Create the first PowerShellManager instance when processing the first FunctionLoad request

src/PowerShell/PowerShellManager.cs

@@ -22,6 +22,7 @@ internal class PowerShellManager
     {
         private readonly ILogger _logger;
         private readonly PowerShell _pwsh;
+        private bool _runspaceInited;
 
         /// <summary>
         /// Gets the Runspace InstanceId.
@@ -45,7 +46,7 @@ static PowerShellManager()
             addMethod.Invoke(null, new object[] { "HttpRequestContext", typeof(HttpRequestContext) });
         }
 
-        internal PowerShellManager(ILogger logger)
+        internal PowerShellManager(ILogger logger, bool delayInit = false)
         {
             if (FunctionLoader.FunctionAppRootPath == null)
             {
@@ -65,7 +66,22 @@ internal PowerShellManager(ILogger logger)
             _pwsh.Streams.Warning.DataAdding += streamHandler.WarningDataAdding;
 
             // Initialize the Runspace
-            InvokeProfile(FunctionLoader.FunctionAppProfilePath);
+            if (!delayInit)
+            {
+                Initialize();
+            }
+        }
+
+        /// <summary>
+        /// Extra initialization of the Runspace.
+        /// </summary>
+        internal void Initialize()
+        {
+            if (!_runspaceInited)
+            {
+                InvokeProfile(FunctionLoader.FunctionAppProfilePath);
+                _runspaceInited = true;
+            }
         }
 
         /// <summary>
@@ -76,7 +92,8 @@ internal void InvokeProfile(string profilePath)
             Exception exception = null;
             if (profilePath == null)
             {
-                RpcLogger.WriteSystemLog(string.Format(PowerShellWorkerStrings.FileNotFound, "profile.ps1", FunctionLoader.FunctionAppRootPath));
+                string noProfileMsg = string.Format(PowerShellWorkerStrings.FileNotFound, "profile.ps1", FunctionLoader.FunctionAppRootPath);
+                _logger.Log(LogLevel.Trace, noProfileMsg);
                 return;
             }
 

src/PowerShell/PowerShellManagerPool.cs

@@ -46,6 +46,16 @@ internal PowerShellManagerPool(MessagingStream msgStream)
             RpcLogger.WriteSystemLog(string.Format(PowerShellWorkerStrings.LogConcurrencyUpperBound, _upperBound.ToString()));
         }
 
+        /// <summary>
+        /// Initialize the pool and populate it with PowerShellManager instances.
+        /// We instantiate PowerShellManager instances in a lazy way, starting from size 1 and increase the number of workers as needed.
+        /// </summary>
+        internal void Initialize()
+        {
+            _pool.Add(new PowerShellManager(new RpcLogger(_msgStream), delayInit: true));
+            _poolSize = 1;
+        }
+
         /// <summary>
         /// Checkout an idle PowerShellManager instance in a non-blocking asynchronous way.
         /// </summary>
@@ -78,9 +88,14 @@ internal PowerShellManager CheckoutIdleWorker(StreamingMessage request, AzFuncti
                 }
             }
 
+            // Finish the initialization if not yet.
+            // This applies only to the very first PowerShellManager instance, whose initialization was deferred.
+            psManager.Initialize();
+
             // Register the function with the Runspace before returning the idle PowerShellManager.
             FunctionMetadata.RegisterFunctionMetadata(psManager.InstanceId, functionInfo);
             psManager.Logger.SetContext(requestId, invocationId);
+
             return psManager;
         }
 

src/RequestProcessor.cs

@@ -171,6 +171,11 @@ internal StreamingMessage ProcessFunctionLoadRequest(StreamingMessage request)
                     // Setup the FunctionApp root path and module path.
                     FunctionLoader.SetupWellKnownPaths(functionLoadRequest);
                     _dependencyManager.ProcessDependencyDownload(_msgStream, request);
+
+                    // Create the first Runspace so that the debugger has the target to attach to.
+                    // The further initialization of the Runspace (e.g. invoking profile.ps1) is delayed until
+                    // the first invocation and completion of the dependency download.
+                    _powershellPool.Initialize();
                 }
                 catch (Exception e)
                 {

test/Unit/PowerShell/PowerShellManagerTests.cs

@@ -43,9 +43,9 @@ static TestUtils()
 
         // Have a single place to get a PowerShellManager for testing.
         // This is to guarantee that the well known paths are setup before calling the constructor of PowerShellManager.
-        internal static PowerShellManager NewTestPowerShellManager(ConsoleLogger logger)
+        internal static PowerShellManager NewTestPowerShellManager(ConsoleLogger logger, bool delayInit = false)
         {
-            return new PowerShellManager(logger);
+            return new PowerShellManager(logger, delayInit);
         }
 
         internal static AzFunctionInfo NewAzFunctionInfo(string scriptFile, string entryPoint)
@@ -235,5 +235,26 @@ public void ProfileWithNonTerminatingError()
             Assert.Equal("Error: ERROR: help me!", _testLogger.FullLog[0]);
             Assert.Matches("Error: Fail to run profile.ps1. See logs for detailed errors. Profile location: ", _testLogger.FullLog[1]);
         }
+
+        [Fact]
+        public void PSManagerCtorRunsProfileByDefault()
+        {
+            //initialize fresh log
+            _testLogger.FullLog.Clear();
+            TestUtils.NewTestPowerShellManager(_testLogger);
+
+            Assert.Single(_testLogger.FullLog);
+            Assert.Equal($"Trace: No 'profile.ps1' is found at the FunctionApp root folder: {FunctionLoader.FunctionAppRootPath}.", _testLogger.FullLog[0]);
+        }
+
+        [Fact]
+        public void PSManagerCtorDoesNotRunProfileIfDelayInit()
+        {
+            //initialize fresh log
+            _testLogger.FullLog.Clear();
+            TestUtils.NewTestPowerShellManager(_testLogger, delayInit: true);
+
+            Assert.Empty(_testLogger.FullLog);
+        }
     }
 }