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Add ExecuteAsync, Fix CancelAsync Deadlock #1343

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@zeotuan zeotuan commented Mar 5, 2024

@zeotuan zeotuan marked this pull request as ready for review March 5, 2024 02:51
@zeotuan zeotuan force-pushed the develop branch 2 times, most recently from 751d5ad to c04d6fb Compare March 5, 2024 09:10
@zeotuan zeotuan marked this pull request as draft March 5, 2024 10:39
zeotuan and others added 3 commits March 6, 2024 22:03
* Add ExecuteAsync with cancellation

* Deprecate Error and Result property

* Fix Deadlock with cancel Async
@zeotuan zeotuan marked this pull request as ready for review March 6, 2024 11:03

try
{
var status = await Task<int>.Factory.FromAsync(BeginExecute(), EndExecuteWithStatus).ConfigureAwait(false);
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I want to add Async overloaded methods but I think this is not a real async code. I've prepared a POC here: #1318

I know that your approach is easier to implement, but this is similar to nuget: https://www.nuget.org/packages/Renci.SshNet.Async#versions-body-tab

You can find code here: https://github.com/JohnTheGr8/Renci.SshNet.Async/blob/master/Renci.SshNet.Async/SshNetExtensions.cs

@@ -105,56 +107,72 @@ public Stream CreateInputStream()
/// <summary>
/// Gets the command execution result.
/// </summary>
#pragma warning disable S1133 // Deprecated code should be removed
[Obsolete("Please read the result from the OutputStream. I.e. new StreamReader(shell.OutputStream).ReadToEnd().")]
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Why should we make it obsolete?

}

/// <summary>
/// Gets the command execution error.
/// </summary>
#pragma warning disable S1133 // Deprecated code should be removed
[Obsolete("Please read the error result from the ExtendedOutputStream. I.e. new StreamReader(shell.ExtendedOutputStream).ReadToEnd().")]
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Why should we make it obsolete?

@Rob-Hague
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@WojciechNagorski commented just as I was commenting some similar feedback, so sorry for the duplication 🙂 :

I think you are still working on this so just some high-level thoughts:

There are a few semi-related changes here. The cancellation via signal is good. I would suggest splitting that to a standalone PR to start with.

I understand the reason for obsoleting the Result/Error properties (because they consume the stream properties) but I do not think the change is justified. Especially given how many changes it causes just in our own code (forwarding to a now internal version at that). I would suggest reverting that.

I'm a little uneasy about using TaskFactory.FromAsync in this library because many of the Begin/End (APM) methods are not implemented so well and we end up spawning new threads/blocking on more threads than we need. I basically share the same sentiment as #931 (comment). But at first glance it is not so bad here.

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zeotuan commented Mar 6, 2024

@Rob-Hague @WojciechNagorski Very Interesting. I would love to help with the project.

https://www.nuget.org/packages/Renci.SshNet.Async#versions-body-tab unfortunately does not support CancellationToken.
So I was thinking of adding a simple TAP over APM wrapper here until we get a proper TAP rewrite.

I also expect the execution of command to leave the OutputStream and ExtendedOutputStream intact and provide my own way to consuming them. for example: I want to forward the stdout and stderr to another program while the command is being executed not after.

Therefore, I would suggest Future ExecuteAsync Implementation to at least just return an exit status code instead of consuming those stream. Also Providing a public helper method to let people get Result/Error from those stream. It would require refactoring for any downstream project that will migrate to Async anyway

I have submitted a standalone PR for CancelAsync: #1345

@WojciechNagorski
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@zeotuan Sory for the delay. If you want you can continue to help us add true asynchronous methods. let us know.

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zeotuan commented Mar 22, 2024

@WojciechNagorski Hi! Yes, I would like to help with adding true async methods for sshnet.

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3 participants