path: root/storage/innobase/include/sync0rw.ic

/******************************************************
The read-write lock (for threads)

(c) 1995 Innobase Oy

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

/**********************************************************************
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 */
#ifdef UNIV_SYNC_DEBUG
/**********************************************************************
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 */
/**********************************************************************
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 */
#endif /* UNIV_SYNC_DEBUG */

/************************************************************************
Accessor functions for rw lock. */
UNIV_INLINE
ulint
rw_lock_get_waiters(
/*================*/
	rw_lock_t*	lock)
{
	return(lock->waiters);
}
UNIV_INLINE
void
rw_lock_set_waiters(
/*================*/
	rw_lock_t*	lock,
	ulint		flag)
{
	lock->waiters = flag;
}
UNIV_INLINE
ulint
rw_lock_get_writer(
/*===============*/
	rw_lock_t*	lock)
{
	return(lock->writer);
}
UNIV_INLINE
void
rw_lock_set_writer(
/*===============*/
	rw_lock_t*	lock,
	ulint		flag)
{
	lock->writer = flag;
}
UNIV_INLINE
ulint
rw_lock_get_reader_count(
/*=====================*/
	rw_lock_t*	lock)
{
	return(lock->reader_count);
}
UNIV_INLINE
void
rw_lock_set_reader_count(
/*=====================*/
	rw_lock_t*	lock,
	ulint		count)
{
	lock->reader_count = count;
}
UNIV_INLINE
mutex_t*
rw_lock_get_mutex(
/*==============*/
	rw_lock_t*	lock)
{
	return(&(lock->mutex));
}

/**********************************************************************
Returns the value of writer_count for the lock. Does not reserve the lock
mutex, so the caller must be sure it is not changed during the call. */
UNIV_INLINE
ulint
rw_lock_get_x_lock_count(
/*=====================*/
				/* out: value of writer_count */
	rw_lock_t*	lock)	/* in: rw-lock */
{
	return(lock->writer_count);
}

/**********************************************************************
Low-level function which tries to lock an rw-lock in s-mode. Performs no
spinning. */
UNIV_INLINE
ibool
rw_lock_s_lock_low(
/*===============*/
				/* out: TRUE if success */
	rw_lock_t*	lock,	/* in: pointer to rw-lock */
	ulint		pass __attribute__((unused)),
				/* 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 */
{
	ut_ad(mutex_own(rw_lock_get_mutex(lock)));

	/* Check if the writer field is free */

	if (UNIV_LIKELY(lock->writer == RW_LOCK_NOT_LOCKED)) {
		/* Set the shared lock by incrementing the reader count */
		lock->reader_count++;

#ifdef UNIV_SYNC_DEBUG
		rw_lock_add_debug_info(lock, pass, RW_LOCK_SHARED, file_name,
				       line);
#endif
		lock->last_s_file_name = file_name;
		lock->last_s_line = line;

		return(TRUE);	/* locking succeeded */
	}

	return(FALSE);	/* locking did not succeed */
}

/**********************************************************************
Low-level function which locks an rw-lock in s-mode when we know that it
is possible and none else is currently accessing the rw-lock structure.
Then we can do the locking without reserving the mutex. */
UNIV_INLINE
void
rw_lock_s_lock_direct(
/*==================*/
	rw_lock_t*	lock,		/* in: pointer to rw-lock */
	const char*	file_name,	/* in: file name where requested */
	ulint		line)		/* in: line where lock requested */
{
	ut_ad(lock->writer == RW_LOCK_NOT_LOCKED);
	ut_ad(rw_lock_get_reader_count(lock) == 0);

	/* Set the shared lock by incrementing the reader count */
	lock->reader_count++;

	lock->last_s_file_name = file_name;
	lock->last_s_line = line;

#ifdef UNIV_SYNC_DEBUG
	rw_lock_add_debug_info(lock, 0, RW_LOCK_SHARED, file_name, line);
#endif
}

/**********************************************************************
Low-level function which locks an rw-lock in x-mode when we know that it
is not locked and none else is currently accessing the rw-lock structure.
Then we can do the locking without reserving the mutex. */
UNIV_INLINE
void
rw_lock_x_lock_direct(
/*==================*/
	rw_lock_t*	lock,		/* in: pointer to rw-lock */
	const char*	file_name,	/* in: file name where requested */
	ulint		line)		/* in: line where lock requested */
{
	ut_ad(rw_lock_validate(lock));
	ut_ad(rw_lock_get_reader_count(lock) == 0);
	ut_ad(rw_lock_get_writer(lock) == RW_LOCK_NOT_LOCKED);

	rw_lock_set_writer(lock, RW_LOCK_EX);
	lock->writer_thread = os_thread_get_curr_id();
	lock->writer_count++;
	lock->pass = 0;

	lock->last_x_file_name = file_name;
	lock->last_x_line = line;

