Refixing SyncVars, fixes #4094.

No review.

1 files changed, 17 insertions, 33 deletions

diff --git a/src/library/scala/concurrent/SyncVar.scala b/src/library/scala/concurrent/SyncVar.scala
index bf39fef27c..eebdd9b528 100644
--- a/src/library/scala/concurrent/SyncVar.scala
+++ b/src/library/scala/concurrent/SyncVar.scala
@@ -15,61 +15,45 @@ package scala.concurrent
  *  @version 1.0, 10/03/2003
  */
 class SyncVar[A] {
-  @volatile private var isDefined: Boolean = false
-  @volatile private var value: A = _
+  private var isDefined: Boolean = false
+  private var value: A = _
 
   def get = synchronized {
     while (!isDefined) wait()
     value
   }
 
-  /** Like Object.wait but reports millis elapsed.
+  /** Waits `timeout` millis. If `timeout <= 0` just returns 0. If the system clock
+   *  went backward, it will return 0, so it never returns negative results.
    */
-  private def waitMeasuringElapsed(timeout: Long): Long = {
+  private def waitMeasuringElapsed(timeout: Long): Long = if (timeout <= 0) 0 else {
     val start = System.currentTimeMillis
     wait(timeout)
-    System.currentTimeMillis - start
+    val elapsed = System.currentTimeMillis - start
+    if (elapsed < 0) 0 else elapsed
   }
 
+  /** 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, 0 means forever
+   *  @return            `None` if variable is undefined after `timeout`, `Some(value)` otherwise
+   */
   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
+    while (!isDefined && rest > 0) {
+      val elapsed = waitMeasuringElapsed(rest)
+      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()