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.
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);
}