#ifdef UNIV_SYNC_DEBUG
	rw_lock_add_debug_info(lock, 0, RW_LOCK_EX, file_name, line);
#endif
}

/**********************************************************************
NOTE! Use the corresponding macro, not directly this function! 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. */
UNIV_INLINE
void
rw_lock_s_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 */
{
	/* NOTE: As we do not know the thread ids for threads which have
	s-locked a latch, and s-lockers will be served only after waiting
	x-lock requests have been fulfilled, then if this thread already
	owns an s-lock here, it may end up in a deadlock with another thread
	which requests an x-lock here. Therefore, we will forbid recursive
	s-locking of a latch: the following assert will warn the programmer
	of the possibility of this kind of a deadlock. If we want to implement
	safe recursive s-locking, we should keep in a list the thread ids of
	the threads which have s-locked a latch. This would use some CPU
	time. */

#ifdef UNIV_SYNC_DEBUG
	ut_ad(!rw_lock_own(lock, RW_LOCK_SHARED)); /* see NOTE above */
	ut_ad(!rw_lock_own(lock, RW_LOCK_EX));
#endif /* UNIV_SYNC_DEBUG */

	mutex_enter(rw_lock_get_mutex(lock));

	if (UNIV_LIKELY(rw_lock_s_lock_low(lock, pass, file_name, line))) {
		mutex_exit(rw_lock_get_mutex(lock));

		return; /* Success */
	} else {
		/* Did not succeed, try spin wait */
		mutex_exit(rw_lock_get_mutex(lock));

		rw_lock_s_lock_spin(lock, pass, file_name, line);

		return;
	}
}

/**********************************************************************
NOTE! Use the corresponding macro, not directly this function! Lock an
rw-lock in shared mode for the current thread if the lock can be acquired
immediately. */
UNIV_INLINE
ibool
rw_lock_s_lock_func_nowait(
/*=======================*/
				/* out: TRUE if success */
	rw_lock_t*	lock,	/* in: pointer to rw-lock */
	const char*	file_name,/* in: file name where lock requested */
	ulint		line)	/* in: line where requested */
{
	ibool	success	= FALSE;

	mutex_enter(rw_lock_get_mutex(lock));

	if (lock->writer == RW_LOCK_NOT_LOCKED) {
		/* Set the shared lock by incrementing the reader count */
		lock->reader_count++;

#ifdef UNIV_SYNC_DEBUG
		rw_lock_add_debug_info(lock, 0, RW_LOCK_SHARED, file_name,
				       line);
#endif

		lock->last_s_file_name = file_name;
		lock->last_s_line = line;

		success = TRUE;
	}

	mutex_exit(rw_lock_get_mutex(lock));

	return(success);
}

/**********************************************************************
NOTE! Use the corresponding macro, not directly this function! Lock an
rw-lock in exclusive mode for the current thread if the lock can be
obtained immediately. */
UNIV_INLINE
ibool
rw_lock_x_lock_func_nowait(
/*=======================*/
				/* out: TRUE if success */
	rw_lock_t*	lock,	/* in: pointer to rw-lock */
	const char*	file_name,/* in: file name where lock requested */
	ulint		line)	/* in: line where requested */
{
	ibool		success		= FALSE;
	os_thread_id_t	curr_thread	= os_thread_get_curr_id();
	mutex_enter(rw_lock_get_mutex(lock));

	if (UNIV_UNLIKELY(rw_lock_get_reader_count(lock) != 0)) {
	} else if (UNIV_LIKELY(rw_lock_get_writer(lock)
			       == RW_LOCK_NOT_LOCKED)) {
		rw_lock_set_writer(lock, RW_LOCK_EX);
		lock->writer_thread = curr_thread;
		lock->pass = 0;
relock:
		lock->writer_count++;

#ifdef UNIV_SYNC_DEBUG
		rw_lock_add_debug_info(lock, 0, RW_LOCK_EX, file_name, line);
#endif

		lock->last_x_file_name = file_name;
		lock->last_x_line = line;

		success = TRUE;
	} else if (rw_lock_get_writer(lock) == RW_LOCK_EX
		   && lock->pass == 0
		   && os_thread_eq(lock->writer_thread, curr_thread)) {
		goto relock;
	}

	mutex_exit(rw_lock_get_mutex(lock));

	ut_ad(rw_lock_validate(lock));

	return(success);
}

/**********************************************************************
Releases a shared mode lock. */
UNIV_INLINE
void
rw_lock_s_unlock_func(
/*==================*/
	rw_lock_t*	lock	/* in: rw-lock */
#ifdef UNIV_SYNC_DEBUG
	,ulint		pass	/* in: pass value; != 0, if the lock may have
				been passed to another thread to unlock */
#endif
	)
{
	mutex_t*	mutex	= &(lock->mutex);
	ibool		sg	= FALSE;

