I am trying to retrieve the AST from scala souce file. I have simplified the code (only relevant code) to following.
trait GetAST {
val settings = new Settings
val global = new Global(settings, new ConsoleReporter(settings))
def getSt = "hello" //global.typedTree(src, true)
}
object Tre extends GetAST {
def main(args:Array[String])
{
println(getSt.getClass)
println("exiting program")
}
}
The above code compiles fine and runs fine. But the problem is the program does not exit. The prompt is not displayed after printing "exiting program". I have to use ^c to exit.
Any idea what the problem might be
I believe Michael is correct, the compiler uses Threads and therefore the JVM doesn't just exit.
The good news is that interactive.Global mixes in interactive.CompilerControl trait whose askShutdown method you can call at the end of your main to let the program exit.
Without knowing what Settings, Global and ConsoleReporter are nobody can give you an exact answer. I would guess that at least one of them is creating a thread. The JVM waits until all threads are done (or all running are deamon threads). See here.
I would bet if you comment out the settings and global lines it will exit as expected.
Related
I implemented a simple
trait Logging {
...
object log {
def info(msg: String)
...
}
//saves stuff
def logOut(path) = {}
setting up a full log4j takes a ton of time with all the properties file required
Logging seems to be working fine except for the fact that I need to make a logOut at the end of my main() to print or save those logs somewhere, which is inconvenient and ugly
So the questions are :
Is there a way to force Logging to do something at the end of the program?
Is there another good way to approach the problem?
You can add Shutdown hook at the end of your program. But keep in mind that it will only be executed in case of graceful shutdown. Killing the process will not invoke this hook.
sys.addShutdownHook { println("Bye-bye") }
complete stranger/newbie question, sorry to bother you:
I want to run a scala project in IDEA 13 (on Mac OSX), there is no run/debug configuration. I tried some options, however I don't know what to choose (and what should happen, then).
I tried:
Scala Console
Scala Script
Scala Test
Specs2
Choosing Scala Console: something happens, but I get no message box from my showMessage(message = "Hello World") messagebox. (It did work in Eclipse, so far).
Scala Script: I suppose this is meant for single lines of code, not an app, is that?
Specs2: Error in options-dialog: Specs2 is not specified. What is spec2? What should I enter and where? Error while debugging: no main class detected. OK, there is none, I can see that.
Any other option I should use, or normally is used?
Would any help appreciate very much!
This is my (very simple) scala app. Somehow, I'd expect to get an message box while running from IDEA.
import swing._
import swing.Dialog._
import scala.swing.event.ButtonClicked
object HW {
def main(args: Array[String]): Unit = {}
showMessage(message = "Hello World")
}
by the way: the closest tread I've found was this, but it didn't really help, looked too different:
How to run scala code on Intellij Idea 11?
Just use "Application". You have to select a main class and a module.
In terms of your example, I recommend not mixing a def main with a "free" standing constructor body. Also, Swing code should be called only from the event dispatch thread (Swing.onEDT). The easiest for desktop applications is to extend trait SwingApplication which handles that for you:
import swing._
import swing.Dialog._
object HW extends SwingApplication {
def startup(args: Array[String]): Unit =
showMessage(message = "Hello World")
}
It seems like there is no need in a class with a main method in it to be able to run Akka How to run akka actors in IntelliJ IDEA. However, here is what I have:
object Application extends App {
val system = ActorSystem()
val supervisor = system.actorOf(Props[Supervisor])
implicit val timeout = Timeout(100 seconds)
import system.dispatcher
system.scheduler.schedule(1 seconds, 600 seconds) {
val future = supervisor ? Supervisor.Start
val list = Await.result(future, timeout.duration).asInstanceOf[List[Int]]
supervisor ! list
}
}
I know I have to specify a main method called "akka.Main" in the configuration. But nonetheless, where should I move the current code from object Application ?
You can write something like
import _root_.akka.Main
object Application extends App {
Main.main(Array("somepackage.Supervisor"))
}
and Supervisor actor should have overriden preStart function as #cmbaxter suggested.
Then run sbt console in intellij and write run.
