问题
In the code below i have javascript running in a separate thread from the main one. That script is an infinite loop, so it needs to be terminated somehow. How?
Calling .cancel() is not working AFTER the script begins running. But if i call .cancel() just after the thread initialization, it will terminate it (the commented out line).
package testscriptterminate;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.Timer;
import java.util.TimerTask;
public class TestScriptTerminate extends TimerTask{
private ExecutorService threads;
private Future runScript;
private Timer t;
public TestScriptTerminate(){
t = new Timer();
t.schedule(this, 6000); //let the script run for a while before attempt to cancel
threads = Executors.newFixedThreadPool(1);
runScript = threads.submit(new ScriptExec());
//runScript.cancel(true); //will cancel here, before the script had a change to run, but useless, i want to cancel at any time on demand
}
@Override
public void run(){
//after script has fully initialized and ran for a while - attempt to cancel.
//DOESN'T WORK, thread still active
System.out.println("Canceling now...");
runScript.cancel(true);
}
public static void main(String[] args) {
new TestScriptTerminate();
}
}
class ScriptExec implements Runnable{
private ScriptEngine js;
private ScriptEngineManager scriptManager;
public ScriptExec(){
init();
}
@Override
public void run() {
try {
js.eval("while(true){}");
} catch (ScriptException ex) {
System.out.println(ex.toString());
}
}
private void init(){
scriptManager = new ScriptEngineManager();
js = scriptManager.getEngineByName("nashorn");
}
}
回答1:
JavaScript (under Nashorn), like Java, will not respond to an interrupt in the middle of a tight loop. The script needs to poll for interruption and terminate the loop voluntarily, or it can call something that checks for interruption and let InterruptedException propagate.
You might think that Nashorn is "just running a script" and that it should be interrupted immediately. This doesn't apply, for the same reason that it doesn't apply in Java: asynchronous interruption risks corruption of the application's data structures, and there is essentially no way to avoid it or recover from it.
Asynchronous interruption brings in the same problems as the long-deprecated Thread.stop method. This is explained in this document, which is an updated version of the document linked in the comments.
Java Thread Primitive Deprecation
See also Goetz, Java Concurrency In Practice, Chapter 7, Cancellation and Shutdown.
The easiest way to check for interruption is to call Thread.interrupted(). You can call this quite easily from JavaScript. Here's a rewrite of the example program that cancels the running script after five seconds:
public class TestScriptTerminate {
ScheduledExecutorService pool = Executors.newScheduledThreadPool(2);
void script() {
ScriptEngineManager scriptManager = new ScriptEngineManager();
ScriptEngine js = scriptManager.getEngineByName("nashorn");
try {
System.out.println("Script starting.");
js.eval("while (true) { if (java.lang.Thread.interrupted()) break; }");
System.out.println("Script finished.");
} catch (ScriptException ex) {
ex.printStackTrace();
}
}
void init() throws Exception {
Future<?> scriptTask = pool.submit(this::script);
pool.schedule(() -> {
System.out.println("Canceling now...");
scriptTask.cancel(true);
}, 5, TimeUnit.SECONDS);
pool.shutdown();
}
public static void main(String[] args) throws Exception {
new TestScriptTerminate().init();
}
}
Since we're starting up a thread pool, might as well make it a scheduled thread pool so that we can use it for both the script task and the timeout. That way we can avoid Timer and TimerTask, which are mostly replaced by ScheduledExecutorService anyway.
The usual convention when handling and interrupt is either to restore the interrupt bit or to let an InterruptedException propagate. (One should never ignore an interrupt.) Since breaking out of the loop can be considered to have completed the handling of the interrupt, neither is necessary, and it seems sufficient simply to let the script exit normally.
This rewrite also moves a lot of work out of the constructor into an init() method. This prevents the instance from being leaked to other threads from within the constructor. There is no obvious danger from this in the original example code -- in fact, there almost never is -- but it's always good practice to avoid leaking the instance from the constructor.
回答2:
So this is old, but i just wrote this up and thought it would probably be valuable to share. By default there is ~nothing you can do to stop a Nashorn script executing, .cancel() Thread.stop() Thread.interrupt() do nothing, but if you are willing to put in a bit of effort and are ok with rewriting some bytecode, it is achieveable. Details:
http://blog.getsandbox.com/2018/01/15/nashorn-interupt/
回答3:
Unfortunately it does not work for simple infinite loops: while (true) { }. I tried Thread.cancel(); does not cause the thread to exit. I wanted something foolproof for running scripts in an IntelliJ plugin where a user can make a mistake an cause an infinite loop, hanging the plugin.
The only thing I found to work in most cases is Thread.stop(). Even that does not work for a script like this:
while(true) {
try {
java.lang.Thread.sleep(100);
} catch (e) {
}
}
javascript catches the java.lang.ThreadDeath exception and keeps going. I found that the above sample is impossible to interrupt even with several Thread.stop() issued one after the other. Why would I use several? Hoping that one of them will catch the thread in its exception processing code and abort it. Which does work if there is something in the catch block to process as simple as var i = "" + e; that is enough to cause the second Thread.stop() to end it.
So the moral of the story is there is no fail safe way of ending a runaway script in Nashorn, but there is something that will work on most cases.
My implementation issues a Thread.interrupt(), then politely waits 2 seconds for the thread to terminate and if that fails then it issues Thread.stop() twice. If that does not work, then nothing else will either.
Hope it helps someone eliminate hours of experimentation to find a more reliable method to stop nashorn runaway scripts than hoping on the cooperation of the running script to respect Thread.cancel().
回答4:
I have a similar problem where I let users write their own scripts. But before I allow the script to be executed, I parse the script. and if I find any of the following (System.sleep. Exit, Thread.sleep, goto) etc I don't even start the script, and I give user an error.
and then I do a search for all
(for,loops, while, doWhile), and I inject a method.
checkForLoop() just after the loop identifier.
I inject checkForLoop(); into allow user submitted script.
while(users code)
{
}
becomes
while ( checkForLoop() && users code )
{
}
This way before every iteration of their loop, my method is called. and I can count how many times I was called or check internal timers. Than I can stop the loops or timers from inside checkForLoop();
Honestly I think its a big security issue anyway, just to blindly let users write script and just execute it. You need to build in a system that injects your code into their code loops. Which is not that hard.
There are 100s of safety mechanisms you can apply to users submitted code, there is no RULE that says you need to run their code as is.
I have edited this answer to include a very simple example.
//Step 1 put the users submitted JS code into a Java String called userJSCode;
Step 2 //inject code at the start of their code.
String safeWhile ="var sCount=0; var sMax=10;
function safeWhileCheck(){ sCount++;
if ( return ( sCount > sMax )}";
userJSCode = safeWhile + userJSCode;
//Step 3: inject the custom while code
String injectSsafeWHile = "while( safeWhileCheck() && ";
userJSCode = userJSCode.replace("while(", injectSsafeWHile);
//Step 4: execute custom JS code
nashhorn.execute(injectSsafeWHile);
//Here is users bad submitted code, note no i increment in the loop, it would go on for ever.
var i=0;
while ( i <1000 )
console.log("I am number " + i);
using the steps above we end up with
var sCount=0;var sMax=10;
function safeWhileCheck(){
sCount++;
return ( sCount > sMax )};
var i=0;
while ( safeWhileCheck() && i <1000 )
console.log("I am number " + i)"
Here the while loop only executes a max of 10 times, so whatever you set the limit to.
来源：https://stackoverflow.com/questions/24855182/interrupt-java-thread-running-nashorn-script