Add MemoryMappedFileHandler for SelfDiagnostics

BASE/Test/Microsoft.ApplicationInsights.Test/Microsoft.ApplicationInsights.Tests/Extensibility/Implementation/Tracing/SelfDiagnostics/MemoryMappedFileHandlerTest.cs

@@ -0,0 +1,73 @@
+namespace Microsoft.ApplicationInsights.Extensibility.Implementation.Tracing.SelfDiagnostics
+{
+    using System;
+    using System.Diagnostics;
+    using System.IO;
+    using System.Text;
+
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+    [TestClass]
+    public class MemoryMappedFileHandlerTest
+    {
+        public static readonly byte[] MessageOnNewFile = MemoryMappedFileHandler.MessageOnNewFile;
+
+        [TestMethod]
+        public void MemoryMappedFileHandler_Success()
+        {
+            var fileName = Path.GetFileName(Process.GetCurrentProcess().MainModule.FileName) + "."
+                    + Process.GetCurrentProcess().Id + ".log";
+            var fileSize = 1024;
+            using (var handler = new MemoryMappedFileHandler())
+            {
+                handler.CreateLogFile(".", fileSize);
+            }
+
+            var actualBytes = ReadFile(fileName, MessageOnNewFile.Length);
+
+            CollectionAssert.AreEqual(MessageOnNewFile, actualBytes);
+        }
+
+        [TestMethod]
+        public void MemoryMappedFileHandler_Circular_Success()
+        {
+            var fileSize = 1024;
+            var buffer = new byte[1024];
+            var messageToOverflow = Encoding.UTF8.GetBytes("1234567");
+            var expectedBytesAtEnd = Encoding.UTF8.GetBytes("1234");
+            var expectedBytesAtStart = Encoding.UTF8.GetBytes("567cessfully opened file.\n");
+            using (var handler = new MemoryMappedFileHandler())
+            {
+                handler.CreateLogFile(".", fileSize);
+
+                handler.Write(buffer, fileSize - MessageOnNewFile.Length - expectedBytesAtEnd.Length);
+
+                handler.Write(messageToOverflow, messageToOverflow.Length);
+            }
+
+            var fileName = Path.GetFileName(Process.GetCurrentProcess().MainModule.FileName) + "."
+                    + Process.GetCurrentProcess().Id + ".log";
+            var actualBytes = ReadFile(fileName, buffer.Length);
+
+            CollectionAssert.AreEqual(expectedBytesAtStart, SubArray(actualBytes, 0, expectedBytesAtStart.Length));
+            CollectionAssert.AreEqual(expectedBytesAtEnd, SubArray(actualBytes, actualBytes.Length - expectedBytesAtEnd.Length, expectedBytesAtEnd.Length));
+        }
+
+        private static byte[] ReadFile(string fileName, int byteCount)
+        {
+            byte[] actualBytes = new byte[byteCount];
+            using (var file = File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
+            {
+                file.Read(actualBytes, 0, byteCount);
+            }
+            return actualBytes;
+        }
+
+        private static byte[] SubArray(byte[] array, int offset, int length)
+        {
+            byte[] result = new byte[length];
+            Array.Copy(array, offset, result, 0, length);
+            return result;
+        }
+    }
+}

BASE/src/Microsoft.ApplicationInsights/Extensibility/Implementation/Tracing/CoreEventSource.cs

@@ -656,6 +656,9 @@ public void IngestionResponseTimeEventCounter(float responseDurationInMs)
         [Event(71, Keywords = Keywords.UserActionable, Message = "TransmissionStatusEvent has failed. Error: {0}. Monitoring will continue.", Level = EventLevel.Error)]
         public void TransmissionStatusEventError(string error, string appDomainName = "Incorrect") => this.WriteEvent(71, error, this.nameProvider.Name);
 
+        [Event(72, Keywords = Keywords.UserActionable, Message = "Failed to create file for self diagnostics at {0}. Error message: {1}.", Level = EventLevel.Error)]
+        public void SelfDiagnosticsFileCreateException(string logDirectory, string exception, string appDomainName = "Incorrect") => this.WriteEvent(72, logDirectory, exception, this.nameProvider.Name);
+
         [NonEvent]
         public void TransmissionStatusEventFailed(Exception ex)
         {

