I am running an app in Play using activator run, and maybe 3 out of 5 times, it will just hang, when I go to http://localhost:9000/, it just sits there spinning forever.
I'm seeing a lot of promise timed out errors also.
Where should I look for this issue?
I turned up logging with logLevel := Level.Debug, but I see nothing amiss. While the app is spinning, I see no logging at all.
If I just let it sit and spin for a long time (~5 min) it will eventually give this error:
[info] play.api.http.HttpErrorHandlerExceptions$$anon$1: Execution exception[[PrivilegedActionException: null]]
[info] at play.api.http.HttpErrorHandlerExceptions$.throwableToUsefulException(HttpErrorHandler.scala:265) ~[play_2.11-2.4.3.jar:2.4.3]
[info] at play.api.http.DefaultHttpErrorHandler.onServerError(HttpErrorHandler.scala:191) ~[play_2.11-2.4.3.jar:2.4.3]
[info] at play.core.server.Server$class.logExceptionAndGetResult$1(Server.scala:50) [play-server_2.11-2.4.3.jar:2.4.3]
[info] at play.core.server.Server$$anonfun$getHandlerFor$4.apply(Server.scala:59) [play-server_2.11-2.4.3.jar:2.4.3]
[info] at play.core.server.Server$$anonfun$getHandlerFor$4.apply(Server.scala:57) [play-server_2.11-2.4.3.jar:2.4.3]
[info] at scala.util.Either$RightProjection.flatMap(Either.scala:522) [scala-library.jar:na]
[info] at play.core.server.Server$class.getHandlerFor(Server.scala:57) [play-server_2.11-2.4.3.jar:2.4.3]
[info] at play.core.server.NettyServer.getHandlerFor(NettyServer.scala:33) [play-netty-server_2.11-2.4.3.jar:2.4.3]
[info] at play.core.server.netty.PlayDefaultUpstreamHandler$$anonfun$8.apply(PlayDefaultUpstreamHandler.scala:139) [play-netty-server_2.11-2.4.3.jar:2.4.3]
[info] at play.core.server.netty.PlayDefaultUpstreamHandler$$anonfun$8.apply(PlayDefaultUpstreamHandler.scala:139) [play-netty-server_2.11-2.4.3.jar:2.4.3]
[info] Caused by: java.security.PrivilegedActionException: null
[info] at java.security.AccessController.doPrivileged(Native Method) ~[na:1.8.0_20]
[info] at play.runsupport.Reloader$.play$runsupport$Reloader$$withReloaderContextClassLoader(Reloader.scala:39) ~[na:na]
[info] at play.runsupport.Reloader.reload(Reloader.scala:321) ~[na:na]
[info] at play.core.server.DevServerStart$$anonfun$mainDev$1$$anon$1$$anonfun$get$1.apply(DevServerStart.scala:113) ~[play-server_2.11-2.4.3.jar:2.4.3]
[info] at play.core.server.DevServerStart$$anonfun$mainDev$1$$anon$1$$anonfun$get$1.apply(DevServerStart.scala:111) ~[play-server_2.11-2.4.3.jar:2.4.3]
[info] at scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24) ~[scala-library.jar:na]
[info] at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24) ~[scala-library.jar:na]
[info] at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1423) ~[na:1.8.0_20]
[info] at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289) ~[na:1.8.0_20]
[info] at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:902) ~[na:1.8.0_20]
[info] Caused by: java.util.concurrent.TimeoutException: Futures timed out after [300000 milliseconds]
[info] at scala.concurrent.impl.Promise$DefaultPromise.ready(Promise.scala:219) ~[scala-library.jar:na]
[info] at scala.concurrent.impl.Promise$DefaultPromise.result(Promise.scala:223) ~[scala-library.jar:na]
[info] at scala.concurrent.Await$$anonfun$result$1.apply(package.scala:190) ~[scala-library.jar:na]
[info] at scala.concurrent.BlockContext$DefaultBlockContext$.blockOn(BlockContext.scala:53) ~[scala-library.jar:na]
[info] at scala.concurrent.Await$.result(package.scala:190) ~[scala-library.jar:na]
[info] at play.forkrun.ForkRun$$anonfun$askForReload$1.apply(ForkRun.scala:127) ~[na:na]
[info] at play.forkrun.ForkRun$$anonfun$askForReload$1.apply(ForkRun.scala:125) ~[na:na]
[info] at play.runsupport.Reloader$$anonfun$reload$1.apply(Reloader.scala:323) ~[na:na]
[info] at play.runsupport.Reloader$$anon$3.run(Reloader.scala:43) ~[na:na]
[info] at java.security.AccessController.doPrivileged(Native Method) ~[na:1.8.0_20]
I should mention that this is a very simple app. It is doing nothing but rendering some HTML so far.
Its too bad, because it seems like there is a lot of good in the framework, but it is just slow and terribly unreliable.
fork in run := true is added always when starting the app from Activators UI (for spawning processes) so stop using UI for given app (maybe add startup config in your IDE) or always remember to clear/comment/set to false.
来源：https://stackoverflow.com/questions/33445666/play-framework-hanging-when-hitting-app-in-browser