src/Pure/General/logger.scala

avoid race condition between current_state().stable_tip_version and model.rendering();

/*  Title:      Pure/General/logger.scala
    Author:     Makarius

Minimal logging support.
*/

package isabelle


object Logger
{
  def make(log_file: Option[Path]): Logger =
    log_file match { case Some(file) => new File_Logger(file) case None => No_Logger }
}

trait Logger
{
  def apply(msg: => String): Unit
}

object No_Logger extends Logger
{
  def apply(msg: => String) { }
}

class File_Logger(path: Path) extends Logger
{
  def apply(msg: => String) { synchronized { File.append(path, msg + "\n") } }

  override def toString: String = path.toString
}