Add 1ton readonly waiter model

[urcu.git] / futex-wakeup / 1ton-readonly-waiter / futex.spin

diff --git a/futex-wakeup/1ton-readonly-waiter/futex.spin b/futex-wakeup/1ton-readonly-waiter/futex.spin
new file mode 100644 (file)
index 0000000..2038308
--- /dev/null
+++ b/futex-wakeup/1ton-readonly-waiter/futex.spin
@@ -0,0 +1,153 @@
+/*
+ * futex.spin: Promela code to validate 1 waker to n waiters futex
+ * wakeup algorithm, where waiters have read-only access to the futex.
+ *
+ * In this model, the waker thread unconditionally wakes all waiters if
+ * they need to be awakened. We guarantee that all waiters will never
+ * wait forever if they need to be awakened, even if the waker is
+ * inactive after requiring the wakeup. When "active" is set (e.g. a
+ * daemon is available to service waiter requests), the waiter should
+ * progress.
+ *
+ * Algorithm verified :
+ *
+ * active = 0;   (waker daemon is active)
+ * futex = 0;
+ * futex_wake = 0;
+ *
+ *                          1 waker (2 loops)
+ *
+ *                          futex = 0;
+ *                          active = 1;   (e.g. listen())
+ *                          futex_wake = 1;
+ *                          active = 0;   (e.g. close())
+ *                          futex = -1;
+ *
+ * n waiters (read-only)
+ *
+ * while (1) {
+ *   if (active == 0) {
+ *     if (futex == -1) {
+ *       futex_wake = (futex == -1 ? 0 : 1);  (atomic)
+ *       while (futex_wake == 0) { };
+ *     }
+ *   }
+ * progress:
+ * }
+ *
+ * if active = 1, then !_np
+ *
+ * By testing progress, i.e. [] <> ((!np_) || (!isactive)), we
+ * check that waiters we can never block forever if the waker is active.
+ *
+ * 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
+ * running.
+ *
+ * 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 _active = 0;
+int futex = 0;
+int futex_wake = 0;
+
+active proctype waker()
+{
+       /* loop 1 */
+       futex = 0;
+       _active = 1;
+       futex_wake = 1;
+       _active = 0;
+       futex = -1;
+
+       /* loop 2 */
+#ifndef INJ_MISORDER_WAKE
+       futex = 0;
+       _active = 1;
+       futex_wake = 1;
+#else
+       futex_wake = 1;
+       futex = 0;
+       _active = 1;
+#endif
+
+#ifdef INJ_QUEUE_NO_WAKE
+       _active = 0;
+       futex = -1;
+
+       /* loop 3 */
+       futex = 0;
+       _active = 1;
+#endif
+}
+
+/*
+ * The INJ_MISORDER error-injection test case succeeds, which means
+ * order of active vs futex value read does not matter. It is
+ * understandable because every time the active value is enabled by the
+ * waker, a wake is performed.
+ *
+ * However, the order in which wakeup sets the futex value vs sending
+ * the wakeup DOES matter, as shows the INJ_MISORDER_WAKE
+ * error-injection.
+ */
+active [2] proctype waiter()
+{
+       do
+       :: 1 ->
+               if
+#ifndef INJ_MISORDER
+               :: (_active == 0) ->
+#else
+               :: (futex == -1) ->
+#endif
+                       if
+#ifndef INJ_MISORDER
+                       :: (futex == -1) ->
+#else
+                       :: (_active == 0) ->
+#endif
+                               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;
+               :: else ->
+                       skip;
+               fi;
+progress:
+               skip;
+       od;
+}