GraalJS with non-GraalVM fails to read/parse script in BufferedReader

[rschmunk]

I"m exploring what it will take to migrate from Nashorn to GraalJS for whenever it is that Nashorn is removed from Java. I'm trying to use the GraalJS jars in conjunction with a non-Graal VM, and have followed instructions in the docs at https://github.com/graalvm/graaljs/blob/master/docs/user/RunOnJDK.md and https://github.com/graalvm/graaljs/blob/master/docs/user/ScriptEngine.md

(There are, BTW, a couple errors on the RunOnJDK.md page regarding necessary jars that I had to figure out.)

My Project allows for the user to either manually enter Javascript commands line by line, or to provide the path to a script file to read in, parse and execute. The former seems to work just fine. However, the latter fails.

Omitting a bunch of try-catch code, I create the engine, feed it a BufferedReader with the script like the following.

   ScriptEngine engine = new ScriptEngineManager ( ).getEngineByName ("javascript");
   Bindings bindings = engine.createBindings ( );
   bindings.put ("polyglot.js.allowAllAccess", true);
   engine.setBindings(bindings, ScriptContext.ENGINE_SCOPE);

   File sfile = new File (spath);   // spath is the path to the script file
   FileInputStream fstream  = new FileInputStream (sfile);    
   InputStreamReader isr = new InputStreamReader (fstream, "UTF-8");
   BufferedReader breader = new BufferedReader (isr);

   engine.eval ( breader );

That last line comes back with an exception thrown by GraalJSScriptEngine that the stream was closed.

javax.script.ScriptException: java.io.IOException: Stream closed
	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.createSource(GraalJSScriptEngine.java:317)
	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.eval(GraalJSScriptEngine.java:310)
	at javax.script.AbstractScriptEngine.eval(AbstractScriptEngine.java:249)
	at myapp.CLParser.evaluateScript(CLParser.java:682)
	at myapp.CLParser.evaluateScript(CLParser.java:616)
	at myapp.CLParser.<init>(CLParser.java:174)
	at myapp.CLParser.main(CLParser.java:113)
Caused by: java.io.IOException: Stream closed
	at sun.nio.cs.StreamDecoder.ensureOpen(StreamDecoder.java:46)
	at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:148)
	at java.io.InputStreamReader.read(InputStreamReader.java:184)
	at java.io.BufferedReader.fill(BufferedReader.java:161)
	at java.io.BufferedReader.read1(BufferedReader.java:212)
	at java.io.BufferedReader.read(BufferedReader.java:286)
	at java.io.Reader.read(Reader.java:140)
	at com.oracle.truffle.api.source.Source.read(Source.java:1209)
	at com.oracle.truffle.api.source.Source.buildSource(Source.java:1134)
	at com.oracle.truffle.api.source.Source$SourceBuilder.build(Source.java:1667)
	at com.oracle.truffle.api.source.Source$LiteralBuilder.build(Source.java:1801)
	at com.oracle.truffle.polyglot.PolyglotSource.build(PolyglotSource.java:296)
	at org.graalvm.polyglot.Source$Builder.build(Source.java:920)
	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.createSource(GraalJSScriptEngine.java:315)
	... 6 more

Any ideas on whether this is something I can fix in my own code? Am I omitting something?

[iamstolis]

I am sorry but I am not able to reproduce your problem. The mentioned test-case works fine for me.