	/* Acquire the mutex protecting the rw-lock fields */
	mutex_enter(mutex);

	/* Reset the shared lock by decrementing the reader count */

	ut_a(lock->reader_count > 0);
	lock->reader_count--;

#ifdef UNIV_SYNC_DEBUG
	rw_lock_remove_debug_info(lock, pass, RW_LOCK_SHARED);
#endif

	/* If there may be waiters and this was the last s-lock,
	signal the object */

	if (UNIV_UNLIKELY(lock->waiters)
	    && lock->reader_count == 0) {
		sg = TRUE;

		rw_lock_set_waiters(lock, 0);
	}

	mutex_exit(mutex);

	if (UNIV_UNLIKELY(sg)) {
#ifdef __WIN__
		os_event_set(lock->wait_ex_event);
#endif
		os_event_set(lock->event);
		sync_array_object_signalled(sync_primary_wait_array);
	}

	ut_ad(rw_lock_validate(lock));

#ifdef UNIV_SYNC_PERF_STAT
	rw_s_exit_count++;
#endif
}

/**********************************************************************
Releases a shared mode lock when we know there are no waiters and none
else will access the lock during the time this function is executed. */
UNIV_INLINE
void
rw_lock_s_unlock_direct(
/*====================*/
	rw_lock_t*	lock)	/* in: rw-lock */
{
	/* Reset the shared lock by decrementing the reader count */

	ut_ad(lock->reader_count > 0);

	lock->reader_count--;

#ifdef UNIV_SYNC_DEBUG
	rw_lock_remove_debug_info(lock, 0, RW_LOCK_SHARED);
#endif

	ut_ad(!lock->waiters);
	ut_ad(rw_lock_validate(lock));
#ifdef UNIV_SYNC_PERF_STAT
	rw_s_exit_count++;
#endif
}

/**********************************************************************
Releases an exclusive mode lock. */
UNIV_INLINE
void
rw_lock_x_unlock_func(
/*==================*/
	rw_lock_t*	lock	/* in: rw-lock */
#ifdef UNIV_SYNC_DEBUG
	,ulint		pass	/* in: pass value; != 0, if the lock may have
				been passed to another thread to unlock */
#endif
	)
{
	ibool	sg	= FALSE;

	/* Acquire the mutex protecting the rw-lock fields */
	mutex_enter(&(lock->mutex));

	/* Reset the exclusive lock if this thread no longer has an x-mode
	lock */

	ut_ad(lock->writer_count > 0);

	lock->writer_count--;

	if (lock->writer_count == 0) {
		rw_lock_set_writer(lock, RW_LOCK_NOT_LOCKED);
	}

#ifdef UNIV_SYNC_DEBUG
	rw_lock_remove_debug_info(lock, pass, RW_LOCK_EX);
#endif

	/* If there may be waiters, signal the lock */
	if (UNIV_UNLIKELY(lock->waiters)
	    && lock->writer_count == 0) {

		sg = TRUE;
		rw_lock_set_waiters(lock, 0);
	}

	mutex_exit(&(lock->mutex));

	if (UNIV_UNLIKELY(sg)) {
#ifdef __WIN__
		os_event_set(lock->wait_ex_event);
#endif
		os_event_set(lock->event);
		sync_array_object_signalled(sync_primary_wait_array);
	}

	ut_ad(rw_lock_validate(lock));

#ifdef UNIV_SYNC_PERF_STAT
	rw_x_exit_count++;
#endif
}

/**********************************************************************
Releases an exclusive mode lock when we know there are no waiters, and
none else will access the lock durint the time this function is executed. */
UNIV_INLINE
void
rw_lock_x_unlock_direct(
/*====================*/
	rw_lock_t*	lock)	/* in: rw-lock */
{
	/* Reset the exclusive lock if this thread no longer has an x-mode
	lock */

	ut_ad(lock->writer_count > 0);

	lock->writer_count--;

	if (lock->writer_count == 0) {
		rw_lock_set_writer(lock, RW_LOCK_NOT_LOCKED);
	}

#ifdef UNIV_SYNC_DEBUG
	rw_lock_remove_debug_info(lock, 0, RW_LOCK_EX);
#endif

	ut_ad(!lock->waiters);
	ut_ad(rw_lock_validate(lock));

#ifdef UNIV_SYNC_PERF_STAT
	rw_x_exit_count++;
#endif
}