/***************************************************************************** Copyright (c) 1995, 2011, Oracle and/or its affiliates. All Rights Reserved. Copyright (c) 2008, Google Inc. Portions of this file contain modifications contributed and copyrighted by Google, Inc. Those modifications are gratefully acknowledged and are described briefly in the InnoDB documentation. The contributions by Google are incorporated with their permission, and subject to the conditions contained in the file COPYING.Google. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA *****************************************************************************/ /**************************************************//** @file sync/sync0sync.cc Mutex, the basic synchronization primitive Created 9/5/1995 Heikki Tuuri *******************************************************/ #include "sync0sync.h" #ifdef UNIV_NONINL #include "sync0sync.ic" #endif #include "sync0rw.h" #include "buf0buf.h" #include "srv0srv.h" #include "buf0types.h" #include "os0sync.h" /* for HAVE_ATOMIC_BUILTINS */ #ifdef UNIV_SYNC_DEBUG # include "srv0start.h" /* srv_is_being_started */ #endif /* UNIV_SYNC_DEBUG */ #include "ha_prototypes.h" /* REASONS FOR IMPLEMENTING THE SPIN LOCK MUTEX ============================================ Semaphore operations in operating systems are slow: Solaris on a 1993 Sparc takes 3 microseconds (us) for a lock-unlock pair and Windows NT on a 1995 Pentium takes 20 microseconds for a lock-unlock pair. Therefore, we have to implement our own efficient spin lock mutex. Future operating systems may provide efficient spin locks, but we cannot count on that. Another reason for implementing a spin lock is that on multiprocessor systems it can be more efficient for a processor to run a loop waiting for the semaphore to be released than to switch to a different thread. A thread switch takes 25 us on both platforms mentioned above. See Gray and Reuter's book Transaction processing for background. How long should the spin loop last before suspending the thread? On a uniprocessor, spinning does not help at all, because if the thread owning the mutex is not executing, it cannot be released. Spinning actually wastes resources. On a multiprocessor, we do not know if the thread owning the mutex is executing or not. Thus it would make sense to spin as long as the operation guarded by the mutex would typically last assuming that the thread is executing. If the mutex is not released by that time, we may assume that the thread owning the mutex is not executing and suspend the waiting thread. A typical operation (where no i/o involved) guarded by a mutex or a read-write lock may last 1 - 20 us on the current Pentium platform. The longest operations are the binary searches on an index node. We conclude that the best choice is to set the spin time at 20 us. Then the system should work well on a multiprocessor. On a uniprocessor we have to make sure that thread swithches due to mutex collisions are not frequent, i.e., they do not happen every 100 us or so, because that wastes too much resources. If the thread switches are not frequent, the 20 us wasted in spin loop is not too much. Empirical studies on the effect of spin time should be done for different platforms. IMPLEMENTATION OF THE MUTEX =========================== For background, see Curt Schimmel's book on Unix implementation on modern architectures. The key points in the implementation are atomicity and serialization of memory accesses. The test-and-set instruction (XCHG in Pentium) must be atomic. As new processors may have weak memory models, also serialization of memory references may be necessary. The successor of Pentium, P6, has at least one mode where the memory model is weak. As far as we know, in Pentium all memory accesses are serialized in the program order and we do not have to worry about the memory model. On other processors there are special machine instructions called a fence, memory barrier, or storage barrier (STBAR in Sparc), which can be used to serialize the memory accesses to happen in program order relative to the fence instruction. Leslie Lamport has devised a "bakery algorithm" to implement a mutex without the atomic test-and-set, but his algorithm should be modified for weak memory models. We do not use Lamport's algorithm, because we guess it is slower than the atomic test-and-set. Our mutex implementation works as follows: After that we perform the atomic test-and-set instruction on the memory word. If the test returns zero, we know we got the lock first. If the test returns not zero, some other thread was quicker and got the lock: then we spin in a loop reading the memory word, waiting it to become zero. It is wise to just read the word in the loop, not perform numerous test-and-set instructions, because they generate memory traffic between the cache and the main memory. The read loop can just access the cache, saving bus bandwidth. If we cannot acquire the mutex lock in the specified time, we reserve a cell in the wait array, set the waiters byte in the mutex to 1. To avoid a race condition, after setting the waiters byte and before suspending the waiting thread, we still have to check that the mutex is reserved, because it may have happened that the thread which was holding the mutex has just released it and did not see the waiters byte set to 1, a case which