mariadb/storage/innobase/sync/sync0rw.c

/******************************************************
The read-write lock (for thread synchronization)

(c) 1995 Innobase Oy

Created 9/11/1995 Heikki Tuuri
*******************************************************/

#include "sync0rw.h"
#ifdef UNIV_NONINL
#include "sync0rw.ic"
#endif

#include "os0thread.h"
#include "mem0mem.h"
#include "srv0srv.h"

/*
	IMPLEMENTATION OF THE RW_LOCK
	=============================
The status of a rw_lock is held in lock_word. The initial value of lock_word is
X_LOCK_DECR. lock_word is decremented by 1 for each s-lock and by X_LOCK_DECR
for each x-lock. This describes the lock state for each value of lock_word:
 
lock_word == X_LOCK_DECR:      Unlocked.
0 < lock_word < X_LOCK_DECR:   Read locked, no waiting writers.
 			       (X_LOCK_DECR - lock_word) is the
 			       number of readers that hold the lock.
lock_word == 0:		       Write locked
-X_LOCK_DECR < lock_word < 0:  Read locked, with a waiting writer.
 			       (-lock_word) is the number of readers
 			       that hold the lock.
lock_word <= -X_LOCK_DECR:     Recursively write locked. lock_word has been
 			       decremented by X_LOCK_DECR once for each lock,
 			       so the number of locks is:
 			       ((-lock_word) / X_LOCK_DECR) + 1
When lock_word <= -X_LOCK_DECR, we also know that lock_word % X_LOCK_DECR == 0:
other values of lock_word are invalid.
 
The lock_word is always read and updated atomically and consistently, so that
it always represents the state of the lock, and the state of the lock changes
with a single atomic operation. This lock_word holds all of the information
that a thread needs in order to determine if it is eligible to gain the lock
or if it must spin or sleep. The one exception to this is that writer_thread
must be verified before recursive write locks: to solve this scenario, we make
writer_thread readable by all threads, but only writeable by the x-lock holder.

The other members of the lock obey the following rules to remain consistent:
 
pass:		This is only set to 1 to prevent recursive x-locks. It must
 		be set as specified by x_lock caller after the lock_word
 		indicates that the thread holds the lock, but before that
 		thread resumes execution. It must be reset to 0 during the
 		final x_unlock, but before the lock_word status is updated.
 		When an x_lock or move_ownership call wishes to change
 		pass, it must first update the writer_thread appropriately.
writer_thread:	Must be set to the writers thread_id after the lock_word
 		indicates that the thread holds the lock, but before that
 		thread resumes execution. It  must be reset to -1 during the
 		final x_unlock, but before the lock_word status is updated.
 		This ensures that when the lock_word indicates that an x_lock
 		is held, the only legitimate values for writer_thread are -1
 		(x_lock function hasn't completed) or the writer's thread_id.
waiters:	May be set to 1 anytime, but to avoid unnecessary wake-up
 		signals, it should only be set to 1 when there are threads
 		waiting on event. Must be 1 when a writer starts waiting to
 		ensure the current x-locking thread sends a wake-up signal
 		during unlock. May only be reset to 0 immediately before a
 		a wake-up signal is sent to event.
event:		Threads wait on event for read or writer lock when another
 		thread has an x-lock or an x-lock reservation (wait_ex). A
 		thread may only	wait on event after performing the following
 		actions in order:
 		   (1) Record the counter value of event (with os_event_reset).
 		   (2) Set waiters to 1.
 		   (3) Verify lock_word <= 0.
 		(1) must come before (2) to ensure signal is not missed.
 		(2) must come before (3) to ensure a signal is sent.
 		These restrictions force the above ordering.
 		Immediately before sending the wake-up signal, we should:
 		   (1) Verify lock_word == X_LOCK_DECR (unlocked)
 		   (2) Reset waiters to 0.
wait_ex_event:	A thread may only wait on the wait_ex_event after it has
 		performed the following actions in order:
 		   (1) Decrement lock_word by X_LOCK_DECR.
 		   (2) Record counter value of wait_ex_event (os_event_reset,
                        called from sync_array_reserve_cell).
 		   (3) Verify that lock_word < 0.
 		(1) must come first to ensures no other threads become reader
                 or next writer, and notifies unlocker that signal must be sent.
                 (2) must come before (3) to ensure the signal is not missed.
 		These restrictions force the above ordering.
 		Immediately before sending the wake-up signal, we should:
		   Verify lock_word == 0 (waiting thread holds x_lock)
*/


