Replace magic string with constant.

Author: timcassell

src/BenchmarkDotNet/Engines/Engine.cs

@@ -319,6 +319,7 @@ internal static void ForceGcCollect()
         public static class Signals
         {
             public const string Acknowledgment = "Acknowledgment";
+            public const string Cancel = "CANCEL";
 
             private static readonly Dictionary<HostSignal, string> SignalsToMessages = new()
             {

src/BenchmarkDotNet/Engines/FileStdOutConnection.cs

@@ -23,7 +23,7 @@ public override void Dispose()
 
     internal override async ValueTask WriteLineAsync(string line)
     {
-        if (line == "CANCEL")
+        if (line == Engine.Signals.Cancel)
         {
             // mjs checks for file existence, so we just write an empty file.
             File.WriteAllBytes(Path.Combine(ipcDirectory, "cancel.txt"), []);

src/BenchmarkDotNet/Engines/JsHost.cs

@@ -28,7 +28,7 @@ public sealed partial class JsHost : IHost
     [JSExport]
     public static void ReceiveMessage(string message)
     {
-        if (message == "CANCEL")
+        if (message == Engine.Signals.Cancel)
         {
             s_cancellationTokenSource.Cancel();
             return;

src/BenchmarkDotNet/Engines/TcpHost.cs

@@ -43,7 +43,7 @@ private async Task ReceiveMessages()
                 break;
             }
 
-            if (message == "CANCEL")
+            if (message == Engine.Signals.Cancel)
             {
                 cancellationTokenSource.Cancel();
                 // When the benchmark process is canceled, it still sends the final AfterAll signal back to the host in a finally block,

src/BenchmarkDotNet/Loggers/Broker.cs

@@ -97,7 +97,7 @@ async void Cancel()
                 {
                     using (await writeSemaphore.EnterScopeAsync(CancellationToken.None).ConfigureAwait(false))
                     {
-                        await ipcConnection.WriteLineAsync("CANCEL").ConfigureAwait(false);
+                        await ipcConnection.WriteLineAsync(Engine.Signals.Cancel).ConfigureAwait(false);
                     }
                 }