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diff --git a/lib/xray/xray_recursion_guard.h b/lib/xray/xray_recursion_guard.h
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+//===-- xray_recursion_guard.h ---------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of XRay, a dynamic runtime instrumentation system.
+//
+//===----------------------------------------------------------------------===//
+#ifndef XRAY_XRAY_RECURSION_GUARD_H
+#define XRAY_XRAY_RECURSION_GUARD_H
+
+#include "sanitizer_common/sanitizer_atomic.h"
+
+namespace __xray {
+
+/// The RecursionGuard is useful for guarding against signal handlers which are
+/// also potentially calling XRay-instrumented functions. To use the
+/// RecursionGuard, you'll typically need a thread_local atomic_uint8_t:
+///
+///   thread_local atomic_uint8_t Guard{0};
+///
+///   // In a handler function:
+///   void handleArg0(int32_t F, XRayEntryType T) {
+///     RecursionGuard G(Guard);
+///     if (!G)
+///       return;  // Failed to acquire the guard.
+///     ...
+///   }
+///
+class RecursionGuard {
+  atomic_uint8_t &Running;
+  const bool Valid;
+
+public:
+  explicit inline RecursionGuard(atomic_uint8_t &R)
+      : Running(R), Valid(!atomic_exchange(&R, 1, memory_order_acq_rel)) {}
+
+  inline RecursionGuard(const RecursionGuard &) = delete;
+  inline RecursionGuard(RecursionGuard &&) = delete;
+  inline RecursionGuard &operator=(const RecursionGuard &) = delete;
+  inline RecursionGuard &operator=(RecursionGuard &&) = delete;
+
+  explicit inline operator bool() const { return Valid; }
+
+  inline ~RecursionGuard() noexcept {
+    if (Valid)
+      atomic_store(&Running, 0, memory_order_release);
+  }
+};
+
+} // namespace __xray
+
+#endif // XRAY_XRAY_RECURSION_GUARD_H