Maintain a seperate buffer for each thread

activesupport/lib/active_support/buffered_logger.rb

@@ -33,11 +33,10 @@ def silence(temporary_level = ERROR)
 
     attr_accessor :level
     attr_reader :auto_flushing
-    attr_reader :buffer
 
     def initialize(log, level = DEBUG)
       @level         = level
-      @buffer        = []
+      @buffer        = {}
       @auto_flushing = 1
       @guard = Mutex.new
 
@@ -60,9 +59,7 @@ def add(severity, message = nil, progname = nil, &block)
       # If a newline is necessary then create a new message ending with a newline.
       # Ensures that the original message is not mutated.
       message = "#{message}\n" unless message[-1] == ?\n
-      @guard.synchronize do
-        buffer << message
-      end
+      buffer << message
       auto_flush
       message
     end
@@ -96,8 +93,8 @@ def auto_flushing=(period)
     def flush
       @guard.synchronize do
         unless buffer.empty?
-          old_buffer    = @buffer
-          @buffer       = []
+          old_buffer = buffer
+          clear_buffer
           @log.write(old_buffer.join)
         end
       end
@@ -113,5 +110,13 @@ def close
       def auto_flush
         flush if buffer.size >= @auto_flushing
       end
+
+      def buffer
+        @buffer[Thread.current] ||= []
+      end
+
+      def clear_buffer
+        @buffer[Thread.current] = []
+      end
   end
 end

activesupport/test/buffered_logger_test.rb

@@ -70,7 +70,7 @@ def test_should_not_mutate_message
       end
 
       @logger.flush
-      assert !@output.string.empty?, @logger.buffer.size
+      assert !@output.string.empty?, @logger.send(:buffer).size
     end
 
     define_method "test_disabling_auto_flush_with_#{disable.inspect}_should_flush_at_max_buffer_size_as_failsafe" do
@@ -83,10 +83,10 @@ def test_should_not_mutate_message
       end
 
       @logger.info 'there it is.'
-      assert !@output.string.empty?, @logger.buffer.size
+      assert !@output.string.empty?, @logger.send(:buffer).size
     end
   end
-  
+
   def test_should_know_if_its_loglevel_is_below_a_given_level
     ActiveSupport::BufferedLogger::Severity.constants.each do |level|
       @logger.level = ActiveSupport::BufferedLogger::Severity.const_get(level) - 1
@@ -105,7 +105,7 @@ def test_should_auto_flush_every_n_messages
     @logger.info 'there it is.'
     assert !@output.string.empty?, @output.string
   end
-  
+
   def test_should_create_the_log_directory_if_it_doesnt_exist
     tmp_directory = File.join(File.dirname(__FILE__), "tmp")
     log_file = File.join(tmp_directory, "development.log")
@@ -115,4 +115,25 @@ def test_should_create_the_log_directory_if_it_doesnt_exist
   ensure
     FileUtils.rm_rf(tmp_directory)
   end
+
+  def test_logger_should_maintain_separate_buffers_for_each_thread
+    @logger.auto_flushing = false
+
+    a = Thread.new do
+      @logger.info("a"); Thread.pass;
+      @logger.info("b"); Thread.pass;
+      @logger.info("c"); @logger.flush
+    end
+
+    b = Thread.new do
+      @logger.info("x"); Thread.pass;
+      @logger.info("y"); Thread.pass;
+      @logger.info("z"); @logger.flush
+    end
+
+    a.join
+    b.join
+
+    assert_equal "a\nb\nc\nx\ny\nz\n", @output.string
+  end
 end