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The C and C++ Include Header Files

/usr/include/nodejs/deps/v8/include/cppgc/internal/atomic-entry-flag.h


$ cat -n /usr/include/nodejs/deps/v8/include/cppgc/internal/atomic-entry-flag.h

     1	// Copyright 2020 the V8 project authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style license that can be
     3	// found in the LICENSE file.
     4	
     5	#ifndef INCLUDE_CPPGC_INTERNAL_ATOMIC_ENTRY_FLAG_H_
     6	#define INCLUDE_CPPGC_INTERNAL_ATOMIC_ENTRY_FLAG_H_
     7	
     8	#include <atomic>
     9	
    10	namespace cppgc {
    11	namespace internal {
    12	
    13	// A flag which provides a fast check whether a scope may be entered on the
    14	// current thread, without needing to access thread-local storage or mutex.  Can
    15	// have false positives (i.e., spuriously report that it might be entered), so
    16	// it is expected that this will be used in tandem with a precise check that the
    17	// scope is in fact entered on that thread.
    18	//
    19	// Example:
    20	//   g_frobnicating_flag.MightBeEntered() &&
    21	//   ThreadLocalFrobnicator().IsFrobnicating()
    22	//
    23	// Relaxed atomic operations are sufficient, since:
    24	// - all accesses remain atomic
    25	// - each thread must observe its own operations in order
    26	// - no thread ever exits the flag more times than it enters (if used correctly)
    27	// And so if a thread observes zero, it must be because it has observed an equal
    28	// number of exits as entries.
    29	class AtomicEntryFlag final {
    30	 public:
    31	  void Enter() { entries_.fetch_add(1, std::memory_order_relaxed); }
    32	  void Exit() { entries_.fetch_sub(1, std::memory_order_relaxed); }
    33	
    34	  // Returns false only if the current thread is not between a call to Enter
    35	  // and a call to Exit. Returns true if this thread or another thread may
    36	  // currently be in the scope guarded by this flag.
    37	  bool MightBeEntered() const {
    38	    return entries_.load(std::memory_order_relaxed) != 0;
    39	  }
    40	
    41	 private:
    42	  std::atomic_int entries_{0};
    43	};
    44	
    45	}  // namespace internal
    46	}  // namespace cppgc
    47	
    48	#endif  // INCLUDE_CPPGC_INTERNAL_ATOMIC_ENTRY_FLAG_H_