/* number of spin waits on rw-latches,
resulted during shared (read) locks */
ib_longlong	rw_s_spin_wait_count	= 0;
ib_longlong	rw_s_spin_round_count	= 0;

/* number of OS waits on rw-latches,
resulted during shared (read) locks */
ib_longlong	rw_s_os_wait_count	= 0;

/* number of unlocks (that unlock shared locks),
set only when UNIV_SYNC_PERF_STAT is defined */
ib_longlong	rw_s_exit_count		= 0;

/* number of spin waits on rw-latches,
resulted during exclusive (write) locks */
ib_longlong	rw_x_spin_wait_count	= 0;
ib_longlong	rw_x_spin_round_count	= 0;

/* number of OS waits on rw-latches,
resulted during exclusive (write) locks */
ib_longlong	rw_x_os_wait_count	= 0;

/* number of unlocks (that unlock exclusive locks),
set only when UNIV_SYNC_PERF_STAT is defined */
ib_longlong	rw_x_exit_count		= 0;

/* The global list of rw-locks */
rw_lock_list_t	rw_lock_list;
mutex_t		rw_lock_list_mutex;

#ifdef UNIV_SYNC_DEBUG
/* The global mutex which protects debug info lists of all rw-locks.
To modify the debug info list of an rw-lock, this mutex has to be
acquired in addition to the mutex protecting the lock. */

mutex_t		rw_lock_debug_mutex;
os_event_t	rw_lock_debug_event;	/* If deadlock detection does not
					get immediately the mutex, it may
					wait for this event */
ibool		rw_lock_debug_waiters;	/* This is set to TRUE, if there may
					be waiters for the event */

/**********************************************************************
Creates a debug info struct. */
static
rw_lock_debug_t*
rw_lock_debug_create(void);
/*======================*/
/**********************************************************************
Frees a debug info struct. */
static
void
rw_lock_debug_free(
/*===============*/
	rw_lock_debug_t* info);

/**********************************************************************
Creates a debug info struct. */
static
rw_lock_debug_t*
rw_lock_debug_create(void)
/*======================*/
{
	return((rw_lock_debug_t*) mem_alloc(sizeof(rw_lock_debug_t)));
}

/**********************************************************************
Frees a debug info struct. */
static
void
rw_lock_debug_free(
/*===============*/
	rw_lock_debug_t* info)
{
	mem_free(info);
}
#endif /* UNIV_SYNC_DEBUG */

/**********************************************************************
Creates, or rather, initializes an rw-lock object in a specified memory
location (which must be appropriately aligned). The rw-lock is initialized
to the non-locked state. Explicit freeing of the rw-lock with rw_lock_free
is necessary only if the memory block containing it is freed. */

void
rw_lock_create_func(
/*================*/
	rw_lock_t*	lock,		/* in: pointer to memory */
#ifdef UNIV_DEBUG
# ifdef UNIV_SYNC_DEBUG
	ulint		level,		/* in: level */
# endif /* UNIV_SYNC_DEBUG */
	const char*	cmutex_name, 	/* in: mutex name */
#endif /* UNIV_DEBUG */
	const char*	cfile_name,	/* in: file name where created */
	ulint 		cline)		/* in: file line where created */
{
	/* If this is the very first time a synchronization object is
	created, then the following call initializes the sync system. */

#ifndef UNIV_SYNC_ATOMIC
	mutex_create(rw_lock_get_mutex(lock), SYNC_NO_ORDER_CHECK);

	lock->mutex.cfile_name = cfile_name;
	lock->mutex.cline = cline;

#if defined UNIV_DEBUG && !defined UNIV_HOTBACKUP
	lock->mutex.cmutex_name = cmutex_name;
	lock->mutex.mutex_type = 1;
#endif /* UNIV_DEBUG && !UNIV_HOTBACKUP */