would lead the other thread to an infinite wait. LEMMA 1: After a thread resets the event of a mutex (or rw_lock), some ======= thread will eventually call os_event_set() on that particular event. Thus no infinite wait is possible in this case. Proof: After making the reservation the thread sets the waiters field in the mutex to 1. Then it checks that the mutex is still reserved by some thread, or it reserves the mutex for itself. In any case, some thread (which may be also some earlier thread, not necessarily the one currently holding the mutex) will set the waiters field to 0 in mutex_exit, and then call os_event_set() with the mutex as an argument. Q.E.D. LEMMA 2: If an os_event_set() call is made after some thread has called ======= the os_event_reset() and before it starts wait on that event, the call will not be lost to the second thread. This is true even if there is an intervening call to os_event_reset() by another thread. Thus no infinite wait is possible in this case. Proof (non-windows platforms): os_event_reset() returns a monotonically increasing value of signal_count. This value is increased at every call of os_event_set() If thread A has called os_event_reset() followed by thread B calling os_event_set() and then some other thread C calling os_event_reset(), the is_set flag of the event will be set to FALSE; but now if thread A calls os_event_wait_low() with the signal_count value returned from the earlier call of os_event_reset(), it will return immediately without waiting. Q.E.D. Proof (windows): If there is a writer thread which is forced to wait for the lock, it may be able to set the state of rw_lock to RW_LOCK_WAIT_EX The design of rw_lock ensures that there is one and only one thread that is able to change the state to RW_LOCK_WAIT_EX and this thread is guaranteed to acquire the lock after it is released by the current holders and before any other waiter gets the lock. On windows this thread waits on a separate event i.e.: wait_ex_event. Since only one thread can wait on this event there is no chance of this event getting reset before the writer starts wait on it. Therefore, this thread is guaranteed to catch the os_set_event() signalled unconditionally at the release of the lock. Q.E.D. */ /* Number of spin waits on mutexes: for performance monitoring */ /** The number of iterations in the mutex_spin_wait() spin loop. Intended for performance monitoring. */ static ib_int64_t mutex_spin_round_count = 0; /** The number of mutex_spin_wait() calls. Intended for performance monitoring. */ static ib_int64_t mutex_spin_wait_count = 0; /** The number of OS waits in mutex_spin_wait(). Intended for performance monitoring. */ static ib_int64_t mutex_os_wait_count = 0; /** The number of mutex_exit() calls. Intended for performance monitoring. */ UNIV_INTERN ib_int64_t mutex_exit_count = 0; /** This variable is set to TRUE when sync_init is called */ UNIV_INTERN ibool sync_initialized = FALSE; #ifdef UNIV_SYNC_DEBUG /** An acquired mutex or rw-lock and its level in the latching order */ typedef struct sync_level_struct sync_level_t; /** Mutexes or rw-locks held by a thread */ typedef struct sync_thread_struct sync_thread_t; /** The latch levels currently owned by threads are stored in this data structure; the size of this array is OS_THREAD_MAX_N */ UNIV_INTERN sync_thread_t* sync_thread_level_arrays; /** Mutex protecting sync_thread_level_arrays */ UNIV_INTERN mutex_t sync_thread_mutex; # ifdef UNIV_PFS_MUTEX UNIV_INTERN mysql_pfs_key_t sync_thread_mutex_key; # endif /* UNIV_PFS_MUTEX */ #endif /* UNIV_SYNC_DEBUG */ /** Global list of database mutexes (not OS mutexes) created. */ UNIV_INTERN ut_list_base_node_t mutex_list; /** Mutex protecting the mutex_list variable */ UNIV_INTERN mutex_t mutex_list_mutex; #ifdef UNIV_PFS_MUTEX UNIV_INTERN mysql_pfs_key_t mutex_list_mutex_key; #endif /* UNIV_PFS_MUTEX */ #ifdef UNIV_SYNC_DEBUG /** Latching order checks start when this is set TRUE */ UNIV_INTERN ibool sync_order_checks_on = FALSE; /** Number of slots reserved for each OS thread in the sync level array */ static const ulint SYNC_THREAD_N_LEVELS = 10000; typedef struct sync_arr_struct sync_arr_t; /** Array for tracking sync levels per thread. */ struct sync_arr_struct { ulint in_use; /*!< Number of active cells */ ulint n_elems; /*!< Number of elements in the array */ ulint max_elems; /*!< Maximum elements */ ulint next_free; /*!< ULINT_UNDEFINED or index of next free slot */ sync_level_t* elems; /*!< Array elements */ }; /** Mutexes or rw-locks held by a thread */ struct sync_thread_struct{ os_thread_id_t id; /*!< OS thread id */ sync_arr_t* levels; /*!< level array for this thread; if this is NULL this slot is unused */ }; /** An acquired mutex or rw-lock and its level in the latching order */ struct sync_level_struct{ void* latch; /*!< pointer to a mutex or an rw-lock; NULL means that the slot is empty */ ulint level; /*!< level of the latch in the latching order. This field is overloaded to serve as a node in a linked list of free nodes too. When latch == NULL then this will contain the ordinal value of the next free element */ }; #endif /* UNIV_SYNC_DEBUG */ /******************************************************************//** Creates, or rather, initializes a mutex object in a specified memory location (which must be appropriately aligned). The mutex is initialized in the reset state. Explicit freeing of the mutex with mutex_free is necessary only if the memory block containing it is freed. */ UNIV_INTERN void mutex_create_func( /*==============*/ mutex_t* mutex, /*!