text: // Copyright 2010 the V8 project authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  // The routines exported by this module are subtle.  If you use them, even if
  // you get the code right, it will depend on careful reasoning about atomicity
  // and memory ordering; it will be less readable, and harder to maintain.  If
  // you plan to use these routines, you should have a good reason, such as solid
  // evidence that performance would otherwise suffer, or there being no
  // alternative.  You should assume only properties explicitly guaranteed by the
  // specifications in this file.  You are almost certainly _not_ writing code
  // just for the x86; if you assume x86 semantics, x86 hardware bugs and
  // implementations on other archtectures will cause your code to break.  If you
  // do not know what you are doing, avoid these routines, and use a Mutex.
  //
  // It is incorrect to make direct assignments to/from an atomic variable.
  // You should use one of the Load or Store routines.  The Relaxed  versions
  // are provided when no fences are needed:
  //   Relaxed_Store()
  //   Relaxed_Load()
  // Although there are currently no compiler enforcement, you are encouraged
  // to use these.
  //
  
  #ifndef V8_BASE_ATOMICOPS_H_
  #define V8_BASE_ATOMICOPS_H_
  
  #include <stdint.h>
  
  // Small C++ header which defines implementation specific macros used to
  // identify the STL implementation.
  // - libc++: captures __config for _LIBCPP_VERSION
  // - libstdc++: captures bits/c++config.h for __GLIBCXX__
  #include <cstddef>
  
  #include "src/base/base-export.h"
  #include "src/base/build_config.h"
  
  namespace v8 {
  namespace base {
  
  using Atomic8 = char;
  using Atomic16 = int16_t;
  using Atomic32 = int32_t;
  #if defined(V8_HOST_ARCH_64_BIT)
  // We need to be able to go between Atomic64 and AtomicWord implicitly.  This
  // means Atomic64 and AtomicWord should be the same type on 64-bit.
  #if defined(__ILP32__)
  using Atomic64 = int64_t;
  #else
  using Atomic64 = intptr_t;
  #endif  // defined(__ILP32__)
  #endif  // defined(V8_HOST_ARCH_64_BIT)
  
  // Use AtomicWord for a machine-sized pointer.  It will use the Atomic32 or
  // Atomic64 routines below, depending on your architecture.
  using AtomicWord = intptr_t;
  
  // Atomically execute:
  //      result = *ptr;
  //      if (*ptr == old_value)
  //        *ptr = new_value;
  //      return result;
  //
  // I.e., replace "*ptr" with "new_value" if "*ptr" used to be "old_value".
  // Always return the old value of "*ptr"
  //
  // This routine implies no memory barriers.
  Atomic16 Relaxed_CompareAndSwap(volatile Atomic16* ptr, Atomic16 old_value,
                                  Atomic16 new_value);
  Atomic32 Relaxed_CompareAndSwap(volatile Atomic32* ptr, Atomic32 old_value,
                                  Atomic32 new_value);
  
  // Atomically store new_value into *ptr, returning the previous value held in
  // *ptr.  This routine implies no memory barriers.
  Atomic32 Relaxed_AtomicExchange(volatile Atomic32* ptr, Atomic32 new_value);
  
  // Atomically increment *ptr by "increment".  Returns the new value of
  // *ptr with the increment applied.  This routine implies no memory barriers.
  Atomic32 Relaxed_AtomicIncrement(volatile Atomic32* ptr, Atomic32 increment);
  
  Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
                                   Atomic32 increment);
  
  // These following lower-level operations are typically useful only to people
  // implementing higher-level synchronization operations like spinlocks,
  // mutexes, and condition-variables.  They combine CompareAndSwap(), a load,
  // or a store with appropriate memory-ordering instructions.  "Acquire"
  // operations ensure that no later memory access can be reordered ahead of the
  // operation. "Release" operations ensure that no previous memory access can
  // be reordered after the operation.  "Fence" operations have both "Acquire"
  // and "Release" semantics. A SeqCst_MemoryFence() has "Fence" semantics, but
  // does no memory access.
  Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
                                  Atomic32 old_value,
                                  Atomic32 new_value);
  Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
                                  Atomic32 old_value,
                                  Atomic32 new_value);
  Atomic32 AcquireRelease_CompareAndSwap(volatile Atomic32* ptr,
                                         Atomic32 old_value, Atomic32 new_value);
  
  void SeqCst_MemoryFence();
  void Relaxed_Store(volatile Atomic8* ptr, Atomic8 value);
  void Relaxed_Store(volatile Atomic16* ptr, Atomic16 value);
  void Relaxed_Store(volatile Atomic32* ptr, Atomic32 value);
  void Release_Store(volatile Atomic32* ptr, Atomic32 value);
  
  Atomic8 Relaxed_Load(volatile const Atomic8* ptr);
  Atomic16 Relaxed_Load(volatile const Atomic16* ptr);
  Atomic32 Relaxed_Load(volatile const Atomic32* ptr);
  Atomic32 Acquire_Load(volatile const Atomic32* ptr);
  
  // 64-bit atomic operations (only available on 64-bit processors).
  #ifdef V8_HOST_ARCH_64_BIT
  Atomic64 Relaxed_CompareAndSwap(volatile Atomic64* ptr, Atomic64 old_value,
                                  Atomic64 new_value);
  Atomic64 Relaxed_AtomicExchange(volatile Atomic64* ptr, Atomic64 new_value);
  Atomic64 Relaxed_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment);
  Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment);
  
  Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr,
                                  Atomic64 old_value,
                                  Atomic64 new_value);
  Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr, Atomic64 old_value,
                                  Atomic64 new_value);
  Atomic64 AcquireRelease_CompareAndSwap(volatile Atomic64* ptr,
                                         Atomic64 old_value, Atomic64 new_value);
  void Relaxed_Store(volatile Atomic64* ptr, Atomic64 value);
  void Release_Store(volatile Atomic64* ptr, Atomic64 value);
  Atomic64 Relaxed_Load(volatile const Atomic64* ptr);
  Atomic64 Acquire_Load(volatile const Atomic64* ptr);
  #endif  // V8_HOST_ARCH_64_BIT
  
  }  // namespace base
  }  // namespace v8
  
  #if defined(V8_OS_WIN)
  #include "src/base/atomicops_internals_std.h"
  #else
  // TODO(ulan): Switch to std version after performance regression with Wheezy
  // sysroot is no longer relevant. Debian Wheezy LTS ends on 31st of May 2018.
  #include "src/base/atomicops_internals_portable.h"
  #endif
  
  // On some platforms we need additional declarations to make
  // AtomicWord compatible with our other Atomic* types.
  #if defined(V8_OS_MACOSX) || defined(V8_OS_OPENBSD) || defined(V8_OS_AIX)
  #include "src/base/atomicops_internals_atomicword_compat.h"
  #endif
  
  #endif  // V8_BASE_ATOMICOPS_H_
  