#endif /* UNIV_SYNC_ATOMIC */

	lock->lock_word = X_LOCK_DECR;
	lock->waiters = 0;
	lock->writer_thread = -1;
	lock->pass = 0;

#ifdef UNIV_SYNC_DEBUG
	UT_LIST_INIT(lock->debug_list);

	lock->level = level;
#endif /* UNIV_SYNC_DEBUG */

	lock->magic_n = RW_LOCK_MAGIC_N;

	lock->cfile_name = cfile_name;
	lock->cline = (unsigned int) cline;

	lock->count_os_wait = 0;
	lock->last_s_file_name = "not yet reserved";
	lock->last_x_file_name = "not yet reserved";
	lock->last_s_line = 0;
	lock->last_x_line = 0;
	lock->event = os_event_create(NULL);
	lock->wait_ex_event = os_event_create(NULL);

	mutex_enter(&rw_lock_list_mutex);

	if (UT_LIST_GET_LEN(rw_lock_list) > 0) {
		ut_a(UT_LIST_GET_FIRST(rw_lock_list)->magic_n
		     == RW_LOCK_MAGIC_N);
	}

	UT_LIST_ADD_FIRST(list, rw_lock_list, lock);

	mutex_exit(&rw_lock_list_mutex);
}

/**********************************************************************
Calling this function is obligatory only if the memory buffer containing
the rw-lock is freed. Removes an rw-lock object from the global list. The
rw-lock is checked to be in the non-locked state. */

void
rw_lock_free(
/*=========*/
	rw_lock_t*	lock)	/* in: rw-lock */
{
	ut_ad(rw_lock_validate(lock));
	ut_a(lock->lock_word == X_LOCK_DECR);

	lock->magic_n = 0;

#ifndef UNIV_SYNC_ATOMIC
	mutex_free(rw_lock_get_mutex(lock));
#endif /* UNIV_SYNC_ATOMIC */

	mutex_enter(&rw_lock_list_mutex);
	os_event_free(lock->event);

	os_event_free(lock->wait_ex_event);

	if (UT_LIST_GET_PREV(list, lock)) {
		ut_a(UT_LIST_GET_PREV(list, lock)->magic_n == RW_LOCK_MAGIC_N);
	}
	if (UT_LIST_GET_NEXT(list, lock)) {
		ut_a(UT_LIST_GET_NEXT(list, lock)->magic_n == RW_LOCK_MAGIC_N);
	}

	UT_LIST_REMOVE(list, rw_lock_list, lock);

	mutex_exit(&rw_lock_list_mutex);
}

#ifdef UNIV_DEBUG
/**********************************************************************
Checks that the rw-lock has been initialized and that there are no
simultaneous shared and exclusive locks. */

ibool
rw_lock_validate(
/*=============*/
	rw_lock_t*	lock)
{
	ut_a(lock);

	ulint waiters = rw_lock_get_waiters(lock);
	lint lock_word = lock->lock_word;

	ut_a(lock->magic_n == RW_LOCK_MAGIC_N);
	ut_a(waiters == 0 || waiters == 1);
	ut_a(lock_word > -X_LOCK_DECR ||(-lock_word) % X_LOCK_DECR == 0);

	return(TRUE);
}
#endif /* UNIV_DEBUG */

/**********************************************************************
Lock an rw-lock in shared mode for the current thread. If the rw-lock is
locked in exclusive mode, or there is an exclusive lock request waiting,
the function spins a preset time (controlled by SYNC_SPIN_ROUNDS), waiting
for the lock, before suspending the thread. */

void
rw_lock_s_lock_spin(
/*================*/
	rw_lock_t*	lock,	/* in: pointer to rw-lock */
	ulint		pass,	/* in: pass value; != 0, if the lock
				will be passed to another thread to unlock */
	const char*	file_name, /* in: file name where lock requested */
	ulint		line)	/* in: line where requested */
{
	ulint	 index;	/* index of the reserved wait cell */
	ulint	 i = 0;	/* spin round count */

	ut_ad(rw_lock_validate(lock));

	rw_s_spin_wait_count++;	/* Count calls to this function */
lock_loop:

