Support multi-process shared file sets

Author: nblumhardt

src/Serilog.Sinks.RollingFile/RollingFileLoggerConfigurationExtensions.cs

@@ -53,8 +53,9 @@ public static class RollingFileLoggerConfigurationExtensions
         /// including the current log file. For unlimited retention, pass null. The default is 31.</param>
         /// <param name="buffered">Indicates if flushing to the output file can be buffered or not. The default
         /// is false.</param>
+        /// <param name="shared">Allow the log files to be shared by multiple processes. The default is false.</param>
         /// <returns>Configuration object allowing method chaining.</returns>
-        /// <remarks>The file will be written using the UTF-8 character set.</remarks>
+        /// <remarks>The file will be written using the UTF-8 encoding without a byte-order mark.</remarks>
         public static LoggerConfiguration RollingFile(
             this LoggerSinkConfiguration sinkConfiguration,
             string pathFormat,
@@ -64,11 +65,12 @@ public static LoggerConfiguration RollingFile(
             long? fileSizeLimitBytes = DefaultFileSizeLimitBytes,
             int? retainedFileCountLimit = DefaultRetainedFileCountLimit,
             LoggingLevelSwitch levelSwitch = null,
-            bool buffered = false)
+            bool buffered = false,
+            bool shared = false)
         {
             var formatter = new MessageTemplateTextFormatter(outputTemplate, formatProvider);
             return RollingFile(sinkConfiguration, formatter, pathFormat, restrictedToMinimumLevel, fileSizeLimitBytes,
-                retainedFileCountLimit, levelSwitch, buffered);
+                retainedFileCountLimit, levelSwitch, buffered, shared);
         }
 
         /// <summary>
@@ -92,8 +94,9 @@ public static LoggerConfiguration RollingFile(
         /// including the current log file. For unlimited retention, pass null. The default is 31.</param>
         /// <param name="buffered">Indicates if flushing to the output file can be buffered or not. The default
         /// is false.</param>
+        /// <param name="shared">Allow the log files to be shared by multiple processes. The default is false.</param>
         /// <returns>Configuration object allowing method chaining.</returns>
-        /// <remarks>The file will be written using the UTF-8 character set.</remarks>
+        /// <remarks>The file will be written using the UTF-8 encoding without a byte-order mark.</remarks>
         public static LoggerConfiguration RollingFile(
             this LoggerSinkConfiguration sinkConfiguration,
             ITextFormatter formatter,
@@ -102,11 +105,19 @@ public static LoggerConfiguration RollingFile(
             long? fileSizeLimitBytes = DefaultFileSizeLimitBytes,
             int? retainedFileCountLimit = DefaultRetainedFileCountLimit,
             LoggingLevelSwitch levelSwitch = null,
-            bool buffered = false)
+            bool buffered = false,
+            bool shared = false)
         {
             if (sinkConfiguration == null) throw new ArgumentNullException(nameof(sinkConfiguration));
             if (formatter == null) throw new ArgumentNullException(nameof(formatter));
-            var sink = new RollingFileSink(pathFormat, formatter, fileSizeLimitBytes, retainedFileCountLimit, buffered: buffered);
+
+            if (shared)
+            {
+                if (buffered)
+                    throw new ArgumentException("Buffered writes are not available when file sharing is enabled.", nameof(buffered));
+            }
+
+            var sink = new RollingFileSink(pathFormat, formatter, fileSizeLimitBytes, retainedFileCountLimit, buffered: buffered, shared: shared);
             return sinkConfiguration.Sink(sink, restrictedToMinimumLevel, levelSwitch);
         }
     }

src/Serilog.Sinks.RollingFile/Sinks/RollingFile/RollingFileSink.cs

@@ -39,11 +39,12 @@ public sealed class RollingFileSink : ILogEventSink, IDisposable
         readonly int? _retainedFileCountLimit;
         readonly Encoding _encoding;
         readonly bool _buffered;
+        readonly bool _shared;
         readonly object _syncRoot = new object();
 
         bool _isDisposed;
         DateTime? _nextCheckpoint;
-        FileSink _currentFile;
+        ILogEventSink _currentFile;
 
