diff options
| -rw-r--r-- | config.h.cmake | 1 | ||||
| -rw-r--r-- | configure.cmake | 1 | ||||
| -rw-r--r-- | configure.in | 2 | ||||
| -rw-r--r-- | include/my_pthread.h | 106 | ||||
| -rw-r--r-- | include/mysql/psi/mysql_thread.h | 88 | ||||
| -rw-r--r-- | mysys/thr_rwlock.c | 137 |
6 files changed, 185 insertions, 150 deletions
diff --git a/config.h.cmake b/config.h.cmake index c484edb65a5..7047cc6bbf5 100644 --- a/config.h.cmake +++ b/config.h.cmake @@ -220,7 +220,6 @@ #cmakedefine HAVE_PTHREAD_KEY_DELETE 1 #cmakedefine HAVE_PTHREAD_KILL 1 #cmakedefine HAVE_PTHREAD_RWLOCK_RDLOCK 1 -#cmakedefine HAVE_PTHREAD_RWLOCKATTR_SETKIND_NP 1 #cmakedefine HAVE_PTHREAD_SETPRIO_NP 1 #cmakedefine HAVE_PTHREAD_SETSCHEDPARAM 1 #cmakedefine HAVE_PTHREAD_SIGMASK 1 diff --git a/configure.cmake b/configure.cmake index c2e1dc4647b..91c39fc5b09 100644 --- a/configure.cmake +++ b/configure.cmake @@ -346,7 +346,6 @@ CHECK_FUNCTION_EXISTS (pthread_condattr_setclock HAVE_PTHREAD_CONDATTR_SETCLOCK) CHECK_FUNCTION_EXISTS (pthread_init HAVE_PTHREAD_INIT) CHECK_FUNCTION_EXISTS (pthread_key_delete HAVE_PTHREAD_KEY_DELETE) CHECK_FUNCTION_EXISTS (pthread_rwlock_rdlock HAVE_PTHREAD_RWLOCK_RDLOCK) -CHECK_FUNCTION_EXISTS (pthread_rwlockattr_setkind_np HAVE_PTHREAD_RWLOCKATTR_SETKIND_NP) CHECK_FUNCTION_EXISTS (pthread_sigmask HAVE_PTHREAD_SIGMASK) CHECK_FUNCTION_EXISTS (pthread_threadmask HAVE_PTHREAD_THREADMASK) CHECK_FUNCTION_EXISTS (pthread_yield_np HAVE_PTHREAD_YIELD_NP) diff --git a/configure.in b/configure.in index 1f56d958a7f..48385ba2491 100644 --- a/configure.in +++ b/configure.in @@ -2169,7 +2169,7 @@ AC_CHECK_FUNCS(alarm bfill bmove bsearch bzero \ mkstemp mlockall perror poll pread pthread_attr_create mmap mmap64 getpagesize \ pthread_attr_getstacksize pthread_attr_setstacksize pthread_condattr_create \ pthread_getsequence_np pthread_key_delete pthread_rwlock_rdlock \ - pthread_rwlockattr_setkind_np pthread_sigmask \ + pthread_sigmask \ readlink realpath rename rint rwlock_init setupterm \ shmget shmat shmdt shmctl sigaction sigemptyset sigaddset \ sighold sigset sigthreadmask port_create sleep thr_yield \ diff --git a/include/my_pthread.h b/include/my_pthread.h index 5cf181596ad..27ab5ba23fe 100644 --- a/include/my_pthread.h +++ b/include/my_pthread.h @@ -594,7 +594,7 @@ int my_pthread_fastmutex_lock(my_pthread_fastmutex_t *mp); /* Use our own version of read/write locks */ #define NEED_MY_RW_LOCK 1 #define rw_lock_t my_rw_lock_t -#define my_rwlock_init(A,B) my_rw_init((A), 0) +#define my_rwlock_init(A,B) my_rw_init((A)) #define rw_rdlock(A) my_rw_rdlock((A)) #define rw_wrlock(A) my_rw_wrlock((A)) #define rw_tryrdlock(A) my_rw_tryrdlock((A)) @@ -606,49 +606,82 @@ int my_pthread_fastmutex_lock(my_pthread_fastmutex_t *mp); #endif /* USE_MUTEX_INSTEAD_OF_RW_LOCKS */ -/* - Portable read-write locks which prefer readers. - - Required by some algorithms in order to provide correctness. +/** + Portable implementation of special type of read-write locks. + + These locks have two properties which are unusual for rwlocks: + 1) They "prefer readers" in the sense that they do not allow + situations in which rwlock is rd-locked and there is a + pending rd-lock which is blocked (e.g. due