BASE/src/Microsoft.ApplicationInsights/Extensibility/Implementation/Tracing/SelfDiagnostics/MemoryMappedFileHandler.cs

@@ -1,10 +1,263 @@
 namespace Microsoft.ApplicationInsights.Extensibility.Implementation.Tracing.SelfDiagnostics
 {
-    internal class MemoryMappedFileHandler
+    using System;
+    using System.Diagnostics;
+    using System.IO;
+    using System.IO.MemoryMappedFiles;
+    using System.Text;
+    using System.Threading;
+
+    /// <summary>
+    /// MemoryMappedFileHandler open a MemoryMappedFile of a certain size at a certain file path.
+    /// The class provides a stream object with proper write position.
+    /// The stream is cached in ThreadLocal to be thread-safe.
+    /// </summary>
+    internal class MemoryMappedFileHandler : IDisposable
     {
+        public static readonly byte[] MessageOnNewFile = Encoding.UTF8.GetBytes("Successfully opened file.\n");
+
+        /// <summary>
+        /// memoryMappedFileCache is a handle kept in thread-local storage as a cache to indicate whether the cached
+        /// viewStream is created from the current m_memoryMappedFile.
+        /// </summary>
+        private readonly ThreadLocal<MemoryMappedFile> memoryMappedFileCache = new ThreadLocal<MemoryMappedFile>(true);
+        private readonly ThreadLocal<MemoryMappedViewStream> viewStream = new ThreadLocal<MemoryMappedViewStream>(true);
+
+#pragma warning disable CA2213 // Disposed in CloseLogFile, which is called in Dispose
+        private volatile FileStream underlyingFileStreamForMemoryMappedFile;
+        private volatile MemoryMappedFile memoryMappedFile;
+#pragma warning restore CA2213 // Disposed in CloseLogFile, which is called in Dispose
+
+        private bool disposedValue;
+
+        private string logDirectory;  // Log directory for log files
+        private int logFileSize;  // Log file size in bytes
+        private long logFilePosition;  // The logger will write into the byte at this position
+
+        public string LogDirectory { get => this.logDirectory; set => this.logDirectory = value; }
+
+        public int LogFileSize { get => this.logFileSize; private set => this.logFileSize = value; }
+
+        /// <summary>
+        /// Create a log file. If the file already exists, it will be overwritten.
+        /// </summary>
+        /// <param name="logDirectory">The directory the log file will be created.</param>
+        /// <param name="fileSize">The size of the log file.</param>
+        public void CreateLogFile(string logDirectory, int fileSize)
+        {
+            try
+            {
+                Directory.CreateDirectory(logDirectory);
+                var fileName = Path.GetFileName(Process.GetCurrentProcess().MainModule.FileName) + "."
+                    + Process.GetCurrentProcess().Id + ".log";
+                var filePath = Path.Combine(logDirectory, fileName);
+
+                // Because the API [MemoryMappedFile.CreateFromFile][1](the string version) behaves differently on
+                // .NET Framework and .NET Core, here I am using the [FileStream version][2] of it.
+                // Taking the last four prameter values from [.NET Framework]
+                // (https://referencesource.microsoft.com/#system.core/System/IO/MemoryMappedFiles/MemoryMappedFile.cs,148)
+                // and [.NET Core]
+                // (https://github.com/dotnet/runtime/blob/master/src/libraries/System.IO.MemoryMappedFiles/src/System/IO/MemoryMappedFiles/MemoryMappedFile.cs#L152)
+                // The parameter for FileAccess is different in type but the same in rules, both are Read and Write.
+                // The parameter for FileShare is different in values and in behavior.
+                // .NET Framework doesn't allow sharing but .NET Core allows reading by other programs.
+                // The last two parameters are the same values for both frameworks.
+                // [1]: https://docs.microsoft.com/dotnet/api/system.io.memorymappedfiles.memorymappedfile.createfromfile?view=net-5.0#System_IO_MemoryMappedFiles_MemoryMappedFile_CreateFromFile_System_String_System_IO_FileMode_System_String_System_Int64_
+                // [2]: https://docs.microsoft.com/dotnet/api/system.io.memorymappedfiles.memorymappedfile.createfromfile?view=net-5.0#System_IO_MemoryMappedFiles_MemoryMappedFile_CreateFromFile_System_IO_FileStream_System_String_System_Int64_System_IO_MemoryMappedFiles_MemoryMappedFileAccess_System_IO_HandleInheritability_System_Boolean_
+                this.underlyingFileStreamForMemoryMappedFile =
