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High-performance SLF4J wrapper for Scala

There is a newer version: 1.3.2

package org.log4s

import java.util.{ Map => JMap }
import java.util.Collections.EMPTY_MAP

import scala.collection.JavaConversions._

import org.slf4j.{ MDC => JMDC }

/** A singleton used for accessing the mapped diagnostic context of your
  * loggers. This acts like a regular map, except that the values are different
  * in every thread.
  *
  * Getting and setting single values and clearing the map are fast operations
  * operations, but other operations, including getting the size, requires
  * making a copy of the MDC.
  */
object MDC extends collection.mutable.Map[String,String] {
  @inline private[this] final def copyMap: JMap[String,String] = {
    val mdcMap = JMDC.getCopyOfContextMap()
    if (mdcMap != null)
      mdcMap
    else
      EMPTY_MAP.asInstanceOf[JMap[String,String]]
  }

  final def += (kv: (String,String)): this.type = {
    val (key, value) = kv
    JMDC.put(key, value)
    this
  }

  final def -= (key: String): this.type = {
    JMDC.remove(key)
    this
  }

  override final def clear() { JMDC.clear() }

  final def get(key: String): Option[String] = Option(JMDC.get(key))

  /** Get an iterator over the values of this map. This requires making a copy of
    * the map, so it may cause performance problems if called frequently.
    */
  final def iterator: Iterator[(String,String)] = copyMap.iterator

  /** Get the size of this map This requires making a copy of the map, so it may
    * cause performance problems if called frequently.
    */
  override final def size: Int = copyMap.size

  /** Execute a block of code with MDC variables set. After the block completes,
    * any variables you've set will be returned to their previous values.
    */
  def withCtx[A](kvs: (String,String)*)(v: => A): A = {
    val old =
      ( for {
          (a,b) <- kvs.toMap
        } yield {
          val tmp = (a, get(a))
          this(a) = b
          tmp
        }
      ).toMap

    try { v }
    finally {
      for {
        (a, o) <- old
      } {
        o match {
          case None => this -= a
          case Some(v) => this(a) = v
        }
      }
    }
  }
}