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leveldb: Replace AtomicPointer with std::atomic.
This CL removes AtomicPointer from leveldb's port interface. Its usage is replaced with std::atomic<> from the C++11 standard library. AtomicPointer was used to wrap flags, numbers, and pointers, so its instances are replaced with std::atomic<bool>, std::atomic<int>, std::atomic<size_t> and std::atomic<Node*>. This CL does not revise the memory ordering. AtomicPointer's methods are replaced mechanically with their std::atomic equivalents, even when the underlying usage is incorrect. (Example: DBImpl::has_imm_ is written using release stores, even though it is always read using relaxed ordering.) Revising the memory ordering is left for future CLs. ------------- Created by MOE: https://github.com/google/moe MOE_MIGRATED_REVID=237865146xry
costan
5 years ago
committed by
Chris Mumford
Chris Mumford
13 changed files with 210 additions and 419 deletions
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+0 -20db/db_bench.cc
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+17 -16db/db_impl.cc
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+5 -2db/db_impl.h
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+71 -64db/db_test.cc
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+38 -39db/skiplist.h
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+12 -9db/skiplist_test.cc
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+0 -171port/atomic_pointer.h
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+0 -29port/port_example.h
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+0 -1port/port_stdcxx.h
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+2 -3util/arena.cc
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+10 -7util/arena.h
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+31 -26util/env_test.cc
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+24 -32util/env_windows.cc
+ 0
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db/db_bench.cc
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+ 17
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db/db_impl.cc
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+ 5
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db/db_impl.h
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+ 71
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db/db_test.cc
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+ 38
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db/skiplist.h
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db/skiplist_test.cc
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port/atomic_pointer.h
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| @ -1,171 +0,0 @@ | |||
| // Copyright (c) 2011 The LevelDB Authors. All rights reserved. | |||
| // Use of this source code is governed by a BSD-style license that can be | |||
| // found in the LICENSE file. See the AUTHORS file for names of contributors. | |||
| // AtomicPointer provides storage for a lock-free pointer. | |||
| // Platform-dependent implementation of AtomicPointer: | |||
| // - If the platform provides a cheap barrier, we use it with raw pointers | |||
| // - If <atomic> is present (on newer versions of gcc, it is), we use | |||
| // a <atomic>-based AtomicPointer. However we prefer the memory | |||
| // barrier based version, because at least on a gcc 4.4 32-bit build | |||
| // on linux, we have encountered a buggy <atomic> implementation. | |||
| // Also, some <atomic> implementations are much slower than a memory-barrier | |||
| // based implementation (~16ns for <atomic> based acquire-load vs. ~1ns for | |||
| // a barrier based acquire-load). | |||
| // This code is based on atomicops-internals-* in Google's perftools: | |||
| // http://code.google.com/p/google-perftools/source/browse/#svn%2Ftrunk%2Fsrc%2Fbase | |||
| #ifndef PORT_ATOMIC_POINTER_H_ | |||
| #define PORT_ATOMIC_POINTER_H_ | |||
| #include <stdint.h> | |||
| #include <atomic> | |||
| #if defined(_M_X64) || defined(__x86_64__) | |||
| #define ARCH_CPU_X86_FAMILY 1 | |||
| #elif defined(_M_IX86) || defined(__i386__) || defined(__i386) | |||
| #define ARCH_CPU_X86_FAMILY 1 | |||
| #elif defined(__ARMEL__) | |||
| #define ARCH_CPU_ARM_FAMILY 1 | |||
| #elif defined(__aarch64__) | |||
| #define ARCH_CPU_ARM64_FAMILY 1 | |||
| #elif defined(__ppc__) || defined(__powerpc__) || defined(__powerpc64__) | |||
| #define ARCH_CPU_PPC_FAMILY 1 | |||
| #elif defined(__mips__) | |||
| #define ARCH_CPU_MIPS_FAMILY 1 | |||
| #endif | |||
| namespace leveldb { | |||
| namespace port { | |||