+                    new FileStream(filePath, FileMode.Create, FileAccess.ReadWrite, FileShare.Read, 0x1000, FileOptions.None);
+
+                // The parameter values for MemoryMappedFileSecurity, HandleInheritability and leaveOpen are the same
+                // values for .NET Framework and .NET Core:
+                // https://referencesource.microsoft.com/#system.core/System/IO/MemoryMappedFiles/MemoryMappedFile.cs,172
+                // https://github.com/dotnet/runtime/blob/master/src/libraries/System.IO.MemoryMappedFiles/src/System/IO/MemoryMappedFiles/MemoryMappedFile.cs#L168-L179
+                this.memoryMappedFile = MemoryMappedFile.CreateFromFile(
+                    this.underlyingFileStreamForMemoryMappedFile,
+                    null,
+                    fileSize,
+                    MemoryMappedFileAccess.ReadWrite,
+#if NET452
+                    // Only .NET Framework 4.5.2 among all .NET Framework versions is lacking a method omitting this
+                    // default value for MemoryMappedFileSecurity.
+                    // https://docs.microsoft.com/dotnet/api/system.io.memorymappedfiles.memorymappedfile.createfromfile?view=netframework-4.5.2
+                    // .NET Core simply doesn't support this parameter.
+                    null,
+#endif
+                    HandleInheritability.None,
+                    false);
+                this.logDirectory = logDirectory;
+                this.logFileSize = fileSize;
+                this.logFilePosition = 0;
+                this.Write(MessageOnNewFile, MessageOnNewFile.Length);
+            }
+            catch (Exception ex)
+            {
+                CoreEventSource.Log.SelfDiagnosticsFileCreateException(logDirectory, ex.ToInvariantString());
+            }
+        }
+
+        /// <summary>
+        /// Close the all the resources related to the file created for MemoryMappedFile.
+        /// </summary>
+        public void CloseLogFile()
+        {
+            MemoryMappedFile mmf = Interlocked.CompareExchange(ref this.memoryMappedFile, null, this.memoryMappedFile);
+            if (mmf != null)
+            {
+                // Each thread has its own MemoryMappedViewStream created from the only one MemoryMappedFile.
+                // Once worker thread closes the MemoryMappedFile, all the ViewStream objects should be disposed
+                // properly.
+                foreach (MemoryMappedViewStream stream in this.viewStream.Values)
+                {
+                    if (stream != null)
+                    {
+                        stream.Dispose();
+                    }
+                }
+
+                mmf.Dispose();
+            }
+
+            FileStream fs = Interlocked.CompareExchange(
+                ref this.underlyingFileStreamForMemoryMappedFile,
+                null,
+                this.underlyingFileStreamForMemoryMappedFile);
+            fs?.Dispose();
+        }
+
+        /// <inheritdoc/>
+        public void Dispose()
+        {
+            this.Dispose(true);
+            GC.SuppressFinalize(this);
+        }
+
+        /// <summary>
+        /// Circularly write to the file. If write operation reaches the end of the file, start writing from the beginning of the file.
+        /// </summary>
+        /// <param name="buffer">The buffer which contains the data to be written.</param>
+        /// <param name="byteCount">The count of bytes to be written.</param>
         public void Write(byte[] buffer, int byteCount)
         {
-            // TODO. Placeholder for SelfDiagnosticsEventListener
+            try
+            {
+                if (this.TryGetLogStream(byteCount, out Stream stream, out int availableByteCount))
+                {
+                    if (availableByteCount >= byteCount)
+                    {
+                        stream.Write(buffer, 0, byteCount);
+                    }
+                    else
+                    {
+                        stream.Write(buffer, 0, availableByteCount);
+                        stream.Seek(0, SeekOrigin.Begin);
+                        stream.Write(buffer, availableByteCount, byteCount - availableByteCount);
+                    }
+                }
+            }
+            catch (Exception)
+            {
+                // A concurrent race condition: memory mapped file is disposed in another thread after TryGetLogStream() finishes.
+                // In this case, silently fail.
+            }
+        }
+
+        /// <summary>
