+/*
+ * futex.spin: Promela code to validate n wakers to 1 waiter selective
+ * futex wakeup algorithm.
+ *
+ * In this model, waker threads are told whether they are still being
+ * waited on, and skip the futex wakeup if not.
+ *
+ * Algorithm verified :
+ *
+ * queue = 0;
+ * waiting = 0;
+ * gp_futex = 0;
+ * gp = 1;
+ *
+ * Waker
+ * while (1) {
+ * this.queue = gp;
+ * if (this.waiting == 1) {
+ * this.waiting = 0;
+ * if (gp_futex == -1) {
+ * gp_futex = 0;
+ * futex_wake = 1;
+ * }
+ * }
+ * }
+ *
+ * Waiter
+ * in_registry = 1;
+ * while (1) {
+ * gp_futex = -1;
+ * waiting |= (queue != gp);
+ * in_registry &= (queue != gp);
+ * if (all in_registry == 0) {
+ * progress:
+ * gp_futex = 0;
+ * gp = !gp;
+ * restart;
+ * } else {
+ * futex_wake = (gp_futex == -1 ? 0 : 1);
+ * while (futex_wake == 0) { }
+ * }
+ * queue = 0;
+ * }
+ *
+ * By testing progress, i.e. [] <> !np_, we check that an infinite sequence
+ * of update_counter_and_wait (and consequently of synchronize_rcu) will
+ * not block.
+ *
+ * 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) 2009-2011 Mathieu Desnoyers
+ */
+
+#define get_pid() (_pid)
+
+int queue[2] = 0;
+int waiting[2] = 0;
+int futex_wake = 0;
+int gp_futex = 0;
+int gp = 1;
+int in_registry[2] = 0;
+
+active [2] proctype waker()
+{
+ assert(get_pid() < 2);
+
+ do
+ :: 1 ->
+ queue[get_pid()] = gp;
+
+ if
+ :: (waiting[get_pid()] == 1) ->
+ waiting[get_pid()] = 0;
+ if
+ :: (gp_futex == -1) ->
+ gp_futex = 0;
+#ifndef INJ_QUEUE_NO_WAKE
+ futex_wake = 1;
+#endif
+ :: else ->
+ skip;
+ fi;
+ fi;
+ od;
+}
+
+
+active proctype waiter()
+{
+restart:
+ in_registry[0] = 1;
+ in_registry[1] = 1;
+ do
+ :: 1 ->
+#if (!defined(INJ_LATE_DEC) && !defined(INJ_INVERT_WAITING_VS_GP_FUTEX))
+ gp_futex = -1;
+#endif
+ if
+ :: (in_registry[0] == 1 && queue[0] != gp) ->
+ waiting[0] = 1;
+ :: else ->
+ skip;
+ fi;
+ if
+ :: (in_registry[1] == 1 && queue[1] != gp) ->
+ waiting[1] = 1;
+ :: else ->
+ skip;
+ fi;
+
+ if
+ :: (in_registry[0] == 1 && queue[0] == gp) ->
+ in_registry[0] = 0;
+ :: else ->
+ skip;
+ fi;
+ if
+ :: (in_registry[1] == 1 && queue[1] == gp) ->
+ in_registry[1] = 0;
+ :: else ->
+ skip;
+ fi;
+#ifdef INJ_INVERT_WAITING_VS_GP_FUTEX
+ gp_futex = -1;
+#endif
+
+ if
+ :: (in_registry[0] == 0 && in_registry[1] == 0) ->
+progress:
+#ifndef INJ_LATE_DEC
+ gp_futex = 0;
+#endif
+ gp = !gp;
+ goto restart;
+ :: else ->
+#ifdef INJ_LATE_DEC
+ gp_futex = -1;
+#endif
+ futex_wake = gp_futex + 1;
+ do
+ :: 1 ->
+ if
+ :: (futex_wake == 0) ->
+ skip;
+ :: else ->
+ break;
+ fi;
+ od;
+ fi;
+ od;
+}