atomicops.h

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// Protocol Buffers - Google's data interchange format
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// 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 NoBarrier
// versions are provided when no barriers are needed:
// NoBarrier_Store()
// NoBarrier_Load()
// Although there are currently no compiler enforcement, you are encouraged
// to use these.

// This header and the implementations for each platform (located in
// atomicops_internals_*) must be kept in sync with the upstream code (V8).

#ifndef GOOGLE_PROTOBUF_ATOMICOPS_H_
#define GOOGLE_PROTOBUF_ATOMICOPS_H_

// Don't include this file for people not concerned about thread safety.
#ifndef GOOGLE_PROTOBUF_NO_THREAD_SAFETY

#include <google/protobuf/stubs/platform_macros.h>

namespace google {
namespace protobuf {
namespace internal {

typedef int32 Atomic32;
#ifdef GOOGLE_PROTOBUF_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__) || defined(GOOGLE_PROTOBUF_OS_NACL) || defined(GOOGLE_PROTOBUF_ARCH_SPARC)
// NaCl's intptr_t is not actually 64-bits on 64-bit!
// http://code.google.com/p/nativeclient/issues/detail?id=1162
// sparcv9's pointer type is 32bits
typedef int64 Atomic64;
#else
typedef intptr_t Atomic64;
#endif
#endif

// Use AtomicWord for a machine-sized pointer. It will use the Atomic32 or
// Atomic64 routines below, depending on your architecture.
typedef intptr_t AtomicWord;

// 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.
Atomic32 NoBarrier_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 NoBarrier_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 NoBarrier_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. "Barrier" operations have both "Acquire" and "Release"
// semantics. A MemoryBarrier() has "Barrier" 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);

#if defined(__MINGW32__) && defined(MemoryBarrier)
#undef MemoryBarrier
#endif
void MemoryBarrier();
void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value);
void Acquire_Store(volatile Atomic32* ptr, Atomic32 value);
void Release_Store(volatile Atomic32* ptr, Atomic32 value);

Atomic32 NoBarrier_Load(volatile const Atomic32* ptr);
Atomic32 Acquire_Load(volatile const Atomic32* ptr);
Atomic32 Release_Load(volatile const Atomic32* ptr);

// 64-bit atomic operations (only available on 64-bit processors).
#ifdef GOOGLE_PROTOBUF_ARCH_64_BIT
Atomic64 NoBarrier_CompareAndSwap(volatile Atomic64* ptr,
 Atomic64 old_value,
 Atomic64 new_value);
Atomic64 NoBarrier_AtomicExchange(volatile Atomic64* ptr, Atomic64 new_value);
Atomic64 NoBarrier_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);
void NoBarrier_Store(volatile Atomic64* ptr, Atomic64 value);
void Acquire_Store(volatile Atomic64* ptr, Atomic64 value);
void Release_Store(volatile Atomic64* ptr, Atomic64 value);
Atomic64 NoBarrier_Load(volatile const Atomic64* ptr);
Atomic64 Acquire_Load(volatile const Atomic64* ptr);
Atomic64 Release_Load(volatile const Atomic64* ptr);
#endif // GOOGLE_PROTOBUF_ARCH_64_BIT

} // namespace internal
} // namespace protobuf
} // namespace google

// Include our platform specific implementation.
#define GOOGLE_PROTOBUF_ATOMICOPS_ERROR \
#error "Atomic operations are not supported on your platform"

// ThreadSanitizer, http://clang.llvm.org/docs/ThreadSanitizer.html.
#if defined(THREAD_SANITIZER)
#include <google/protobuf/stubs/atomicops_internals_tsan.h>
// MSVC.
#elif defined(_MSC_VER)
#if defined(GOOGLE_PROTOBUF_ARCH_IA32) || defined(GOOGLE_PROTOBUF_ARCH_X64)
#include <google/protobuf/stubs/atomicops_internals_x86_msvc.h>
#else
GOOGLE_PROTOBUF_ATOMICOPS_ERROR
#endif

// Solaris
#elif defined(GOOGLE_PROTOBUF_OS_SOLARIS)
#include <google/protobuf/stubs/atomicops_internals_solaris.h>

// Apple.
#elif defined(GOOGLE_PROTOBUF_OS_APPLE)
#include <google/protobuf/stubs/atomicops_internals_macosx.h>

// GCC.
#elif defined(__GNUC__)
#if defined(GOOGLE_PROTOBUF_ARCH_IA32) || defined(GOOGLE_PROTOBUF_ARCH_X64)
#include <google/protobuf/stubs/atomicops_internals_x86_gcc.h>
#elif defined(GOOGLE_PROTOBUF_ARCH_ARM) && defined(__linux__)
#include <google/protobuf/stubs/atomicops_internals_arm_gcc.h>
#elif defined(GOOGLE_PROTOBUF_ARCH_AARCH64)
#include <google/protobuf/stubs/atomicops_internals_arm64_gcc.h>
#elif defined(GOOGLE_PROTOBUF_ARCH_ARM_QNX)
#include <google/protobuf/stubs/atomicops_internals_arm_qnx.h>
#elif defined(GOOGLE_PROTOBUF_ARCH_MIPS) || defined(GOOGLE_PROTOBUF_ARCH_MIPS64)
#include <google/protobuf/stubs/atomicops_internals_mips_gcc.h>
#elif defined(__native_client__)
#include <google/protobuf/stubs/atomicops_internals_pnacl.h>
#elif (((__GNUC__ == 4) && (__GNUC_MINOR__ >= 7)) || (__GNUC__ > 4))
#include <google/protobuf/stubs/atomicops_internals_generic_gcc.h>
#elif defined(__clang__)
#if __has_extension(c_atomic)
#include <google/protobuf/stubs/atomicops_internals_generic_gcc.h>
#else
GOOGLE_PROTOBUF_ATOMICOPS_ERROR
#endif
#else
GOOGLE_PROTOBUF_ATOMICOPS_ERROR
#endif

// Unknown.
#else
GOOGLE_PROTOBUF_ATOMICOPS_ERROR
#endif

// On some platforms we need additional declarations to make AtomicWord
// compatible with our other Atomic* types.
#if defined(GOOGLE_PROTOBUF_OS_APPLE)
#include <google/protobuf/stubs/atomicops_internals_atomicword_compat.h>
#endif

#undef GOOGLE_PROTOBUF_ATOMICOPS_ERROR

#endif // GOOGLE_PROTOBUF_NO_THREAD_SAFETY

#endif // GOOGLE_PROTOBUF_ATOMICOPS_H_