User-configurable synchronized writes

src/Serilog.Sinks.Console/ConsoleLoggerConfigurationExtensions.cs

@@ -28,6 +28,7 @@ namespace Serilog
     /// </summary>
     public static class ConsoleLoggerConfigurationExtensions
     {
+        private static object DefaultSyncRoot = new object();
         const string DefaultConsoleOutputTemplate = "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj}{NewLine}{Exception}";
 
         /// <summary>
@@ -38,6 +39,9 @@ public static class ConsoleLoggerConfigurationExtensions
         /// events passed through the sink. Ignored when <paramref name="levelSwitch"/> is specified.</param>
         /// <param name="outputTemplate">A message template describing the format used to write to the sink.
         /// The default is <code>"[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj}{NewLine}{Exception}"</code>.</param>
+        /// <param name="syncRoot">An object that will be used to `lock` (sync) access to the console output. If you specify this, you
+        /// will have the ability to lock on this object, and guarantee that the console sink will not be about to output anything while
+        /// the lock is held.</param>
         /// <param name="formatProvider">Supplies culture-specific formatting information, or null.</param>
         /// <param name="levelSwitch">A switch allowing the pass-through minimum level
         /// to be changed at runtime.</param>
@@ -52,7 +56,8 @@ public static LoggerConfiguration Console(
             IFormatProvider formatProvider = null,
             LoggingLevelSwitch levelSwitch = null,
             LogEventLevel? standardErrorFromLevel = null,
-            ConsoleTheme theme = null)
+            ConsoleTheme theme = null,
+            object syncRoot = null)
         {
             if (sinkConfiguration == null) throw new ArgumentNullException(nameof(sinkConfiguration));
             if (outputTemplate == null) throw new ArgumentNullException(nameof(outputTemplate));
@@ -61,8 +66,10 @@ public static LoggerConfiguration Console(
                 ConsoleTheme.None :
                 theme ?? SystemConsoleThemes.Literate;
 
+            syncRoot = syncRoot ?? DefaultSyncRoot;
+
             var formatter = new OutputTemplateRenderer(appliedTheme, outputTemplate, formatProvider);
-            return sinkConfiguration.Sink(new ConsoleSink(appliedTheme, formatter, standardErrorFromLevel), restrictedToMinimumLevel, levelSwitch);
+            return sinkConfiguration.Sink(new ConsoleSink(appliedTheme, formatter, standardErrorFromLevel, syncRoot), restrictedToMinimumLevel, levelSwitch);
         }
 
         /// <summary>
@@ -71,6 +78,9 @@ public static LoggerConfiguration Console(
         /// <param name="sinkConfiguration">Logger sink configuration.</param>
         /// <param name="formatter">Controls the rendering of log events into text, for example to log JSON. To
         /// control plain text formatting, use the overload that accepts an output template.</param>
+        /// <param name="syncRoot">An object that will be used to `lock` (sync) access to the console output. If you specify this, you
+        /// will have the ability to lock on this object, and guarantee that the console sink will not be about to output anything while
+        /// the lock is held.</param>
         /// <param name="restrictedToMinimumLevel">The minimum level for
         /// events passed through the sink. Ignored when <paramref name="levelSwitch"/> is specified.</param>
         /// <param name="levelSwitch">A switch allowing the pass-through minimum level
@@ -82,12 +92,14 @@ public static LoggerConfiguration Console(
             ITextFormatter formatter,
             LogEventLevel restrictedToMinimumLevel = LevelAlias.Minimum,
             LoggingLevelSwitch levelSwitch = null,
-            LogEventLevel? standardErrorFromLevel = null)
+            LogEventLevel? standardErrorFromLevel = null,
+            object syncRoot = null)
         {
             if (sinkConfiguration == null) throw new ArgumentNullException(nameof(sinkConfiguration));
             if (formatter == null) throw new ArgumentNullException(nameof(formatter));
 
-            return sinkConfiguration.Sink(new ConsoleSink(ConsoleTheme.None, formatter, standardErrorFromLevel), restrictedToMinimumLevel, levelSwitch);
+            syncRoot = syncRoot ?? DefaultSyncRoot;
+            return sinkConfiguration.Sink(new ConsoleSink(ConsoleTheme.None, formatter, standardErrorFromLevel, syncRoot), restrictedToMinimumLevel, levelSwitch);
         }
     }
 }

src/Serilog.Sinks.Console/Sinks/SystemConsole/ConsoleSink.cs

@@ -28,7 +28,7 @@ class ConsoleSink : ILogEventSink
         readonly LogEventLevel? _standardErrorFromLevel;
         readonly ConsoleTheme _theme;
         readonly ITextFormatter _formatter;
-        readonly object _syncRoot = new object();
+        readonly object _syncRoot;
 
         const int DefaultWriteBufferCapacity = 256;
 
@@ -40,11 +40,13 @@ static ConsoleSink()
         public ConsoleSink(
             ConsoleTheme theme,
             ITextFormatter formatter,
-            LogEventLevel? standardErrorFromLevel)
+            LogEventLevel? standardErrorFromLevel,
+            object syncRoot)
         {
             _standardErrorFromLevel = standardErrorFromLevel;
             _theme = theme ?? throw new ArgumentNullException(nameof(theme));
             _formatter = formatter;
+            _syncRoot = syncRoot ?? throw new ArgumentNullException(nameof(syncRoot));
         }
 
         public void Emit(LogEvent logEvent)