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/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2011, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.concurrent
/** A class to provide safe concurrent access to a mutable cell.
* All methods are synchronized.
*
* @author Martin Odersky
* @version 1.0, 10/03/2003
*/
class SyncVar[A] {
@volatile private var isDefined: Boolean = false
@volatile private var value: A = _
def get = synchronized {
while (!isDefined) wait()
value
}
/** Like Object.wait but reports millis elapsed.
*/
private def waitMeasuringElapsed(timeout: Long): Long = {
val start = System.currentTimeMillis
wait(timeout)
System.currentTimeMillis - start
}
def get(timeout: Long): Option[A] = synchronized {
/** Defending against the system clock going backward
* by counting time elapsed directly. Loop required
* to deal with spurious wakeups.
*/
var rest = timeout
while (!isDefined && rest >= 0) {
val elapsed = waitMeasuringElapsed(timeout)
if (!isDefined && elapsed > 0)
rest -= elapsed
}
if (isDefined) Some(value)
else None
}
// /** Waits for this SyncVar to become defined at least for
// * `timeout` milliseconds (possibly more), and gets its
// * value.
// *
// * @param timeout the amount of milliseconds to wait
// * @return `None` if variable is undefined after `timeout`, `Some(value)` otherwise
// */
// def get(timeout: Long): Option[A] = synchronized {
// if (timeout == 0L) Some(get)
// else {
// val start = System.currentTimeMillis
// var left = timeout
// while (!isDefined && left > 0) {
// wait(left)
// if (!isDefined) {
// val elapsed = System.currentTimeMillis - start
// left = timeout - elapsed
// }
// }
// if (isDefined) Some(value)
// else None
// }
// }
def take() = synchronized {
try get
finally unset()
}
def set(x: A) = synchronized {
value = x
isDefined = true
notifyAll()
}
def put(x: A) = synchronized {
while (isDefined) wait()
set(x)
}
def isSet: Boolean = synchronized {
isDefined
}
def unset(): Unit = synchronized {
isDefined = false
notifyAll()
}
}
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