lib/xcflushd/logger.rb in xcflushd-1.0.0.rc2 vs lib/xcflushd/logger.rb in xcflushd-1.0.0

@@ -1,9 +1,31 @@
 require 'logger'
 
 module Xcflushd
   class Logger
     def self.new(*args)
+      # Logging to a IO-like object.
+      #
+      # When the IO object is a TTY, Ruby sets line buffered mode, which is
+      # ok for logs. However, when it is not a TTY, Ruby sets up a buffer
+      # of unspecified size that causes applications that write few logs to
+      # appear as inactive in the log stream. This is a problem when trying
+      # to diagnose issues.
+      #
+      # Unfortunately Ruby only exposes a couple of limited ways to control
+      # the underlying buffering: IO#(f)sync and IO#flush. Apparently the C
+      # runtime stdio buffering is replaced by Ruby's own, so there is no
+      # point in trying to call setvbuf, and no point either in trying to
+      # control a TTY, since that case is fine.
+      #
+      # Since our logging stream activity is fairly low it's reasonable to
+      # use IO#sync for the non TTY case to have (hopefully) a behaviour
+      # similar to line-buffered standard I/O.
+      #
+      # More info on http://tuxdna.in/files/notes/ruby-io.html.
+      #
+      io = args[0]
+      io.sync = true unless io.tty?
       ::Logger.new(*args)
     end
   end
 end