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 57