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Fix WebSocket tool registration to run on main thread #442

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Jordonh18 wants to merge 1 commit into from
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Fix WebSocket tool registration to run on main thread #442

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26 changes: 25 additions & 1 deletion MCPForUnity/Editor/Services/Transport/Transports/WebSocketTransportClient.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,9 +8,11 @@
using System.Threading.Tasks;
using MCPForUnity.Editor.Config;
using MCPForUnity.Editor.Helpers;
using MCPForUnity.Editor.Services;
using MCPForUnity.Editor.Services.Transport;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using UnityEditor;
using UnityEngine;

namespace MCPForUnity.Editor.Services.Transport.Transports
Expand Down Expand Up @@ -65,6 +67,26 @@ public WebSocketTransportClient(IToolDiscoveryService toolDiscoveryService = nul
public string TransportName => TransportDisplayName;
public TransportState State => _state;

private Task<List<ToolMetadata>> GetEnabledToolsOnMainThreadAsync()
{
var tcs = new TaskCompletionSource<List<ToolMetadata>>(TaskCreationOptions.RunContinuationsAsynchronously);

EditorApplication.delayCall += () =>
{
try
{
var tools = _toolDiscoveryService?.GetEnabledTools() ?? new List<ToolMetadata>();
tcs.TrySetResult(tools);
}
catch (Exception ex)
{
tcs.TrySetException(ex);
}
};

return tcs.Task;
}
Comment on lines +70 to +88
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@coderabbitai coderabbitai bot Dec 8, 2025

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🛠️ Refactor suggestion | 🟠 Major

Consider adding cancellation/timeout safeguards to prevent hanging.

The implementation correctly marshals tool discovery to Unity's main thread. However, if EditorApplication.delayCall callback never executes (e.g., during Unity shutdown or domain reload), the TaskCompletionSource would hang indefinitely, potentially blocking Dispose() which awaits the receive loop.

Consider registering a cancellation callback to handle scenarios where Unity stops executing delayCall callbacks:

-private Task<List<ToolMetadata>> GetEnabledToolsOnMainThreadAsync()
+private Task<List<ToolMetadata>> GetEnabledToolsOnMainThreadAsync(CancellationToken cancellationToken = default)
 {
     var tcs = new TaskCompletionSource<List<ToolMetadata>>(TaskCreationOptions.RunContinuationsAsynchronously);
+    
+    // Register cancellation to prevent indefinite hanging
+    if (cancellationToken.CanBeCanceled)
+    {
+        cancellationToken.Register(() => tcs.TrySetCanceled(cancellationToken));
+    }
 
     EditorApplication.delayCall += () =>
     {
         try
         {
             var tools = _toolDiscoveryService?.GetEnabledTools() ?? new List<ToolMetadata>();
             tcs.TrySetResult(tools);
         }
         catch (Exception ex)
         {
             tcs.TrySetException(ex);
         }
     };
 
     return tcs.Task;
 }

Then update the call site:

 token.ThrowIfCancellationRequested();
-var tools = await GetEnabledToolsOnMainThreadAsync().ConfigureAwait(false);
+var tools = await GetEnabledToolsOnMainThreadAsync(token).ConfigureAwait(false);
 token.ThrowIfCancellationRequested();

Committable suggestion skipped: line range outside the PR's diff.


public async Task<bool> StartAsync()
{
// Capture identity values on the main thread before any async context switching
Expand Down Expand Up @@ -421,7 +443,9 @@ private async Task SendRegisterToolsAsync(CancellationToken token)
{
if (_toolDiscoveryService == null) return;

var tools = _toolDiscoveryService.GetEnabledTools();
token.ThrowIfCancellationRequested();
var tools = await GetEnabledToolsOnMainThreadAsync().ConfigureAwait(false);
token.ThrowIfCancellationRequested();
McpLog.Info($"[WebSocket] Preparing to register {tools.Count} tool(s) with the bridge.");
var toolsArray = new JArray();

Expand Down