X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=1aa00fec9278929996fed4183ebe2acf40d5b61f;hp=b4a5a7db948b8d57a03960747c5257d9631b1c7c;hb=a4922ed92bea8e5552a3e66b7dd7b4721b754c90;hpb=06f22bdbb0c4c4d5db42a2e2dc35818aa61415be diff --git a/urcu.c b/urcu.c index b4a5a7d..1aa00fe 100644 --- a/urcu.c +++ b/urcu.c @@ -24,22 +24,67 @@ */ #define _BSD_SOURCE +#define _GNU_SOURCE +#define _LGPL_SOURCE +#define _DEFAULT_SOURCE #include #include #include #include #include +#include #include #include #include -#include "urcu-static.h" +#include "urcu/wfcqueue.h" +#include "urcu/map/urcu.h" +#include "urcu/static/urcu.h" +#include "urcu-pointer.h" +#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 #include "urcu.h" +#define _LGPL_SOURCE + +/* + * 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 10 loops waiting for it. + */ +#define KICK_READER_LOOPS 10 + +/* + * Active attempts to check for reader Q.S. before calling futex(). + */ +#define RCU_QS_ACTIVE_ATTEMPTS 100 + +/* + * RCU_MEMBARRIER is only possibly available on Linux. + */ +#if defined(RCU_MEMBARRIER) && defined(__linux__) +#include +#endif + +/* If the headers do not support SYS_membarrier, fall back on RCU_MB */ +#ifdef SYS_membarrier +# define membarrier(...) syscall(SYS_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 has_sys_membarrier; +int rcu_has_sys_membarrier; void __attribute__((constructor)) rcu_init(void); #endif @@ -57,30 +102,36 @@ 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; - -int 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 * writers. */ -struct rcu_reader __thread rcu_reader; +DEFINE_URCU_TLS(struct rcu_reader, rcu_reader); -#ifdef DEBUG_YIELD -unsigned int yield_active; -unsigned int __thread rand_yield; -#endif +static CDS_LIST_HEAD(registry); -static 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) { @@ -88,23 +139,18 @@ 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 (CAA_LOAD_SHARED(rcu_reader.need_mb)) { + if (ret != EBUSY && ret != EINTR) + urcu_die(ret); + if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) { cmm_smp_mb(); - _CAA_STORE_SHARED(rcu_reader.need_mb, 0); + _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 */ } @@ -114,24 +160,22 @@ 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); } #ifdef RCU_MEMBARRIER -static void smp_mb_master(int group) +static void smp_mb_master(void) { - if (likely(has_sys_membarrier)) - membarrier(MEMBARRIER_EXPEDITED); + if (caa_likely(rcu_has_sys_membarrier)) + (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(); } @@ -146,7 +190,7 @@ static void force_mb_all_readers(void) * Ask for each threads to execute a cmm_smp_mb() so we can consider the * compiler barriers around rcu read lock as real memory barriers. */ - if (list_empty(®istry)) + if (cds_list_empty(®istry)) return; /* * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs @@ -154,8 +198,8 @@ static void force_mb_all_readers(void) * safe and don't assume anything : we use cmm_smp_mc() to make sure the * cache flush is enforced. */ - list_for_each_entry(index, ®istry, node) { - CAA_STORE_SHARED(index->need_mb, 1); + cds_list_for_each_entry(index, ®istry, node) { + CMM_STORE_SHARED(index->need_mb, 1); pthread_kill(index->tid, SIGRCU); } /* @@ -171,16 +215,16 @@ static void force_mb_all_readers(void) * relevant bug report. For Linux kernels, we recommend getting * the Linux Test Project (LTP). */ - list_for_each_entry(index, ®istry, node) { - while (CAA_LOAD_SHARED(index->need_mb)) { + 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(); } @@ -192,126 +236,208 @@ static void smp_mb_master(int group) static void wait_gp(void) { /* Read reader_gp before read futex */ - smp_mb_master(RCU_MB_GROUP); - if (uatomic_read(&gp_futex) == -1) - futex_async(&gp_futex, FUTEX_WAIT, -1, - NULL, NULL, 0); + smp_mb_master(); + if (uatomic_read(&rcu_gp.futex) != -1) + return; + while (futex_async(&rcu_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); + } + } } -void update_counter_and_wait(void) +/* + * 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) { - LIST_HEAD(qsreaders); - int wait_loops = 0; + unsigned int wait_loops = 0; struct rcu_reader *index, *tmp; - - /* Switch parity: 0 -> 1, 1 -> 0 */ - CAA_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE); - - /* - * 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. - */ - cmm_barrier(); - - /* - * - * 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(); +#ifdef HAS_INCOHERENT_CACHES + unsigned int wait_gp_loops = 0; +#endif /* HAS_INCOHERENT_CACHES */ /* - * 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++; - 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_dec(&rcu_gp.futex); /* Write futex before read reader_gp */ - smp_mb_master(RCU_MB_GROUP); + smp_mb_master(); } - list_for_each_entry_safe(index, tmp, ®istry, node) { - if (!rcu_gp_ongoing(&index->ctr)) - 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; + } } #ifndef HAS_INCOHERENT_CACHES - if (list_empty(®istry)) { - if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + if (cds_list_empty(input_readers)) { + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ - smp_mb_master(RCU_MB_GROUP); - uatomic_set(&gp_futex, 0); + smp_mb_master(); + uatomic_set(&rcu_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 caa_cpu_relax(); + /* Re-lock the registry lock before the next loop. */ + mutex_lock(&rcu_registry_lock); } #else /* #ifndef HAS_INCOHERENT_CACHES */ /* * BUSY-LOOP. Force the reader thread to commit its - * rcu_reader.ctr update to memory if we wait for too long. + * URCU_TLS(rcu_reader).ctr update to memory if we wait + * for too long. */ - if (list_empty(®istry)) { - if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + if (cds_list_empty(input_readers)) { + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ - smp_mb_master(RCU_MB_GROUP); - uatomic_set(&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; + } + /* Temporarily unlock the registry lock. */ + mutex_unlock(&rcu_registry_lock); + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { 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 { caa_cpu_relax(); } + /* Re-lock the registry lock before the next loop. */ + mutex_lock(&rcu_registry_lock); } #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } - /* put back the reader list in the registry */ - list_splice(&qsreaders, ®istry); } 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); - if (list_empty(®istry)) + /* + * 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 previous parity to be empty of readers. + * Wait for readers to observe original parity or be quiescent. + * wait_for_readers() can release and grab again rcu_registry_lock + * interally. */ - update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */ + wait_for_readers(®istry, &cur_snap_readers, &qsreaders); /* - * Must finish waiting for quiescent state for parity 0 before - * committing next rcu_gp_ctr update to memory. Failure to do so could + * Must finish waiting for quiescent state for original parity 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 - * rcu_reader ctr before store to rcu_gp_ctr. + * URCU_TLS(rcu_reader).ctr before store to rcu_gp.ctr. + */ + cmm_barrier(); + + /* + * 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 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. */ cmm_barrier(); /* + * * 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. @@ -319,16 +445,33 @@ 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() can release and grab again rcu_registry_lock + * interally. + */ + 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 - * 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); } /* @@ -345,33 +488,46 @@ void rcu_read_unlock(void) _rcu_read_unlock(); } +int rcu_read_ongoing(void) +{ + return _rcu_read_ongoing(); +} + void rcu_register_thread(void) { - rcu_reader.tid = pthread_self(); - assert(rcu_reader.need_mb == 0); - assert(!(rcu_reader.ctr & RCU_GP_CTR_NEST_MASK)); + 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 */ - list_add(&rcu_reader.node, ®istry); - mutex_unlock(&rcu_gp_lock); + cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); + mutex_unlock(&rcu_registry_lock); } void rcu_unregister_thread(void) { - mutex_lock(&rcu_gp_lock); - list_del(&rcu_reader.node); - mutex_unlock(&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_registry_lock); } #ifdef RCU_MEMBARRIER void rcu_init(void) { + int ret; + if (init_done) return; init_done = 1; - if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY)) - has_sys_membarrier = 1; + ret = membarrier(MEMBARRIER_CMD_QUERY, 0); + if (ret >= 0 && (ret & MEMBARRIER_CMD_SHARED)) { + rcu_has_sys_membarrier = 1; + } } #endif @@ -384,7 +540,7 @@ static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context) * executed on. */ cmm_smp_mb(); - _CAA_STORE_SHARED(rcu_reader.need_mb, 0); + _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0); cmm_smp_mb(); } @@ -392,9 +548,9 @@ 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) { @@ -409,23 +565,25 @@ void rcu_init(void) act.sa_flags = SA_SIGINFO | SA_RESTART; sigemptyset(&act.sa_mask); ret = sigaction(SIGRCU, &act, NULL); - if (ret) { - perror("Error in sigaction"); - exit(-1); - } + if (ret) + urcu_die(errno); } void rcu_exit(void) { - struct sigaction act; - int ret; - - ret = sigaction(SIGRCU, NULL, &act); - if (ret) { - perror("Error in sigaction"); - exit(-1); - } - assert(act.sa_sigaction == sigrcu_handler); - assert(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 */ + +DEFINE_RCU_FLAVOR(rcu_flavor); + +#include "urcu-call-rcu-impl.h" +#include "urcu-defer-impl.h"