+        /// Try to get the log stream which is seeked to the position where the next line of log should be written.
+        /// </summary>
+        /// <param name="byteCount">The number of bytes that need to be written.</param>
+        /// <param name="stream">When this method returns, contains the Stream object where `byteCount` of bytes can be written.</param>
+        /// <param name="availableByteCount">The number of bytes that is remaining until the end of the stream.</param>
+        /// <returns>Whether the logger should log in the stream.</returns>
+        private bool TryGetLogStream(int byteCount, out Stream stream, out int availableByteCount)
+        {
+            if (this.memoryMappedFile == null)
+            {
+                stream = null;
+                availableByteCount = 0;
+                return false;
+            }
+
+            try
+            {
+                var cachedViewStream = this.GetStream();
+
+                long beginPosition, endPosition;
+                do
+                {
+                    beginPosition = this.logFilePosition;
+                    endPosition = beginPosition + byteCount;
+                    if (endPosition >= this.logFileSize)
+                    {
+                        endPosition %= this.logFileSize;
+                    }
+                }
+                while (beginPosition != Interlocked.CompareExchange(ref this.logFilePosition, endPosition, beginPosition));
+                availableByteCount = (int)(this.logFileSize - beginPosition);
+                cachedViewStream.Seek(beginPosition, SeekOrigin.Begin);
+                stream = cachedViewStream;
+                return true;
+            }
+            catch (Exception)
+            {
+                stream = null;
+                availableByteCount = 0;
+                return false;
+            }
+        }
+
+        /// <summary>
+        /// Get a MemoryMappedViewStream for the MemoryMappedFile object for the current thread.
+        /// If no MemoryMappedFile is created yet, return null.
+        /// </summary>
+        /// <returns>A MemoryMappedViewStream for the MemoryMappedFile object.</returns>
+        /// <exception cref="System.UnauthorizedAccessException">Thrown when access to the memory-mapped file is unauthorized.</exception>
+        /// <exception cref="System.NullReferenceException">Thrown in a race condition when the memory-mapped file is closed after null check.</exception>
+        private MemoryMappedViewStream GetStream()
+        {
+            if (this.memoryMappedFile == null)
+            {
+                return null;
+            }
+
+            var cachedViewStream = this.viewStream.Value;
+
+            // Each thread has its own MemoryMappedViewStream created from the only one MemoryMappedFile.
+            // Once worker thread updates the MemoryMappedFile, all the cached ViewStream objects become
+            // obsolete.
+            // Each thread creates a new MemoryMappedViewStream the next time it tries to retrieve it.
+            // Whether the MemoryMappedViewStream is obsolete is determined by comparing the current
+            // MemoryMappedFile object with the MemoryMappedFile object cached at the creation time of the
+            // MemoryMappedViewStream.
+            if (cachedViewStream == null || this.memoryMappedFileCache.Value != this.memoryMappedFile)
+            {
+                // Race condition: The code might reach here right after the worker thread sets memoryMappedFile
+                // to null in CloseLogFile().
+                // In this case, let the NullReferenceException be caught and fail silently.
+                // By design, all events captured will be dropped during a configuration file refresh if
+                // the file changed, regardless whether the file is deleted or updated.
+                cachedViewStream = this.memoryMappedFile.CreateViewStream();
+                this.viewStream.Value = cachedViewStream;
+                this.memoryMappedFileCache.Value = this.memoryMappedFile;
+            }
+
+            return cachedViewStream;
+        }
+
+        private void Dispose(bool disposing)
+        {
+            if (!this.disposedValue)
+            {
+                if (disposing)
+                {
+                    this.CloseLogFile();
+
+                    this.viewStream.Dispose();
+                    this.memoryMappedFileCache.Dispose();
+                }
+
+                this.disposedValue = true;
+            }
         }
     }
 }