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-// 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>
-#ifdef LEVELDB_ATOMIC_PRESENT
-#include <atomic>
-#endif
-#ifdef OS_WIN
-#include <windows.h>
-#endif
-#ifdef OS_MACOSX
-#include <libkern/OSAtomic.h>
-#endif
-
-#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 {
-
-// AtomicPointer based on <cstdatomic> if available
-#if defined(LEVELDB_ATOMIC_PRESENT)
-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);
- }
-};
-
-#else
-
-// 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(OS_MACOSX)
-inline void MemoryBarrier() {
- OSMemoryBarrier();
-}
-#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;
- }
-};
-
-// Atomic pointer based on sparc memory barriers
-#elif defined(__sparcv9) && defined(__GNUC__)
-class AtomicPointer {
- private:
- void* rep_;
- public:
- AtomicPointer() { }
- explicit AtomicPointer(void* v) : rep_(v) { }
- inline void* Acquire_Load() const {
- void* val;
- __asm__ __volatile__ (
- "ldx [%[rep_]], %[val] \n\t"
- "membar #LoadLoad|#LoadStore \n\t"
- : [val] "=r" (val)
- : [rep_] "r" (&rep_)
- : "memory");
- return val;
- }
- inline void Release_Store(void* v) {
- __asm__ __volatile__ (
- "membar #LoadStore|#StoreStore \n\t"
- "stx %[v], [%[rep_]] \n\t"
- :
- : [rep_] "r" (&rep_), [v] "r" (v)
- : "memory");
- }
- inline void* NoBarrier_Load() const { return rep_; }
- inline void NoBarrier_Store(void* v) { rep_ = v; }
-};
-
-// Atomic pointer based on ia64 acq/rel
-#elif defined(__ia64) && defined(__GNUC__)
-class AtomicPointer {
- private:
- void* rep_;
- public:
- AtomicPointer() { }
- explicit AtomicPointer(void* v) : rep_(v) { }
- inline void* Acquire_Load() const {
- void* val ;
- __asm__ __volatile__ (
- "ld8.acq %[val] = [%[rep_]] \n\t"
- : [val] "=r" (val)
- : [rep_] "r" (&rep_)
- : "memory"
- );
- return val;
- }
- inline void Release_Store(void* v) {
- __asm__ __volatile__ (
- "st8.rel [%[rep_]] = %[v] \n\t"
- :
- : [rep_] "r" (&rep_), [v] "r" (v)
- : "memory"
- );
- }
- inline void* NoBarrier_Load() const { return rep_; }
- inline void NoBarrier_Store(void* v) { rep_ = v; }
-};
-
-// We have neither MemoryBarrier(), nor <atomic>
-#else
-#error Please implement AtomicPointer for this platform.
-
-#endif
-#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_