turn locks into no-ops when compiled with -DSINGLE_THREAD

src/util/mutex.h

@@ -0,0 +1,35 @@
+/*++
+Copyright (c) 2019 Microsoft Corporation
+
+Module Name:
+
+    mutex.h
+
+Abstract:
+
+    Auxiliary macros for mutual exclusion
+
+--*/
+#pragma once
+
+#ifdef SINGLE_THREAD
+
+template<typename T> using atomic = T;
+
+struct mutex {
+  void lock() {}
+  void unlock() {}
+};
+
+struct lock_guard {
+  lock_guard(mutex &) {}
+};
+
+#else
+#include <atomic>
+#include <mutex>
+
+template<typename T> using atomic = std::atomic<T>;
+typedef std::mutex mutex;
+typedef std::lock_guard<std::mutex> lock_guard;
+#endif