TPL Dataflow，Post() 和 SendAsync() 之间的功能区别是什么? [英] TPL Dataflow, whats the functional difference between Post() and SendAsync()?

问题描述

我对通过 Post() 或 SendAsync() 发送项目之间的区别感到困惑.我的理解是，在所有情况下，一旦项目到达数据块的输入缓冲区，控制权就会返回到调用上下文，对吗?那我为什么需要 SendAsync 呢?如果我的假设不正确，那么我想知道相反，如果使用数据块的整个想法是建立并发和异步环境，为什么有人会使用 Post().

I am confused about the difference between sending items through Post() or SendAsync(). My understanding is that in all cases once an item reached the input buffer of a data block, control is returned to the calling context, correct? Then why would I ever need SendAsync? If my assumption is incorrect then I wonder, on the contrary, why anyone would ever use Post() if the whole idea of using data blocks is to establish a concurrent and async environment.

我当然理解技术上的区别在于 Post() 返回一个 bool 而 SendAsync 返回一个可等待的 bool 任务.但这有什么影响呢?什么时候返回布尔值(我的理解是确认该项目是否被放入数据块的队列中)会被延迟?我理解 async/await 并发框架的一般思想，但在这里它没有多大意义，因为除了 bool 之外，对传入项所做的任何操作的结果都不会返回给调用者，而是放在一个出队列"并转发到链接的数据块或丢弃.

I understand of course the difference technically in that Post() returns a bool whereas SendAsync returns an awaitable Task of bool. But what implications does that have? When would the return of a bool (which I understand is a confirmation whether the item was placed in the queue of the data block or not) ever be delayed? I understand the general idea of the async/await concurrency framework but here it does not make a whole lot sense because other than a bool the results of whatever is done to the passed-in item is never returned to the caller but instead placed in an "out-queue" and either forwarded to linked data blocks or discarded.

发送物品时这两种方法之间有什么性能差异吗?

And is there any performance difference between the two methods when sending items?

推荐答案

要查看不同之处，您需要在块将其消息推迟的情况下.在这种情况下，Post 将立即返回 false，而 SendAsync 将返回一个 Task块决定如何处理消息.如果消息被接受，Task 将有一个 true 结果，否则将有一个 false 结果.

To see the difference, you need a situation where blocks will postpone their messages. In this case, Post will return false immediately, whereas SendAsync will return a Task that will be completed when the block decides what to do with the message. The Task will have a true result if the message is accepted, and a false result if not.

非贪婪联接是推迟情况的一个示例.一个更简单的例子是当你设置 BoundedCapacity:

One example of a postponing situation is a non-greedy join. A simpler example is when you set BoundedCapacity:

[TestMethod]
public void Post_WhenNotFull_ReturnsTrue()
{
    var block = new BufferBlock<int>(new DataflowBlockOptions {BoundedCapacity = 1});

    var result = block.Post(13);

    Assert.IsTrue(result);
}

[TestMethod]
public void Post_WhenFull_ReturnsFalse()
{
    var block = new BufferBlock<int>(new DataflowBlockOptions { BoundedCapacity = 1 });
    block.Post(13);

    var result = block.Post(13);

    Assert.IsFalse(result);
}

[TestMethod]
public void SendAsync_WhenNotFull_ReturnsCompleteTask()
{
    // This is an implementation detail; technically, SendAsync could return a task that would complete "quickly" instead of already being completed.
    var block = new BufferBlock<int>(new DataflowBlockOptions { BoundedCapacity = 1 });

    var result = block.SendAsync(13);

    Assert.IsTrue(result.IsCompleted);
}

[TestMethod]
public void SendAsync_WhenFull_ReturnsIncompleteTask()
{
    var block = new BufferBlock<int>(new DataflowBlockOptions { BoundedCapacity = 1 });
    block.Post(13);

    var result = block.SendAsync(13);

    Assert.IsFalse(result.IsCompleted);
}

[TestMethod]
public async Task SendAsync_BecomesNotFull_CompletesTaskWithTrueResult()
{
    var block = new BufferBlock<int>(new DataflowBlockOptions { BoundedCapacity = 1 });
    block.Post(13);
    var task = block.SendAsync(13);

    block.Receive();

    var result = await task;
    Assert.IsTrue(result);
}

[TestMethod]
public async Task SendAsync_BecomesDecliningPermanently_CompletesTaskWithFalseResult()
{
    var block = new BufferBlock<int>(new DataflowBlockOptions { BoundedCapacity = 1 });
    block.Post(13);
    var task = block.SendAsync(13);

    block.Complete();

    var result = await task;
    Assert.IsFalse(result);
}

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