< in: pointer to memory */ #ifdef UNIV_DEBUG const char* cmutex_name, /*!< in: mutex name */ # ifdef UNIV_SYNC_DEBUG ulint level, /*!< in: level */ # endif /* UNIV_SYNC_DEBUG */ #endif /* UNIV_DEBUG */ const char* cfile_name, /*!< in: file name where created */ ulint cline) /*!< in: file line where created */ { #if defined(HAVE_ATOMIC_BUILTINS) mutex_reset_lock_word(mutex); #else os_fast_mutex_init(PFS_NOT_INSTRUMENTED, &mutex->os_fast_mutex); mutex->lock_word = 0; #endif mutex->event = os_event_create(NULL); mutex_set_waiters(mutex, 0); #ifdef UNIV_DEBUG mutex->magic_n = MUTEX_MAGIC_N; #endif /* UNIV_DEBUG */ #ifdef UNIV_SYNC_DEBUG mutex->line = 0; mutex->file_name = "not yet reserved"; mutex->level = level; #endif /* UNIV_SYNC_DEBUG */ mutex->cfile_name = cfile_name; mutex->cline = cline; mutex->count_os_wait = 0; #ifdef UNIV_DEBUG mutex->cmutex_name= cmutex_name; mutex->count_using= 0; mutex->mutex_type= 0; mutex->lspent_time= 0; mutex->lmax_spent_time= 0; mutex->count_spin_loop= 0; mutex->count_spin_rounds= 0; mutex->count_os_yield= 0; #endif /* UNIV_DEBUG */ /* Check that lock_word is aligned; this is important on Intel */ ut_ad(((ulint)(&(mutex->lock_word))) % 4 == 0); /* NOTE! The very first mutexes are not put to the mutex list */ if ((mutex == &mutex_list_mutex) #ifdef UNIV_SYNC_DEBUG || (mutex == &sync_thread_mutex) #endif /* UNIV_SYNC_DEBUG */ ) { return; } mutex_enter(&mutex_list_mutex); ut_ad(UT_LIST_GET_LEN(mutex_list) == 0 || UT_LIST_GET_FIRST(mutex_list)->magic_n == MUTEX_MAGIC_N); UT_LIST_ADD_FIRST(list, mutex_list, mutex); mutex_exit(&mutex_list_mutex); } /******************************************************************//** NOTE! Use the corresponding macro mutex_free(), not directly this function! Calling this function is obligatory only if the memory buffer containing the mutex is freed. Removes a mutex object from the mutex list. The mutex is checked to be in the reset state. */ UNIV_INTERN void mutex_free_func( /*============*/ mutex_t* mutex) /*!< in: mutex */ { ut_ad(mutex_validate(mutex)); ut_a(mutex_get_lock_word(mutex) == 0); ut_a(mutex_get_waiters(mutex) == 0); #ifdef UNIV_MEM_DEBUG if (mutex == &mem_hash_mutex) { ut_ad(UT_LIST_GET_LEN(mutex_list) == 1); ut_ad(UT_LIST_GET_FIRST(mutex_list) == &mem_hash_mutex); UT_LIST_REMOVE(list, mutex_list, mutex); goto func_exit; } #endif /* UNIV_MEM_DEBUG */ if (mutex != &mutex_list_mutex #ifdef UNIV_SYNC_DEBUG && mutex != &sync_thread_mutex #endif /* UNIV_SYNC_DEBUG */ ) { mutex_enter(&mutex_list_mutex); ut_ad(!UT_LIST_GET_PREV(list, mutex) || UT_LIST_GET_PREV(list, mutex)->magic_n == MUTEX_MAGIC_N); ut_ad(!UT_LIST_GET_NEXT(list, mutex) || UT_LIST_GET_NEXT(list, mutex)->magic_n == MUTEX_MAGIC_N); UT_LIST_REMOVE(list, mutex_list, mutex); mutex_exit(&mutex_list_mutex); } os_event_free(mutex->event); #ifdef UNIV_MEM_DEBUG func_exit: #endif /* UNIV_MEM_DEBUG */ #if !defined(HAVE_ATOMIC_BUILTINS) os_fast_mutex_free(&(mutex->os_fast_mutex)); #endif /* If we free the mutex protecting the mutex list (freeing is not necessary), we have to reset the magic number AFTER removing it from the list. */ #ifdef UNIV_DEBUG mutex->magic_n = 0; #endif /* UNIV_DEBUG */ return; } /********************************************************************//** NOTE! Use the corresponding macro in the header file, not this function directly. Tries to lock the mutex for the current thread. If the lock is not acquired immediately, returns with return value 1. @return 0 if succeed, 1 if not */ UNIV_INTERN ulint mutex_enter_nowait_func( /*====================*/ mutex_t* mutex, /*!< in: pointer to mutex */ const char* file_name __attribute__((unused)), /*!< in: file name where mutex requested */ ulint line __attribute__((unused))) /*!< in: line where requested */ { ut_ad(mutex_validate(mutex)); if (!mutex_test_and_set(mutex)) { ut_d(mutex->thread_id = os_thread_get_curr_id()); #ifdef UNIV_SYNC_DEBUG mutex_set_debug_info(mutex, file_name, line); #endif return(0); /* Succeeded! */ } return(1); } #ifdef UNIV_DEBUG /******************************************************************//** Checks that the mutex has been initialized. @return TRUE */ UNIV_INTERN ibool mutex_validate( /*===========*/ const mutex_t* mutex) /*!< in: mutex */ { ut_a(mutex); ut_a(mutex->magic_n == MUTEX_MAGIC_N); return(TRUE); } /******************************************************************//** Checks that the current thread owns the mutex. Works only in the debug version. @return TRUE if owns */ UNIV_INTERN ibool mutex_own( /*======*/ const mutex_t* mutex) /*!< in: mutex */ { ut_ad(mutex_validate(mutex)); return(mutex_get_lock_word(mutex) == 1 && os_thread_eq(mutex->thread_id, os_thread_get_curr_id())); } #endif /* UNIV_DEBUG */ /******************************************************************//** Sets the waiters field in a mutex. */ UNIV_INTERN void mutex_set_waiters( /*==============*/ mutex_t* mutex, /*!< in: mutex */ ulint n) /*!