Error de-serializing a continuation: Can't find top level scope for ClassCache.get

[Michael Bar-sinai]

Hello all,

I have a JS script that generates a continuation (by calling a Java function that throws Context.getCurrentContext().captureContinuation()). I then serialize the continuation using ScriptableOutputStream. This works well, as all connected Java objects are serializable.

In some situations, when I de-serialize the stream, I get the error: "Can't find top level scope for ClassCache.get"

This will throw an error:

A = bp.Event("A");

B = bp.Event("B");

C = bp.Event("C");

var r;

bp.registerBThread(function() {

r=bsync({ waitFor : A }); // The problem is with this assignment.

bsync({ waitFor : B });

bsync({ waitFor : C });

});

while this won't (the assignment to r is removed):

/* global bp  */

A = bp.Event("A");

B = bp.Event("B");

C = bp.Event("C");

var r;

bp.registerBThread(function() {

bsync({ waitFor : A }); // The problem is with this assignment.

bsync({ waitFor : B });

bsync({ waitFor : C });

});

Any ideas?

Thanks!

[ian]

Hi Michael,

Just wondering if you've made any discoveries relating to this. I'm seeing some unexpected behavior around continuations storing the variables declared in global scope (such as `var r` in your example).

Thank you for your time!

[Michael Bar-Sinai]

Not yet. I plan to revisit this in the next few days.

Meanwhile, I did find a reliable source code about how to do continuations here:

https://github.com/mozilla/rhino/blob/master/testsrc/org/mozilla/javascript/tests/ContinuationsApiTest.java

I'll update once I have something.

-- Michael

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[Michael Bar-sinai]

Some advancement: This is only happening when a JS variable holds a Java object. That Java object is serializable, though.

Any ideas?

On Sunday, April 30, 2017 at 8:00:25 AM UTC+3, Michael Bar-sinai wrote:

Not yet. I plan to revisit this in the next few days.

Meanwhile, I did find a reliable source code about how to do continuations here:

https://github.com/mozilla/rhino/blob/master/testsrc/org/mozilla/javascript/tests/ContinuationsApiTest.java

I'll update once I have something.

-- Michael

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[CL Yao]

This error too.

I'm using rhino 1.7R4.

This error is because ScriptableObject mark parentScope/prototype as transient. When deserialize it restore slots first and parent/prototype last.

So If a slot ref a NativeJavaObject, It will call ClassCache.get with uninitialized parent scope. Which cause Error.

BTW The last source code in github/master branch seems fixed the problem.

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