c# – 如何取消执行非托管C外部例程的任务

我正在尝试修复C#异步代码,启动在非托管C例程中编写的外部dll中执行的可取消操作.

有没有办法在创建时使用传递给Task的Cancellation Token取消任务,如果用户委托调用外部非托管C例程？

据我所知,任务取消涉及用户代表与请求取消的代码之间的合作.成功取消涉及请求代码调用CancellationTokenSource.Cancel方法,并且用户委托及时终止操作,方法是在他注意到已经提出取消请求时通过简单地从委托返回(通过轮询CancellationToken.IsCancellationRequested方法)或使用CancellationToken.ThrowIfCancellationRequested方法抛出OperationCanceledException. (cf http://msdn.microsoft.com/en-us/library/dd997396%28v=vs.110%29.aspx)

这两种方式涉及由用户委托执行的非托管C例程通过接收CancellationToken作为参数并通过定期调用其IsCancellationRequested和/或ThrowIfCancellationRequested方法来进行协作.

是否可以通过非托管外部C例程执行此操作？

如果没有,当请求代码请求取消时,是否有办法强制终止执行用户委托的任务(执行非托管c例程)？

下面是我正在尝试修复的混合C#/ C Cli / Unmanaged C代码的示例(摘录),以便能够取消C非托管代码部分中用户委托执行的操作：

FrmDemo.cs：———————————————- —————————

public class FrmDemo : Form
{
    private CliClass m_CliObject;
    private System.Threading.CancellationTokenSource m_Cts;
    private System.Threading.CancellationToken m_Ct;

    private void FrmDemo_Load(object sender, EventArgs e)
    {
        // Creating the external CliObject:
        this.m_CliObject = new NSDemo.CliClass();
        ...
    }

    // Event handler of the button starting the cancelable asynchrone operation:
    private async void btnStart_Click(object sender, EventArgs e)
    {
        m_Cts = new System.Threading.CancellationTokenSource();
        m_Ct = m_Cts.Token;
        await Task.Factory.StartNew(() =>
        {
              // Launching a cancelable operation performed by a managed C++Cli Object :
              this.m_CliObject.DoSomething();   // How to eventually pass the CancellationToken m_ct to the m_CliObject ?
        }, m_ct);
        ...
    }


    //Event handler of the cancel button:
    private void btnCancel_Click(object sender, EventArgs e)
    {
        // Requesting cancellation:
        m_Cts.Cancel();
        // (Or alternatively, how to eventually force the termination of the async Task without collaboration from it ?)
    }

CliClass.h：———————————————- ——-

#include "DemoCore.h"

using namespace System;
using namespace System::Runtime::InteropServices;
using namespace cli;

namespace NSDemo
{
    public ref class CliClass
    {

    public:

        CliClass();

        ~CliClass(); 

        void DoSomething()
        {
            // Performing the operation in the unmanaged coreObject:
            _coreObject->DoSomething();
        }

    private:
        UNSDemo::CoreClass *_coreObject;
        bool _disposed;

    };
}

CliClass.cpp：——————————————

namespace NSDemo
{
    CliClass::CliClass()
    {
         _coreObject = new UNSDemo::CoreClass(...);
        ....
    }

    CliClass::~CliClass()
    {
        if (_disposed)
            return;               
        if (_coreObject != nullptr) {
            delete _coreObject;
            _coreObject = nullptr;
        }
        _disposed = true;
        GC::SuppressFinalize(this);
    }

CoreClass.h-----------------------------------------------------------------

namespace UNSDemo {

    class __declspec(dllexport) CoreClass {
    public:
        ScanningCore();

        ~ScanningCore();

        void DoSomething();

    private:

    ...

    };

}

CoreClass.cpp：———————————————- ——————————

#include "CoreClass.h"

namespace UNSDemo {

    CoreClass::CoreClass()
    {
        ...
    }

    CoreClass::~CoreClass()
    {
        ...
    }

    // Method actually performing the cancelable operation:
    void CoreClass::DoSomething()
    {
        // Main loop of the unmanaged cancelable operation:
        while (...) {
            ...
            // How to check the cancellation request from here ? (How to access the CancellationToken ?)
            // and if cancellation is requested, how to eventually throw the OperationCanceledException ?

        }
    }
}

感谢您的任何帮助.

解决方法:

如果你正在处理纯粹的非托管代码,它不知道CancellationToken类,所以你不能像托管代码那样传递它.

我要做的是声明你的非托管方法获取指向布尔值的指针,如果布尔值设置为true,则让非托管代码自行中止.在您的包装器中,使用CancellationToken.Register注册一个回调,该回调将取消CancellationToken时将Boolean设置为true.

这听起来很简单,但它有点复杂,因为您需要一个托管事件处理程序,它可以访问您允许获取地址的布尔值.

public ref class CancelableTaskWrapper
{
private:
    bool* isCanceled;
    void (*unmanagedFunctionPointer)(bool*);

    void Canceled() { if (isCanceled != nullptr) *isCanceled = true; }

public:
    CancelableTaskWrapper(void (*unmanagedFunctionPointer)(bool*))
    {
        this->unmanagedFunctionPointer = unmanagedFunctionPointer;

        isCanceled = new bool;
    }

    ~CancelableTaskWrapper() { if (isCanceled != nullptr) delete isCanceled; isCanceled = nullptr; }
    !CancelableTaskWrapper() { if (isCanceled != nullptr) delete isCanceled; isCanceled = nullptr; }

    void RunTask(CancellationToken cancelToken)
    {
        *isCanceled = false;
        CancellationTokenRegistration reg = cancelToken.Register(
            gcnew Action(this, &CancelableTaskWrapper::Canceled));
        unmanagedFunctionPointer(isCanceled);
    }
};

void someUnmanagedFunction(bool* isCanceled)
{
    doSomethingLongRunning();
    if(*isCanceled) return;
    doSomethingLongRunning();
}

>因为isCanceled是指向bool的指针,所以它在堆上.因此,我们被允许传递一个指向它的指针,而不需要做任何特殊的事情(例如,固定托管对象).
> CancellationTokenRegistration实现IDisposable,当reg超出范围时,它将自动取消注册. (你可以用C#中的using语句来完成这个.)

免责声明：我现在不在编译器中;可能存在语法错误.

标签：c,interop,task,c-cli,cancellation
来源： https://codeday.me/bug/20190628/1319754.html