Skip Named Pipe server startup if pipe already exists

Author: yotsuda

.github/workflows/cross-platform-test.yml

@@ -309,10 +309,32 @@ jobs:
           if ($IsWindows) {
             $pipeReady = Test-Path "\\.\pipe\$pipeName"
           } else {
-            $pipeReady = Test-Path "/tmp/CoreFxPipe_$pipeName"
+            # Check both /tmp and $TMPDIR on macOS/Linux
+            $pipeReady = (Test-Path "/tmp/CoreFxPipe_$pipeName") -or 
+                         ($env:TMPDIR -and (Test-Path "$env:TMPDIR/CoreFxPipe_$pipeName"))
           }
           if ($pipeReady) {
             Write-Host "Named Pipe ready after $($i * 500)ms"
+            
+            # Debug: Show pipe details
+            if ($IsWindows) {
+              Write-Host "=== Windows Named Pipes matching pattern ===" -ForegroundColor Cyan
+              Get-ChildItem "\\.\pipe\" -ErrorAction SilentlyContinue | Where-Object { $_.Name -match "PowerShell|MCP|Communication" } | ForEach-Object { Write-Host "  $($_.Name)" }
+              Write-Host "=== All pipes with our name ===" -ForegroundColor Cyan
+              $pipes = Get-ChildItem "\\.\pipe\" -ErrorAction SilentlyContinue | Where-Object { $_.Name -eq $pipeName }
+              Write-Host "  Found $($pipes.Count) pipe(s) named '$pipeName'"
+            } else {
+              Write-Host "=== macOS/Linux: TMPDIR and pipe locations ===" -ForegroundColor Cyan
+              Write-Host "  TMPDIR: $env:TMPDIR"
+              Write-Host "  Checking /tmp..."
+              bash -c "ls -la /tmp/CoreFxPipe_* 2>/dev/null || echo '  No CoreFxPipe files in /tmp'"
+              if ($env:TMPDIR) {
+                Write-Host "  Checking TMPDIR..."
+                bash -c "ls -la `$TMPDIR/CoreFxPipe_* 2>/dev/null || echo '  No CoreFxPipe files in TMPDIR'"
+              }
+              Write-Host "=== lsof for background pwsh ===" -ForegroundColor Cyan
+              bash -c "lsof -p $($bgProcess.Id) 2>/dev/null | grep -E 'unix|PIPE|sock' | head -10 || echo '  No matching descriptors'"
+            }
             break
           }
           
@@ -329,15 +351,22 @@ jobs:
           
           # Debug: List pipe-related files and sockets
           if (-not $IsWindows) {
+            Write-Host "=== Environment ===" -ForegroundColor Yellow
+            Write-Host "  TMPDIR: $env:TMPDIR"
             Write-Host "=== /tmp pipe files (PowerShell) ===" -ForegroundColor Yellow
             Get-ChildItem /tmp -Filter "CoreFxPipe_*" -ErrorAction SilentlyContinue | ForEach-Object { Write-Host $_.FullName }
             Write-Host "=== /tmp (native ls) ===" -ForegroundColor Yellow
             bash -c "ls -la /tmp/ | grep -i 'corefx\|pipe\|mcp\|communication' || echo 'No matching files'"
             bash -c "ls -la /tmp/ | head -20"
+            if ($env:TMPDIR) {
+              Write-Host "=== TMPDIR contents ===" -ForegroundColor Yellow
+              bash -c "ls -la $env:TMPDIR/ 2>/dev/null | grep -i 'corefx\|pipe\|mcp' || echo 'No matching files in TMPDIR'"
+              bash -c "ls -la $env:TMPDIR/ 2>/dev/null | head -20"
+            }
             Write-Host "=== lsof for background pwsh ===" -ForegroundColor Yellow
-            bash -c "lsof -p $($bgProcess.Id) 2>/dev/null | grep -i 'unix\|pipe\|socket' | head -20 || echo 'No sockets found'"
+            bash -c "lsof -p $($bgProcess.Id) 2>/dev/null | grep -iE 'unix|pipe|socket|stream' | head -20 || echo 'No sockets found'"
             Write-Host "=== All CoreFx sockets (find) ===" -ForegroundColor Yellow
-            bash -c "find /tmp /var/folders -name '*CoreFx*' -o -name '*PowerShell*' 2>/dev/null | head -10 || echo 'None found'"
+            bash -c "find /tmp \$TMPDIR /var/folders -name '*CoreFx*' -o -name '*Communication*' 2>/dev/null | head -20 || echo 'None found'"
           }
           
           # Kill process first, then read outputs

PowerShell.MCP/MCPModuleInitializer.cs

@@ -33,21 +33,67 @@ public class MCPModuleInitializer : IModuleAssemblyInitializer
 
         public void OnImport()
         {
-            // TODO: Fail module import if named pipe already exists
-            // Throw exception?
-
             try
             {
+                // Check if Named Pipe already exists (another pwsh session is running)
+                bool pipeExists = false;
+                
+                if (OperatingSystem.IsWindows())
+                {
+                    // On Windows, try to connect briefly to check if pipe exists
+                    try
+                    {
+                        using var testClient = new System.IO.Pipes.NamedPipeClientStream(".", NamedPipeServer.PipeName, System.IO.Pipes.PipeDirection.InOut);
+                        testClient.Connect(100); // 100ms timeout
+                        pipeExists = true;
+                        Console.Error.WriteLine($"[DEBUG] Named Pipe '{NamedPipeServer.PipeName}' already exists (connected successfully)");
+                    }
+                    catch (TimeoutException)
+                    {
+                        // Pipe exists but no server is listening yet - this is OK, we can try to be the server
+                        pipeExists = false;
+                    }
+                    catch (System.IO.IOException)
+                    {
+                        // Pipe doesn't exist or connection failed
+                        pipeExists = false;
+                    }
+                }
+                else
+                {
+                    // On Linux/macOS, check for the socket file
+                    string pipePath = $"/tmp/CoreFxPipe_{NamedPipeServer.PipeName}";
+                    pipeExists = File.Exists(pipePath);
+                    if (pipeExists)
+                    {
+                        Console.Error.WriteLine($"[DEBUG] Named Pipe socket exists at {pipePath}");
+                    }
+                }
+                
+                if (pipeExists)
+                {
+                    Console.Error.WriteLine("[DEBUG] Named Pipe already exists, skipping server start");
+                    
+                    // Still load the polling script for other functionality
+                    var pollingScript = EmbeddedResourceLoader.LoadScript("MCPPollingEngine.ps1");
+                    using (var ps = System.Management.Automation.PowerShell.Create(RunspaceMode.CurrentRunspace))
+                    {
+                        ps.AddScript(pollingScript);
+                        ps.Invoke();
+                    }
+                    return;
+                }
+
                 _tokenSource = new CancellationTokenSource();
                 _namedPipeServer = new NamedPipeServer();
 
                 // Load and execute MCP polling engine script
-                var pollingScript = EmbeddedResourceLoader.LoadScript("MCPPollingEngine.ps1");
+                var pollingScriptMain = EmbeddedResourceLoader.LoadScript("MCPPollingEngine.ps1");
 
                 // Execute as ScriptBlock for PowerShell execution
                 using (var ps = System.Management.Automation.PowerShell.Create(RunspaceMode.CurrentRunspace))
                 {
-                    ps.AddScript(pollingScript);
+                    ps.AddScript(pollingScriptMain);
                     ps.Invoke();
                 }