs to + * be called with the rcu registry lock held in RCU_SIGNAL + * flavor. + */ + smp_mb_master(); + /* Temporarily unlock the registry lock. */ + mutex_unlock(&rcu_registry_lock); + if (uatomic_read(&rcu_gp.futex) != -1) + goto end; + while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1, + NULL, NULL, 0)) { + switch (errno) { + case EWOULDBLOCK: + /* Value already changed. */ + goto end; + case EINTR: + /* Retry if interrupted by signal. */ + break; /* Get out of switch. */ + default: + /* Unexpected error. */ + urcu_die(errno); + } + } +end: + /* + * Re-lock the registry lock before the next loop. + */ + mutex_lock(&rcu_registry_lock); } +/* + * Always called with rcu_registry lock held. Releases this lock between + * iterations and grabs it again. Holds the lock when it returns. + */ static void wait_for_readers(struct cds_list_head *input_readers, struct cds_list_head *cur_snap_readers, struct cds_list_head *qsreaders) { - int wait_loops = 0; + unsigned int wait_loops = 0; struct rcu_reader *index, *tmp; +#ifdef HAS_INCOHERENT_CACHES + unsigned int wait_gp_loops = 0; +#endif /* HAS_INCOHERENT_CACHES */ /* * Wait for each thread URCU_TLS(rcu_reader).ctr to either * indicate quiescence (not nested), or observe the current - * rcu_gp_ctr value. + * rcu_gp.ctr value. */ for (;;) { - wait_loops++; - if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { - uatomic_dec(&rcu_gp_futex); + if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS) + wait_loops++; + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + uatomic_dec(&rcu_gp.futex); /* Write futex before read reader_gp */ - smp_mb_master(RCU_MB_GROUP); + smp_mb_master(); } cds_list_for_each_entry_safe(index, tmp, input_readers, node) { @@ -260,17 +315,26 @@ static void wait_for_readers(struct cds_list_head *input_readers, #ifndef HAS_INCOHERENT_CACHES if (cds_list_empty(input_readers)) { - if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ - smp_mb_master(RCU_MB_GROUP); - uatomic_set(&rcu_gp_futex, 0); + smp_mb_master(); + uatomic_set(&rcu_gp.futex, 0); } break; } else { - if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + /* wait_gp unlocks/locks registry lock. */ wait_gp(); - else + } else { + /* Temporarily unlock the registry lock. */ + mutex_unlock(&rcu_registry_lock); caa_cpu_relax(); + /* + * Re-lock the registry lock before the + * next loop. + */ + mutex_lock(&rcu_registry_lock); + } } #else /* #ifndef HAS_INCOHERENT_CACHES */ /* @@ -279,23 +343,30 @@ static void wait_for_readers(struct cds_list_head *input_readers, * for too long. */ if (cds_list_empty(input_readers)) { - if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ - smp_mb_master(RCU_MB_GROUP); - uatomic_set(&rcu_gp_futex, 0); + smp_mb_master(); + uatomic_set(&rcu_gp.futex, 0); } break; } else { - switch (wait_loops) { - case RCU_QS_ACTIVE_ATTEMPTS: + if (wait_gp_loops == KICK_READER_LOOPS) { + smp_mb_master(); + wait_gp_loops = 0; + } + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + /* wait_gp unlocks/locks registry lock. */ wait_gp(); - break; /* only escape switch */ - case KICK_READER_LOOPS: - smp_mb_master(RCU_MB_GROUP); - wait_loops = 0; - break; /* only escape switch */ - default: + wait_gp_loops++; + } else { + /* Temporarily unlock the registry lock. */ + mutex_unlock(&rcu_registry_lock); caa_cpu_relax(); + /* + * Re-lock the registry lock before the + * next loop. + */ + mutex_lock(&rcu_registry_lock); } } #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ @@ -306,29 +377,60 @@ void synchronize_rcu(void) { CDS_LIST_HEAD(cur_snap_readers); CDS_LIST_HEAD(qsreaders); + DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); + struct urcu_waiters waiters; + + /* + * 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. + * The implicit memory barrier before urcu_wait_add() + * orders prior memory accesses of threads put into the wait + * queue before their insertion into the wait queue. + */ + if (urcu_wait_add(&gp_waiters, &wait) != 0) { + /* Not first in queue: will be awakened by another thread. */ + urcu_adaptative_busy_wait(&wait); + /* Order following memory accesses after grace period. */ + cmm_smp_mb(); + return; + } + /* 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); + + mutex_lock(&rcu_registry_lock); + if (cds_list_empty(®istry)) goto out; - /* All threads should read qparity before accessing data structure - * where new ptr points to. Must be done within rcu_gp_lock because it - * iterates on reader threads.