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/*
 * Copyright 2001-2013 Artima, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.scalatest

import org.scalatest.events.Ordinal

// Note: The reason Tracker is mutable is that methods would have to pass back, and that's hard because exceptions can
// also be thrown. So this mutable object is how methods invoked "returns" updates to the current ordinal whether those
// methods return normally or complete abruptly with an exception. Also, sometimes with closures capturing free variables,
// those free variables may want to grab an ordinal in the context of a callee even after the callee has already called
// some other method. So in other words the calling method may need to know the "current ordinal" even before the method
// it calls has completed in any manner, i.e., while it is running. (The example is the info stuff in FunSuite, which sets
// up an info that's useful during a run, then calls super.run(...).

/**
 * Class that tracks the progress of a series of Ordinals produced by invoking
 * next and nextNewOldPair on the current Ordinal.
 *
 * 
 * Instances of this class are thread safe. Multiple threads can invoke nextOrdinal
 * and nextTracker concurrently. This facilitates multi-threaded tests that send
 * infoProvided reports concurrently. When using a Dispatcher to execute
 * suites in parallel, the intention is that each Tracker will only be used by one
 * thread. For example, if the optional Dispatcher  passed to Suite's implementation
 * of runNestedSuites is defined, that method will obtain a new Tracker by invoking
 * nextTracker for each nested suite it passes to the Dispatcher.
 * 
 *
 * @param firstOrdinal the first Ordinal in the series of Ordinals
 *        tracked by this Tracker, which will be used to initialize this Tracker's
 *        current Ordinal.
 *
 * @author Bill Venners
 */
final class Tracker(firstOrdinal: Ordinal = new Ordinal(0)) {

  private var currentOrdinal = firstOrdinal

  /**
   * Returns the next Ordinal in the series tracked by this Tracker.
   *
   * 
   * This method saves the current Ordinal in a local variable, reassigns the current Ordinal
   * with the value returned by invoking nextOrdinal on the saved Ordinal, then
   * returns the saved Ordinal. As a result, if this method is invoked immediately after construction,
   * this method will return the Ordinal passed as firstOrdinal.
   * 
   *
   * @return the next Ordinal in the series
   */
  def nextOrdinal(): Ordinal = {
    synchronized {
      val ordinalToReturn = currentOrdinal
      currentOrdinal = currentOrdinal.next
      ordinalToReturn
    }
  }

  /**
   * Returns a Tracker initialized with the first element in the tuple returned by invoking
   * nextNewOldPair on the current Ordinal, and reassigns the current Ordinal
   * with the second element that was returned by the nextNewOldPair invocation.
   *
   * 
   * The Ordinal series of the returned Tracker will be placed after all the
   * Ordinals previously returned by invoking nextOrdinal on this Tracker and
   * before all the Ordinals subsequently returned by invoking nextOrdinal on
   * this Tracker in the future. This method is intended to be used when executing nested suites
   * in parallel. Each nested suite passed to the Distributor will get its own Tracker
   * obtained by invoking nextTracker on the current thread's Tracker.
   * 
   *
   * @return the next Tracker in this series
   */
  def nextTracker(): Tracker = {
    synchronized {
      val (nextForNewThread, nextForThisThread) = currentOrdinal.nextNewOldPair
      currentOrdinal = nextForThisThread
      new Tracker(nextForNewThread)
    }
  }
}

/**
 * Companion object to `Tracker` offering a default `Tracker`.
 */
object Tracker {
  private val defaultTracker = new Tracker()
  /**
   * A default `Tracker`.
   */
  def default: Tracker = defaultTracker
}