This document provides an introduction to Byteman and The Jokre. Byteman is a scriptable Java agent that allows testing code behavior at runtime without changing sources by simulating unexpected events. The Jokre is an optimization technique that modifies the Infinispan API to avoid unnecessary remote procedure calls. A demonstration shows using standard map operations while The Jokre fixes performance issues transparently. Questions are welcomed about these projects.

1. OpenBlend Ljubljana
September 15th, 2011
Introduction to Byteman
and
The Jokre
Sanne Grinovero
Software Engineer at Red Hat
1

2. Byteman
• It's a scriptable java agent
• Lets you change behavior at runtime
– Without changing any sources
– Simulating unexpected behaviour
– Setting up specific scenarios

3. How are you going to test for...
• How is your flush operation going to
behave when the disk crashes ?
• Is your code good enough to not corrupt
in-flight processed data when an OOM
excepion happens?
• What if the TCP connection is terminated
during that?

4. Byteman can crash your disk

5. Byteman can cut your LAN cable

6. Byteman can generate an OutOfMemory
exception right where you want it

7. Or it can do simple things too

8. Code deep dive: disk full
Proper error handling for IO exceptions are
tested by:
org.hibernate.search.test.errorhandling.Co
ncurrentMergeErrorHandledTest

9. Event-driven scripts
• You can avoid mocks, conditional
builds, and have the code change when
chosen conditions trigger.
– Cleaner code
• Can attach dynamically after the
running code was written
– Used for “debug” and hot-patching of
running production applications

10. Byte(code) man(ipulation)
Available right now in a JVM near you
– transform code/class structure at load
– retransform code only after load
– java.lang.instrument

11. Byte(code) man(ipulation)
• Byteman makes it easy
– inject Java code direct into Java code
• Byteman makes it cheap
– low transformation cost
– tightly scoped changes
• Byteman produces reversible changes
– no structural changes

12. Byteman built-in methods
Tracing
• traceOpen, traceClose, traceln,
traceStack, ...
Managing Shared Rule State
• flag, clear, countDown, incrementCounter,
Timing
• createTimer, getElapsedTime, resetTimer,

13. Helper Classes
Built-ins are POJO public methods
• take a look
org.jboss.byteman.rule.Helper
• You can use any POJO you like
class DBHelper {
public void trace(String msg,
Record rec);

14. Timing issues
• org.hibernate.search.test.query.timeout.
JPATimeoutTest
– Verifies a timeout is thrown if the query is
too slow

15. How to enable it
• As an explicit agent
-javaagent:/path/to/agent.jar=agentoptions
Auto-loading the agent
– As with the BMunit examples
– Works with JUnit and TestNG
– Requires the JDK's /lib/tools.jar on
classpath
• See website and our projects for details

16. The Jokre
• https://github.com/infinispan/jokre
• A proof of concept of an advanced
optimization technique
• Requires some knowledge of Infinispan

17. Infinispan API:
mandates a return value
map.put( “user-34”, userInstance );
V put(K key, V value);

18. A return value forces an RPC
Assuming a DIST_ASYNC Infinispan cache:
map.put( “k-1”, userInstance );
1) ask the node storing “k-1” what the
current value is
2) return that.. to nobody
3) eventually perform the put
asynchronously

19. A return value forces an RPC
• So even async caches often perform as
sync caches, unless flags are used:
cache.withFlags(
Flag.SKIP_REMOTE_LOOKUP,
Flag.SKIP_CACHE_LOAD
).put( “k-1”, “hi!” );

20. A return value forces an RPC
• So even async caches often perform as
sync caches, unless flags are used:
cache.withFlags(
Flag.SKIP_REMOTE_LOOKUP,
Flag.SKIP_CACHE_LOAD
).put( “k-1”, “hi!” );
Hey, that's not the Map API anymore!

21. Tradeoff: use proprietary or
standard API?
• We all prefer well known APIs
– JPA/Hibernate ?
– Interface and standardization often lags
behind: there is a performance hit you pay.
• It seems in some cases you can have
both: let's see some magic in action

22. Jokr demo

23. 2011-09-15 10:43:15,794 WARN [Skynet]
(main) JKR-00012 Problem XYZ detected
within your code. No worries, we just fixed
it for you.

24. Just use Map, we fix it
• This is a new concept: an “illegal”
optimization is performed.
• It's a proof of concept
– feel free to suggest more use cases.

25. Questions?
Project Page
http://www.jboss.org/byteman
– downloads
– documentation
– user & developer forums
– code repository
https://github.com/bytemanproject
https://github.com/infinispan