	/* Spin waiting for the writer field to become free */
	while (i < SYNC_SPIN_ROUNDS && lock->lock_word <= 0) {
		if (srv_spin_wait_delay) {
			ut_delay(ut_rnd_interval(0, srv_spin_wait_delay));
		}

		i++;
	}

	if (i == SYNC_SPIN_ROUNDS) {
		os_thread_yield();
	}

	if (srv_print_latch_waits) {
		fprintf(stderr,
			"Thread %lu spin wait rw-s-lock at %p"
			" cfile %s cline %lu rnds %lu\n",
			(ulong) os_thread_pf(os_thread_get_curr_id()),
			(void*) lock,
			lock->cfile_name, (ulong) lock->cline, (ulong) i);
	}

	/* We try once again to obtain the lock */
	if (TRUE == rw_lock_s_lock_low(lock, pass, file_name, line)) {
		rw_s_spin_round_count += i;

		return; /* Success */
	} else {

		if (i < SYNC_SPIN_ROUNDS) {
			goto lock_loop;
		}

		rw_s_spin_round_count += i;

		sync_array_reserve_cell(sync_primary_wait_array,
					lock, RW_LOCK_SHARED,
					file_name, line,
					&index);

		/* Set waiters before checking lock_word to ensure wake-up
                signal is sent. This may lead to some unnecessary signals. */
		rw_lock_set_waiters(lock);

		if (TRUE == rw_lock_s_lock_low(lock, pass, file_name, line)) {
			sync_array_free_cell(sync_primary_wait_array, index);
			return; /* Success */
		}

		if (srv_print_latch_waits) {
			fprintf(stderr,
				"Thread %lu OS wait rw-s-lock at %p"
				" cfile %s cline %lu\n",
				os_thread_pf(os_thread_get_curr_id()),
				(void*) lock, lock->cfile_name,
				(ulong) lock->cline);
		}

		/* these stats may not be accurate */
		lock->count_os_wait++;
		rw_s_os_wait_count++;

		sync_array_wait_event(sync_primary_wait_array, index);

		i = 0;
		goto lock_loop;
	}
}

/**********************************************************************
This function is used in the insert buffer to move the ownership of an
x-latch on a buffer frame to the current thread. The x-latch was set by
the buffer read operation and it protected the buffer frame while the
read was done. The ownership is moved because we want that the current
thread is able to acquire a second x-latch which is stored in an mtr.
This, in turn, is needed to pass the debug checks of index page
operations. */

void
rw_lock_x_lock_move_ownership(
/*==========================*/
	rw_lock_t*	lock)	/* in: lock which was x-locked in the
				buffer read */
{
	ut_ad(rw_lock_is_locked(lock, RW_LOCK_EX));

#ifdef UNIV_SYNC_ATOMIC
        os_thread_id_t local_writer_thread = lock->writer_thread;
        os_thread_id_t new_writer_thread = os_thread_get_curr_id();
        while (TRUE) {
                if ((int)local_writer_thread != -1) {
                        if(os_compare_and_swap(
                               (volatile lint*)&(lock->writer_thread),
                               local_writer_thread,
                               new_writer_thread)) {
                                break;
                        }
                }
                local_writer_thread = lock->writer_thread;
        }
	lock->pass = 0;
#else /* UNIV_SYNC_ATOMIC */
	mutex_enter(&(lock->mutex));
	lock->writer_thread = os_thread_get_curr_id();
	lock->pass = 0;
	mutex_exit(&(lock->mutex));
#endif /* UNIV_SYNC_ATOMIC */
}