< in: value to set */ { volatile ulint* ptr; /* declared volatile to ensure that the value is stored to memory */ ut_ad(mutex); ptr = &(mutex->waiters); *ptr = n; /* Here we assume that the write of a single word in memory is atomic */ } /******************************************************************//** Reserves a mutex for the current thread. If the mutex is reserved, the function spins a preset time (controlled by SYNC_SPIN_ROUNDS), waiting for the mutex before suspending the thread. */ UNIV_INTERN void mutex_spin_wait( /*============*/ mutex_t* mutex, /*!< in: pointer to mutex */ const char* file_name, /*!< in: file name where mutex requested */ ulint line) /*!< in: line where requested */ { ulint i; /* spin round count */ ulint index; /* index of the reserved wait cell */ sync_array_t* sync_arr; ut_ad(mutex); /* This update is not thread safe, but we don't mind if the count isn't exact. Moved out of ifdef that follows because we are willing to sacrifice the cost of counting this as the data is valuable. Count the number of calls to mutex_spin_wait. */ mutex_spin_wait_count++; mutex_loop: i = 0; /* Spin waiting for the lock word to become zero. Note that we do not have to assume that the read access to the lock word is atomic, as the actual locking is always committed with atomic test-and-set. In reality, however, all processors probably have an atomic read of a memory word. */ spin_loop: ut_d(mutex->count_spin_loop++); while (mutex_get_lock_word(mutex) != 0 && i < SYNC_SPIN_ROUNDS) { if (srv_spin_wait_delay) { ut_delay(ut_rnd_interval(0, srv_spin_wait_delay)); } i++; } if (i == SYNC_SPIN_ROUNDS) { #ifdef UNIV_DEBUG mutex->count_os_yield++; #endif /* UNIV_DEBUG */ os_thread_yield(); } #ifdef UNIV_SRV_PRINT_LATCH_WAITS fprintf(stderr, "Thread %lu spin wait mutex at %p" " cfile %s cline %lu rnds %lu\n", (ulong) os_thread_pf(os_thread_get_curr_id()), (void*) mutex, innobase_basename(mutex->cfile_name), (ulong) mutex->cline, (ulong) i); #endif mutex_spin_round_count += i; ut_d(mutex->count_spin_rounds += i); if (mutex_test_and_set(mutex) == 0) { /* Succeeded! */ ut_d(mutex->thread_id = os_thread_get_curr_id()); #ifdef UNIV_SYNC_DEBUG mutex_set_debug_info(mutex, file_name, line); #endif return; } /* We may end up with a situation where lock_word is 0 but the OS fast mutex is still reserved. On FreeBSD the OS does not seem to schedule a thread which is constantly calling pthread_mutex_trylock (in mutex_test_and_set implementation). Then we could end up spinning here indefinitely. The following 'i++' stops this infinite spin. */ i++; if (i < SYNC_SPIN_ROUNDS) { goto spin_loop; } sync_arr = sync_array_get(); sync_array_reserve_cell( sync_arr, mutex, SYNC_MUTEX, file_name, line, &index); /* The memory order of the array reservation and the change in the waiters field is important: when we suspend a thread, we first reserve the cell and then set waiters field to 1. When threads are released in mutex_exit, the waiters field is first set to zero and then the event is set to the signaled state. */ mutex_set_waiters(mutex, 1); /* Try to reserve still a few times */ for (i = 0; i < 4; i++) { if (mutex_test_and_set(mutex) == 0) { /* Succeeded! Free the reserved wait cell */ sync_array_free_cell(sync_arr, index); ut_d(mutex->thread_id = os_thread_get_curr_id()); #ifdef UNIV_SYNC_DEBUG mutex_set_debug_info(mutex, file_name, line); #endif #ifdef UNIV_SRV_PRINT_LATCH_WAITS fprintf(stderr, "Thread %lu spin wait succeeds at 2:" " mutex at %p\n", (ulong) os_thread_pf(os_thread_get_curr_id()), (void*) mutex); #endif return; /* Note that in this case we leave the waiters field set to 1. We cannot reset it to zero, as we do not know if there are other waiters. */ } } /* Now we know that there has been some thread holding the mutex after the change in the wait array and the waiters field was made. Now there is no risk of infinite wait on the event. */ #ifdef UNIV_SRV_PRINT_LATCH_WAITS fprintf(stderr, "Thread %lu OS wait mutex at %p cfile %s cline %lu rnds %lu\n", (ulong) os_thread_pf(os_thread_get_curr_id()), (void*) mutex, innobase_basename(mutex->cfile_name), (ulong) mutex->cline, (ulong) i); #endif mutex_os_wait_count++; mutex->count_os_wait++; sync_array_wait_event(sync_arr, index); goto mutex_loop; } /******************************************************************//** Releases the threads waiting in the primary wait array for this mutex. */ UNIV_INTERN void mutex_signal_object( /*================*/ mutex_t* mutex) /*!< in: mutex */ { mutex_set_waiters(mutex, 0); /* The memory order of resetting the waiters field and signaling the object is important. See LEMMA 1 above. */ os_event_set(mutex->event); sync_array_object_signalled(); } #ifdef UNIV_SYNC_DEBUG /******************************************************************//** Sets the debug information for a reserved mutex. */ UNIV_INTERN void mutex_set_debug_info( /*=================*/ mutex_t* mutex, /*!< in: mutex */ const char* file_name, /*!< in: file where requested */ ulint line) /*!< in: line where requested */ { ut_ad(mutex); ut_ad(file_name); sync_thread_add_level(mutex, mutex->level, FALSE); mutex->file_name = file_name; mutex->line = line; } /******************************************************************//** Gets the debug information for a reserved mutex. */ UNIV_INTERN void mutex_get_debug_info( /*=================*/ mutex_t* mutex, /*!< in: mutex */ const char** file_name, /*!< out: file where requested */ ulint* line, /*!< out: line where requested */ os_thread_id_t* thread_id) /*!