如何强制Task.Factory.StartNew到后台线程？

问题描述

我已经看到了很多类似这样的其他问题，但并没有发现我的答案在那里。

I have seen numerous other questions similar to this but did not find my answer there.

我的问题是，我是创建具有以下流线：

My problem was that I was creating threads with the following flow:

private void btn_Click(object sender, EventArgs e)
{
    service.GetCount(
        (count, ex) =>
        {
            if (ex != null)
                return;

            for (int i = 0; i < count; i++)
            {
                service.Get(onItemReceived, i);
            }
        }
    );
}

public void GetCount(Action<int, Exception> callback)
{
    var callingThread = TaskScheduler.FromCurrentSynchronizationContext();

    Func<int> action = () =>
    {
        return client.GetCount(); // Synchronous method, could take a long time
    };

    Action<Task<int>> completeAction = (task) =>
    {
        Exception ex = (task.Exception != null) ? task.Exception.InnerException : task.Exception;

        if (callback != null)
            callback(task.Result, ex);
    };

    Task.Factory.StartNew(action).ContinueWith(completeAction, callingThread);
}

public void Get(Action<object, Exception> callback, int index)
{
    var callingThread = TaskScheduler.FromCurrentSynchronizationContext();

    Func<object> action = () =>
    {
        return client.Get(index); // Synchronous method, could take a long time
    };

    Action<Task<object>> completeAction = (task) =>
    {
        Exception ex = (task.Exception != null) ? task.Exception.InnerException : task.Exception;

        if (callback != null)
            callback(task.Result, ex);
    };

    Task.Factory.StartNew(action).ContinueWith(completeAction, callingThread);
}

在这种方式，我的每一个服务的异步方法会回调，他们最初呼吁线程（通常是UI线程）。所以，我模拟如何计谋/异步关键字的工作（我不能用.NET 4.5）。

In this way, each of my service's asynchronous methods would callback the thread they were originally called on (generally the UI thread). So I am simulating how the await/async keywords work (I cannot use .NET 4.5).

这种模式的问题是，我得到莫名其妙地锁定在UI线程第一次调用ContinueWith之后。因此，在这种情况下，如果我试图产卵5线程每个进程的同步功能获取，他们将执行1：1，而不是并行，甚至他们是否会阻止用户界面线程，而这样做，我请尝试指定TaskCreationOptions.LongRunning。

The problem with this pattern is that I get inexplicably locked to the UI thread after the first call to "ContinueWith". So in this case if I attempt to spawn 5 threads to each process a synchronous function Get, they will execute 1 by 1 instead of in parallel and they will block the UI thread while doing so, even if I try specifying TaskCreationOptions.LongRunning.

这永远不会发生与我为Task.Factory.StartNew第一个电话，它只是发生在后续调用从第一个回调中

This never happens with my first call to Task.Factory.StartNew, it only happens to subsequent calls from within the first callback.

推荐答案

为了强制推出一个新的线程，你应该在调用Task.Factory.StartNew指定TaskScheduler.Default如下：

In order to force the launch of a new thread, you should specify TaskScheduler.Default in the call to Task.Factory.StartNew as follows:

Task.Factory.StartNew(action,
                      CancellationToken.None,
                      TaskCreationOptions.None,
                      TaskScheduler.Default).ContinueWith(completeAction);

在我的测试中，你不需要为了逼后台线程指定TaskCreationOptions.LongRunning，但它不应该受到伤害。

In my testing you do not need to specify TaskCreationOptions.LongRunning in order to force a background thread, though it shouldn't hurt.

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