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DefaultRequestDispatcher.cs
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DefaultRequestDispatcher.cs
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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Diagnostics;
using System.Runtime;
namespace Microsoft.NET.Sdk.Razor.Tool
{
// Heavily influenced by:
// https://github.com/dotnet/roslyn/blob/14aed138a01c448143b9acf0fe77a662e3dfe2f4/src/Compilers/Server/ServerShared/ServerDispatcher.cs#L15
internal class DefaultRequestDispatcher : RequestDispatcher
{
private readonly CancellationToken _cancellationToken;
private readonly CompilerHost _compilerHost;
private readonly ConnectionHost _connectionHost;
private readonly EventBus _eventBus;
private KeepAlive _keepAlive;
private State _state;
private Task _timeoutTask;
private Task _gcTask;
private Task<Connection> _listenTask;
private CancellationTokenSource _listenCancellationTokenSource;
private List<Task<ConnectionResult>> _connections = new();
public DefaultRequestDispatcher(
ConnectionHost connectionHost,
CompilerHost compilerHost,
CancellationToken cancellationToken,
EventBus eventBus = null,
TimeSpan? keepAlive = null)
{
_connectionHost = connectionHost;
_compilerHost = compilerHost;
_cancellationToken = cancellationToken;
_eventBus = eventBus ?? EventBus.Default;
var keepAliveTimeout = DefaultServerKeepAlive;
if (keepAlive.HasValue)
{
keepAliveTimeout = keepAlive.Value;
}
_keepAlive = new KeepAlive(keepAliveTimeout, isDefault: true);
}
// The server accepts connections until we reach a state that requires a shutdown. At that
// time no new connections will be accepted and the server will drain existing connections.
//
// The idea is that it's better to let clients fallback to in-proc (and slow down) than it is to keep
// running in an undesired state.
public override void Run()
{
_state = State.Running;
try
{
Listen();
do
{
Debug.Assert(_listenTask != null);
MaybeCreateTimeoutTask();
MaybeCreateGCTask();
WaitForAnyCompletion(_cancellationToken);
CheckCompletedTasks(_cancellationToken);
}
while (_connections.Count > 0 || _state == State.Running);
}
finally
{
_state = State.Completed;
_gcTask = null;
_timeoutTask = null;
if (_listenTask != null)
{
CloseListenTask();
}
}
}
private void CheckCompletedTasks(CancellationToken cancellationToken)
{
if (cancellationToken.IsCancellationRequested)
{
HandleCancellation();
return;
}
if (_listenTask.IsCompleted)
{
HandleCompletedListenTask(cancellationToken);
}
if (_timeoutTask?.IsCompleted == true)
{
HandleCompletedTimeoutTask();
}
if (_gcTask?.IsCompleted == true)
{
HandleCompletedGCTask();
}
HandleCompletedConnections();
}
private void HandleCancellation()
{
Debug.Assert(_listenTask != null);
// If cancellation has been requested then the server needs to be in the process
// of shutting down.
_state = State.ShuttingDown;
CloseListenTask();
try
{
Task.WaitAll(_connections.ToArray());
}
catch
{
// It's expected that some will throw exceptions, in particular OperationCanceledException. It's
// okay for them to throw so long as they complete.
}
HandleCompletedConnections();
Debug.Assert(_connections.Count == 0);
}
/// <summary>
/// The server farms out work to Task values and this method needs to wait until at least one of them
/// has completed.
/// </summary>
private void WaitForAnyCompletion(CancellationToken cancellationToken)
{
var all = new List<Task>(_connections.Count + 3);
all.AddRange(_connections);
all.Add(_timeoutTask);
all.Add(_listenTask);
all.Add(_gcTask);
try
{
var waitArray = all.Where(x => x != null).ToArray();
Task.WaitAny(waitArray, cancellationToken);
}
catch (OperationCanceledException)
{
// Thrown when the provided cancellationToken is cancelled. This is handled in the caller,
// here it just serves to break out of the WaitAny call.
