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_InterlockedCompareExchange 内部函数

  • 项目

Microsoft 专用

执行联锁比较和交换。

语法

long _InterlockedCompareExchange(
   long volatile * Destination,
   long Exchange,
   long Comparand
);
long _InterlockedCompareExchange_acq(
   long volatile * Destination,
   long Exchange,
   long Comparand
);
long _InterlockedCompareExchange_HLEAcquire(
   long volatile * Destination,
   long Exchange,
   long Comparand
);
long _InterlockedCompareExchange_HLERelease(
   long volatile * Destination,
   long Exchange,
   long Comparand
);
long _InterlockedCompareExchange_nf(
   long volatile * Destination,
   long Exchange,
   long Comparand
);
long _InterlockedCompareExchange_np(
   long volatile * Destination,
   long Exchange,
   long Comparand
);
long _InterlockedCompareExchange_rel(
   long volatile * Destination,
   long Exchange,
   long Comparand
);
char _InterlockedCompareExchange8(
   char volatile * Destination,
   char Exchange,
   char Comparand
);
char _InterlockedCompareExchange8_acq(
   char volatile * Destination,
   char Exchange,
   char Comparand
);
char _InterlockedCompareExchange8_nf(
   char volatile * Destination,
   char Exchange,
   char Comparand
);
char _InterlockedCompareExchange8_rel(
   char volatile * Destination,
   char Exchange,
   char Comparand
);
short _InterlockedCompareExchange16(
   short volatile * Destination,
   short Exchange,
   short Comparand
);
short _InterlockedCompareExchange16_acq(
   short volatile * Destination,
   short Exchange,
   short Comparand
);
short _InterlockedCompareExchange16_nf(
   short volatile * Destination,
   short Exchange,
   short Comparand
);
short _InterlockedCompareExchange16_np(
   short volatile * Destination,
   short Exchange,
   short Comparand
);
short _InterlockedCompareExchange16_rel(
   short volatile * Destination,
   short Exchange,
   short Comparand
);
__int64 _InterlockedCompareExchange64(
   __int64 volatile * Destination,
   __int64 Exchange,
   __int64 Comparand
);
__int64 _InterlockedCompareExchange64_acq(
   __int64 volatile * Destination,
   __int64 Exchange,
   __int64 Comparand
);
__int64 _InterlockedCompareExchange64_HLEAcquire (
   __int64 volatile * Destination,
   __int64 Exchange,
   __int64 Comparand
);
__int64 _InterlockedCompareExchange64_HLERelease(
   __int64 volatile * Destination,
   __int64 Exchange,
   __int64 Comparand
);
__int64 _InterlockedCompareExchange64_nf(
   __int64 volatile * Destination,
   __int64 Exchange,
   __int64 Comparand
);
__int64 _InterlockedCompareExchange64_np(
   __int64 volatile * Destination,
   __int64 Exchange,
   __int64 Comparand
);
__int64 _InterlockedCompareExchange64_rel(
   __int64 volatile * Destination,
   __int64 Exchange,
   __int64 Comparand
);

参数

Destination
[in, out] 指向目标值的指针。 忽略此标记。

Exchange
[in] 交换值。 忽略此标记。

Comparand
[in] 与 Destination 指向的值进行比较的值。 忽略此标记。

返回值

返回值是 Destination 指针指向的初始值。

要求

Intrinsic 体系结构 标头
_InterlockedCompareExchange, _InterlockedCompareExchange8, _InterlockedCompareExchange16, _InterlockedCompareExchange64 x86、ARM、x64、ARM64 <intrin.h>
_InterlockedCompareExchange_acq, _InterlockedCompareExchange_nf, _InterlockedCompareExchange_rel, _InterlockedCompareExchange8_acq, _InterlockedCompareExchange8_nf, _InterlockedCompareExchange8_rel,_InterlockedCompareExchange16_acq, _InterlockedCompareExchange16_nf, _InterlockedCompareExchange16_rel, _InterlockedCompareExchange64_acq, _InterlockedCompareExchange64_nf, _InterlockedCompareExchange64_rel, ARM、ARM64 <intrin.h>
_InterlockedCompareExchange_np, _InterlockedCompareExchange16_np, _InterlockedCompareExchange64_np x64 <intrin.h>
_InterlockedCompareExchange_HLEAcquire, _InterlockedCompareExchange_HLERelease, _InterlockedCompareExchange64_HLEAcquire, _InterlockedCompareExchange64_HLERelease x86、x64 <immintrin.h>

注解

_InterlockedCompareExchange 将 Destination 指向的值与 Comparand 值进行原子比较。 如果 Destination 值等于 Comparand 值，Exchange 值将存储在由 Destination 指定的地址。 否则，不执行任何操作。

_InterlockedCompareExchange 为 Win32 Windows SDK InterlockedCompareExchange 函数提供编译器内部支持。

_InterlockedCompareExchange 存在几种变体，这些变体根据其涉及的数据类型和是否使用特定于处理器获取或发布语义而有所不同。

当 _InterlockedCompareExchange 函数对 32 位 long 整数值操作时，_InterlockedCompareExchange8 对 8 位整数值操作，_InterlockedCompareExchange16 对 16 位 short 整数值操作且 _InterlockedCompareExchange64 对 64 位整数值操作。 若要详细了解 128 位值的类似内部函数，请参阅 _InterlockedCompareExchange128。

在所有 ARM 平台上，可以使用带 _acq 和 _rel 后缀的内部函数获取和发布语义，例如在关键部分的起始位置。 带 _nf（“无围墙”）后缀的 ARM 内部函数不能充当内存屏障。

