/// <summary>
/// Runs the child process task. This method reads and validates the command line
/// arguments, starts listening to the parent process (for cancellation/termination),
/// runs the specified function, and returns the result to the parent process.
/// Should be called by the child process when it starts.
/// </summary>
/// <typeparam name="TInput">The child process input type</typeparam>
/// <typeparam name="TOutput">The child process output type</typeparam>
/// <param name="args">The command line arguments</param>
/// <param name="functionToRun">The function to run</param>
/// <param name="exceptionToExitCodeConverter">A function used to convert an exception thrown by the process to the exit code to return to the parent.</param>
/// <param name="waitAfterFlush">Whether to wait after flushing the telemetry, to allow all traces to be sent.</param>
/// <exception cref="ArgumentException">The wrong number of arguments was provided</exception>
/// <returns>A <see cref="Task"/>, running the specified function and listening to the parent, returning the exit code to be returned from the process</returns>
public async Task <int> RunAndListenToParentAsync <TInput, TOutput>(
string[] args,
Func <TInput, CancellationToken, Task <TOutput> > functionToRun,
Func <Exception, int> exceptionToExitCodeConverter,
bool waitAfterFlush = true)
where TOutput : class
{
ChildProcessArguments arguments = ChildProcessArguments.FromCommandLineArguments(args);
string pipeParentToChildHandle = arguments.PipeParentToChildHandle;
string pipeChildToParentHandle = arguments.PipeChildToParentHandle;
try
{
using (PipeStream pipe = new AnonymousPipeClientStream(PipeDirection.In, pipeParentToChildHandle))
{
CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
try
{
// Read the input
var input = await this.ReadFromStream <TInput>(pipe, cancellationTokenSource.Token);
// Start listening to parent process - run the listeners in separate tasks
// We should not wait on these tasks, since:
// * If any of these tasks fail, it will requests cancellation, and it is enough to wait on the main method and
// let it handle cancellation gracefully
// * The cancellation listener is blocking, and cannot be canceled (anonymous pipes do not support cancellation).
// Waiting on it will block the current thread.
#pragma warning disable 4014
this.ParentLiveListenerAsync(pipe, cancellationTokenSource);
this.ParentCancellationListenerAsync(pipe, cancellationTokenSource);
#pragma warning restore 4014
// Run the main function
TOutput output = await functionToRun(input, cancellationTokenSource.Token);
// Write the output back to the parent
await this.WriteChildProcessResult(pipeChildToParentHandle, output);
// Success - return zero for exit code
return(0);
}
catch (Exception e)
{
// If the exception is due to cancellation, than return dedicated error codes
if (cancellationTokenSource.IsCancellationRequested)
{
await this.WriteChildProcessResult(pipeChildToParentHandle, "Child process was canceled by the parent");
return((int)HttpStatusCode.InternalServerError);
}
return(await this.HandleChildProcessException(e, pipeChildToParentHandle, exceptionToExitCodeConverter));
}
finally
{
// Cancel the token to stop the listener tasks
cancellationTokenSource.Cancel();
}
}
}
catch (Exception e)
{
return(await this.HandleChildProcessException(e, pipeChildToParentHandle, exceptionToExitCodeConverter));
}
finally
{
this.tracer.Flush();
if (waitAfterFlush)
{
await Task.Delay(1000 * 5);
}
}
}
/// <summary>
/// Converts the specified instance of <see cref="ChildProcessArguments"/> to command line arguments
/// </summary>
/// <param name="arguments">The <see cref="ChildProcessArguments"/> instance</param>
/// <returns>The command line arguments (as string)</returns>
public static string ToCommandLineArguments(ChildProcessArguments arguments)
{
return(Convert.ToBase64String(Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(arguments, Formatting.None))));
}
/// <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 <typeparamref name="TOutput"/>.
/// </summary>
/// <example>
/// Parent process:
/// <code>
/// private async cTask<OutputData> RunInChildProcess(string childProcessName, InputData input, IExtendedTracer 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)
/// {
/// IExtendedTracer 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($"Starting to run child process {exePath}");
// Create a temporary folder for the child process
string tempFolder = FileSystemExtensions.CreateTempFolder(TempSubFolderName);
this.tracer.TraceInformation($"Created temporary folder for child process: {tempFolder}");
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();
// Prepare command line arguments
ChildProcessArguments arguments = new ChildProcessArguments(
pipeParentToChildHandle,
pipeChildToParentHandle,
this.tracer.SessionId,
this.tracer.GetCustomProperties(),
tempFolder);
// Setup the child process
childProcess.StartInfo = new ProcessStartInfo(exePath)
{
Arguments = ChildProcessArguments.ToCommandLineArguments(arguments),
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();
}
// If the child process has exited with an error code, throw appropriate exception
if (childProcess.ExitCode != 0)
{
// This read ignores the cancellation token - if there was a cancellation, the process output will contain the appropriate exception
outputStream.Seek(0, SeekOrigin.Begin);
string processOutput = await this.ReadFromStream <string>(outputStream, default(CancellationToken));
throw new ChildProcessFailedException(childProcess.ExitCode, processOutput);
}
// Read the process result from the stream
outputStream.Seek(0, SeekOrigin.Begin);
TOutput processResult = await this.ReadFromStream <TOutput>(outputStream, cancellationToken);
// Return process result
this.CurrentStatus = RunChildProcessStatus.Completed;
return(processResult);
}
}
}
}
catch (Exception)
{
this.CurrentStatus = cancellationToken.IsCancellationRequested ? RunChildProcessStatus.Canceled : RunChildProcessStatus.Failed;
throw;
}
finally
{
FileSystemExtensions.TryDeleteFolder(tempFolder, this.tracer);
FileSystemExtensions.CleanupTempFolders(TempSubFolderName, tracer: this.tracer);
}
}