| // Define MemoryBarrier() if available | |||
| // Windows on x86 | |||
| #if defined(OS_WIN) && defined(COMPILER_MSVC) && defined(ARCH_CPU_X86_FAMILY) | |||
| // windows.h already provides a MemoryBarrier(void) macro | |||
| // http://msdn.microsoft.com/en-us/library/ms684208(v=vs.85).aspx | |||
| #define LEVELDB_HAVE_MEMORY_BARRIER | |||
| // Mac OS | |||
| #elif defined(__APPLE__) | |||
| inline void MemoryBarrier() { | |||
| std::atomic_thread_fence(std::memory_order_seq_cst); | |||
| } | |||
| #define LEVELDB_HAVE_MEMORY_BARRIER | |||
| // Gcc on x86 | |||
| #elif defined(ARCH_CPU_X86_FAMILY) && defined(__GNUC__) | |||
| inline void MemoryBarrier() { | |||
| // See http://gcc.gnu.org/ml/gcc/2003-04/msg01180.html for a discussion on | |||
| // this idiom. Also see http://en.wikipedia.org/wiki/Memory_ordering. | |||
| __asm__ __volatile__("" : : : "memory"); | |||
| } | |||
| #define LEVELDB_HAVE_MEMORY_BARRIER | |||
| // Sun Studio | |||
| #elif defined(ARCH_CPU_X86_FAMILY) && defined(__SUNPRO_CC) | |||
| inline void MemoryBarrier() { | |||
| // See http://gcc.gnu.org/ml/gcc/2003-04/msg01180.html for a discussion on | |||
| // this idiom. Also see http://en.wikipedia.org/wiki/Memory_ordering. | |||
| asm volatile("" : : : "memory"); | |||
| } | |||
| #define LEVELDB_HAVE_MEMORY_BARRIER | |||
| // ARM Linux | |||
| #elif defined(ARCH_CPU_ARM_FAMILY) && defined(__linux__) | |||
| typedef void (*LinuxKernelMemoryBarrierFunc)(void); | |||
| // The Linux ARM kernel provides a highly optimized device-specific memory | |||
| // barrier function at a fixed memory address that is mapped in every | |||
| // user-level process. | |||
| // | |||
| // This beats using CPU-specific instructions which are, on single-core | |||
| // devices, un-necessary and very costly (e.g. ARMv7-A "dmb" takes more | |||
| // than 180ns on a Cortex-A8 like the one on a Nexus One). Benchmarking | |||
| // shows that the extra function call cost is completely negligible on | |||
| // multi-core devices. | |||
| // | |||
| inline void MemoryBarrier() { | |||
| (*(LinuxKernelMemoryBarrierFunc)0xffff0fa0)(); | |||
| } | |||
| #define LEVELDB_HAVE_MEMORY_BARRIER | |||
| // ARM64 | |||
| #elif defined(ARCH_CPU_ARM64_FAMILY) | |||
| inline void MemoryBarrier() { | |||
| asm volatile("dmb sy" : : : "memory"); | |||
| } | |||
| #define LEVELDB_HAVE_MEMORY_BARRIER | |||
| // PPC | |||
| #elif defined(ARCH_CPU_PPC_FAMILY) && defined(__GNUC__) | |||
| inline void MemoryBarrier() { | |||
| // TODO for some powerpc expert: is there a cheaper suitable variant? | |||
| // Perhaps by having separate barriers for acquire and release ops. | |||
| asm volatile("sync" : : : "memory"); | |||
| } | |||
| #define LEVELDB_HAVE_MEMORY_BARRIER | |||
| // MIPS | |||
| #elif defined(ARCH_CPU_MIPS_FAMILY) && defined(__GNUC__) | |||
| inline void MemoryBarrier() { | |||
| __asm__ __volatile__("sync" : : : "memory"); | |||
| } | |||
| #define LEVELDB_HAVE_MEMORY_BARRIER | |||
| #endif | |||
| // AtomicPointer built using platform-specific MemoryBarrier(). | |||
| #if defined(LEVELDB_HAVE_MEMORY_BARRIER) | |||
| class AtomicPointer { | |||
| private: | |||
| void* rep_; | |||
| public: | |||
| AtomicPointer() { } | |||
| explicit AtomicPointer(void* p) : rep_(p) {} | |||
| inline void* NoBarrier_Load() const { return rep_; } | |||
| inline void NoBarrier_Store(void* v) { rep_ = v; } | |||
| inline void* Acquire_Load() const { | |||
| void* result = rep_; | |||
| MemoryBarrier(); | |||
| return result; | |||
| } | |||
| inline void Release_Store(void* v) { | |||
| MemoryBarrier(); | |||
| rep_ = v; | |||
| } | |||
| }; | |||
| // AtomicPointer based on C++11 <atomic>. | |||
| #else | |||
| class AtomicPointer { | |||
| private: | |||
| std::atomic<void*> rep_; | |||
| public: | |||
| AtomicPointer() { } | |||
| explicit AtomicPointer(void* v) : rep_(v) { } | |||
| inline void* Acquire_Load() const { | |||
| return rep_.load(std::memory_order_acquire); | |||
| } | |||
| inline void Release_Store(void* v) { | |||
| rep_.store(v, std::memory_order_release); | |||
| } | |||
| inline void* NoBarrier_Load() const { | |||
| return rep_.load(std::memory_order_relaxed); | |||
| } | |||
| inline void NoBarrier_Store(void* v) { | |||
| rep_.store(v, std::memory_order_relaxed); | |||
| } | |||
| }; | |||
| #endif | |||
| #undef LEVELDB_HAVE_MEMORY_BARRIER | |||
| #undef ARCH_CPU_X86_FAMILY | |||
| #undef ARCH_CPU_ARM_FAMILY | |||
| #undef ARCH_CPU_ARM64_FAMILY | |||
| #undef ARCH_CPU_PPC_FAMILY | |||
| } // namespace port | |||
| } // namespace leveldb | |||
| #endif // PORT_ATOMIC_POINTER_H_ | |||