/**********************************************************************
Function for the next writer to call. Waits for readers to exit.
The caller must have already decremented lock_word by X_LOCK_DECR.*/
UNIV_INLINE
void
rw_lock_x_lock_wait(
/*================*/
	rw_lock_t*	lock,	/* in: pointer to rw-lock */
#ifdef UNIV_SYNC_DEBUG
	ulint		pass,	/* in: pass value; != 0, if the lock will
				be passed to another thread to unlock */
#endif
	const char*	file_name,/* in: file name where lock requested */
	ulint		line)	/* in: line where requested */
{
	ulint index;
	ulint i = 0;

	ut_ad(lock->lock_word <= 0);

	while (lock->lock_word < 0) {
		if (srv_spin_wait_delay) {
			ut_delay(ut_rnd_interval(0, srv_spin_wait_delay));
		}
		if(i < SYNC_SPIN_ROUNDS) {
			i++;
			continue;
		}

		/* If there is still a reader, then go to sleep.*/
		rw_x_spin_round_count += i;
		i = 0;
		sync_array_reserve_cell(sync_primary_wait_array,
					lock,
					RW_LOCK_WAIT_EX,
					file_name, line,
					&index);
		/* Check lock_word to ensure wake-up isn't missed.*/
		if(lock->lock_word < 0) {

			/* these stats may not be accurate */
			lock->count_os_wait++;
			rw_x_os_wait_count++;

                        /* Add debug info as it is needed to detect possible
                        deadlock. We must add info for WAIT_EX thread for
                        deadlock detection to work properly. */
#ifdef UNIV_SYNC_DEBUG
			rw_lock_add_debug_info(lock, pass, RW_LOCK_WAIT_EX,
					       file_name, line);
#endif

 			sync_array_wait_event(sync_primary_wait_array,
 					      index);
#ifdef UNIV_SYNC_DEBUG
			rw_lock_remove_debug_info(lock, pass,
					       RW_LOCK_WAIT_EX);
#endif
                        /* It is possible to wake when lock_word < 0.
                        We must pass the while-loop check to proceed.*/
		} else {
			sync_array_free_cell(sync_primary_wait_array,
					     index);
		}
	}
	rw_x_spin_round_count += i;
}

/**********************************************************************
Low-level function for acquiring an exclusive lock. */
UNIV_INLINE
ibool
rw_lock_x_lock_low(
/*===============*/
				/* out: RW_LOCK_NOT_LOCKED if did
				not succeed, RW_LOCK_EX if success. */
	rw_lock_t*	lock,	/* in: pointer to rw-lock */
	ulint		pass,	/* in: pass value; != 0, if the lock will
				be passed to another thread to unlock */
	const char*	file_name,/* in: file name where lock requested */
	ulint		line)	/* in: line where requested */
{
	os_thread_id_t	curr_thread	= os_thread_get_curr_id();
	ut_ad(curr_thread != -1); /* We use -1 as the unlocked value. */

	if(rw_lock_lock_word_decr(lock, X_LOCK_DECR)) {
		ut_ad(lock->writer_thread == -1);

		/* Decrement occurred: we are writer or next-writer. */
		lock->writer_thread = curr_thread;
		lock->pass = pass;
		rw_lock_x_lock_wait(lock,
#ifdef UNIV_SYNC_DEBUG
				    pass,
#endif
                                    file_name, line);

	} else {
		/* Decrement failed: relock or failed lock */
		/* Must verify pass first: otherwise another thread can
		call move_ownership suddenly allowing recursive locks.
		and after we have verified our thread_id matches
		(though move_ownership has since changed it).*/
		if(!pass && !(lock->pass) &&
                   os_thread_eq(lock->writer_thread, curr_thread)) {
			/* Relock */
                        lock->lock_word -= X_LOCK_DECR;
		} else {
			/* Another thread locked before us */
			return(FALSE);
		}
	}
#ifdef UNIV_SYNC_DEBUG
	rw_lock_add_debug_info(lock, pass, RW_LOCK_EX,
			       file_name, line);
#endif
	lock->last_x_file_name = file_name;
	lock->last_x_line = (unsigned int) line;

	return(TRUE);
}

/**********************************************************************
NOTE! Use the corresponding macro, not directly this function! Lock an
rw-lock in exclusive mode for the current thread. If the rw-lock is locked
in shared or exclusive mode, or there is an exclusive lock request waiting,
the function spins a preset time (controlled by SYNC_SPIN_ROUNDS), waiting
for the lock before suspending the thread. If the same thread has an x-lock
on the rw-lock, locking succeed, with the following exception: if pass != 0,
only a single x-lock may be taken on the lock. NOTE: If the same thread has
an s-lock, locking does not succeed! */