< out: id of the thread which owns the mutex */ { ut_ad(mutex); *file_name = mutex->file_name; *line = mutex->line; *thread_id = mutex->thread_id; } /******************************************************************//** Prints debug info of currently reserved mutexes. */ static void mutex_list_print_info( /*==================*/ FILE* file) /*!< in: file where to print */ { mutex_t* mutex; const char* file_name; ulint line; os_thread_id_t thread_id; ulint count = 0; fputs("----------\n" "MUTEX INFO\n" "----------\n", file); mutex_enter(&mutex_list_mutex); mutex = UT_LIST_GET_FIRST(mutex_list); while (mutex != NULL) { count++; if (mutex_get_lock_word(mutex) != 0) { mutex_get_debug_info(mutex, &file_name, &line, &thread_id); fprintf(file, "Locked mutex: addr %p thread %ld" " file %s line %ld\n", (void*) mutex, os_thread_pf(thread_id), file_name, line); } mutex = UT_LIST_GET_NEXT(list, mutex); } fprintf(file, "Total number of mutexes %ld\n", count); mutex_exit(&mutex_list_mutex); } /******************************************************************//** Counts currently reserved mutexes. Works only in the debug version. @return number of reserved mutexes */ UNIV_INTERN ulint mutex_n_reserved(void) /*==================*/ { mutex_t* mutex; ulint count = 0; mutex_enter(&mutex_list_mutex); for (mutex = UT_LIST_GET_FIRST(mutex_list); mutex != NULL; mutex = UT_LIST_GET_NEXT(list, mutex)) { if (mutex_get_lock_word(mutex) != 0) { count++; } } mutex_exit(&mutex_list_mutex); ut_a(count >= 1); /* Subtract one, because this function itself was holding one mutex (mutex_list_mutex) */ return(count - 1); } /******************************************************************//** Returns TRUE if no mutex or rw-lock is currently locked. Works only in the debug version. @return TRUE if no mutexes and rw-locks reserved */ UNIV_INTERN ibool sync_all_freed(void) /*================*/ { return(mutex_n_reserved() + rw_lock_n_locked() == 0); } /******************************************************************//** Looks for the thread slot for the calling thread. @return pointer to thread slot, NULL if not found */ static sync_thread_t* sync_thread_level_arrays_find_slot(void) /*====================================*/ { ulint i; os_thread_id_t id; id = os_thread_get_curr_id(); for (i = 0; i < OS_THREAD_MAX_N; i++) { sync_thread_t* slot; slot = &sync_thread_level_arrays[i]; if (slot->levels && os_thread_eq(slot->id, id)) { return(slot); } } return(NULL); } /******************************************************************//** Looks for an unused thread slot. @return pointer to thread slot */ static sync_thread_t* sync_thread_level_arrays_find_free(void) /*====================================*/ { ulint i; for (i = 0; i < OS_THREAD_MAX_N; i++) { sync_thread_t* slot; slot = &sync_thread_level_arrays[i]; if (slot->levels == NULL) { return(slot); } } return(NULL); } /******************************************************************//** Print warning. */ static void sync_print_warning( /*===============*/ const sync_level_t* slot) /*!< in: slot for which to print warning */ { mutex_t* mutex; mutex = static_cast(slot->latch); if (mutex->magic_n == MUTEX_MAGIC_N) { fprintf(stderr, "Mutex created at %s %lu\n", innobase_basename(mutex->cfile_name), (ulong) mutex->cline); if (mutex_get_lock_word(mutex) != 0) { ulint line; const char* file_name; os_thread_id_t thread_id; mutex_get_debug_info( mutex, &file_name, &line, &thread_id); fprintf(stderr, "InnoDB: Locked mutex:" " addr %p thread %ld file %s line %ld\n", (void*) mutex, os_thread_pf(thread_id), file_name, (ulong) line); } else { fputs("Not locked\n", stderr); } } else { rw_lock_t* lock; lock = static_cast(slot->latch); rw_lock_print(lock); } } /******************************************************************//** Checks if all the level values stored in the level array are greater than the given limit. @return TRUE if all greater */ static ibool sync_thread_levels_g( /*=================*/ sync_arr_t* arr, /*!< in: pointer to level array for an OS thread */ ulint limit, /*!< in: level limit */ ulint warn) /*!< in: TRUE=display a diagnostic message */ { ulint i; for (i = 0; i < arr->n_elems; i++) { const sync_level_t* slot; slot = &arr->elems[i]; if (slot->latch != NULL && slot->level <= limit) { if (warn) { fprintf(stderr, "InnoDB: sync levels should be" " > %lu but a level is %lu\n", (ulong) limit, (ulong) slot->level); sync_print_warning(slot); } return(FALSE); } } return(TRUE); } /******************************************************************//** Checks if the level value is stored in the level array. @return slot if found or NULL */ static const sync_level_t* sync_thread_levels_contain( /*=======================*/ sync_arr_t* arr, /*!< in: pointer to level array for an OS thread */ ulint level) /*!< in: level */ { ulint i; for (i = 0; i < arr->n_elems; i++) { const sync_level_t* slot; slot = &arr->elems[i]; if (slot->latch != NULL && slot->level == level) { return(slot); } } return(NULL); } /******************************************************************//** Checks if the level array for the current thread contains a mutex or rw-latch at the specified level. @return a matching latch, or NULL if not found */ UNIV_INTERN void* sync_thread_levels_contains( /*========================*/ ulint level) /*!< in: latching order level (SYNC_DICT, ...)