}
}
private void Listen()
{
Debug.Assert(_listenTask == null);
Debug.Assert(_timeoutTask == null);
_listenCancellationTokenSource = new CancellationTokenSource();
_listenTask = _connectionHost.WaitForConnectionAsync(_listenCancellationTokenSource.Token);
_eventBus.ConnectionListening();
}
private void CloseListenTask()
{
Debug.Assert(_listenTask != null);
_listenCancellationTokenSource.Cancel();
_listenCancellationTokenSource = null;
_listenTask = null;
}
private void HandleCompletedListenTask(CancellationToken cancellationToken)
{
_eventBus.ConnectionReceived();
// Don't accept any new connections once we're in shutdown mode, instead gracefully reject the request.
// This should cause the client to run in process.
var accept = _state == State.Running;
var connectionTask = AcceptConnection(_listenTask, accept, cancellationToken);
_connections.Add(connectionTask);
// Timeout and GC are only done when there are no active connections. Now that we have a new
// connection cancel out these tasks.
_timeoutTask = null;
_gcTask = null;
// Begin listening again for new connections.
_listenTask = null;
Listen();
}
private void HandleCompletedTimeoutTask()
{
_eventBus.KeepAliveReached();
_listenCancellationTokenSource.Cancel();
_timeoutTask = null;
_state = State.ShuttingDown;
}
private void HandleCompletedGCTask()
{
_gcTask = null;
for (var i = 0; i < 10; i++)
{
GC.Collect();
GC.WaitForPendingFinalizers();
}
GCSettings.LargeObjectHeapCompactionMode = GCLargeObjectHeapCompactionMode.CompactOnce;
GC.Collect();
}
private void MaybeCreateTimeoutTask()
{
// If there are no active clients running then the server needs to be in a timeout mode.
if (_connections.Count == 0 && _timeoutTask == null)
{
Debug.Assert(_listenTask != null);
_timeoutTask = Task.Delay(_keepAlive.TimeSpan);
}
}
private void MaybeCreateGCTask()
{
if (_connections.Count == 0 && _gcTask == null)
{
_gcTask = Task.Delay(GCTimeout);
}
}
/// <summary>
/// Checks the completed connection objects.
/// </summary>
/// <returns>False if the server needs to begin shutting down</returns>
private void HandleCompletedConnections()
{
var shutdown = false;
var processedCount = 0;
var i = 0;
while (i < _connections.Count)
{
var current = _connections[i];
if (!current.IsCompleted)
{
i++;
continue;
}
_connections.RemoveAt(i);
processedCount++;
var result = current.Result;
if (result.KeepAlive.HasValue)
{
var updated = _keepAlive.Update(result.KeepAlive.Value);
if (updated.Equals(_keepAlive))
{
_eventBus.UpdateKeepAlive(updated.TimeSpan);
}
}
switch (result.CloseReason)
{
case ConnectionResult.Reason.CompilationCompleted:
case ConnectionResult.Reason.CompilationNotStarted:
// These are all normal end states. Nothing to do here.
break;
case ConnectionResult.Reason.ClientDisconnect:
// Have to assume the worst here which is user pressing Ctrl+C at the command line and
// hence wanting all compilation to end.
_eventBus.ConnectionRudelyEnded();
shutdown = true;
break;
case ConnectionResult.Reason.ClientException:
case ConnectionResult.Reason.ClientShutdownRequest:
_eventBus.ConnectionRudelyEnded();
shutdown = true;
break;
default:
throw new InvalidOperationException($"Unexpected enum value {result.CloseReason}");
}
}
if (processedCount > 0)
{
_eventBus.ConnectionCompleted(processedCount);
}
if (shutdown)
{
_state = State.ShuttingDown;
}
}
internal async Task<ConnectionResult> AcceptConnection(Task<Connection> task, bool accept, CancellationToken cancellationToken)
{
Connection connection;
try
{
connection = await task;
}
catch (Exception ex)
{
// Unable to establish a connection with the client. The client is responsible for
// handling this case. Nothing else for us to do here.
