1//===-- xray_recursion_guard.h ---------------------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file is a part of XRay, a dynamic runtime instrumentation system.
10//
11//===----------------------------------------------------------------------===//
12#ifndef XRAY_XRAY_RECURSION_GUARD_H
13#define XRAY_XRAY_RECURSION_GUARD_H
14
15#include "sanitizer_common/sanitizer_atomic.h"
16
17namespace __xray {
18
19/// The RecursionGuard is useful for guarding against signal handlers which are
20/// also potentially calling XRay-instrumented functions. To use the
21/// RecursionGuard, you'll typically need a thread_local atomic_uint8_t:
22///
23///   thread_local atomic_uint8_t Guard{0};
24///
25///   // In a handler function:
26///   void handleArg0(int32_t F, XRayEntryType T) {
27///     RecursionGuard G(Guard);
28///     if (!G)
29///       return;  // Failed to acquire the guard.
30///     ...
31///   }
32///
33class RecursionGuard {
34  atomic_uint8_t &Running;
35  const bool Valid;
36
37public:
38  explicit inline RecursionGuard(atomic_uint8_t &R)
39      : Running(R), Valid(!atomic_exchange(&R, 1, memory_order_acq_rel)) {}
40
41  inline RecursionGuard(const RecursionGuard &) = delete;
42  inline RecursionGuard(RecursionGuard &&) = delete;
43  inline RecursionGuard &operator=(const RecursionGuard &) = delete;
44  inline RecursionGuard &operator=(RecursionGuard &&) = delete;
45
46  explicit inline operator bool() const { return Valid; }
47
48  inline ~RecursionGuard() noexcept {
49    if (Valid)
50      atomic_store(&Running, 0, memory_order_release);
51  }
52};
53
54} // namespace __xray
55
56#endif // XRAY_XRAY_RECURSION_GUARD_H
57