sync

kyuubi-common/src/main/scala/org/apache/kyuubi/service/FrontendService.scala

@@ -103,7 +103,7 @@ class FrontendService private (name: String, be: BackendService, oomHook: Runnab
 
   def connectionUrl: String = s"${serverAddr.getCanonicalHostName}:$portNum"
 
-  override def start(): Unit = {
+  override def start(): Unit = synchronized {
     super.start()
     if (!isStarted) {
       val thread = new Thread(this)
@@ -122,7 +122,7 @@ class FrontendService private (name: String, be: BackendService, oomHook: Runnab
       System.exit(-1)
   }
 
-  override def stop(): Unit = {
+  override def stop(): Unit = synchronized {
     if (isStarted) {
       server.foreach(_.stop())
       info(this.name + " has stopped")

kyuubi-main/src/main/scala/org/apache/kyuubi/engine/ProcBuilder.scala

@@ -56,7 +56,7 @@ trait ProcBuilder {
 
   @volatile private var error: Throwable = UNCAUGHT_ERROR
 
-  final def start: Process = {
+  final def start: Process = synchronized {
     val procLog = Paths.get(workingDir.toAbsolutePath.toString, s"$module.log")
     processBuilder.redirectError(procLog.toFile)
     processBuilder.redirectOutput(procLog.toFile)
@@ -83,6 +83,8 @@ trait ProcBuilder {
         }
       } catch {
         case _: IOException =>
+      } finally {
+        reader.close()
       }
     }
 
@@ -90,7 +92,7 @@ trait ProcBuilder {
     proc
   }
 
-  def getError: Throwable = {
+  def getError: Throwable = synchronized {
     if (error == UNCAUGHT_ERROR) {
       Thread.sleep(3000)
     }