to pending + request for wr-lock). + This is a stronger guarantee than one which is provided for + PTHREAD_RWLOCK_PREFER_READER_NP rwlocks in Linux. + MDL subsystem deadlock detector relies on this property for + its correctness. + 2) They are optimized for uncontended wr-lock/unlock case. + This is scenario in which they are most oftenly used + within MDL subsystem. Optimizing for it gives significant + performance improvements in some of tests involving many + connections. + + Another important requirement imposed on this type of rwlock + by the MDL subsystem is that it should be OK to destroy rwlock + object which is in unlocked state even though some threads might + have not yet fully left unlock operation for it (of course there + is an external guarantee that no thread will try to lock rwlock + which is destroyed). + Putting it another way the unlock operation should not access + rwlock data after changing its state to unlocked. + + TODO/FIXME: We should consider alleviating this requirement as + it blocks us from doing certain performance optimizations. */ -#if defined(HAVE_PTHREAD_RWLOCK_RDLOCK) && defined(HAVE_PTHREAD_RWLOCKATTR_SETKIND_NP) -/* - On systems which have a way to specify that readers should - be preferred through attribute mechanism (e.g. Linux) we use - system implementation of read/write locks. -*/ -#define rw_pr_lock_t pthread_rwlock_t +typedef struct st_rw_pr_lock_t { + /** + Lock which protects the structure. + Also held for the duration of wr-lock. + */ + pthread_mutex_t lock; + /** + Condition variable which is used to wake-up + writers waiting for readers to go away. + */ + pthread_cond_t no_active_readers; + /** Number of active readers. */ + uint active_readers; + /** Number of writers waiting for readers to go away. */ + uint writers_waiting_readers; + /** Indicates whether there is an active writer. */ + my_bool active_writer; +#ifdef SAFE_MUTEX + /** Thread holding wr-lock (for debug purposes only). */ + pthread_t writer_thread; +#endif +} rw_pr_lock_t; + extern int rw_pr_init(rw_pr_lock_t *); -#define rw_pr_rdlock(A) pthread_rwlock_rdlock(A) -#define rw_pr_wrlock(A) pthread_rwlock_wrlock(A) -#define rw_pr_tryrdlock(A) pthread_rwlock_tryrdlock(A) -#define rw_pr_trywrlock(A) pthread_rwlock_trywrlock(A) -#define rw_pr_unlock(A) pthread_rwlock_unlock(A) -#define rw_pr_destroy(A) pthread_rwlock_destroy(A) +extern int rw_pr_rdlock(rw_pr_lock_t *); +extern int rw_pr_wrlock(rw_pr_lock_t *); +extern int rw_pr_unlock(rw_pr_lock_t *); +extern int rw_pr_destroy(rw_pr_lock_t *); +#ifdef SAFE_MUTEX +#define rw_pr_lock_assert_write_owner(A) \ + DBUG_ASSERT((A)->active_writer && pthread_equal(pthread_self(), \ + (A)->writer_thread)) +#define rw_pr_lock_assert_not_write_owner(A) \ + DBUG_ASSERT(! (A)->active_writer || ! pthread_equal(pthread_self(), \ + (A)->writer_thread)) +#else #define rw_pr_lock_assert_write_owner(A) #define rw_pr_lock_assert_not_write_owner(A) -#else -/* Otherwise we have to use our own implementation of read/write locks. */ -#define NEED_MY_RW_LOCK 1 -struct st_my_rw_lock_t; -#define rw_pr_lock_t my_rw_lock_t -extern int rw_pr_init(struct st_my_rw_lock_t *); -#define rw_pr_rdlock(A) my_rw_rdlock((A)) -#define