*/ { ulint i; sync_arr_t* arr; sync_thread_t* thread_slot; if (!sync_order_checks_on) { return(NULL); } mutex_enter(&sync_thread_mutex); thread_slot = sync_thread_level_arrays_find_slot(); if (thread_slot == NULL) { mutex_exit(&sync_thread_mutex); return(NULL); } arr = thread_slot->levels; for (i = 0; i < arr->n_elems; i++) { sync_level_t* slot; slot = &arr->elems[i]; if (slot->latch != NULL && slot->level == level) { mutex_exit(&sync_thread_mutex); return(slot->latch); } } mutex_exit(&sync_thread_mutex); return(NULL); } /******************************************************************//** Checks that the level array for the current thread is empty. @return a latch, or NULL if empty except the exceptions specified below */ UNIV_INTERN void* sync_thread_levels_nonempty_gen( /*============================*/ ibool dict_mutex_allowed) /*!< in: TRUE if dictionary mutex is allowed to be owned by the thread */ { ulint i; sync_arr_t* arr; sync_thread_t* thread_slot; if (!sync_order_checks_on) { return(NULL); } mutex_enter(&sync_thread_mutex); thread_slot = sync_thread_level_arrays_find_slot(); if (thread_slot == NULL) { mutex_exit(&sync_thread_mutex); return(NULL); } arr = thread_slot->levels; for (i = 0; i < arr->n_elems; ++i) { const sync_level_t* slot; slot = &arr->elems[i]; if (slot->latch != NULL && (!dict_mutex_allowed || (slot->level != SYNC_DICT && slot->level != SYNC_DICT_OPERATION && slot->level != SYNC_FTS_CACHE))) { mutex_exit(&sync_thread_mutex); ut_error; return(slot->latch); } } mutex_exit(&sync_thread_mutex); return(NULL); } /******************************************************************//** Checks if the level array for the current thread is empty, except for the btr_search_latch. @return a latch, or NULL if empty except the exceptions specified below */ UNIV_INTERN void* sync_thread_levels_nonempty_trx( /*============================*/ ibool has_search_latch) /*!< in: TRUE if and only if the thread is supposed to hold btr_search_latch */ { ulint i; sync_arr_t* arr; sync_thread_t* thread_slot; if (!sync_order_checks_on) { return(NULL); } ut_a(!has_search_latch || sync_thread_levels_contains(SYNC_SEARCH_SYS)); mutex_enter(&sync_thread_mutex); thread_slot = sync_thread_level_arrays_find_slot(); if (thread_slot == NULL) { mutex_exit(&sync_thread_mutex); return(NULL); } arr = thread_slot->levels; for (i = 0; i < arr->n_elems; ++i) { const sync_level_t* slot; slot = &arr->elems[i]; if (slot->latch != NULL && (!has_search_latch || slot->level != SYNC_SEARCH_SYS)) { mutex_exit(&sync_thread_mutex); ut_error; return(slot->latch); } } mutex_exit(&sync_thread_mutex); return(NULL); } /******************************************************************//** Adds a latch and its level in the thread level array. Allocates the memory for the array if called first time for this OS thread. Makes the checks against other latch levels stored in the array for this thread. */ UNIV_INTERN void sync_thread_add_level( /*==================*/ void* latch, /*!< in: pointer to a mutex or an rw-lock */ ulint level, /*!< in: level in the latching order; if SYNC_LEVEL_VARYING, nothing is done */ ibool relock) /*!< in: TRUE if re-entering an x-lock */ { ulint i; sync_level_t* slot; sync_arr_t* array; sync_thread_t* thread_slot; if (!sync_order_checks_on) { return; } if ((latch == (void*) &sync_thread_mutex) || (latch == (void*) &mutex_list_mutex) || (latch == (void*) &rw_lock_debug_mutex) || (latch == (void*) &rw_lock_list_mutex)) { return; } if (level == SYNC_LEVEL_VARYING) { return; } mutex_enter(&sync_thread_mutex); thread_slot = sync_thread_level_arrays_find_slot(); if (thread_slot == NULL) { ulint sz; sz = sizeof(*array) + (sizeof(*array->elems) * SYNC_THREAD_N_LEVELS); /* We have to allocate the level array for a new thread */ array = static_cast(calloc(sz, sizeof(char))); ut_a(array != NULL); array->next_free = ULINT_UNDEFINED; array->max_elems = SYNC_THREAD_N_LEVELS; array->elems = (sync_level_t*) &array[1]; thread_slot = sync_thread_level_arrays_find_free(); thread_slot->levels = array; thread_slot->id = os_thread_get_curr_id(); } array = thread_slot->levels; if (relock) { goto levels_ok; } /* NOTE that there is a problem with _NODE and _LEAF levels: if the B-tree height changes, then a leaf can change to an internal node or the other way around. We do not know at present if this can cause unnecessary assertion failures below. */ switch (level) { case SYNC_NO_ORDER_CHECK: case SYNC_EXTERN_STORAGE: case SYNC_TREE_NODE_FROM_HASH: /* Do no order checking */ break; case SYNC_TRX_SYS_HEADER: if (srv_is_being_started) { /* This is violated during trx_sys_create_rsegs() when creating additional rollback segments when upgrading in innobase_start_or_create_for_mysql(). */ break; } case SYNC_MEM_POOL: case SYNC_MEM_HASH: case SYNC_RECV: case SYNC_FTS_BG_THREADS: case SYNC_WORK_QUEUE: case SYNC_FTS_OPTIMIZE: case SYNC_FTS_CACHE: case SYNC_FTS_CACHE_INIT: case SYNC_LOG: case SYNC_LOG_FLUSH_ORDER: case SYNC_ANY_LATCH: case SYNC_FILE_FORMAT_TAG: case SYNC_DOUBLEWRITE: case SYNC_SEARCH_SYS: case SYNC_THREADS: case SYNC_LOCK_SYS: case SYNC_LOCK_WAIT_SYS: case SYNC_TRX_SYS: case SYNC_IBUF_BITMAP_MUTEX: case SYNC_RSEG: case SYNC_TRX_UNDO: case SYNC_PURGE_LATCH: case SYNC_PURGE_QUEUE: case SYNC_DICT_AUTOINC_MUTEX: case SYNC_DICT_OPERATION: case SYNC_DICT_HEADER: case SYNC_TRX_I_S_RWLOCK: case SYNC_TRX_I_S_LAST_READ: case SYNC_IBUF_MUTEX: if (!sync_thread_levels_g(array, level, TRUE)) { fprintf(stderr, "InnoDB: sync_thread_levels_g(array, %lu)" " does not hold!