Parallel ScriptEngine script compilation

[neon-dev]

Using the ScriptEngine API to compile scripts fails when called from different threads.
This is because the GraalJSBindings of the engine context are accessed during compilation, leading to at least three different types of errors:

1.  Exception in thread "main" java.lang.NullPointerException
    	at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:62)
    	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:502)
    	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:486)
    	at java.base/java.util.concurrent.ForkJoinTask.getThrowableException(ForkJoinTask.java:542)
    	at java.base/java.util.concurrent.ForkJoinTask.reportException(ForkJoinTask.java:567)
    	at java.base/java.util.concurrent.ForkJoinTask.invoke(ForkJoinTask.java:670)
    	at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateParallel(ForEachOps.java:160)
    	at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateParallel(ForEachOps.java:174)
    	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:233)
    	at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:596)
    	at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:765)
    	at Test.main(Test.java:25)
    Caused by: java.lang.NullPointerException: Cannot invoke "java.util.Map.entrySet()" because "this.global" is null
    	at com.oracle.truffle.js.scriptengine.GraalJSBindings.entrySet(GraalJSBindings.java:198)
    	at java.base/java.util.AbstractMap.containsKey(AbstractMap.java:148)
    	at java.scripting/javax.script.SimpleScriptContext.getAttribute(SimpleScriptContext.java:158)
    	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.createSource(GraalJSScriptEngine.java:462)
    	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.compile(GraalJSScriptEngine.java:653)
    	...
   

2.  java.lang.IllegalStateException: Multi threaded access requested by thread Thread[#32,ForkJoinPool.commonPool-worker-10,5,main] but is not allowed for language(s) js.
    	at com.oracle.truffle.polyglot.PolyglotEngineException.illegalState(PolyglotEngineException.java:133)
    	at com.oracle.truffle.polyglot.PolyglotContextImpl.throwDeniedThreadAccess(PolyglotContextImpl.java:1392)
    	at com.oracle.truffle.polyglot.PolyglotContextImpl.checkAllThreadAccesses(PolyglotContextImpl.java:1058)
    	at com.oracle.truffle.polyglot.PolyglotContextImpl.enterThreadChanged(PolyglotContextImpl.java:884)
    	at com.oracle.truffle.polyglot.PolyglotEngineImpl.enterCached(PolyglotEngineImpl.java:2080)
    	at com.oracle.truffle.polyglot.HostToGuestRootNode.execute(HostToGuestRootNode.java:109)
    	at com.oracle.truffle.api.impl.DefaultCallTarget.callDirectOrIndirect(DefaultCallTarget.java:85)
    	at com.oracle.truffle.api.impl.DefaultCallTarget.call(DefaultCallTarget.java:102)
    	at com.oracle.truffle.polyglot.PolyglotMap.entrySet(PolyglotMap.java:124)
    	at com.oracle.truffle.js.scriptengine.GraalJSBindings.entrySet(GraalJSBindings.java:198)
    	at java.base/java.util.AbstractMap.containsKey(AbstractMap.java:148)
    	at java.scripting/javax.script.SimpleScriptContext.getAttribute(SimpleScriptContext.java:158)
    	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.createSource(GraalJSScriptEngine.java:462)
    	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.compile(GraalJSScriptEngine.java:653)
    	...
    	Suppressed: Attached Guest Language Frames (1)
   

3.  java.lang.IllegalStateException: Multi threaded access requested by thread Thread[#44,ForkJoinPool.commonPool-worker-11,5,main] but is not allowed for language(s) js.
    	at com.oracle.truffle.polyglot.PolyglotEngineException.illegalState(PolyglotEngineException.java:133)
    	at com.oracle.truffle.polyglot.PolyglotContextImpl.throwDeniedThreadAccess(PolyglotContextImpl.java:1392)
    	at com.oracle.truffle.polyglot.PolyglotContextImpl.checkAllThreadAccesses(PolyglotContextImpl.java:1058)
    	at com.oracle.truffle.polyglot.PolyglotContextImpl.enterThreadChanged(PolyglotContextImpl.java:884)
    	at com.oracle.truffle.polyglot.PolyglotEngineImpl.enterCached(PolyglotEngineImpl.java:2080)
    	at com.oracle.truffle.polyglot.PolyglotEngineImpl.enterIfNeeded(PolyglotEngineImpl.java:2008)
    	at com.oracle.truffle.polyglot.PolyglotValueDispatch.hostEnter(PolyglotValueDispatch.java:1256)
    	at com.oracle.truffle.polyglot.PolyglotContextImpl.parse(PolyglotContextImpl.java:1649)
    	at com.oracle.truffle.polyglot.PolyglotContextDispatch.parse(PolyglotContextDispatch.java:65)
    	at org.graalvm.polyglot.Context.parse(Context.java:483)
    	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.checkSyntax(GraalJSScriptEngine.java:680)
    	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.compile(GraalJSScriptEngine.java:664)
    	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.compile(GraalJSScriptEngine.java:654)
    	...
   

How to reproduce

Here is a simple reproducer: reproducer.zip
Commented out lines work around these issues (explained below).

Possible workaround

1. Synchronize on the engine bindings to fix all compliation errors:

   synchronized (scriptEngine.getBindings(ScriptContext.ENGINE_SCOPE)) {
     ((Compilable) scriptEngine).compile(jsScript);
   }

2. Add this line right after instantiating the script engine:

   scriptEngine.getBindings(ScriptContext.ENGINE_SCOPE).entrySet();

   It resolves compilation slowdowns by initializing the GraalJSBindings context early.
   Synchonization from 1) somehow does not take care of this internal race condition. Maybe it's a thread visibility issue, not sure.

Another workaround would be to just replace the engine bindings with SimpleBindings, but this massively degrades script compilation performance, because the engine will then create new GraalJSBindings + context per compilation.

Solution?

Synchronize on the context here

graaljs/graal-js/src/com.oracle.truffle.js.scriptengine/src/com/oracle/truffle/js/scriptengine/GraalJSScriptEngine.java

Line 462 in 39b63b9

final Object val = ctxt.getAttribute(ScriptEngine.FILENAME);

and here

graaljs/graal-js/src/com.oracle.truffle.js.scriptengine/src/com/oracle/truffle/js/scriptengine/GraalJSScriptEngine.java

Line 680 in 39b63b9

getPolyglotContext().parse(source);

Maybe additional synchronization here would fix performance issues from 2):

graaljs/graal-js/src/com.oracle.truffle.js.scriptengine/src/com/oracle/truffle/js/scriptengine/GraalJSBindings.java

Lines 88 to 92 in 39b63b9

	private void requireContext() {
	if (context == null) {
	initContext();
	}
	}