mariadb/innobase/include/sync0ipm.ic

/******************************************************
A fast mutex for interprocess synchronization.
mutex_t can be used only within single process,
but ip_mutex_t also between processes.

(c) 1995 Innobase Oy

Created 9/30/1995 Heikki Tuuri
*******************************************************/

/* An extra structure created in the private address space of each process
which creates or opens the ip mutex. */

struct ip_mutex_hdl_struct {
	ip_mutex_t*	ip_mutex;	/* pointer to ip mutex */
	os_event_t	released;	/* event which signals that the mutex
					is released; this is obtained from
					create or open of an ip mutex */
	os_mutex_t	exclude;	/* os mutex obtained when ip mutex is
					created or opened */
};


UNIV_INLINE
ulint
ip_mutex_get_waiters(
volatile ip_mutex_t*	ipm);
UNIV_INLINE
void
ip_mutex_set_waiters(
volatile ip_mutex_t*	ipm,
	ulint		flag);
UNIV_INLINE
mutex_t*
ip_mutex_get_mutex(
	ip_mutex_t*	ipm);


/******************************************************************
Accessor functions for ip mutex. */
UNIV_INLINE
ulint
ip_mutex_get_waiters(
volatile ip_mutex_t*	ipm)
{
	return(ipm->waiters);
}
UNIV_INLINE
void
ip_mutex_set_waiters(
volatile ip_mutex_t*	ipm,
	ulint		flag)
{
	ipm->waiters = flag;
}
UNIV_INLINE
mutex_t*
ip_mutex_get_mutex(
	ip_mutex_t*	ipm)
{
	return(&(ipm->mutex));
}

/******************************************************************
Reserves an ip mutex. */
UNIV_INLINE
ulint
ip_mutex_enter(
/*===========*/
					/* out: 0 if success, 
					SYNC_TIME_EXCEEDED if timeout */
	ip_mutex_hdl_t*	ip_mutex_hdl,	/* in: pointer to ip mutex handle */
	ulint		time)		/* in: maximum time to wait, in
					microseconds, or 
					SYNC_INFINITE_TIME */
{
	mutex_t*	mutex;
	os_event_t	released;
	os_mutex_t	exclude;
	ip_mutex_t*	ip_mutex;
	ulint		loop_count;
	ulint		ret;

	ip_mutex = ip_mutex_hdl->ip_mutex;
	released = ip_mutex_hdl->released;
	exclude = ip_mutex_hdl->exclude;

	mutex = ip_mutex_get_mutex(ip_mutex);

	loop_count = 0;
loop:
	loop_count++;
	ut_ad(loop_count < 15);

	if (mutex_enter_nowait(mutex) == 0) {
		/* Succeeded! */

		return(0);
	}
	
	ip_mutex_system_call_count++;

	os_event_reset(released);

	/* Order is important here: FIRST reset event, then set waiters */
	ip_mutex_set_waiters(ip_mutex, 1);

	if (mutex_enter_nowait(mutex) == 0) {
		/* Succeeded! */

		return(0);
	}

	if (time == SYNC_INFINITE_TIME) {
		time = OS_SYNC_INFINITE_TIME;
	}

	/* Suspend to wait for release */

	ip_mutex_system_call_count++;

	ret = os_event_wait_time(released, time);

	ip_mutex_system_call_count++;

	os_mutex_enter(exclude);
	ip_mutex_system_call_count++;
	os_mutex_exit(exclude);

	if (ret != 0) {
		ut_a(ret == OS_SYNC_TIME_EXCEEDED);

		return(SYNC_TIME_EXCEEDED);
	}

	goto loop;
}

/******************************************************************
Releases an ip mutex. */
UNIV_INLINE
void
ip_mutex_exit(
/*==========*/
	ip_mutex_hdl_t*	ip_mutex_hdl)	/* in: pointer to ip mutex handle */
{
	mutex_t*	mutex;
	os_event_t	released;
	os_mutex_t	exclude;
	ip_mutex_t*	ip_mutex;

	ip_mutex = ip_mutex_hdl->ip_mutex;
	released = ip_mutex_hdl->released;
	exclude = ip_mutex_hdl->exclude;

	mutex = ip_mutex_get_mutex(ip_mutex);

	mutex_exit(mutex);

	if (ip_mutex_get_waiters(ip_mutex) != 0) {
		
		ip_mutex_set_waiters(ip_mutex, 0);

		/* Order is important here: FIRST reset waiters, 
		then set event */

		ip_mutex_system_call_count++;
		os_mutex_enter(exclude);					

		/* The use of the exclude mutex seems to prevent some
		kind of a convoy problem in the test tsproc.c. We do
		not know why. */

		ip_mutex_system_call_count++;

		os_event_set(released);
	
		ip_mutex_system_call_count++;

		os_mutex_exit(exclude);
	}
}