Update placeholder channel check for Python (#7608)

Author: pgombar

src/WebJobs.Script/Workers/Rpc/FunctionRegistration/RpcFunctionInvocationDispatcher.cs

@@ -187,7 +187,10 @@ public async Task InitializeAsync(IEnumerable<FunctionMetadata> functions, Cance
         {
             cancellationToken.ThrowIfCancellationRequested();
 
-            if (_environment.IsPlaceholderModeEnabled())
+            var placeholderModeEnabled = _environment.IsPlaceholderModeEnabled();
+            _logger.LogDebug($"Placeholder mode is enabled: {placeholderModeEnabled}");
+
+            if (placeholderModeEnabled)
             {
                 return;
             }

src/WebJobs.Script/Workers/Rpc/RpcInitializationService.cs

@@ -189,9 +189,14 @@ internal bool ShouldStartStandbyPlaceholderChannels()
         internal bool ShouldStartAsPlaceholderPool()
         {
             // We are in placeholder mode but a worker runtime IS set
-            return _environment.IsPlaceholderModeEnabled()
+            _logger.LogDebug($"Placeholder mode enabled is {_environment.IsPlaceholderModeEnabled()} for worker {_workerRuntime}");
+
+            var ret = _environment.IsPlaceholderModeEnabled()
                 && !string.IsNullOrEmpty(_workerRuntime)
                 && _placeholderPoolRuntimesAllowList.Contains(_workerRuntime, StringComparer.OrdinalIgnoreCase);
+
+            _logger.LogDebug($"Starting language worker in placeholder mode: {ret}");
+            return ret;
         }
 
         // To help with unit tests

src/WebJobs.Script/Workers/Rpc/WebHostRpcWorkerChannelManager.cs

@@ -145,7 +145,8 @@ private bool UsePlaceholderChannel(string workerRuntime)
                 // Also cannot use placeholder worker that is targeting ~3 but has backwards compatibility with V2 enabled
                 // TODO: Remove special casing when resolving https://github.com/Azure/azure-functions-host/issues/4534
                 if (string.Equals(workerRuntime, RpcWorkerConstants.NodeLanguageWorkerName, StringComparison.OrdinalIgnoreCase)
-                    || string.Equals(workerRuntime, RpcWorkerConstants.PowerShellLanguageWorkerName, StringComparison.OrdinalIgnoreCase))
+                    || string.Equals(workerRuntime, RpcWorkerConstants.PowerShellLanguageWorkerName, StringComparison.OrdinalIgnoreCase)
+                    || string.Equals(workerRuntime, RpcWorkerConstants.PythonLanguageWorkerName, StringComparison.OrdinalIgnoreCase))
                 {
                     // Use if readonly and not v2 compatible on ~3 extension
                     return _applicationHostOptions.CurrentValue.IsFileSystemReadOnly && !_environment.IsV2CompatibileOnV3Extension();

test/WebJobs.Script.Tests/Workers/Rpc/WebHostRpcWorkerChannelManagerTests.cs

@@ -167,6 +167,8 @@ public async Task ShutdownStandyChannels_WorkerRuntime_Node_Set()
         [InlineData("Node", RpcWorkerConstants.NodeLanguageWorkerName)]
         [InlineData("PowerShell", RpcWorkerConstants.PowerShellLanguageWorkerName)]
         [InlineData("pOwerShell", RpcWorkerConstants.PowerShellLanguageWorkerName)]
+        [InlineData("python", RpcWorkerConstants.PythonLanguageWorkerName)]
+        [InlineData("pythoN", RpcWorkerConstants.PythonLanguageWorkerName)]
         public async Task SpecializeAsync_ReadOnly_KeepsProcessAlive(string runtime, string languageWorkerName)
         {
             var testMetricsLogger = new TestMetricsLogger();
@@ -258,6 +260,7 @@ await TestHelpers.Await(() =>
         [Theory]
         [InlineData(RpcWorkerConstants.NodeLanguageWorkerName)]
         [InlineData(RpcWorkerConstants.PowerShellLanguageWorkerName)]
+        [InlineData(RpcWorkerConstants.PythonLanguageWorkerName)]
         public async Task SpecializeAsync_NotReadOnly_KillsProcess(string languageWorkerName)
         {
             var testMetricsLogger = new TestMetricsLogger();
@@ -316,6 +319,7 @@ public async Task SpecializeAsync_LanguageWorkerArguments_KillsProcess(string la
         [Theory]
         [InlineData(RpcWorkerConstants.NodeLanguageWorkerName)]
         [InlineData(RpcWorkerConstants.PowerShellLanguageWorkerName)]
+        [InlineData(RpcWorkerConstants.PythonLanguageWorkerName)]
         public async Task SpecializeAsync_Node_V2CompatibilityWithV3Extension_KillsProcess(string languageWorkerName)
         {
             var testMetricsLogger = new TestMetricsLogger();