*/ + /* + * All threads should read qparity before accessing data structure + * where new ptr points to. Must be done within rcu_registry_lock + * because it iterates on reader threads. + */ /* Write new ptr before changing the qparity */ - smp_mb_master(RCU_MB_GROUP); + smp_mb_master(); /* * Wait for readers to observe original parity or be quiescent. + * wait_for_readers() can release and grab again rcu_registry_lock + * interally. */ wait_for_readers(®istry, &cur_snap_readers, &qsreaders); /* * Must finish waiting for quiescent state for original parity before - * committing next rcu_gp_ctr update to memory. Failure to do so could + * 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. + * URCU_TLS(rcu_reader).ctr before store to rcu_gp.ctr. */ cmm_barrier(); @@ -340,13 +442,13 @@ 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_PHASE); + CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE); /* - * Must commit rcu_gp_ctr update to memory before waiting for quiescent + * 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 before load rcu_reader ctr. + * compiler-order of store to rcu_gp.ctr before load rcu_reader ctr. */ cmm_barrier(); @@ -360,6 +462,8 @@ void synchronize_rcu(void) /* * Wait for readers to observe new parity or be quiescent. + * wait_for_readers() can release and grab again rcu_registry_lock + * interally. */ wait_for_readers(&cur_snap_readers, NULL, &qsreaders); @@ -368,12 +472,22 @@ void synchronize_rcu(void) */ cds_list_splice(&qsreaders, ®istry); - /* Finish waiting for reader threads before letting the old ptr being - * freed. Must be done within rcu_gp_lock because it iterates on reader - * threads. */ - smp_mb_master(RCU_MB_GROUP); + /* + * Finish waiting for reader threads before letting the old ptr + * being freed. Must be done within rcu_registry_lock because it + * iterates on reader threads. + */ + smp_mb_master(); out: + mutex_unlock(&rcu_registry_lock); mutex_unlock(&rcu_gp_lock); + + /* + * Wakeup waiters only after we have completed the grace period + * and have ensured the memory barriers at the end of the grace + * period have been issued. + */ + urcu_wake_all_waiters(&waiters); } /* @@ -390,33 +504,46 @@ void rcu_read_unlock(void) _rcu_read_unlock(); } +int rcu_read_ongoing(void) +{ + return _rcu_read_ongoing(); +} + void rcu_register_thread(void) { URCU_TLS(rcu_reader).tid = pthread_self(); assert(URCU_TLS(rcu_reader).need_mb == 0); assert(!(URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK)); - mutex_lock(&rcu_gp_lock); + mutex_lock(&rcu_registry_lock); + assert(!URCU_TLS(rcu_reader).registered); + URCU_TLS(rcu_reader).registered = 1; rcu_init(); /* In case gcc does not support constructor attribute */ cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); - mutex_unlock(&rcu_gp_lock); + mutex_unlock(&rcu_registry_lock); } void rcu_unregister_thread(void) { - mutex_lock(&rcu_gp_lock); + mutex_lock(&rcu_registry_lock); + assert(URCU_TLS(rcu_reader).registered); + URCU_TLS(rcu_reader).registered = 0; cds_list_del(&URCU_TLS(rcu_reader).node); - mutex_unlock(&rcu_gp_lock); + mutex_unlock(&rcu_registry_lock); } #ifdef RCU_MEMBARRIER void rcu_init(void) { + int ret; + if (init_done) return; init_done = 1; - if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY)) + ret = membarrier(MEMBARRIER_CMD_QUERY, 0); + if (ret >= 0 && (ret & MEMBARRIER_CMD_SHARED)) { rcu_has_sys_membarrier = 1; + } } #endif @@ -437,9 +564,9 @@ static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context) * rcu_init constructor. Called when the library is linked, but also when * reader threads are calling rcu_register_thread(). * Should only be called by a single thread at a given time. This is ensured by - * holing the rcu_gp_lock from rcu_register_thread() or by running at library - * load time, which should not be executed by multiple threads nor concurrently - * with rcu_register_thread() anyway. + * holing the rcu_registry_lock from rcu_register_thread() or by running + * at library load time, which should not be executed by multiple + * threads nor concurrently with rcu_register_thread() anyway. */ void rcu_init(void) { @@ -460,14 +587,14 @@ void rcu_init(void) void rcu_exit(void) { - struct sigaction act; - int ret; - - ret = sigaction(SIGRCU, NULL, &act); - if (ret) - urcu_die(errno); - assert(act.sa_sigaction == sigrcu_handler); - assert(cds_list_empty(®istry)); + /* + * Don't unregister the SIGRCU signal handler anymore, because + * call_rcu threads could still be using it shortly before the + * application exits. + * Assertion disabled because call_rcu threads are now rcu + * readers, and left running at exit. + * assert(cds_list_empty(®istry)); + */ } #endif /* #ifdef RCU_SIGNAL */