void
rw_lock_x_lock_func(
/*================*/
	rw_lock_t*	lock,	/* in: pointer to rw-lock */
	ulint		pass,	/* in: pass value; != 0, if the lock will
				be passed to another thread to unlock */
	const char*	file_name,/* in: file name where lock requested */
	ulint		line)	/* in: line where requested */
{
	ulint	index;	/* index of the reserved wait cell */
	ulint	i;	/* spin round count */
	ibool   spinning = FALSE;

	ut_ad(rw_lock_validate(lock));

	i = 0;

lock_loop:

	if (rw_lock_x_lock_low(lock, pass, file_name, line)) {
		rw_x_spin_round_count += i;

		return;	/* Locking succeeded */

	} else {

                if (!spinning) {
                        spinning = TRUE;
                        rw_x_spin_wait_count++;
		}

		/* Spin waiting for the lock_word to become free */
		while (i < SYNC_SPIN_ROUNDS
		       && lock->lock_word <= 0) {
			if (srv_spin_wait_delay) {
				ut_delay(ut_rnd_interval(0,
							 srv_spin_wait_delay));
			}

			i++;
		}
		if (i == SYNC_SPIN_ROUNDS) {
			os_thread_yield();
		} else {
			goto lock_loop;
		}
	}

	rw_x_spin_round_count += i;

	if (srv_print_latch_waits) {
		fprintf(stderr,
			"Thread %lu spin wait rw-x-lock at %p"
			" cfile %s cline %lu rnds %lu\n",
			os_thread_pf(os_thread_get_curr_id()), (void*) lock,
			lock->cfile_name, (ulong) lock->cline, (ulong) i);
	}

	sync_array_reserve_cell(sync_primary_wait_array,
				lock,
				RW_LOCK_EX,
				file_name, line,
				&index);

	/* Waiters must be set before checking lock_word, to ensure signal
	is sent. This could lead to a few unnecessary wake-up signals. */
	rw_lock_set_waiters(lock);

	if (rw_lock_x_lock_low(lock, pass, file_name, line)) {
		sync_array_free_cell(sync_primary_wait_array, index);
		return; /* Locking succeeded */
	}

	if (srv_print_latch_waits) {
		fprintf(stderr,
			"Thread %lu OS wait for rw-x-lock at %p"
			" cfile %s cline %lu\n",
			os_thread_pf(os_thread_get_curr_id()), (void*) lock,
			lock->cfile_name, (ulong) lock->cline);
	}

	/* these stats may not be accurate */
	lock->count_os_wait++;
	rw_x_os_wait_count++;

	sync_array_wait_event(sync_primary_wait_array, index);

	i = 0;
	goto lock_loop;
}

#ifdef UNIV_SYNC_DEBUG
/**********************************************************************
Acquires the debug mutex. We cannot use the mutex defined in sync0sync,
because the debug mutex is also acquired in sync0arr while holding the OS
mutex protecting the sync array, and the ordinary mutex_enter might
recursively call routines in sync0arr, leading to a deadlock on the OS
mutex. */

void
rw_lock_debug_mutex_enter(void)
/*==========================*/
{
loop:
	if (0 == mutex_enter_nowait(&rw_lock_debug_mutex)) {
		return;
	}

	os_event_reset(rw_lock_debug_event);

	rw_lock_debug_waiters = TRUE;

	if (0 == mutex_enter_nowait(&rw_lock_debug_mutex)) {
		return;
	}

	os_event_wait(rw_lock_debug_event);

	goto loop;
}

/**********************************************************************
Releases the debug mutex. */

void
rw_lock_debug_mutex_exit(void)
/*==========================*/
{
	mutex_exit(&rw_lock_debug_mutex);

	if (rw_lock_debug_waiters) {
		rw_lock_debug_waiters = FALSE;
		os_event_set(rw_lock_debug_event);
	}
}

