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      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:
     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 
     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