X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=69ebcaa9cb0fbfa07a264ab94fa5261513c72424;hp=e6ff0f349e9e4fef17d6d366b5e7197acb841b84;hb=9ba261bd496f2dfac38a16e341259553335dd165;hpb=fd189fa57fa46b28d59275476993f6a730cde086 diff --git a/urcu.c b/urcu.c index e6ff0f3..69ebcaa 100644 --- a/urcu.c +++ b/urcu.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 @@ -61,6 +62,24 @@ */ #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 + +#define MEMBARRIER_EXPEDITED (1 << 0) +#define MEMBARRIER_DELAYED (1 << 1) +#define MEMBARRIER_QUERY (1 << 16) + #ifdef RCU_MEMBARRIER static int init_done; int rcu_has_sys_membarrier; @@ -82,16 +101,7 @@ void __attribute__((destructor)) rcu_exit(void); #endif 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. - */ -unsigned long rcu_gp_ctr = RCU_GP_COUNT; +struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT }; /* * Written to only by each individual reader. Read by both the reader and the @@ -106,6 +116,12 @@ 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; @@ -141,7 +157,7 @@ static void mutex_unlock(pthread_mutex_t *mutex) static void smp_mb_master(int group) { if (caa_likely(rcu_has_sys_membarrier)) - membarrier(MEMBARRIER_EXPEDITED); + (void) membarrier(MEMBARRIER_EXPEDITED); else cmm_smp_mb(); } @@ -210,8 +226,8 @@ 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, + if (uatomic_read(&rcu_gp.futex) == -1) + futex_async(&rcu_gp.futex, FUTEX_WAIT, -1, NULL, NULL, 0); } @@ -225,12 +241,12 @@ static void wait_for_readers(struct cds_list_head *input_readers, /* * Wait for each thread URCU_TLS(rcu_reader).ctr to either * indicate quiescence (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); + uatomic_dec(&rcu_gp.futex); /* Write futex before read reader_gp */ smp_mb_master(RCU_MB_GROUP); } @@ -263,7 +279,7 @@ static void wait_for_readers(struct cds_list_head *input_readers, if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ smp_mb_master(RCU_MB_GROUP); - uatomic_set(&rcu_gp_futex, 0); + uatomic_set(&rcu_gp.futex, 0); } break; } else { @@ -282,7 +298,7 @@ static void wait_for_readers(struct cds_list_head *input_readers, if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ smp_mb_master(RCU_MB_GROUP); - uatomic_set(&rcu_gp_futex, 0); + uatomic_set(&rcu_gp.futex, 0); } break; } else { @@ -306,9 +322,34 @@ 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); + if (cds_list_empty(®istry)) goto out; @@ -325,10 +366,10 @@ void synchronize_rcu(void) /* * 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 +381,13 @@ 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(); @@ -374,6 +415,13 @@ void synchronize_rcu(void) smp_mb_master(RCU_MB_GROUP); out: 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); } /* @@ -390,6 +438,11 @@ 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(); @@ -460,14 +513,14 @@ 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 */