rw_pr_wrlock(A) my_rw_wrlock((A)) -#define rw_pr_tryrdlock(A) my_rw_tryrdlock((A)) -#define rw_pr_trywrlock(A) my_rw_trywrlock((A)) -#define rw_pr_unlock(A) my_rw_unlock((A)) -#define rw_pr_destroy(A) my_rw_destroy((A)) -#define rw_pr_lock_assert_write_owner(A) my_rw_lock_assert_write_owner((A)) -#define rw_pr_lock_assert_not_write_owner(A) my_rw_lock_assert_not_write_owner((A)) -#endif /* defined(HAVE_PTHREAD_RWLOCK_RDLOCK) && defined(HAVE_PTHREAD_RWLOCKATTR_SETKIND_NP) */ +#endif /* SAFE_MUTEX */ #ifdef NEED_MY_RW_LOCK /* - On systems which don't support native read/write locks, or don't support - read/write locks which prefer readers we have to use own implementation. + On systems which don't support native read/write locks we have + to use own implementation. */ typedef struct st_my_rw_lock_t { pthread_mutex_t lock; /* lock for structure */ @@ -656,13 +689,12 @@ typedef struct st_my_rw_lock_t { pthread_cond_t writers; /* waiting writers */ int state; /* -1:writer,0:free,>0:readers */ int waiters; /* number of waiting writers */ - my_bool prefer_readers; #ifdef SAFE_MUTEX pthread_t write_thread; #endif } my_rw_lock_t; -extern int my_rw_init(my_rw_lock_t *, my_bool *); +extern int my_rw_init(my_rw_lock_t *); extern int my_rw_destroy(my_rw_lock_t *); extern int my_rw_rdlock(my_rw_lock_t *); extern int my_rw_wrlock(my_rw_lock_t *); diff --git a/include/mysql/psi/mysql_thread.h b/include/mysql/psi/mysql_thread.h index 60b4f5d6ef4..5b8ea3dc5dc 100644 --- a/include/mysql/psi/mysql_thread.h +++ b/include/mysql/psi/mysql_thread.h @@ -141,9 +141,7 @@ typedef struct st_mysql_rwlock mysql_rwlock_t; @c mysql_prlock_t is a drop-in replacement for @c rw_pr_lock_t. @sa mysql_prlock_init @sa mysql_prlock_rdlock - @sa mysql_prlock_tryrdlock @sa mysql_prlock_wrlock - @sa mysql_prlock_trywrlock @sa mysql_prlock_unlock @sa mysql_prlock_destroy */ @@ -421,20 +419,6 @@ typedef struct st_mysql_cond mysql_cond_t; #endif /** - @def mysql_prlock_tryrdlock(RW) - Instrumented rw_pr_tryrdlock. - @c mysql_prlock_tryrdlock is a drop-in replacement - for @c rw_pr_tryrdlock. -*/ -#ifdef HAVE_PSI_INTERFACE - #define mysql_prlock_tryrdlock(RW) \ - inline_mysql_prlock_tryrdlock(RW, __FILE__, __LINE__) -#else - #define mysql_prlock_tryrdlock(RW) \ - inline_mysql_prlock_tryrdlock(RW) -#endif - -/** @def mysql_rwlock_trywrlock(RW) Instrumented rwlock_trywrlock. @c mysql_rwlock_trywrlock is a drop-in replacement @@ -449,20 +433,6 @@ typedef struct st_mysql_cond mysql_cond_t; #endif /** - @def mysql_prlock_trywrlock(RW) - Instrumented rw_pr_trywrlock. - @c mysql_prlock_trywrlock is a drop-in replacement - for @c rw_pr_trywrlock. -*/ -#ifdef HAVE_PSI_INTERFACE - #define mysql_prlock_trywrlock(RW) \ - inline_mysql_prlock_trywrlock(RW, __FILE__, __LINE__) -#else - #define mysql_prlock_trywrlock(RW) \ - inline_mysql_prlock_trywrlock(RW) -#endif - -/** @def mysql_rwlock_unlock(RW) Instrumented rwlock_unlock. @c mysql_rwlock_unlock is a drop-in replacement @@ -905,35 +875,6 @@ static inline int inline_mysql_rwlock_tryrdlock( return result; } -#ifndef DISABLE_MYSQL_PRLOCK_H -static inline int inline_mysql_prlock_tryrdlock( - mysql_prlock_t *that -#ifdef HAVE_PSI_INTERFACE - , const char *src_file, uint