/// <summary>
/// Write the child process result to the pipe
/// </summary>
/// <typeparam name="TOutput">The output type</typeparam>
/// <param name="pipeChildToParentHandle">The pipe name</param>
/// <param name="output">The output</param>
/// <param name="e">The exception</param>
/// <returns>A <see cref="Task"/>, writing the result to the pipe</returns>
private async Task WriteChildProcessResult <TOutput>(string pipeChildToParentHandle, TOutput output, Exception e)
{
ChildProcessResult <TOutput> result = new ChildProcessResult <TOutput>(output, e);
using (PipeStream pipe = new AnonymousPipeClientStream(PipeDirection.Out, pipeChildToParentHandle))
{
if (pipe.IsConnected)
{
// When writing process output, we do not support cancellation since we always want to write the output to the stream
await this.WriteToStream(result, pipe, default(CancellationToken));
}
}
}
/// <summary>
/// Runs a child process, synchronously, with the specified input.
/// This method should be called by the parent process. It starts the child process, providing it
/// with specific command line arguments that will allow the child process to support cancellation
/// and error handling.
/// The child process should call <see cref="RunAndListenToParentAsync{TInput,TOutput}"/>, provide
/// it with the command line arguments and the main method that receives the input object and returns
/// an object of type <see cref="TOutput"/>.
/// </summary>
/// <example>
/// Parent process:
/// <code>
/// private async cTask<OutputData> RunInChildProcess(string childProcessName, InputData input, ITracer tracer, CancellationToken cancellationToken)
/// {
/// IChildProcessManager childProcessManager = new ChildProcessManager();
/// OutputData output = await childProcessManager.RunChildProcessAsync<OutputData>(childProcessName, input, tracer, cancellationToken);
/// return output;
/// }
/// </code>
/// Child process:
/// <code>
/// public static void Main(string[] args)
/// {
/// ITracer tracer;
/// // Initialize tracer...
///
/// IChildProcessManager childProcessManager = new ChildProcessManager();
/// childProcessManager.RunAndListenToParentAsync<InputData, OutputData>(args, MainFunction, tracer).Wait();
/// }
///
/// private static OutputData MainFunction(InputData input, CancellationToken cancellationToken)
/// {
/// // ...
///
/// return output;
/// }
/// </code>
/// </example>
/// <typeparam name="TOutput">The child process output type</typeparam>
/// <param name="exePath">The child process' executable file path</param>
/// <param name="input">The child process input</param>
/// <param name="cancellationToken">The cancellation token</param>
/// <exception cref="InvalidOperationException">The child process could not be started</exception>
/// <exception cref="ChildProcessException">The child process failed - see InnerException ro details</exception>
/// <returns>A <see cref="Task{TResult}"/>, returning the child process output</returns>
public async Task <TOutput> RunChildProcessAsync <TOutput>(string exePath, object input, CancellationToken cancellationToken)
{
this.CurrentStatus = RunChildProcessStatus.Initializing;
this.tracer.TraceInformation($"Starting to run child process {exePath}");
try
{
// The pipe from the parent to the child is used to pass a cancellation instruction
// The pipe from the child to the parent is used to pass the child process output
using (AnonymousPipeServerStream pipeParentToChild = new AnonymousPipeServerStream(PipeDirection.Out, HandleInheritability.Inheritable))
{
using (AnonymousPipeServerStream pipeChildToParent = new AnonymousPipeServerStream(PipeDirection.In, HandleInheritability.Inheritable))
{
using (Process childProcess = new Process())
{
// Write the output to the pipe
await this.WriteToStream(input, pipeParentToChild, cancellationToken);
// Get pipe handles
string pipeParentToChildHandle = pipeParentToChild.GetClientHandleAsString();
string pipeChildToParentHandle = pipeChildToParent.GetClientHandleAsString();
// Setup the child process
childProcess.StartInfo = new ProcessStartInfo(exePath)
{
Arguments = pipeParentToChildHandle + " " + pipeChildToParentHandle + " " + this.tracer.SessionId,
CreateNoWindow = true,
UseShellExecute = false,
RedirectStandardError = true
};
// Start the child process
Stopwatch sw = Stopwatch.StartNew();
childProcess.Start();
this.tracer.TraceInformation($"Started to run child process '{Path.GetFileName(exePath)}', process ID {childProcess.Id}");
this.CurrentStatus = RunChildProcessStatus.WaitingForProcessToExit;
this.ChildProcessIds.Add(childProcess.Id);
// Dispose the local copy of the client handle
pipeParentToChild.DisposeLocalCopyOfClientHandle();
pipeChildToParent.DisposeLocalCopyOfClientHandle();
// Wait for the child process to finish
bool wasChildTerminatedByParent = false;
MemoryStream outputStream = new MemoryStream();
using (cancellationToken.Register(() => { this.CancelChildProcess(childProcess, pipeParentToChild, ref wasChildTerminatedByParent); }))
{
// Read the child's output
// We do not use the cancellation token here - we want to wait for the child to gracefully cancel
await pipeChildToParent.CopyToAsync(outputStream, 2048, default(CancellationToken));
// Ensure the child existed
childProcess.WaitForExit();
}
this.CurrentStatus = RunChildProcessStatus.Finalizing;
sw.Stop();
this.tracer.TraceInformation($"Process {exePath} completed, duration {sw.ElapsedMilliseconds / 1000}s, exit code {childProcess.ExitCode}");
// If the child process was terminated by the parent, throw appropriate exception
if (wasChildTerminatedByParent)
{
throw new ChildProcessTerminatedByParentException();
}
// Read the process result from the stream
// This read ignores the cancellation token - if there was a cancellation, the process output will contain the appropriate exception
outputStream.Seek(0, SeekOrigin.Begin);
ChildProcessResult <TOutput> processResult = await this.ReadFromStream <ChildProcessResult <TOutput> >(outputStream, default(CancellationToken));
// Return process result
if (processResult == null)
{
throw new ChildProcessException("The child process returned empty results");
}
else if (processResult.Exception != null)
{
throw new ChildProcessException("The child process threw an exception: " + processResult.Exception.Message, processResult.Exception);
}
this.CurrentStatus = RunChildProcessStatus.Completed;
return(processResult.Output);
}
}
}
}
catch (Exception)
{
this.CurrentStatus = cancellationToken.IsCancellationRequested ? RunChildProcessStatus.Canceled : RunChildProcessStatus.Failed;
throw;
}
}
