compiler-rt/lib/xray/xray_recursion_guard.h

   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
  17 namespace __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 ///
  33 class RecursionGuard {
  34   atomic_uint8_t &Running;
  35   const bool Valid;
  36
  37 public:
  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