         /// <summary>Construct a <see cref="RollingFileSink"/>.</summary>
         /// <param name="pathFormat">String describing the location of the log files,
@@ -54,28 +55,36 @@ public sealed class RollingFileSink : ILogEventSink, IDisposable
         /// For unrestricted growth, pass null. The default is 1 GB.</param>
         /// <param name="retainedFileCountLimit">The maximum number of log files that will be retained,
         /// including the current log file. For unlimited retention, pass null. The default is 31.</param>
-        /// <param name="encoding">Character encoding used to write the text file. The default is UTF-8.</param>
+        /// <param name="encoding">Character encoding used to write the text file. The default is UTF-8 without BOM.</param>
         /// <param name="buffered">Indicates if flushing to the output file can be buffered or not. The default
         /// is false.</param>
+        /// <param name="shared">Allow the log files to be shared by multiple processes. The default is false.</param>
         /// <returns>Configuration object allowing method chaining.</returns>
         /// <remarks>The file will be written using the UTF-8 character set.</remarks>
         public RollingFileSink(string pathFormat,
                               ITextFormatter textFormatter,
                               long? fileSizeLimitBytes,
                               int? retainedFileCountLimit,
                               Encoding encoding = null,
-                              bool buffered = false)
+                              bool buffered = false,
+                              bool shared = false)
         {
             if (pathFormat == null) throw new ArgumentNullException(nameof(pathFormat));
             if (fileSizeLimitBytes.HasValue && fileSizeLimitBytes < 0) throw new ArgumentException("Negative value provided; file size limit must be non-negative");
             if (retainedFileCountLimit.HasValue && retainedFileCountLimit < 1) throw new ArgumentException("Zero or negative value provided; retained file count limit must be at least 1");
 
+#if !SHARING
+            if (shared)
+                throw new NotSupportedException("File sharing is not supported on this platform.");
+#endif
+
             _roller = new TemplatedPathRoller(pathFormat);
             _textFormatter = textFormatter;
             _fileSizeLimitBytes = fileSizeLimitBytes;
             _retainedFileCountLimit = retainedFileCountLimit;
-            _encoding = encoding ?? new UTF8Encoding(encoderShouldEmitUTF8Identifier: false);
+            _encoding = encoding;
             _buffered = buffered;
+            _shared = shared;
         }
 
         /// <summary>
@@ -98,8 +107,7 @@ public void Emit(LogEvent logEvent)
                 // If the file was unable to be opened on the last attempt, it will remain
                 // null until the next checkpoint passes, at which time another attempt will be made to
                 // open it.
-                if (_currentFile != null)
-                    _currentFile.Emit(logEvent);
+                _currentFile?.Emit(logEvent);
             }
         }
 
@@ -148,7 +156,13 @@ void OpenFile(DateTime now)
 
                 try
                 {
+#if SHARING
+                    _currentFile = _shared ?
+                        (ILogEventSink)new SharedFileSink(path, _textFormatter, _fileSizeLimitBytes, _encoding) :
+                        new FileSink(path, _textFormatter, _fileSizeLimitBytes, _encoding, _buffered);
+#else
                     _currentFile = new FileSink(path, _textFormatter, _fileSizeLimitBytes, _encoding, _buffered);
+#endif
                 }
                 catch (IOException ex)
                 {
@@ -223,7 +237,7 @@ void CloseFile()
         {
             if (_currentFile != null)
             {
-                _currentFile.Dispose();
+                (_currentFile as IDisposable)?.Dispose();
                 _currentFile = null;
             }
 

src/Serilog.Sinks.RollingFile/project.json

@@ -1,5 +1,5 @@
 {
-  "version": "2.3.0-*",
+  "version": "3.0.0-*",
   "description": "The rolling file sink for Serilog - Simple .NET logging with fully-structured events",
   "authors": [ "Serilog Contributors" ],
   "packOptions": {
@@ -9,16 +9,17 @@
     "iconUrl": "http://serilog.net/images/serilog-sink-nuget.png"
   },
   "dependencies": {
-    "Serilog": "2.0.0",
-    "Serilog.Sinks.File": "2.0.0"
+    "Serilog.Sinks.File": "3.0.0-dev-00735"
   },
   "buildOptions": {
     "keyFile": "../../assets/Serilog.snk",
     "xmlDoc": true,
     "warningsAsErrors": true
   },
   "frameworks": {
-    "net4.5": {},
+    "net4.5": {
+      "buildOptions": {"define": ["SHARING"]}
+    },
     "netstandard1.3": {
       "dependencies": {
         "System.IO": "4.1.0",

test/Serilog.Sinks.RollingFile.Tests/RollingFileLoggerConfigurationExtensionsTests.cs

@@ -0,0 +1,16 @@
+using System;
+using Xunit;
+
+namespace Serilog.Tests
+{
+    public class RollingFileLoggerConfigurationExtensionsTests
+    {
+        [Fact]
+        public void BuffferingIsNotAvailableWhenSharingEnabled()
+        {
+            Assert.Throws<ArgumentException>(() => 
+                new LoggerConfiguration()   
+                    .WriteTo.RollingFile("logs", buffered: true, shared: true));
+        }
+    }
+}

test/Serilog.Sinks.RollingFile.Tests/project.json

@@ -1,11 +1,9 @@
 {
-  "version": "2.0.0",
   "testRunner": "xunit",
   "dependencies": {
     "Serilog.Sinks.RollingFile": { "target": "project" },
     "xunit": "2.1.0",
-    "dotnet-test-xunit": "1.0.0-rc2-build10025",
-    "Serilog.Sinks.File": "2.0.0"
+    "dotnet-test-xunit": "1.0.0-rc2-build10025"
   },
   "buildOptions": {
     "keyFile": "../../assets/Serilog.snk",