X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=futex-wakeup%2F1ton-readonly-waiter%2Ffutex.spin;fp=futex-wakeup%2F1ton-readonly-waiter%2Ffutex.spin;h=20383080b954cca8a2c9c859185d53691bfae070;hb=ef781656a07c5a52fd09508336994f29c8bb8cb3;hp=0000000000000000000000000000000000000000;hpb=3646de2f5d9217207c3b5340baae0a2c988f165e;p=urcu.git

diff --git a/futex-wakeup/1ton-readonly-waiter/futex.spin b/futex-wakeup/1ton-readonly-waiter/futex.spin
new file mode 100644
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--- /dev/null
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+/*
+ * 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;
+}