[PlaceholderMode]Read RuntimeAssemblyFiles (#8341)

Author: pragnagopa

src/WebJobs.Script.WebHost/Middleware/HostWarmupMiddleware.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.IO;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
@@ -20,6 +21,7 @@ public class HostWarmupMiddleware
         private readonly IEnvironment _environment;
         private readonly IScriptHostManager _hostManager;
         private readonly ILogger _logger;
+        private string _assemblyLocalPath;
 
         public HostWarmupMiddleware(RequestDelegate next, IScriptWebHostEnvironment webHostEnvironment, IEnvironment environment, IScriptHostManager hostManager, ILogger<HostWarmupMiddleware> logger)
         {
@@ -28,6 +30,7 @@ public HostWarmupMiddleware(RequestDelegate next, IScriptWebHostEnvironment webH
             _environment = environment;
             _hostManager = hostManager;
             _logger = logger;
+            _assemblyLocalPath = Path.GetDirectoryName(new Uri(typeof(HostWarmupMiddleware).Assembly.CodeBase).LocalPath);
         }
 
         public async Task Invoke(HttpContext httpContext)
@@ -40,17 +43,58 @@ public async Task Invoke(HttpContext httpContext)
                     PreJitPrepare(WarmUpConstants.LinuxJitTraceFileName);
                 }
 
+                ReadRuntimeAssemblyFiles();
+
                 await WarmUp(httpContext.Request);
             }
 
             await _next.Invoke(httpContext);
         }
 
+        internal void ReadRuntimeAssemblyFiles()
+        {
+            try
+            {
+                string[] allFiles = Directory.GetFiles(_assemblyLocalPath, "*.dll", SearchOption.TopDirectoryOnly);
+                foreach (string file in allFiles)
+                {
+                    // Read file content to avoid disk reads during specialization. This is only to page-in bytes.
+                    ReadFileInChunks(file);
+                }
+                _logger.LogDebug(new EventId(100, nameof(ReadRuntimeAssemblyFiles)), $"Number of files read: {allFiles.Count()}.");
+            }
+            catch (Exception ex)
+            {
+                _logger.LogDebug(new EventId(100, nameof(ReadRuntimeAssemblyFiles)), ex, "Reading ReadRuntimeAssemblyFiles failed");
+            }
+        }
+
+        private void ReadFileInChunks(string file)
+        {
+            try
+            {
+                // Read File content in 4K chunks
+                const int MAX_BUFFER = 4 * 1024;
+                byte[] chunk = new byte[MAX_BUFFER];
+                int bytesRead;
+                using (FileStream fileStream = new FileStream(file, FileMode.Open, FileAccess.Read))
+                {
+                    while ((bytesRead = fileStream.Read(chunk, 0, MAX_BUFFER)) != 0)
+                    {
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                _logger.LogDebug(new EventId(100, nameof(ReadFileInChunks)), ex, $"Reading file '{file}' failed");
+            }
+        }
+
         private void PreJitPrepare(string jitTraceFileName)
         {
             // This is to PreJIT all methods captured in coldstart.jittrace file to improve cold start time
             var path = Path.Combine(
-                Path.GetDirectoryName(new Uri(typeof(HostWarmupMiddleware).Assembly.CodeBase).LocalPath),
+                _assemblyLocalPath,
                 WarmUpConstants.PreJitFolderName, jitTraceFileName);
 
             var file = new FileInfo(path);

test/WebJobs.Script.Tests/Middleware/HostWarmupMiddlewareTests.cs

@@ -2,8 +2,12 @@
 // Licensed under the MIT License. See License.txt in the project root for license information.
 
 using System;
+using System.Linq;
+using Microsoft.AspNetCore.Hosting;
 using Microsoft.Azure.WebJobs.Script.WebHost;
+using Microsoft.Azure.WebJobs.Script.WebHost.Diagnostics.Extensions;
 using Microsoft.Azure.WebJobs.Script.WebHost.Middleware;
+using Microsoft.Extensions.Logging;
 using Microsoft.WebJobs.Script.Tests;
 using Moq;
 using Xunit;
@@ -53,5 +57,21 @@ public void IsWarmUpRequest_ReturnsExpectedValue()
             Assert.True(environment.IsLinuxConsumption());
             Assert.True(HostWarmupMiddleware.IsWarmUpRequest(request, hostEnvironment.InStandbyMode, environment));
         }
+
+        [Fact]
+        public void ReadRuntimeAssemblyFiles_VerifyLogs()
+        {
+            var environment = new TestEnvironment();
+            var hostEnvironment = new ScriptWebHostEnvironment(environment);
+            var testLoggerFactory = new LoggerFactory();
+            TestLoggerProvider testLoggerProvider = new TestLoggerProvider();
+            testLoggerFactory.AddProvider(testLoggerProvider);
+            ILogger<HostWarmupMiddleware> testLogger = testLoggerFactory.CreateLogger<HostWarmupMiddleware>();
+            HostWarmupMiddleware hostWarmupMiddleware = new HostWarmupMiddleware(null, new Mock<IScriptWebHostEnvironment>().Object, environment, new Mock<IScriptHostManager>().Object, testLogger);
+            hostWarmupMiddleware.ReadRuntimeAssemblyFiles();
+            // Assert
+            var traces = testLoggerProvider.GetAllLogMessages();
+            Assert.True(traces.Any(m => m.FormattedMessage.Contains("Number of files read:")));
+        }
     }
 }