package sbt.internal

// minimal copy of scala.concurrent.SyncVar since that version deprecated put and unset
private[sbt] final class SyncVar[A] {
  private var isDefined: Boolean = false
  private var value: Option[A] = None

  /** Waits until a value is set and then gets it.  Does not clear the value */
  def get: A = synchronized {
    while (!isDefined) wait()
    value.get
  }

  /** Waits until a value is set, gets it, and finally clears the value. */
  def take(): A = synchronized {
    try get finally unset()
  }

  /** Sets the value, whether or not it is currently defined. */
  def set(x: A): Unit = synchronized {
    isDefined = true
    value = Some(x)
    notifyAll()
  }

  /** Sets the value, first waiting until it is undefined if it is currently defined. */
  def put(x: A): Unit = synchronized {
    while (isDefined) wait()
    set(x)
  }

  /** Clears the value, whether or not it is current defined. */
  def unset(): Unit = synchronized {
    isDefined = false
    value = None
    notifyAll()
  }
}