I agree with #kdrakon that your code is fine the way it is, but if you wanted to leverage the akka.Main functionality, then a simple refactor like so will make things work:
package code
class ApplicationActor extends Actor {
override def preStart = {
val supervisor = context.actorOf(Props[Supervisor])
implicit val timeout = Timeout(100 seconds)
import context.dispatcher
context.system.scheduler.schedule(1 seconds, 600 seconds) {
val future = (supervisor ? Supervisor.Start).mapTo[List[Int]]
val list = Await.result(future, timeout.duration)
supervisor ! list
}
}
def receive = {
case _ => //Not sure what to do here
}
}
In this case, the ApplicationActor is the arg you would pass to akka.Main and it would basically be the root supervisor to all other actors created in your hierarchy. The only fishy thing here is that being an Actor, it needs a receive implementation and I don't imagine any other actors will be sending messages here thus it doesn't really do anything. But the power to this approach is that when the ApplicationActor is stopped, the stop will also be cascaded down to all other actors that it started, simplifying a graceful shutdown. I suppose you could have the ApplicationActor handle a message to shutdown the actor system given some kind of input (maybe a ShutdownHookThread could initiate this) and give this actor some kind of a purpose after all. Anyway, as stated earlier, your current approach seems fine but this could also be an option if you so desire.
EDIT
So if you wanted to run this ApplicationActor via akka.Main, according to the instructions here, you would execute this from your command prompt:
java -classpath <all those JARs> akka.Main code.ApplicationActor
You will of course need to supply <all those JARS> with your dependencies including akka. At a minimum you will need scala-library and akka-actor in your classpath to make this run.
If you refer to http://doc.akka.io/docs/akka/snapshot/scala/hello-world.html, you'll find that akka.Main expects your root/parent Actor. In your case, Supervisor. As for your already existing code, it can be copied directly into the actors code, possibly in some initialisation calls. For example, refer to the HelloWorld's preStart function.
However, in my opinion, your already existing code is just fine too. Akka.main is a nice helper, as is the microkernel binary. But creating your own main executable is a viable option too.
I just had a look at the new scala.sys and scala.sys.process packages to see if there is something helpful here. However, I am at a complete loss.
Has anybody got an example on how to actually start a process?
And, which is most interesting for me: Can you detach processes?
A detached process will continue to run when the parent process ends and is one of the weak spots of Ant.
UPDATE:
There seem to be some confusion what detach is. Have a real live example from my current project. Once with z-Shell and once with TakeCommand:
Z-Shell:
if ! ztcp localhost 5554; then
echo "[ZSH] Start emulator"
emulator \
-avd Nexus-One \
-no-boot-anim \
1>~/Library/Logs/${PROJECT_NAME}-${0:t:r}.out \
2>~/Library/Logs/${PROJECT_NAME}-${0:t:r}.err &
disown
else
ztcp -c "${REPLY}"
fi;
Take-Command:
IFF %#Connect[localhost 5554] lt 0 THEN
ECHO [TCC] Start emulator
DETACH emulator -avd Nexus-One -no-boot-anim
ENDIFF
In both cases it is fire and forget, the emulator is started and will continue to run even after the script has ended. Of course having to write the scripts twice is a waste. So I look into Scala now for unified process handling without cygwin or xml syntax.
First import:
import scala.sys.process.Process
then create a ProcessBuilder
val pb = Process("""ipconfig.exe""")
Then you have two options:
run and block until the process exits
val exitCode = pb.!
run the process in background (detached) and get a Process instance
val p = pb.run
Then you can get the exitcode from the process with (If the process is still running it blocks until it exits)
val exitCode = p.exitValue
If you want to handle the input and output of the process you can use ProcessIO:
import scala.sys.process.ProcessIO
val pio = new ProcessIO(_ => (),
stdout => scala.io.Source.fromInputStream(stdout)
.getLines.foreach(println),
_ => ())
pb.run(pio)
I'm pretty sure detached processes work just fine, considering that you have to explicitly wait for it to exit, and you need to use threads to babysit the stdout and stderr. This is pretty basic, but it's what I've been using:
/** Run a command, collecting the stdout, stderr and exit status */
def run(in: String): (List[String], List[String], Int) = {
val qb = Process(in)
var out = List[String]()
var err = List[String]()
val exit = qb ! ProcessLogger((s) => out ::= s, (s) => err ::= s)
(out.reverse, err.reverse, exit)
}
Process was imported from SBT. Here's a thorough guide on how to use the process library as it appears in SBT.
https://github.com/harrah/xsbt/wiki/Process
Has anybody got an example on how to
actually start a process?
import sys.process._ // Package object with implicits!
"ls"!
And, which is most interesting for me:
Can you detach processes?
"/path/to/script.sh".run()
Most of what you'll do is related to sys.process.ProcessBuilder, the trait. Get to know that.
There are implicits that make usage less verbose, and they are available through the package object sys.process. Import its contents, like shown in the examples. Also, take a look at its scaladoc as well.