带 _np（“无预取”）后缀的函数可以阻止编译器插入可能的预取操作。

在支持硬件锁省略 (HLE) 指令的 Intel 平台，带 _HLEAcquire 和 _HLERelease 后缀的内部函数包括一个发送到处理器的提示，可以通过消除硬件中的锁写步骤来提升速度。 如果在不支持 HLE 的平台上调用这些内部函数，则忽略此提示。

这些例程只能用作内部函数。

示例

在以下示例中，_InterlockedCompareExchange 用于简单的低等级线程同步。 此方法作为多线程编程基础时有其自身的局限性；介绍此方法旨在说明联锁内部函数的典型用法。 要得到最佳结果，请使用 Windows API。 有关多线程编程的详细信息，请参阅编写多线程 Win32 程序。

// intrinExample.cpp
// compile with: /EHsc /O2
// Simple example of using _Interlocked* intrinsics to
// do manual synchronization
//
// Add [-DSKIP_LOCKING] to the command line to disable
// the locking. This will cause the threads to execute out
// of sequence.

#define _CRT_RAND_S

#include "windows.h"

#include <iostream>
#include <queue>
#include <intrin.h>

using namespace std;

// --------------------------------------------------------------------

// if defined, will not do any locking on shared data
//#define SKIP_LOCKING

// A common way of locking using _InterlockedCompareExchange.
// Refer to other sources for a discussion of the many issues
// involved. For example, this particular locking scheme performs well
// when lock contention is low, as the while loop overhead is small and
// locks are acquired very quickly, but degrades as many callers want
// the lock and most threads are doing a lot of interlocked spinning.
// There are also no guarantees that a caller will ever acquire the
// lock.
namespace MyInterlockedIntrinsicLock
{
    typedef unsigned LOCK, *PLOCK;

#pragma intrinsic(_InterlockedCompareExchange, _InterlockedExchange)

    enum {LOCK_IS_FREE = 0, LOCK_IS_TAKEN = 1};

    void Lock(PLOCK pl)
    {
#if !defined(SKIP_LOCKING)
        // If *pl == LOCK_IS_FREE, it is set to LOCK_IS_TAKEN
        // atomically, so only 1 caller gets the lock.
        // If *pl == LOCK_IS_TAKEN,
        // the result is LOCK_IS_TAKEN, and the while loop keeps spinning.
        while (_InterlockedCompareExchange((long *)pl,
                                           LOCK_IS_TAKEN, // exchange
                                           LOCK_IS_FREE)  // comparand
               == LOCK_IS_TAKEN)
        {
            // spin!
        }
        // This will also work.
        //while (_InterlockedExchange(pl, LOCK_IS_TAKEN) ==
        //                             LOCK_IS_TAKEN)
        //{
        //    // spin!
        //}

        // At this point, the lock is acquired.
#endif
    }

    void Unlock(PLOCK pl) {
#if !defined(SKIP_LOCKING)
        _InterlockedExchange((long *)pl, LOCK_IS_FREE);
#endif
    }
}

// ------------------------------------------------------------------
// Data shared by threads

queue<int> SharedQueue;
MyInterlockedIntrinsicLock::LOCK SharedLock;
int TicketNumber;

// ------------------------------------------------------------------

DWORD WINAPI
ProducerThread(
    LPVOID unused
    )
{
    unsigned int randValue;
    while (1) {
        // Acquire shared data. Enter critical section.
        MyInterlockedIntrinsicLock::Lock(&SharedLock);

        //cout << ">" << TicketNumber << endl;
        SharedQueue.push(TicketNumber++);

        // Release shared data. Leave critical section.
        MyInterlockedIntrinsicLock::Unlock(&SharedLock);

        rand_s(&randValue);
        Sleep(randValue % 20);
    }

    return 0;
}

DWORD WINAPI
ConsumerThread(
    LPVOID unused
    )
{
    while (1) {
        // Acquire shared data. Enter critical section
        MyInterlockedIntrinsicLock::Lock(&SharedLock);

        if (!SharedQueue.empty()) {
            int x = SharedQueue.front();
            cout << "<" << x << endl;
            SharedQueue.pop();
        }

        // Release shared data. Leave critical section
        MyInterlockedIntrinsicLock::Unlock(&SharedLock);

        unsigned int randValue;
        rand_s(&randValue);
        Sleep(randValue % 20);
    }
    return 0;
}

int main(
    void
    )
{
    const int timeoutTime = 500;
    int unused1, unused2;
    HANDLE threads[4];

    // The program creates 4 threads:
    // two producer threads adding to the queue
    // and two consumers taking data out and printing it.
    threads[0] = CreateThread(NULL,
                              0,
                              ProducerThread,
                              &unused1,
                              0,
                              (LPDWORD)&unused2);

    threads[1] = CreateThread(NULL,
                              0,
                              ConsumerThread,
                              &unused1,
                              0,
                              (LPDWORD)&unused2);

    threads[2] = CreateThread(NULL,
                              0,
                              ProducerThread,
                              &unused1,
                              0,
                              (LPDWORD)&unused2);

    threads[3] = CreateThread(NULL,
                              0,
                              ConsumerThread,
                              &unused1,
                              0,
                              (LPDWORD)&unused2);

    WaitForMultipleObjects(4, threads, TRUE, timeoutTime);

    return 0;
}

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结束 Microsoft 专用

另请参阅

_InterlockedCompareExchange128
_InterlockedCompareExchangePointer 内部函数
编译器内部函数
关键字
与 x86 编译器冲突