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+/*
+ * This model describes the interaction between aio_set_dispatching()
+ * and aio_notify().
+ *
+ * Author: Paolo Bonzini <pbonzini@redhat.com>
+ *
+ * This file is in the public domain. If you really want a license,
+ * the WTFPL will do.
+ *
+ * To simulate it:
+ * spin -p docs/aio_notify.promela
+ *
+ * To verify it:
+ * spin -a docs/aio_notify.promela
+ * gcc -O2 pan.c
+ * ./a.out -a
+ */
+
+#define MAX 4
+#define LAST (1 << (MAX - 1))
+#define FINAL ((LAST << 1) - 1)
+
+bool dispatching;
+bool event;
+
+int req, done;
+
+active proctype waiter()
+{
+ int fetch, blocking;
+
+ do
+ :: done != FINAL -> {
+ // Computing "blocking" is separate from execution of the
+ // "bottom half"
+ blocking = (req == 0);
+
+ // This is our "bottom half"
+ atomic { fetch = req; req = 0; }
+ done = done | fetch;
+
+ // Wait for a nudge from the other side
+ do
+ :: event == 1 -> { event = 0; break; }
+ :: !blocking -> break;
+ od;
+
+ dispatching = 1;
+
+ // If you are simulating this model, you may want to add
+ // something like this here:
+ //
+ // int foo; foo++; foo++; foo++;
+ //
+ // This only wastes some time and makes it more likely
+ // that the notifier process hits the "fast path".
+
+ dispatching = 0;
+ }
+ :: else -> break;
+ od
+}
+
+active proctype notifier()
+{
+ int next = 1;
+ int sets = 0;
+
+ do
+ :: next <= LAST -> {
+ // generate a request
+ req = req | next;
+ next = next << 1;
+
+ // aio_notify
+ if
+ :: dispatching == 0 -> sets++; event = 1;
+ :: else -> skip;
+ fi;
+
+ // Test both synchronous and asynchronous delivery
+ if
+ :: 1 -> do
+ :: req == 0 -> break;
+ od;
+ :: 1 -> skip;
+ fi;
+ }
+ :: else -> break;
+ od;
+ printf("Skipped %d event_notifier_set\n", MAX - sets);
+}
+
+#define p (done == FINAL)
+
+never {
+ do
+ :: 1 // after an arbitrarily long prefix
+ :: p -> break // p becomes true
+ od;
+ do
+ :: !p -> accept: break // it then must remains true forever after
+ od
+}