Taskified StartProcess

StartProcess.cs

using System;
using System.IO;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;

//MIT license, from MonoDevelop ProcessUtils.cs
public static Task<int> StartProcess (ProcessStartInfo psi, TextWriter stdout, TextWriter stderr, CancellationToken cancellationToken)
{
	var tcs = new TaskCompletionSource<int> ();
	if (cancellationToken.CanBeCanceled && cancellationToken.IsCancellationRequested) {
		tcs.TrySetCanceled ();
		return tcs.Task;
	}

	psi.UseShellExecute = false;
	psi.RedirectStandardOutput |= stdout != null;
	psi.RedirectStandardError |= stderr != null;

	var p = Process.Start (psi);

	if (cancellationToken.CanBeCanceled) {
		cancellationToken.Register (() => {
			try {
				if (!p.HasExited) {
					p.Kill ();
				}
			} catch (InvalidOperationException ex) {
				if (ex.Message.IndexOf ("already exited", StringComparison.Ordinal) < 0)
					throw;
			}
		});
	}

	bool outputDone = false;
	bool errorDone = false;
	bool exitDone = false;

	p.EnableRaisingEvents = true;
	if (psi.RedirectStandardOutput) {
		bool stdOutInitialized = false;
		p.OutputDataReceived += (sender, e) => {
			try {
				if (e.Data == null) {
					outputDone = true;
					if (exitDone && errorDone)
						tcs.TrySetResult (p.ExitCode);
					return;
				}

				if (stdOutInitialized)
					stdout.WriteLine ();
				stdout.Write (e.Data);
				stdOutInitialized = true;
			} catch (Exception ex) {
				tcs.TrySetException (ex);
			}
		};
		p.BeginOutputReadLine ();
	} else {
		outputDone = true;
	}

	if (psi.RedirectStandardError) {
		bool stdErrInitialized = false;
		p.ErrorDataReceived += (sender, e) => {
			try {
				if (e.Data == null) {
					errorDone = true;
					if (exitDone && outputDone)
						tcs.TrySetResult (p.ExitCode);
					return;
				}

				if (stdErrInitialized)
					stderr.WriteLine ();
				stderr.Write (e.Data);
				stdErrInitialized = true;
			} catch (Exception ex) {
				tcs.TrySetException (ex);
			}
		};
		p.BeginErrorReadLine ();
	} else {
		errorDone = true;
	}

	p.Exited += (sender, e) => {
		exitDone = true;
		if (errorDone && outputDone)
			tcs.TrySetResult (p.ExitCode);
	};

	return tcs.Task;
}