1 //===-- xray_recursion_guard.h ---------------------------------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file is a part of XRay, a dynamic runtime instrumentation system. 11 // 12 //===----------------------------------------------------------------------===// 13 #ifndef XRAY_XRAY_RECURSION_GUARD_H 14 #define XRAY_XRAY_RECURSION_GUARD_H 15 16 #include "sanitizer_common/sanitizer_atomic.h" 17 18 namespace __xray { 19 20 /// The RecursionGuard is useful for guarding against signal handlers which are 21 /// also potentially calling XRay-instrumented functions. To use the 22 /// RecursionGuard, you'll typically need a thread_local atomic_uint8_t: 23 /// 24 /// thread_local atomic_uint8_t Guard{0}; 25 /// 26 /// // In a handler function: 27 /// void handleArg0(int32_t F, XRayEntryType T) { 28 /// RecursionGuard G(Guard); 29 /// if (!G) 30 /// return; // Failed to acquire the guard. 31 /// ... 32 /// } 33 /// 34 class RecursionGuard { 35 atomic_uint8_t &Running; 36 const bool Valid; 37 38 public: RecursionGuard(atomic_uint8_t & R)39 explicit inline RecursionGuard(atomic_uint8_t &R) 40 : Running(R), Valid(!atomic_exchange(&R, 1, memory_order_acq_rel)) {} 41 42 inline RecursionGuard(const RecursionGuard &) = delete; 43 inline RecursionGuard(RecursionGuard &&) = delete; 44 inline RecursionGuard &operator=(const RecursionGuard &) = delete; 45 inline RecursionGuard &operator=(RecursionGuard &&) = delete; 46 47 explicit inline operator bool() const { return Valid; } 48 ~RecursionGuard()49 inline ~RecursionGuard() noexcept { 50 if (Valid) 51 atomic_store(&Running, 0, memory_order_release); 52 } 53 }; 54 55 } // namespace __xray 56 57 #endif // XRAY_XRAY_RECURSION_GUARD_H 58