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如何在AppDomain上等待处理C中的异步回调,然后返回结果?

appdomain asynchronous c#

jwize · 技术社区 · 7 年前

我有一些加载的代码,AppDomain(称为domain)调用域中的对象函数。目的是使用设备API从usb设备获取项目列表以检索信息。API需要回调来返回信息。

var AppDomain.CreateDomain(
   $"BiometricsDomain{System.IO.Path.GetRandomFileName()}");
var proxy = domain.CreateInstanceAndUnwrap(proxy.Assembly.FullName, proxy.FullName 
   ?? throw new InvalidOperationException()) as Proxy;
var ids = obj.GetIdentifications();

加载到域中的代理代码如下

public class Proxy : MarshalByRefObject
{ 
    public List<String> GetIdentifications()
    {
        var control = new R100DeviceControl();
        control.OnUserDB += Control_OnUserDB;
        control.Open();
        int nResult = control.DownloadUserDB(out int count);
        // need to be able to return the list here but obviously that is not 
        // going to work.
    }
    private void Control_OnUserDB(List<String> result)
    {
        // Get the list of string from here
    }
}

GetIdentifications() 已经回来了我不知道怎么弄到

3 回复 | 直到 7 年前

Nkosi 7 年前

通过使用 TaskCompletionSource<TResult>

public class Proxy : MarshalByRefObject {
    public List<String> GetIdentifications() {
        var task = GetIdentificationsAsync();
        return task.Result;
    }
    private Task<List<String>> GetIdentificationsAsync() {
        var tcs = new TaskCompletionSource<List<string>>();
        try {
            var control = new R100DeviceControl();
            Action<List<string>> handler = null;
            handler = result => {
                // Once event raised then set the 
                // Result property on the underlying Task.
                control.OnUserDB -= handler;//optional to unsubscribe from event
                tcs.TrySetResult(result);
            };
            control.OnUserDB += handler;
            control.Open();
            int count = 0;
            //call async event
            int nResult = control.DownloadUserDB(out count);
        } catch (Exception ex) {
            //Bubble the error up to be handled by calling client
            tcs.TrySetException(ex);
        }
        // Return the underlying Task. The client code
        // waits on the Result property, and handles exceptions
        // in the try-catch block there.
        return tcs.Task;
    }
}

您还可以通过使用 CancellationToken 超过预期的回调时间。

这样就可以等待代理

List<string> ids = proxy.GetIdentifications();

How to: Wrap EAP Patterns in a Task

Deleted 7 年前

注意 :虽然对于异步处理的问题可能有更优雅的解决方案,但发生在子AppDomain中的事实证明了子AppDomain的最佳实践。(见下面的链接)

即

不允许在父域中执行用于子AppDomain的代码
不允许复杂类型冒泡到父AppDomain
不允许异常以自定义异常类型的形式跨越AppDomain边界

我用它来容错

首先我可能会加上 Open 或类似的方法,为数据的实现提供时间。

var proxy = domain.CreateInstanceAndUnwrap(proxy.Assembly.FullName, proxy.FullName 
   ?? throw new InvalidOperationException()) as Proxy;

proxy.Open();  // <------ new method here
.
. some time later
.
var ids = obj.GetIdentifications();

GetNotifications 数据可能已经准备好了。

public class Proxy : MarshalByRefObject
{ 
    ConcurrentBag<string> _results = new ConcurrentBag<string>();

    public void Open()
    {
        var control = new R100DeviceControl();
        control.OnUserDB += Control_OnUserDB;
        control.Open();
        // you may need to store nResult and count in a field?
        nResult = control.DownloadUserDB(out int count);
    }

    public List<String> GetIdentifications()
    {
        var copy = new List<string>();
        while (_results.TryTake(out var x))
        {
           copy.Add(x);
        }             
        return copy;
    }

    private void Control_OnUserDB(List<String> result)
    {
        // Get the list of string from here
        _results.Add (result);
    }
}

现在你也许可以改进在事件中接受超时 获取通知 在数据准备好之前调用,或者在后续数据到达之前调用乘法。

How to: Run Partially Trusted Code in a Sandbox

Jay 7 年前

不知道为什么不保持一个小状态,然后在调用中等待结果:

public class Proxy : MarshalByRefObject
{ 
    bool runningCommand;
    int lastResult;
    R100DeviceControl DeviceControl { get{ if(deviceControl == null){ deviceControl = new R100DeviceControl(); deviceControl.OnUserDB += Control_OnUserDB; } return deviceControl; } }


    public List<String> GetIdentifications()
    {
        if(runningCommand) return null;
        DeviceControl.Open();
        runningCommand = true;
        lastResult = control.DownloadUserDB(out int count);
    }
    private void Control_OnUserDB(List<String> result)
    {
        runningCommand = false;
        // Get the list of string from here
    }
}