It may help you to investigate what is closing your BufferedReader unexpectedly. You can see that by overriding close() method of your BufferedReader, for example:

        BufferedReader breader = new BufferedReader(isr) {
            @Override
            public void close() throws IOException {
                Thread.dumpStack();
                super.close();
            }
        };

[rschmunk]

Gave it a try. Not seeing anything that gives me a clue.

java.lang.Exception: Stack trace
	at java.lang.Thread.dumpStack(Thread.java:1336)
	at myapp.CLParser$1.close(CLParser.java:671)
	at com.oracle.truffle.api.source.Source.read(Source.java:1216)
	at com.oracle.truffle.api.source.Source.buildSource(Source.java:1134)
	at com.oracle.truffle.api.source.Source$SourceBuilder.build(Source.java:1667)
	at com.oracle.truffle.api.source.Source$LiteralBuilder.build(Source.java:1801)
	at com.oracle.truffle.polyglot.PolyglotSource.build(PolyglotSource.java:296)
	at org.graalvm.polyglot.Source$Builder.build(Source.java:920)
	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.createSource(GraalJSScriptEngine.java:315)
	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.eval(GraalJSScriptEngine.java:310)
	at javax.script.AbstractScriptEngine.eval(AbstractScriptEngine.java:249)
	at myapp.CLParser.evaluateScript(CLParser.java:693)
	at myapp.CLParser.evaluateScript(CLParser.java:617)
	at myapp.CLParser.<init>(CLParser.java:175)
	at myapp.CLParser.main(CLParser.java:114)
ScriptException: Javax.script.ScriptException: java.io.IOException: Stream closed
javax.script.ScriptException: java.io.IOException: Stream closed
	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.createSource(GraalJSScriptEngine.java:317)
	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.eval(GraalJSScriptEngine.java:310)
	at javax.script.AbstractScriptEngine.eval(AbstractScriptEngine.java:249)
	at myapp.CLParser.evaluateScript(CLParser.java:693)
	at myapp.CLParser.evaluateScript(CLParser.java:617)
	at myapp.CLParser.<init>(CLParser.java:175)
	at myapp.CLParser.main(CLParser.java:114)
Caused by: java.io.IOException: Stream closed
	at sun.nio.cs.StreamDecoder.ensureOpen(StreamDecoder.java:46)
	at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:148)
	at java.io.InputStreamReader.read(InputStreamReader.java:184)
	at java.io.BufferedReader.fill(BufferedReader.java:161)
	at java.io.BufferedReader.read1(BufferedReader.java:212)
	at java.io.BufferedReader.read(BufferedReader.java:286)
	at java.io.Reader.read(Reader.java:140)
	at com.oracle.truffle.api.source.Source.read(Source.java:1209)
	at com.oracle.truffle.api.source.Source.buildSource(Source.java:1134)
	at com.oracle.truffle.api.source.Source$SourceBuilder.build(Source.java:1667)
	at com.oracle.truffle.api.source.Source$LiteralBuilder.build(Source.java:1801)
	at com.oracle.truffle.polyglot.PolyglotSource.build(PolyglotSource.java:296)
	at org.graalvm.polyglot.Source$Builder.build(Source.java:920)
	at com.oracle.truffle.js.scriptengine.GraalJSScriptEngine.createSource(GraalJSScriptEngine.java:315)
	... 6 more
java.lang.Exception: Stack trace
	at java.lang.Thread.dumpStack(Thread.java:1336)
	at myapp.CLParser$1.close(CLParser.java:671)
	at myapp.CLParser.evaluateScript(CLParser.java:711)
	at myapp.CLParser.evaluateScript(CLParser.java:617)
	at myapp.CLParser.<init>(CLParser.java:175)
	at myapp.CLParser.main(CLParser.java:114)

[iamstolis]

The first dumpStack() seems to come from a close() after a successful read of your BufferedReader. I assume that this successful read is followed by the execution of the corresponding script. Can you verify that the script was executed?

Then we see the error that you are facing. Any chance that you executed engine.eval ( breader ); twice with the same breader?

BTW: Are you able to reproduce this problem with the minimal test-case mentioned at the beginning of this report or it happens in a more complex context only?

[rschmunk]

Thanks for your help, @iamstolis. It turns out that as written above, the script was evaluated and executed. The problem was that the full version of my code was wrapping part of the process in a try-with-resources block and the FileInputStream or InputStreamReader was getting closed.

It also failed when I reverted to using Nashorn, so I will have to go back and see when/why the try blocks got changed during the past month.