The following function will allow easy use if here documents:
def #<<< (command: String) (hereDoc: String) =
{
val process = Process (command)
val io = new ProcessIO (
in => {in.write (hereDoc getBytes "UTF-8"); in.close},
out => {scala.io.Source.fromInputStream(out).getLines.foreach(println)},
err => {scala.io.Source.fromInputStream(err).getLines.foreach(println)})
process run io
}
Sadly I was not able to (did not have the time to) to make it an infix operation. Suggested calling convention is therefore:
#<<< ("command") {"""
Here Document data
"""}
It would be call if anybody could give me a hint on how to make it a more shell like call:
"command" #<<< """
Here Document data
""" !
Documenting process a little better was second on my list for probably two months. You can infer my list from the fact that I never got to it. Unlike most things I don't do, this is something I said I'd do, so I greatly regret that it remains as undocumented as it was when it arrived. Sword, ready yourself! I fall upon thee!
If I understand the dialog so far, one aspect of the original question is not yet answered:
how to "detach" a spawned process so it continues to run independently of the parent scala script
The primary difficulty is that all of the classes involved in spawning a process must run on the JVM, and they are unavoidably terminated when the JVM exits. However, a workaround is to indirectly achieve the goal by leveraging the shell to do the "detach" on your behalf. The following scala script, which launches the gvim editor, appears to work as desired:
val cmd = List(
"scala",
"-e",
"""import scala.sys.process._ ; "gvim".run ; System.exit(0);"""
)
val proc = cmd.run
It assumes that scala is in the PATH, and it does (unavoidably) leave a JVM parent process running as well.
I almost always have a Scala REPL session or two open, which makes it very easy to give Java or Scala classes a quick test. But if I change a class and recompile it, the REPL continues with the old one loaded. Is there a way to get it to reload the class, rather than having to restart the REPL?
Just to give a concrete example, suppose we have the file Test.scala:
object Test { def hello = "Hello World" }
We compile it and start the REPL:
~/pkg/scala-2.8.0.Beta1-prerelease$ bin/scala
Welcome to Scala version 2.8.0.Beta1-prerelease
(Java HotSpot(TM) Server VM, Java 1.6.0_16).
Type in expressions to have them evaluated.
Type :help for more information.
scala> Test.hello
res0: java.lang.String = Hello World
Then we change the source file to
object Test {
def hello = "Hello World"
def goodbye = "Goodbye, Cruel World"
}
but we can't use it:
scala> Test.goodbye
<console>:5: error: value goodbye is not a member of object Test
Test.goodbye
^
scala> import Test;
<console>:1: error: '.' expected but ';' found.
import Test;
There is an alternative to reloading the class if the goal is to not have to repeat previous commands. The REPL has the command
:replay
which restarts the REPL environment and plays back all previous valid commands. (The invalid ones are skipped, so if it was wrong before, it won't suddenly work.) When the REPL is reset, it does reload classes, so new commands can use the contents of recompiled classes (in fact, the old commands will also use those recompiled classes).
This is not a general solution, but is a useful shortcut to extend an individual session with re-computable state.
Note: this applies to the bare Scala REPL. If you run it from SBT or some other environment, it may or may not work depending on how SBT or the other environment packages up classes--if you don't update what is on the actual classpath being used, of course it won't work!
Class reloading is not an easy problem. In fact, it's something that the JVM makes very difficult. You do have a couple options though:
Start the Scala REPL in debug mode. The JVM debugger has some built-in reloading which works on the method level. It won't help you with the case you gave, but it would handle something simple like changing a method implementation.
Use JRebel (http://www.zeroturnaround.com/jrebel). JRebel is basically a super-charged class reloading solution for the
JVM. It can handle
member addition/removal, new/removed classes, definition changes, etc. Just about the only thing it can't handle is changes in class hierarchy (adding a super-interface, for
example). It's not a free tool, but they do offer a complementary license which is limited to Scala compilation units.
Unfortunately, both of these are limited by the Scala REPL's implementation details. I use JRebel, and it usually does the trick, but there are still cases where the REPL will not reflect the reloaded class(es). Still, it's better than nothing.
There is an command meet you requirement
:load path/to/file.scala
which will reload the scala source file and recompiled to classes , then you can replay you code
This works for me....
If your new source file Test.scala looks something like this...
package com.tests
object Test {
def hello = "Hello World"
def goodbye = "Goodbye, Cruel World"
}
You first have to load the new changes into Scala console (REPL).
:load src/main/scala/com/tests/examples/Test.scala
Then re-import the package so you can reference the new code in Scala console.
import com.tests.Test
Now enjoy your new code without restarting your session :)
scala> Test.goodbye
res0: String = Goodbye, Cruel World
If the .scala file is in the directory where you start the REPL you can ommit the full path, just put :load myfile.scala, and then import.