Single instance mode (#274)

Author: flyingpie

src/10-Core/Wtq/Services/IPlatformService.cs

@@ -90,6 +90,11 @@ public interface IPlatformService
 	/// </summary>
 	bool IsCallable(string? workingDirectory, string fileName);
 
+	/// <summary>
+	/// Returns whether another WTQ process is running, used to prevent multiple WTQ instances.
+	/// </summary>
+	bool IsWtqRunning();
+
 	/// <summary>
 	/// Opens the specified <paramref name="path"/> using the default application (e.g. usually Explorer on Windows).
 	/// </summary>

src/10-Core/Wtq/Services/PlatformServiceBase.cs

@@ -230,6 +230,24 @@ public virtual bool IsCallable(string? workingDirectory, string fileName)
 		return ExecutableExtensions.Any(ex => ResolvePath(fileName + ex) != null);
 	}
 
+	/// <inheritdoc/>
+	public virtual bool IsWtqRunning()
+	{
+		// Get a reference to this process, so we can filter it out when looking for other processes.
+		var self = Process.GetCurrentProcess();
+
+		// Look for other WTQ processes.
+		var otherWtq = Process.GetProcessesByName(self.ProcessName).FirstOrDefault(p => p.Id != self.Id);
+
+		if (otherWtq != null)
+		{
+			Log.LogWarning("Found other WTQ process (PID:{Pid})", otherWtq.Id);
+			return true;
+		}
+
+		return false;
+	}
+
 	/// <inheritdoc/>
 	public virtual bool ShouldUsePollingFileWatcherForPath(string path)
 	{

src/10-Core/Wtq/Services/WtqHost.cs

@@ -15,18 +15,21 @@ public class WtqHost
 	private static readonly TimeSpan DisposeTimeout = TimeSpan.FromSeconds(3);
 
 	private static readonly ILogger _log = Utils.Log.For<WtqHost>();
+	private readonly JoinableTaskFactory _taskFactory = new(JoinableTaskContext.CreateNoOpContext());
 
 	private readonly IEnumerable<IHostedService> _hostedServices;
-	private readonly JoinableTaskFactory _taskFactory = new(JoinableTaskContext.CreateNoOpContext());
+	private readonly IPlatformService _platformService;
 
 	public WtqHost(
 		IHostApplicationLifetime appLifetime,
 		IEnumerable<IHostedService> hostedServices,
+		IPlatformService platformService,
 		Action onExit)
 	{
 		_ = Guard.Against.Null(appLifetime);
 		_ = Guard.Against.Null(onExit);
 		_hostedServices = Guard.Against.Null(hostedServices);
+		_platformService = Guard.Against.Null(platformService);
 
 		// Initializing + Starting
 		_ = appLifetime.ApplicationStarted.Register(() =>
@@ -54,6 +57,12 @@ public WtqHost(
 
 	private async Task InitAsync()
 	{
+		if (_platformService.IsWtqRunning())
+		{
+			_log.LogWarning("WTQ seems to already be running. Running multiple instances can cause some really weird behavior, so I'm stopping this instance. If you don't see another instance already running, try killing all WTQ processes and start again.");
+			Environment.Exit(-1);
+		}
+
 		var sw1 = Stopwatch.StartNew();
 
 		_log.LogDebug("Initializing services");

src/20-Services/Wtq.Services.UI/WtqUIHostBuilder.cs

@@ -53,6 +53,7 @@ public static void Run(Action<IServiceCollection> services)
 		_ = new WtqHost(
 			lifetime,
 			app.Services.GetRequiredService<IEnumerable<IHostedService>>(),
+			app.Services.GetRequiredService<IPlatformService>(),
 			() => ui.Exit());
 
 		lifetime.NotifyStarted();