[urcu.git] / futex-wakeup / nto1 / futex.spin

/*
 * futex.spin: Promela code to validate n wakers to 1 waiter futex
 * wakeup algorithm.
 *
 * In this model, waker threads unconditionally wake the waiter if it
 * needs to be awakened. We guarantee that the waiter will never wait
 * forever if it needs to be awakened, even if the waker is inactive
 * after requiring the wakeup.
 *
 * Algorithm verified :
 *
 * queue = 0;
 * futex = 0;
 * futex_wake = 0;
 *
 *                          n wakers (2 loops)
 *
 *                          queue = 1;
 *                          if (futex == -1) {
 *                            futex = 0;
 *                            futex_wake = 1;
 *                          }
 *
 * 1 waiter
 *
 * while (1) {
 *   futex = -1;
 *   if (queue == 1) {
 *     futex = 0;
 *   } else {
 *     if (futex == -1) {
 *       futex_wake = (futex == -1 ? 0 : 1);  (atomic)
 *       while (futex_wake == 0) { };
 *     }
 *   }
 * progress:
 *   queue = 0;
 * }
 *
 * if queue = 1, then !_np
 *
 * By testing progress, i.e. [] <> ((!np_) || (!queue_has_entry)), we
 * check that we can never block forever if there is an entry in the
 * queue.
 *
 * The waker performs only 2 loops (and NOT an infinite number of loops)
 * because we really want to see what happens when the waker stops
 * enqueuing.
 *
 * 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; either version 2 of the License, or
 * (at your option) any later version.
 *
 * 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright (c) 2009 Mathieu Desnoyers
 */

#define get_pid()       (_pid)

int queue[2] = 0;
int futex = 0;
int futex_wake = 0;

active [2] proctype waker()
{
	assert(get_pid() < 2);

	/* loop 1 */
	queue[get_pid()] = 1;

	if
	:: (futex == -1) ->
		futex = 0;
		futex_wake = 1;
	:: else ->
		skip;
	fi;

	/* loop 2 */
	queue[get_pid()] = 1;

	if
	:: (futex == -1) ->
		futex = 0;
		futex_wake = 1;
	:: else ->
		skip;
	fi;

#ifdef INJ_QUEUE_NO_WAKE
	/* loop 3 */
	queue[get_pid()] = 1;
#endif
}


active proctype waiter()
{
	do
	:: 1 ->
#ifndef INJ_LATE_DEC
		futex = -1;
#endif

		if
		:: (queue[0] == 1 || queue[1] == 1) ->
#ifndef INJ_LATE_DEC
			futex = 0;
#endif
			skip;
		:: else ->
#ifdef INJ_LATE_DEC
			futex = -1;
#endif
			if
			:: (futex == -1) ->
				atomic {
					if
					:: (futex == -1) ->
						futex_wake = 0;
					:: else ->
						futex_wake = 1;
					fi;
				}
				/* block */
				do
				:: 1 ->
					if
					:: (futex_wake == 0) ->
						skip;
					:: else ->
						break;
					fi;
				od;
			:: else ->
				skip;
			fi;
		fi;
progress:	/* Progress on dequeue */
		queue[0] = 0;
		queue[1] = 0;
	od;

}
Commit	Line	Data
e922fbe4 MD	1	/*
	2	* futex.spin: Promela code to validate n wakers to 1 waiter futex
	3	* wakeup algorithm.
	4	*
	5	* In this model, waker threads unconditionally wake the waiter if it
	6	* needs to be awakened. We guarantee that the waiter will never wait
	7	* forever if it needs to be awakened, even if the waker is inactive
	8	* after requiring the wakeup.
	9	*
	10	* Algorithm verified :
	11	*
	12	* queue = 0;
	13	* futex = 0;
	14	* futex_wake = 0;
	15	*
	16	* n wakers (2 loops)
	17	*
	18	* queue = 1;
	19	* if (futex == -1) {
	20	* futex = 0;
	21	* futex_wake = 1;
	22	* }
	23	*
	24	* 1 waiter
	25	*
	26	* while (1) {
e922fbe4 MD	27	* futex = -1;
	28	* if (queue == 1) {
	29	* futex = 0;
	30	* } else {
	31	* if (futex == -1) {
	32	* futex_wake = (futex == -1 ? 0 : 1); (atomic)
	33	* while (futex_wake == 0) { };
7f12dad2	34	* }
e922fbe4	35	* }
7f12dad2	36	* progress:
e922fbe4 MD	37	* queue = 0;
	38	* }
	39	*
	40	* if queue = 1, then !_np
	41	*
	42	* By testing progress, i.e. [] <> ((!np_) \|\| (!queue_has_entry)), we
	43	* check that we can never block forever if there is an entry in the
	44	* queue.
	45	*
	46	* The waker performs only 2 loops (and NOT an infinite number of loops)
	47	* because we really want to see what happens when the waker stops
	48	* enqueuing.
	49	*
	50	* This program is free software; you can redistribute it and/or modify
	51	* it under the terms of the GNU General Public License as published by
	52	* the Free Software Foundation; either version 2 of the License, or
	53	* (at your option) any later version.
	54	*
	55	* This program is distributed in the hope that it will be useful,
	56	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	57	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	58	* GNU General Public License for more details.
	59	*
	60	* You should have received a copy of the GNU General Public License
	61	* along with this program; if not, write to the Free Software
	62	* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
	63	*
	64	* Copyright (c) 2009 Mathieu Desnoyers
	65	*/
	66
	67	#define get_pid() (_pid)
	68
	69	int queue[2] = 0;
	70	int futex = 0;
	71	int futex_wake = 0;
	72
	73	active [2] proctype waker()
	74	{
	75	assert(get_pid() < 2);
	76
	77	/* loop 1 */
	78	queue[get_pid()] = 1;
	79
	80	if
	81	:: (futex == -1) ->
	82	futex = 0;
	83	futex_wake = 1;
	84	:: else ->
	85	skip;
	86	fi;
	87
	88	/* loop 2 */
	89	queue[get_pid()] = 1;
	90
	91	if
	92	:: (futex == -1) ->
	93	futex = 0;
	94	futex_wake = 1;
	95	:: else ->
	96	skip;
	97	fi;
	98
	99	#ifdef INJ_QUEUE_NO_WAKE
	100	/* loop 3 */
101	queue[get_pid()] = 1;
102	#endif
103	}
104
105
106	active proctype waiter()
107	{
108	do
109	:: 1 ->
110	#ifndef INJ_LATE_DEC
111	futex = -1;
112	#endif
113
114	if
115	:: (queue[0] == 1 \|\| queue[1] == 1) ->
116	#ifndef INJ_LATE_DEC
117	futex = 0;
118	#endif
119	skip;
120	:: else ->
121	#ifdef INJ_LATE_DEC
122	futex = -1;
123	#endif
124	if
125	:: (futex == -1) ->
126	atomic {
127	if
128	:: (futex == -1) ->
129	futex_wake = 0;
130	:: else ->
131	futex_wake = 1;
132	fi;
133	}
134	/* block */
135	do
136	:: 1 ->
137	if
138	:: (futex_wake == 0) ->
139	skip;
140	:: else ->
141	break;
142	fi;
143	od;
144	:: else ->
145	skip;
146	fi;
147	fi;
148	progress: /* Progress on dequeue */
149	queue[0] = 0;
150	queue[1] = 0;
151	od;
152
153	}