/**********************************************************************
Inserts the debug information for an rw-lock. */

void
rw_lock_add_debug_info(
/*===================*/
	rw_lock_t*	lock,		/* in: rw-lock */
	ulint		pass,		/* in: pass value */
	ulint		lock_type,	/* in: lock type */
	const char*	file_name,	/* in: file where requested */
	ulint		line)		/* in: line where requested */
{
	rw_lock_debug_t*	info;

	ut_ad(lock);
	ut_ad(file_name);

	info = rw_lock_debug_create();

	rw_lock_debug_mutex_enter();

	info->file_name = file_name;
	info->line	= line;
	info->lock_type = lock_type;
	info->thread_id = os_thread_get_curr_id();
	info->pass	= pass;

	UT_LIST_ADD_FIRST(list, lock->debug_list, info);

	rw_lock_debug_mutex_exit();

	if ((pass == 0) && (lock_type != RW_LOCK_WAIT_EX)) {
		sync_thread_add_level(lock, lock->level);
	}
}

/**********************************************************************
Removes a debug information struct for an rw-lock. */

void
rw_lock_remove_debug_info(
/*======================*/
	rw_lock_t*	lock,		/* in: rw-lock */
	ulint		pass,		/* in: pass value */
	ulint		lock_type)	/* in: lock type */
{
	rw_lock_debug_t*	info;

	ut_ad(lock);

	if ((pass == 0) && (lock_type != RW_LOCK_WAIT_EX)) {
		sync_thread_reset_level(lock);
	}

	rw_lock_debug_mutex_enter();

	info = UT_LIST_GET_FIRST(lock->debug_list);

	while (info != NULL) {
		if ((pass == info->pass)
		    && ((pass != 0)
			|| os_thread_eq(info->thread_id,
					os_thread_get_curr_id()))
		    && (info->lock_type == lock_type)) {

			/* Found! */
			UT_LIST_REMOVE(list, lock->debug_list, info);
			rw_lock_debug_mutex_exit();

			rw_lock_debug_free(info);

			return;
		}

		info = UT_LIST_GET_NEXT(list, info);
	}

	ut_error;
}
#endif /* UNIV_SYNC_DEBUG */

#ifdef UNIV_SYNC_DEBUG
/**********************************************************************
Checks if the thread has locked the rw-lock in the specified mode, with
the pass value == 0. */

ibool
rw_lock_own(
/*========*/
					/* out: TRUE if locked */
	rw_lock_t*	lock,		/* in: rw-lock */
	ulint		lock_type)	/* in: lock type: RW_LOCK_SHARED,
					RW_LOCK_EX */
{
	rw_lock_debug_t*	info;

	ut_ad(lock);
	ut_ad(rw_lock_validate(lock));

	rw_lock_debug_mutex_enter();

	info = UT_LIST_GET_FIRST(lock->debug_list);

	while (info != NULL) {

		if (os_thread_eq(info->thread_id, os_thread_get_curr_id())
		    && (info->pass == 0)
		    && (info->lock_type == lock_type)) {

			rw_lock_debug_mutex_exit();
			/* Found! */

			return(TRUE);
		}

		info = UT_LIST_GET_NEXT(list, info);
	}
	rw_lock_debug_mutex_exit();

	return(FALSE);
}
#endif /* UNIV_SYNC_DEBUG */

/**********************************************************************
Checks if somebody has locked the rw-lock in the specified mode. */

ibool
rw_lock_is_locked(
/*==============*/
					/* out: TRUE if locked */
	rw_lock_t*	lock,		/* in: rw-lock */
	ulint		lock_type)	/* in: lock type: RW_LOCK_SHARED,
					RW_LOCK_EX */
{
	ibool	ret	= FALSE;

	ut_ad(lock);
	ut_ad(rw_lock_validate(lock));

	if (lock_type == RW_LOCK_SHARED) {
		if (rw_lock_get_reader_count(lock) > 0) {
			ret = TRUE;
		}
	} else if (lock_type == RW_LOCK_EX) {
		if (rw_lock_get_writer(lock) == RW_LOCK_EX) {
			ret = TRUE;
		}
	} else {
		ut_error;
	}

	return(ret);
}

#ifdef UNIV_SYNC_DEBUG
/*******************************************************************
Prints debug info of currently locked rw-locks. */

void
rw_lock_list_print_info(
/*====================*/
	FILE*	file)		/* in: file where to print */
{
	rw_lock_t*	lock;
	ulint		count		= 0;
	rw_lock_debug_t* info;

	mutex_enter(&rw_lock_list_mutex);

	fputs("-------------\n"
	      "RW-LATCH INFO\n"
	      "-------------\n", file);

	lock = UT_LIST_GET_FIRST(rw_lock_list);

	while (lock != NULL) {

		count++;