src_line -#endif - ) -{ - int result; -#ifdef HAVE_PSI_INTERFACE - struct PSI_rwlock_locker *locker= NULL; - PSI_rwlock_locker_state state; - if (likely(PSI_server && that->m_psi)) - { - locker= PSI_server->get_thread_rwlock_locker(&state, that->m_psi, - PSI_RWLOCK_TRYREADLOCK); - if (likely(locker != NULL)) - PSI_server->start_rwlock_rdwait(locker, src_file, src_line); - } -#endif - result= rw_pr_tryrdlock(&that->m_prlock); -#ifdef HAVE_PSI_INTERFACE - if (likely(locker != NULL)) - PSI_server->end_rwlock_rdwait(locker, result); -#endif - return result; -} -#endif - static inline int inline_mysql_rwlock_trywrlock( mysql_rwlock_t *that #ifdef HAVE_PSI_INTERFACE @@ -961,35 +902,6 @@ static inline int inline_mysql_rwlock_trywrlock( return result; } -#ifndef DISABLE_MYSQL_PRLOCK_H -static inline int inline_mysql_prlock_trywrlock( - mysql_prlock_t *that -#ifdef HAVE_PSI_INTERFACE - , const char *src_file, uint src_line -#endif - ) -{ - int result; -#ifdef HAVE_PSI_INTERFACE - struct PSI_rwlock_locker *locker= NULL; - PSI_rwlock_locker_state state; - if (likely(PSI_server && that->m_psi)) - { - locker= PSI_server->get_thread_rwlock_locker(&state, that->m_psi, - PSI_RWLOCK_TRYWRITELOCK); - if (likely(locker != NULL)) - PSI_server->start_rwlock_wrwait(locker, src_file, src_line); - } -#endif - result= rw_pr_trywrlock(&that->m_prlock); -#ifdef HAVE_PSI_INTERFACE - if (likely(locker != NULL)) - PSI_server->end_rwlock_wrwait(locker, result); -#endif - return result; -} -#endif - static inline int inline_mysql_rwlock_unlock( mysql_rwlock_t *that) { diff --git a/mysys/thr_rwlock.c b/mysys/thr_rwlock.c index ecd12849822..218cfb251c8 100644 --- a/mysys/thr_rwlock.c +++ b/mysys/thr_rwlock.c @@ -59,7 +59,7 @@ * Mountain View, California 94043 */ -int my_rw_init(my_rw_lock_t *rwp, my_bool *prefer_readers_attr) +int my_rw_init(my_rw_lock_t *rwp) { pthread_condattr_t cond_attr; @@ -74,8 +74,6 @@ int my_rw_init(my_rw_lock_t *rwp, my_bool *prefer_readers_attr) #ifdef SAFE_MUTEX rwp->write_thread = 0; #endif - /* If attribute argument is NULL use default value - prefer writers. */ - rwp->prefer_readers= prefer_readers_attr ? *prefer_readers_attr : FALSE; return(0); } @@ -96,8 +94,7 @@ int my_rw_rdlock(my_rw_lock_t *rwp) pthread_mutex_lock(&rwp->lock); /* active or queued writers */ - while (( rwp->state < 0 ) || - (rwp->waiters && ! rwp->prefer_readers)) + while (( rwp->state < 0 ) || rwp->waiters) pthread_cond_wait( &rwp->readers, &rwp->lock); rwp->state++; @@ -109,8 +106,7 @@ int my_rw_tryrdlock(my_rw_lock_t *rwp) { int res; pthread_mutex_lock(&rwp->lock); - if ((rwp->state < 0 ) || - (rwp->waiters && ! rwp->prefer_readers)) + if ((rwp->state < 0 ) || rwp->waiters) res= EBUSY; /* Can't get lock */ else { @@ -192,30 +188,127 @@ int my_rw_unlock(my_rw_lock_t *rwp) return(0); } +#endif /* defined(NEED_MY_RW_LOCK) */ + -int rw_pr_init(struct st_my_rw_lock_t *rwlock) +int rw_pr_init(rw_pr_lock_t *rwlock) { - my_bool prefer_readers_attr= TRUE; - return my_rw_init(rwlock, &prefer_readers_attr); + pthread_mutex_init(&rwlock->lock, NULL); + pthread_cond_init(&rwlock->no_active_readers, NULL); + rwlock->active_readers= 0; + rwlock->writers_waiting_readers= 0; + rwlock->active_writer= FALSE; +#ifdef