Replace CancellationThread by java.util.Timer

Author: allanrenucci

language-server/src/dotty/tools/languageserver/worksheet/CancellationThread.scala

@@ -4,6 +4,8 @@ import dotty.tools.dotc.core.Contexts.Context
 
 import java.io.{File, PrintStream, IOException}
 import java.lang.ProcessBuilder.Redirect
+import java.util.concurrent.CancellationException
+import java.util.{Timer, TimerTask}
 
 import org.eclipse.lsp4j.jsonrpc.CancelChecker
 
@@ -32,7 +34,7 @@ private object Evaluator {
   def get(cancelChecker: CancelChecker)(implicit ctx: Context): Option[Evaluator] = synchronized {
     val classpath = ctx.settings.classpath.value
     previousEvaluator match {
-      case Some(cp, evaluator) if evaluator.isAlive() && cp == classpath =>
+      case Some(cp, evaluator) if evaluator.isAlive && cp == classpath =>
         evaluator.reset(cancelChecker)
         Some(evaluator)
       case _ =>
@@ -53,7 +55,7 @@ private object Evaluator {
  */
 private class Evaluator private (javaExec: String,
                                  userClasspath: String,
-                                 cancelChecker: CancelChecker) {
+                                 private var cancelChecker: CancelChecker) {
   private val process =
     new ProcessBuilder(
       javaExec,
@@ -70,13 +72,24 @@ private class Evaluator private (javaExec: String,
   // Messages coming out of the REPL
   private val processOutput = new InputStreamConsumer(process.getInputStream())
 
-  // The thread that monitors cancellation
-  private val cancellationThread = new CancellationThread(cancelChecker, this)
-  cancellationThread.start()
+  // A timer that monitors cancellation
+  private val cancellationTimer = new Timer()
+  locally {
+    val task = new TimerTask {
+      def run(): Unit =
+        if (!isAlive)
+          cancellationTimer.cancel()
+        else
+          try cancelChecker.checkCanceled()
+          catch { case _: CancellationException => exit() }
+    }
+    val checkCancelledDelayMs = 50L
+    cancellationTimer.schedule(task, checkCancelledDelayMs, checkCancelledDelayMs)
+  }
 
 
   /** Is the process that runs the REPL still alive? */
-  def isAlive(): Boolean = process.isAlive()
+  def isAlive: Boolean = process.isAlive
 
   /**
    * Submit `command` to the REPL, wait for the result.
@@ -97,16 +110,14 @@ private class Evaluator private (javaExec: String,
    * Reset the REPL to its initial state, update the cancel checker.
    */
   def reset(cancelChecker: CancelChecker): Unit = {
-    cancellationThread.setCancelChecker(cancelChecker)
+    this.cancelChecker = cancelChecker
     eval(":reset")
   }
 
   /** Terminate this JVM. */
   def exit(): Unit = {
     process.destroyForcibly()
     Evaluator.previousEvaluator = None
-    cancellationThread.interrupt()
+    cancellationTimer.cancel()
   }
-
 }
-