#ifndef UNIV_SYNC_ATOMIC
		mutex_enter(&(lock->mutex));
#endif
		if (lock->lock_word != X_LOCK_DECR) {

			fprintf(file, "RW-LOCK: %p ", (void*) lock);

			if (rw_lock_get_waiters(lock)) {
				fputs(" Waiters for the lock exist\n", file);
			} else {
				putc('\n', file);
			}

			info = UT_LIST_GET_FIRST(lock->debug_list);
			while (info != NULL) {
				rw_lock_debug_print(info);
				info = UT_LIST_GET_NEXT(list, info);
			}
		}
#ifndef UNIV_SYNC_ATOMIC
		mutex_exit(&(lock->mutex));
#endif

		lock = UT_LIST_GET_NEXT(list, lock);
	}

	fprintf(file, "Total number of rw-locks %ld\n", count);
	mutex_exit(&rw_lock_list_mutex);
}

/*******************************************************************
Prints debug info of an rw-lock. */

void
rw_lock_print(
/*==========*/
	rw_lock_t*	lock)	/* in: rw-lock */
{
	rw_lock_debug_t* info;

	fprintf(stderr,
		"-------------\n"
		"RW-LATCH INFO\n"
		"RW-LATCH: %p ", (void*) lock);

#ifndef UNIV_SYNC_ATOMIC
	mutex_enter(&(lock->mutex));
#endif
	if (lock->lock_word != X_LOCK_DECR) {

		if (rw_lock_get_waiters(lock)) {
			fputs(" Waiters for the lock exist\n", stderr);
		} else {
			putc('\n', stderr);
		}

		info = UT_LIST_GET_FIRST(lock->debug_list);
		while (info != NULL) {
			rw_lock_debug_print(info);
			info = UT_LIST_GET_NEXT(list, info);
		}
	}
#ifndef UNIV_SYNC_ATOMIC
	mutex_exit(&(lock->mutex));
#endif
}

/*************************************************************************
Prints info of a debug struct. */

void
rw_lock_debug_print(
/*================*/
	rw_lock_debug_t*	info)	/* in: debug struct */
{
	ulint	rwt;

	rwt	  = info->lock_type;

	fprintf(stderr, "Locked: thread %ld file %s line %ld  ",
		(ulong) os_thread_pf(info->thread_id), info->file_name,
		(ulong) info->line);
	if (rwt == RW_LOCK_SHARED) {
		fputs("S-LOCK", stderr);
	} else if (rwt == RW_LOCK_EX) {
		fputs("X-LOCK", stderr);
	} else if (rwt == RW_LOCK_WAIT_EX) {
		fputs("WAIT X-LOCK", stderr);
	} else {
		ut_error;
	}
	if (info->pass != 0) {
		fprintf(stderr, " pass value %lu", (ulong) info->pass);
	}
	putc('\n', stderr);
}

/*******************************************************************
Returns the number of currently locked rw-locks. Works only in the debug
version. */

ulint
rw_lock_n_locked(void)
/*==================*/
{
	rw_lock_t*	lock;
	ulint		count		= 0;

	mutex_enter(&rw_lock_list_mutex);

	lock = UT_LIST_GET_FIRST(rw_lock_list);

	while (lock != NULL) {

		if (lock->lock_word != X_LOCK_DECR) {
			count++;
		}

		lock = UT_LIST_GET_NEXT(list, lock);
	}

	mutex_exit(&rw_lock_list_mutex);

	return(count);
}
#endif /* UNIV_SYNC_DEBUG */