\n", level); ut_error; } break; case SYNC_TRX: /* Either the thread must own the lock_sys->mutex, or it is allowed to own only ONE trx->mutex. */ if (!sync_thread_levels_g(array, level, FALSE)) { ut_a(sync_thread_levels_g(array, level - 1, TRUE)); ut_a(sync_thread_levels_contain(array, SYNC_LOCK_SYS)); } break; case SYNC_BUF_FLUSH_LIST: case SYNC_BUF_POOL: /* We can have multiple mutexes of this type therefore we can only check whether the greater than condition holds. */ if (!sync_thread_levels_g(array, level-1, TRUE)) { fprintf(stderr, "InnoDB: sync_thread_levels_g(array, %lu)" " does not hold!\n", level-1); ut_error; } break; case SYNC_BUF_PAGE_HASH: /* Multiple page_hash locks are only allowed during buf_validate and that is where buf_pool mutex is already held. */ /* Fall through */ case SYNC_BUF_BLOCK: /* Either the thread must own the buffer pool mutex (buf_pool->mutex), or it is allowed to latch only ONE buffer block (block->mutex or buf_pool->zip_mutex). */ if (!sync_thread_levels_g(array, level, FALSE)) { ut_a(sync_thread_levels_g(array, level - 1, TRUE)); ut_a(sync_thread_levels_contain(array, SYNC_BUF_POOL)); } break; case SYNC_REC_LOCK: if (sync_thread_levels_contain(array, SYNC_LOCK_SYS)) { ut_a(sync_thread_levels_g(array, SYNC_REC_LOCK - 1, TRUE)); } else { ut_a(sync_thread_levels_g(array, SYNC_REC_LOCK, TRUE)); } break; case SYNC_IBUF_BITMAP: /* Either the thread must own the master mutex to all the bitmap pages, or it is allowed to latch only ONE bitmap page. */ if (sync_thread_levels_contain(array, SYNC_IBUF_BITMAP_MUTEX)) { ut_a(sync_thread_levels_g(array, SYNC_IBUF_BITMAP - 1, TRUE)); } else { /* This is violated during trx_sys_create_rsegs() when creating additional rollback segments when upgrading in innobase_start_or_create_for_mysql(). */ ut_a(srv_is_being_started || sync_thread_levels_g(array, SYNC_IBUF_BITMAP, TRUE)); } break; case SYNC_FSP_PAGE: ut_a(sync_thread_levels_contain(array, SYNC_FSP)); break; case SYNC_FSP: ut_a(sync_thread_levels_contain(array, SYNC_FSP) || sync_thread_levels_g(array, SYNC_FSP, TRUE)); break; case SYNC_TRX_UNDO_PAGE: /* Purge is allowed to read in as many UNDO pages as it likes, there was a bogus rule here earlier that forced the caller to acquire the purge_sys_t::mutex. The purge mutex did not really protect anything because it was only ever acquired by the single purge thread. The purge thread can read the UNDO pages without any covering mutex. */ ut_a(sync_thread_levels_contain(array, SYNC_TRX_UNDO) || sync_thread_levels_contain(array, SYNC_RSEG) || sync_thread_levels_g(array, level - 1, TRUE)); break; case SYNC_RSEG_HEADER: ut_a(sync_thread_levels_contain(array, SYNC_RSEG)); break; case SYNC_RSEG_HEADER_NEW: ut_a(sync_thread_levels_contain(array, SYNC_FSP_PAGE)); break; case SYNC_TREE_NODE: ut_a(sync_thread_levels_contain(array, SYNC_INDEX_TREE) || sync_thread_levels_contain(array, SYNC_DICT_OPERATION) || sync_thread_levels_g(array, SYNC_TREE_NODE - 1, TRUE)); break; case SYNC_TREE_NODE_NEW: ut_a(sync_thread_levels_contain(array, SYNC_FSP_PAGE)); break; case SYNC_INDEX_TREE: ut_a(sync_thread_levels_g(array, SYNC_TREE_NODE - 1, TRUE)); break; case SYNC_IBUF_TREE_NODE: ut_a(sync_thread_levels_contain(array, SYNC_IBUF_INDEX_TREE) || sync_thread_levels_g(array, SYNC_IBUF_TREE_NODE - 1, TRUE)); break; case SYNC_IBUF_TREE_NODE_NEW: /* ibuf_add_free_page() allocates new pages for the change buffer while only holding the tablespace x-latch. These pre-allocated new pages may only be taken in use while holding ibuf_mutex, in btr_page_alloc_for_ibuf(). */ ut_a(sync_thread_levels_contain(array, SYNC_IBUF_MUTEX) || sync_thread_levels_contain(array, SYNC_FSP)); break; case SYNC_IBUF_INDEX_TREE: if (sync_thread_levels_contain(array, SYNC_FSP)) { ut_a(sync_thread_levels_g(array, level - 1, TRUE)); } else { ut_a(sync_thread_levels_g( array, SYNC_IBUF_TREE_NODE - 1, TRUE)); } break; case SYNC_IBUF_PESS_INSERT_MUTEX: ut_a(sync_thread_levels_g(array, SYNC_FSP - 1, TRUE)); ut_a(!sync_thread_levels_contain(array, SYNC_IBUF_MUTEX)); break; case SYNC_IBUF_HEADER: ut_a(sync_thread_levels_g(array, SYNC_FSP - 1, TRUE)); ut_a(!sync_thread_levels_contain(array, SYNC_IBUF_MUTEX)); ut_a(!sync_thread_levels_contain(array, SYNC_IBUF_PESS_INSERT_MUTEX)); break; case SYNC_DICT: #ifdef UNIV_DEBUG ut_a(buf_debug_prints || sync_thread_levels_g(array, SYNC_DICT, TRUE)); #else /* UNIV_DEBUG */ ut_a(sync_thread_levels_g(array, SYNC_DICT, TRUE)); #endif /* UNIV_DEBUG */ break; default: ut_error; } levels_ok: if (array->next_free == ULINT_UNDEFINED) { ut_a(array->n_elems < array->max_elems); i = array->n_elems++; } else { i = array->next_free; array->next_free = array->elems[i].level; } ut_a(i < array->n_elems); ut_a(i != ULINT_UNDEFINED); ++array->in_use; slot = &array->elems[i]; ut_a(slot->latch == NULL); slot->latch = latch; slot->level = level; mutex_exit(&sync_thread_mutex); } /******************************************************************//** Removes a latch from the thread level array if it is found there. @return TRUE if found in the array; it is no error if the latch is not found, as we presently are not able to determine the level for every latch reservation the program does */ UNIV_INTERN ibool sync_thread_reset_level( /*====================*/ void* latch) /*!