Summary: RocksDB already depends on C++11, so we might as well all the goodness that C++11 provides. This means that we don't need AtomicPointer anymore. The less things in port/, the easier it will be to port to other platforms. Test Plan: make check + careful visual review verifying that NoBarried got memory_order_relaxed, while Acquire/Release methods got memory_order_acquire and memory_order_release Reviewers: rven, yhchiang, ljin, sdong Reviewed By: ljin Subscribers: leveldb Differential Revision: https://reviews.facebook.net/D27543main
Igor Canadi
10 years ago
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f37048ad1d
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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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// AtomicPointer provides storage for a lock-free pointer.
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// Platform-dependent implementation of AtomicPointer:
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// - If the platform provides a cheap barrier, we use it with raw pointers
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// - If cstdatomic is present (on newer versions of gcc, it is), we use
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// a cstdatomic-based AtomicPointer. However we prefer the memory
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// barrier based version, because at least on a gcc 4.4 32-bit build
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// on linux, we have encountered a buggy <cstdatomic>
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// implementation. Also, some <cstdatomic> implementations are much
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// slower than a memory-barrier based implementation (~16ns for
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// <cstdatomic> based acquire-load vs. ~1ns for a barrier based
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// acquire-load).
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// This code is based on atomicops-internals-* in Google's perftools:
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// http://code.google.com/p/google-perftools/source/browse/#svn%2Ftrunk%2Fsrc%2Fbase
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#ifndef PORT_ATOMIC_POINTER_H_ |
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#define PORT_ATOMIC_POINTER_H_ |
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#include <stdint.h> |
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#ifdef ROCKSDB_ATOMIC_PRESENT |
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#include <atomic> |
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#endif |
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#ifdef OS_WIN |
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#include <windows.h> |
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#endif |
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#ifdef OS_MACOSX |
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#include <libkern/OSAtomic.h> |
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#endif |
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#if defined(_M_X64) || defined(__x86_64__) |
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#define ARCH_CPU_X86_FAMILY 1 |
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#elif defined(_M_IX86) || defined(__i386__) || defined(__i386) |
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#define ARCH_CPU_X86_FAMILY 1 |
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#elif defined(__ARMEL__) |
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#define ARCH_CPU_ARM_FAMILY 1 |
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#endif |
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namespace rocksdb { |
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namespace port { |
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// Define MemoryBarrier() if available
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// Windows on x86
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#if defined(OS_WIN) && defined(COMPILER_MSVC) && defined(ARCH_CPU_X86_FAMILY) |
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// windows.h already provides a MemoryBarrier(void) macro
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// http://msdn.microsoft.com/en-us/library/ms684208(v=vs.85).aspx
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#define ROCKSDB_HAVE_MEMORY_BARRIER |
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// Gcc on x86
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#elif defined(ARCH_CPU_X86_FAMILY) && defined(__GNUC__) |
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inline void MemoryBarrier() { |
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// See http://gcc.gnu.org/ml/gcc/2003-04/msg01180.html for a discussion on
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// this idiom. Also see http://en.wikipedia.org/wiki/Memory_ordering.
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__asm__ __volatile__("" : : : "memory"); |
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} |
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#define ROCKSDB_HAVE_MEMORY_BARRIER |
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// Sun Studio
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#elif defined(ARCH_CPU_X86_FAMILY) && defined(__SUNPRO_CC) |
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inline void MemoryBarrier() { |
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// See http://gcc.gnu.org/ml/gcc/2003-04/msg01180.html for a discussion on
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// this idiom. Also see http://en.wikipedia.org/wiki/Memory_ordering.
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asm volatile("" : : : "memory"); |
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} |
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#define ROCKSDB_HAVE_MEMORY_BARRIER |
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// Mac OS
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#elif defined(OS_MACOSX) |
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inline void MemoryBarrier() { |
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OSMemoryBarrier(); |
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} |
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#define ROCKSDB_HAVE_MEMORY_BARRIER |
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// ARM Linux
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#elif defined(ARCH_CPU_ARM_FAMILY) && defined(__linux__) |
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typedef void (*LinuxKernelMemoryBarrierFunc)(void); |
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// The Linux ARM kernel provides a highly optimized device-specific memory
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// barrier function at a fixed memory address that is mapped in every
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// user-level process.
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//
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// This beats using CPU-specific instructions which are, on single-core
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// devices, un-necessary and very costly (e.g. ARMv7-A "dmb" takes more
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// than 180ns on a Cortex-A8 like the one on a Nexus One). Benchmarking
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// shows that the extra function call cost is completely negligible on
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// multi-core devices.
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//
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inline void MemoryBarrier() { |
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(*(LinuxKernelMemoryBarrierFunc)0xffff0fa0)(); |
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} |
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#define ROCKSDB_HAVE_MEMORY_BARRIER |
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#endif |
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// AtomicPointer built using platform-specific MemoryBarrier()
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#if defined(ROCKSDB_HAVE_MEMORY_BARRIER) |
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class AtomicPointer { |
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private: |
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void* rep_; |
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public: |
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AtomicPointer() { } |
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explicit AtomicPointer(void* p) : rep_(p) {} |
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inline void* NoBarrier_Load() const { return rep_; } |
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inline void NoBarrier_Store(void* v) { rep_ = v; } |
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inline void* Acquire_Load() const { |
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void* result = rep_; |
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MemoryBarrier(); |
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return result; |
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} |
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inline void Release_Store(void* v) { |
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MemoryBarrier(); |
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rep_ = v; |
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} |
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}; |
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// AtomicPointer based on <atomic>
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#elif defined(ROCKSDB_ATOMIC_PRESENT) |
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class AtomicPointer { |
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private: |
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std::atomic<void*> rep_; |
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public: |
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AtomicPointer() { } |
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explicit AtomicPointer(void* v) : rep_(v) { } |
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inline void* Acquire_Load() const { |
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return rep_.load(std::memory_order_acquire); |
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} |
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inline void Release_Store(void* v) { |
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rep_.store(v, std::memory_order_release); |
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} |
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inline void* NoBarrier_Load() const { |
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return rep_.load(std::memory_order_relaxed); |
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} |
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inline void NoBarrier_Store(void* v) { |
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rep_.store(v, std::memory_order_relaxed); |
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} |
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}; |
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// We have neither MemoryBarrier(), nor <cstdatomic>
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#else |
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#error Please implement AtomicPointer for this platform. |
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#endif |
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#undef ROCKSDB_HAVE_MEMORY_BARRIER |
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#undef ARCH_CPU_X86_FAMILY |
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#undef ARCH_CPU_ARM_FAMILY |
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} // namespace port
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} // namespace rocksdb
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#endif // PORT_ATOMIC_POINTER_H_
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