SAFE_MUTEX + rwlock->writer_thread= 0; +#endif + return 0; } -#else -/* - We are on system which has native read/write locks which support - preferring of readers. -*/ +int rw_pr_destroy(rw_pr_lock_t *rwlock) +{ + pthread_cond_destroy(&rwlock->no_active_readers); + pthread_mutex_destroy(&rwlock->lock); + return 0; +} -int rw_pr_init(rw_pr_lock_t *rwlock) + +int rw_pr_rdlock(rw_pr_lock_t *rwlock) +{ + pthread_mutex_lock(&rwlock->lock); + /* + The fact that we were able to acquire 'lock' mutex means + that there are no active writers and we can acquire rd-lock. + Increment active readers counter to prevent requests for + wr-lock from succeeding and unlock mutex. + */ + rwlock->active_readers++; + pthread_mutex_unlock(&rwlock->lock); + return 0; +} + + +int rw_pr_wrlock(rw_pr_lock_t *rwlock) { - pthread_rwlockattr_t rwlock_attr; + pthread_mutex_lock(&rwlock->lock); + + if (rwlock->active_readers != 0) + { + /* There are active readers. We have to wait until they are gone. */ + rwlock->writers_waiting_readers++; - pthread_rwlockattr_init(&rwlock_attr); - pthread_rwlockattr_setkind_np(&rwlock_attr, PTHREAD_RWLOCK_PREFER_READER_NP); - pthread_rwlock_init(rwlock, NULL); - pthread_rwlockattr_destroy(&rwlock_attr); + while (rwlock->active_readers != 0) + pthread_cond_wait(&rwlock->no_active_readers, &rwlock->lock); + + rwlock->writers_waiting_readers--; + } + + /* + We own 'lock' mutex so there is no active writers. + Also there are no active readers. + This means that we can grant wr-lock. + Not releasing 'lock' mutex until unlock will block + both requests for rd and wr-locks. + Set 'active_writer' flag to simplify unlock. + + Thanks to the fact wr-lock/unlock in the absence of + contention from readers is essentially mutex lock/unlock + with a few simple checks make this rwlock implementation + wr-lock optimized. + */ + rwlock->active_writer= TRUE; +#ifdef SAFE_MUTEX + rwlock->writer_thread= pthread_self(); +#endif return 0; } -#endif /* defined(NEED_MY_RW_LOCK) */ + +int rw_pr_unlock(rw_pr_lock_t *rwlock) +{ + if (rwlock->active_writer) + { + /* We are unlocking wr-lock. */ +#ifdef SAFE_MUTEX + rwlock->writer_thread= 0; +#endif + rwlock->active_writer= FALSE; + if (rwlock->writers_waiting_readers) + { + /* + Avoid expensive cond signal in case when there is no contention + or it is wr-only. + + Note that from view point of performance it would be better to + signal on the condition variable after unlocking mutex (as it + reduces number of contex switches). + + Unfortunately this would mean that such rwlock can't be safely + used by MDL subsystem, which relies on the fact that it is OK + to destroy rwlock once it is in unlocked state. + */ + pthread_cond_signal(&rwlock->no_active_readers); + } + pthread_mutex_unlock(&rwlock->lock); + } + else + { + /* We are unlocking rd-lock. */ + pthread_mutex_lock(&rwlock->lock); + rwlock->active_readers--; + if (rwlock->active_readers == 0 && + rwlock->writers_waiting_readers) + { + /* + If we are last reader and there are waiting + writers wake them up. + */ + pthread_cond_signal(&rwlock->no_active_readers); + } + pthread_mutex_unlock(&rwlock->lock); + } + return 0; +} + + #endif /* defined(THREAD) */ |