Add nto1 futex wakeup scheme model

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

diff --git a/futex-wakeup/nto1/futex.spin b/futex-wakeup/nto1/futex.spin
new file mode 100644 (file)
index 0000000..f599a00
--- /dev/null
+++ b/futex-wakeup/nto1/futex.spin
@@ -0,0 +1,152 @@
+/*
+ * 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) {
+ * progress:
+ *   futex = -1;
+ *   if (queue == 1) {
+ *     futex = 0;
+ *   } else {
+ *     if (futex == -1) {
+ *       futex_wake = (futex == -1 ? 0 : 1);  (atomic)
+ *       while (futex_wake == 0) { };
+ *   }
+ *   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;
+
+}