search

npgall / mobility-rpc

Add Code Mobility to any application
Apache License 2.0
32 stars 12 forks source link

Mobility RPC cannot migrate when threads are in use #9

Closed GoogleCodeExporter closed 8 years ago

GoogleCodeExporter commented 9 years ago 
What steps will reproduce the problem?
1. Migrating an object that uses threads
2. or Migrating objects in a program that uses threads
3.

What is the expected output? What do you see instead?
I expected mobility to work with my threads, but I get a NoClassDefFoundError. 
If I take these threads out, it works perfectly.

What version of the product are you using? On what operating system?
1.1.0

Please provide any additional information below.
I am just curious if there is a reason threads cause this.

Original issue reported on code.google.com by benjamin...@gmail.com on 24 Nov 2014 at 3:46

GoogleCodeExporter commented 9 years ago 
Hi Benjamin.

Can you provide a stack trace and output from the logs? We need to know if the 
problem occurs in the serialization side before the object is even sent, or 
after the object is received and the remote machine requests the class bytecode 
from the local side.

Multithreading is definitely supported. There might be something strange going 
on with context class loaders or something.

Original comment by ni...@npgall.com on 24 Nov 2014 at 11:07

GoogleCodeExporter commented 9 years ago 
No Problem! When I run my code with threading and simple object migration, I 
will get one of the two errors. Both having to do with serialization I believe. 
As soon as I take out threads or the migration, everything works, unless I 
missed something in my debugging.

EXCEPTION #1

Exception in thread "Thread-0" java.lang.NoClassDefFoundError: 
com/googlecode/mobilityrpc/quickstart/QuickTask
    at Jambient.Ambient.migrate_runone(Ambient.java:138)
    at jambientmovitatingexample.JambientMovitatingExample.run(JambientMovitatingExample.java:113)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.ClassNotFoundException: 
com.googlecode.mobilityrpc.quickstart.QuickTask
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
    ... 3 more

EXCEPTION #2

Exception in thread "main" java.lang.IllegalStateException: Exception 
serializing object to KRYO format: 
com.googlecode.mobilityrpc.quickstart.QuickTask$SessionReleasingRunnable@de96c95
    at com.googlecode.mobilityrpc.session.impl.MobilitySessionImpl.serialize(MobilitySessionImpl.java:508)
    at com.googlecode.mobilityrpc.session.impl.MobilitySessionImpl.execute(MobilitySessionImpl.java:81)
    at com.googlecode.mobilityrpc.session.impl.MobilitySessionImpl.execute(MobilitySessionImpl.java:75)
    at com.googlecode.mobilityrpc.quickstart.QuickTask.execute(QuickTask.java:57)
    at com.googlecode.mobilityrpc.quickstart.QuickTask.execute(QuickTask.java:44)
    at Jambient.Ambient.migrate_runall(Ambient.java:107)
    at jambienttester.JambientTester.main(JambientTester.java:50)
Caused by: 
com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.SerializationException:
 Unable to serialize object of type: 
com.googlecode.mobilityrpc.quickstart.QuickTask$SessionReleasingRunnable
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.Kryo.writeClassAndObject(Kryo.java:493)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.ObjectBuffer.writeClassAndObject(ObjectBuffer.java:230)
    at com.googlecode.mobilityrpc.serialization.impl.KryoSerializer.serialize(KryoSerializer.java:139)
    at com.googlecode.mobilityrpc.session.impl.MobilitySessionImpl.serialize(MobilitySessionImpl.java:502)
    ... 6 more
Caused by: 
com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.SerializationException:
 Unable to serialize object of type: Jambient.Ambient
Serialization trace:
childList (Jambient.Ambient)
parent (Jambient.Ambient)
this$0 (Jambient.Ambient$1)
wrapped 
(com.googlecode.mobilityrpc.quickstart.QuickTask$SessionReleasingRunnable)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.Kryo.writeClassAndObject(Kryo.java:493)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.CollectionSerializer.writeObjectData(CollectionSerializer.java:86)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.Kryo.writeClassAndObject(Kryo.java:489)
    ... 9 more
Caused by: 
com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.SerializationException:
 Unable to serialize object of type: Jambient.Ambient
Serialization trace:
siblingList (Jambient.Ambient)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.Kryo.writeClassAndObject(Kryo.java:493)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.CollectionSerializer.writeObjectData(CollectionSerializer.java:86)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.Kryo.writeClassAndObject(Kryo.java:489)
    ... 19 more
Caused by: 
com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.SerializationException:
 Serialization trace:
classes (sun.misc.Launcher$AppClassLoader)
contextClassLoader (java.lang.Thread)
t_in (Jambient.Ambient)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:191)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.Kryo.writeClassAndObject(Kryo.java:489)
    ... 23 more
Caused by: java.util.ConcurrentModificationException
    at java.util.Vector$Itr.checkForComodification(Vector.java:1156)
    at java.util.Vector$Itr.next(Vector.java:1133)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.CollectionSerializer.writeObjectData(CollectionSerializer.java:85)
    at com.googlecode.mobilityrpc.lib.com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
    ... 29 more
Java Result: 1

