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+/*
+ * This model describes the implementation of QemuEvent in
+ * util/qemu-thread-win32.c.
+ *
+ * Author: Paolo Bonzini <pbonzini@redhat.com>
+ *
+ * This file is in the public domain. If you really want a license,
+ * the WTFPL will do.
+ *
+ * To verify it:
+ * spin -a docs/event.promela
+ * gcc -O2 pan.c -DSAFETY
+ * ./a.out
+ */
+
+bool event;
+int value;
+
+/* Primitives for a Win32 event */
+#define RAW_RESET event = false
+#define RAW_SET event = true
+#define RAW_WAIT do :: event -> break; od
+
+#if 0
+/* Basic sanity checking: test the Win32 event primitives */
+#define RESET RAW_RESET
+#define SET RAW_SET
+#define WAIT RAW_WAIT
+#else
+/* Full model: layer a userspace-only fast path on top of the RAW_*
+ * primitives. SET/RESET/WAIT have exactly the same semantics as
+ * RAW_SET/RAW_RESET/RAW_WAIT, but try to avoid invoking them.
+ */
+#define EV_SET 0
+#define EV_FREE 1
+#define EV_BUSY -1
+
+int state = EV_FREE;
+
+int xchg_result;
+#define SET if :: state != EV_SET -> \
+ atomic { /* xchg_result=xchg(state, EV_SET) */ \
+ xchg_result = state; \
+ state = EV_SET; \
+ } \
+ if :: xchg_result == EV_BUSY -> RAW_SET; \
+ :: else -> skip; \
+ fi; \
+ :: else -> skip; \
+ fi
+
+#define RESET if :: state == EV_SET -> atomic { state = state | EV_FREE; } \
+ :: else -> skip; \
+ fi
+
+int tmp1, tmp2;
+#define WAIT tmp1 = state; \
+ if :: tmp1 != EV_SET -> \
+ if :: tmp1 == EV_FREE -> \
+ RAW_RESET; \
+ atomic { /* tmp2=cas(state, EV_FREE, EV_BUSY) */ \
+ tmp2 = state; \
+ if :: tmp2 == EV_FREE -> state = EV_BUSY; \
+ :: else -> skip; \
+ fi; \
+ } \
+ if :: tmp2 == EV_SET -> tmp1 = EV_SET; \
+ :: else -> tmp1 = EV_BUSY; \
+ fi; \
+ :: else -> skip; \
+ fi; \
+ assert(tmp1 != EV_FREE); \
+ if :: tmp1 == EV_BUSY -> RAW_WAIT; \
+ :: else -> skip; \
+ fi; \
+ :: else -> skip; \
+ fi
+#endif
+
+active proctype waiter()
+{
+ if
+ :: !value ->
+ RESET;
+ if
+ :: !value -> WAIT;
+ :: else -> skip;
+ fi;
+ :: else -> skip;
+ fi;
+ assert(value);
+}
+
+active proctype notifier()
+{
+ value = true;
+ SET;
+}