ServerLogger.LogException(ex, "Error creating client named pipe");
return new ConnectionResult(ConnectionResult.Reason.CompilationNotStarted);
}
try
{
using (connection)
{
ServerRequest request;
try
{
ServerLogger.Log("Begin reading request.");
request = await ServerRequest.ReadAsync(connection.Stream, cancellationToken).ConfigureAwait(false);
ServerLogger.Log("End reading request.");
}
catch (Exception e)
{
ServerLogger.LogException(e, "Error reading build request.");
return new ConnectionResult(ConnectionResult.Reason.CompilationNotStarted);
}
if (request.IsShutdownRequest())
{
// Reply with the PID of this process so that the client can wait for it to exit.
var response = new ShutdownServerResponse(Environment.ProcessId);
await response.WriteAsync(connection.Stream, cancellationToken);
// We can safely disconnect the client, then when this connection gets cleaned up by the event loop
// the server will go to a shutdown state.
return new ConnectionResult(ConnectionResult.Reason.ClientShutdownRequest);
}
else if (!accept)
{
// We're already in shutdown mode, respond gracefully so the client can run in-process.
var response = new RejectedServerResponse();
await response.WriteAsync(connection.Stream, cancellationToken).ConfigureAwait(false);
return new ConnectionResult(ConnectionResult.Reason.CompilationNotStarted);
}
else
{
// If we get here then this is a real request that we will accept and process.
//
// Kick off both the compilation and a task to monitor the pipe for closing.
var buildCancelled = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
var watcher = connection.WaitForDisconnectAsync(buildCancelled.Token);
var worker = ExecuteRequestAsync(request, buildCancelled.Token);
// await will end when either the work is complete or the connection is closed.
await Task.WhenAny(worker, watcher);
// Do an 'await' on the completed task, preference being compilation, to force
// any exceptions to be realized in this method for logging.
ConnectionResult.Reason reason;
if (worker.IsCompleted)
{
var response = await worker;
try
{
ServerLogger.Log("Begin writing response.");
await response.WriteAsync(connection.Stream, cancellationToken);
ServerLogger.Log("End writing response.");
reason = ConnectionResult.Reason.CompilationCompleted;
_eventBus.CompilationCompleted();
}
catch
{
reason = ConnectionResult.Reason.ClientDisconnect;
}
}
else
{
await watcher;
reason = ConnectionResult.Reason.ClientDisconnect;
}
// Begin the tear down of the Task which didn't complete.
buildCancelled.Cancel();
return new ConnectionResult(reason, request.KeepAlive);
}
}
}
catch (Exception ex)
{
ServerLogger.LogException(ex, "Error handling connection");
return new ConnectionResult(ConnectionResult.Reason.ClientException);
}
}
private Task<ServerResponse> ExecuteRequestAsync(ServerRequest buildRequest, CancellationToken cancellationToken)
{
Func<ServerResponse> func = () =>
{
ServerLogger.Log("Begin processing request");
var response = _compilerHost.Execute(buildRequest, cancellationToken);
ServerLogger.Log("End processing request");
return response;
};
var task = new Task<ServerResponse>(func, cancellationToken, TaskCreationOptions.LongRunning);
task.Start();
return task;
}
private enum State
{
/// <summary>
/// Server running and accepting all requests
/// </summary>
Running,
/// <summary>
/// Server processing existing requests, responding to shutdown commands but is not accepting
/// new build requests.
/// </summary>
ShuttingDown,
/// <summary>
/// Server is done.
/// </summary>
Completed,
}
private struct KeepAlive
{
public TimeSpan TimeSpan;
public bool IsDefault;
public KeepAlive(TimeSpan timeSpan, bool isDefault)
{
TimeSpan = timeSpan;
IsDefault = isDefault;
}
public KeepAlive Update(TimeSpan timeSpan)
{
if (IsDefault || timeSpan > TimeSpan)
{
return new KeepAlive(timeSpan, isDefault: false);
}
return this;
}
}
}
}