Original comment by benjamin...@gmail.com on 24 Nov 2014 at 4:26

GoogleCodeExporter commented 9 years ago 
Based on that info I think this might be an issue in your code, not 
Mobility-RPC actually. But you have a few options to solve it...

EXCEPTION #1
In this example, com.googlecode.mobilityrpc is not mentioned in the stack trace 
at all. It seems your application tries to call a class in Mobility-RPC, but 
the Mobility-RPC jar file is somehow missing from your class path (?) This is a 
strange problem, I don't know what it is but your application is not set up 
correctly in this case.

EXCEPTION #2
In this case it looks like you are trying to serialize a java.util.Vector on 
the local machine so that it can be sent to the remote machine, but some other 
threads on the local machine continue to modify the vector at the same time 
while it is being iterated by the serializer, which caused the vector itself to 
throw a ConcurrentModificationException into the serializer.

This is a limitation of java.util.Vector itself. It is a "synchronized" data 
structure, not a "concurrent" data structure. It can be used by multiple 
threads in an application, but only one thread can access it at a time. Vector 
automatically enforces this in most cases (most of its methods are 
synchronized), with one important exception: iteration. See 
http://stackoverflow.com/questions/1775717/explain-synchronization-of-collection
s-when-iterators-are-used - if the vector will be iterated while other threads 
try to modify it, the application programmer needs to manually synchronize on 
the vector while it is being iterated.

You can avoid this problem by having your code synchronize on the vector, 
before you try to send the object to the remote machine. Another workaround 
would be to use a CopyOnWriteArrayList in your code instead of a Vector, which 
would be a drop-in replacement (but would have its own pros and cons).

Vector is basically not a very modern data structure so I'd recommend that you 
use a different data structure (which doesn't require synchronization), if 
possible.

Original comment by ni...@npgall.com on 24 Nov 2014 at 5:59

GoogleCodeExporter commented 9 years ago 
Aw makes sense. I didn't think about the second one having the concurrent 
modification. As far as the first one, I thought the same thing and am fairly 
certain it is all set up correctly, I have the jar imported and everything 
works without threads. I will check it out some more. Thanks for your help! Its 
a great library!

Original comment by benjamin...@gmail.com on 24 Nov 2014 at 6:05

GoogleCodeExporter commented 9 years ago 
Also, I am not using a Vector, but an ArrayList, which is definitely a modern 
data structure. Would that still cause this issue?

Original comment by benjamin...@gmail.com on 24 Nov 2014 at 6:07

GoogleCodeExporter commented 9 years ago 
Yes ArrayList would be susceptible to that problem also.

You basically need a collection which supports concurrent iteration. Take a 
look at the concurrent package, you should find a few options there: 
http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/package-summary.ht
ml

I'll close this ticket. Feel free to post details of the first problem in the 
forum if you get stuck, I'll take a look there: 
http://groups.google.com/group/mobility-rpc-discuss

Original comment by ni...@npgall.com on 24 Nov 2014 at 11:18

GoogleCodeExporter commented 9 years ago 
Awesome. Thanks for your help!

Original comment by benjamin...@gmail.com on 24 Nov 2014 at 11:30