< in: pointer to a mutex or an rw-lock */ { sync_arr_t* array; sync_thread_t* thread_slot; ulint i; if (!sync_order_checks_on) { return(FALSE); } if ((latch == (void*) &sync_thread_mutex) || (latch == (void*) &mutex_list_mutex) || (latch == (void*) &rw_lock_debug_mutex) || (latch == (void*) &rw_lock_list_mutex)) { return(FALSE); } mutex_enter(&sync_thread_mutex); thread_slot = sync_thread_level_arrays_find_slot(); if (thread_slot == NULL) { ut_error; mutex_exit(&sync_thread_mutex); return(FALSE); } array = thread_slot->levels; for (i = 0; i < array->n_elems; i++) { sync_level_t* slot; slot = &array->elems[i]; if (slot->latch != latch) { continue; } slot->latch = NULL; /* Update the free slot list. See comment in sync_level_t for the level field. */ slot->level = array->next_free; array->next_free = i; ut_a(array->in_use >= 1); --array->in_use; /* If all cells are idle then reset the free list. The assumption is that this will save time when we need to scan up to n_elems. */ if (array->in_use == 0) { array->n_elems = 0; array->next_free = ULINT_UNDEFINED; } mutex_exit(&sync_thread_mutex); return(TRUE); } if (((mutex_t*) latch)->magic_n != MUTEX_MAGIC_N) { rw_lock_t* rw_lock; rw_lock = (rw_lock_t*) latch; if (rw_lock->level == SYNC_LEVEL_VARYING) { mutex_exit(&sync_thread_mutex); return(TRUE); } } ut_error; mutex_exit(&sync_thread_mutex); return(FALSE); } #endif /* UNIV_SYNC_DEBUG */ /******************************************************************//** Initializes the synchronization data structures. */ UNIV_INTERN void sync_init(void) /*===========*/ { ut_a(sync_initialized == FALSE); sync_initialized = TRUE; sync_array_init(OS_THREAD_MAX_N); #ifdef UNIV_SYNC_DEBUG /* Create the thread latch level array where the latch levels are stored for each OS thread */ sync_thread_level_arrays = static_cast( calloc(sizeof(sync_thread_t), OS_THREAD_MAX_N)); ut_a(sync_thread_level_arrays != NULL); #endif /* UNIV_SYNC_DEBUG */ /* Init the mutex list and create the mutex to protect it. */ UT_LIST_INIT(mutex_list); mutex_create(mutex_list_mutex_key, &mutex_list_mutex, SYNC_NO_ORDER_CHECK); #ifdef UNIV_SYNC_DEBUG mutex_create(sync_thread_mutex_key, &sync_thread_mutex, SYNC_NO_ORDER_CHECK); #endif /* UNIV_SYNC_DEBUG */ /* Init the rw-lock list and create the mutex to protect it. */ UT_LIST_INIT(rw_lock_list); mutex_create(rw_lock_list_mutex_key, &rw_lock_list_mutex, SYNC_NO_ORDER_CHECK); #ifdef UNIV_SYNC_DEBUG mutex_create(rw_lock_debug_mutex_key, &rw_lock_debug_mutex, SYNC_NO_ORDER_CHECK); rw_lock_debug_event = os_event_create(NULL); rw_lock_debug_waiters = FALSE; #endif /* UNIV_SYNC_DEBUG */ } #ifdef UNIV_SYNC_DEBUG /******************************************************************//** Frees all debug memory. */ static void sync_thread_level_arrays_free(void) /*===============================*/ { ulint i; for (i = 0; i < OS_THREAD_MAX_N; i++) { sync_thread_t* slot; slot = &sync_thread_level_arrays[i]; /* If this slot was allocated then free the slot memory too. */ if (slot->levels != NULL) { free(slot->levels); slot->levels = NULL; } } free(sync_thread_level_arrays); sync_thread_level_arrays = NULL; } #endif /* UNIV_SYNC_DEBUG */ /******************************************************************//** Frees the resources in InnoDB's own synchronization data structures. Use os_sync_free() after calling this. */ UNIV_INTERN void sync_close(void) /*===========*/ { mutex_t* mutex; sync_array_close(); for (mutex = UT_LIST_GET_FIRST(mutex_list); mutex != NULL; /* No op */) { #ifdef UNIV_MEM_DEBUG if (mutex == &mem_hash_mutex) { mutex = UT_LIST_GET_NEXT(list, mutex); continue; } #endif /* UNIV_MEM_DEBUG */ mutex_free(mutex); mutex = UT_LIST_GET_FIRST(mutex_list); } mutex_free(&mutex_list_mutex); #ifdef UNIV_SYNC_DEBUG mutex_free(&sync_thread_mutex); /* Switch latching order checks on in sync0sync.cc */ sync_order_checks_on = FALSE; sync_thread_level_arrays_free(); #endif /* UNIV_SYNC_DEBUG */ sync_initialized = FALSE; } /*******************************************************************//** Prints wait info of the sync system. */ UNIV_INTERN void sync_print_wait_info( /*=================*/ FILE* file) /*!< in: file where to print */ { #ifdef UNIV_SYNC_DEBUG fprintf(file, "Mutex exits "UINT64PF", " "rws exits "UINT64PF", rwx exits "UINT64PF"\n", mutex_exit_count, rw_s_exit_count, rw_x_exit_count); #endif fprintf(file, "Mutex spin waits "UINT64PF", rounds "UINT64PF", " "OS waits "UINT64PF"\n" "RW-shared spins "UINT64PF", rounds "UINT64PF", " "OS waits "UINT64PF"\n" "RW-excl spins "UINT64PF", rounds "UINT64PF", " "OS waits "UINT64PF"\n", mutex_spin_wait_count, mutex_spin_round_count, mutex_os_wait_count, rw_s_spin_wait_count, rw_s_spin_round_count, rw_s_os_wait_count, rw_x_spin_wait_count, rw_x_spin_round_count, rw_x_os_wait_count); fprintf(file, "Spin rounds per wait: %.2f mutex, %.2f RW-shared, " "%.2f RW-excl\n", (double) mutex_spin_round_count / (mutex_spin_wait_count ? mutex_spin_wait_count : 1), (double) rw_s_spin_round_count / (rw_s_spin_wait_count ? rw_s_spin_wait_count : 1), (double) rw_x_spin_round_count / (rw_x_spin_wait_count ? rw_x_spin_wait_count : 1)); } /*******************************************************************//** Prints info of the sync system. */ UNIV_INTERN void sync_print( /*=======*/ FILE* file) /*!< in: file where to print */ { #ifdef UNIV_SYNC_DEBUG mutex_list_print_info(file); rw_lock_list_print_info(file); #endif /* UNIV_SYNC_DEBUG */ sync_array_print(file); sync_print_wait_info(file); }