Nov 1 Deadlock Hunter Project Software Engineering Lab. Winter 07/08 Supervised by: Yonatan Kaspi Yonatan Kaspi Introduced by: Jamil Shehadeh Husam Khshaiboun

Nov Deadlock Hunter Project Our goal is to build a tool that will force the operating system scheduler to make the execution path be truly random. We will do this by examining the byte code of a Java program and adding small code sections in places that effect the execution path. Our job is to locate the deadlock, not to fix it.

Nov Strategy The idea is to enter other wait functions randomly anywhere before a synchronize keyword appears. Dealing with threads in any language can be done using specific commands. Using java enables us to be Platform independent. The specific commands will be searched for in java byte code using a parser. Code sections will be added automatically in these places forcing randomization in the execution path A Java Code with a hidden deadlock will be used as a client. The deadlock hunter will build a new instrumented byte code.

Nov Gaston & Alphonso A Client Example Gaston & Alphonso are two gentle and friendly fellows. They must bow one to the other anytime they meet. Each one of them bows and continue bowing until the other bows back. What if both of them bow at the same time?

Nov Gaston & Alphonso How to find the deadlock The idea is to enter other wait functions randomly anywhere before a synchronize keyword appears. Then, we can shake the stability of the regular execution path. We always enter the same byte code of an invariant function that includes a call of other modifiable function. To do that. “Some” BCEL is needed. BCEL stands for Byte Code Engineering Library Intended to give users a convenient possibility to analyze, create, and manipulate (binary) Java class files. Classes are represented by objects which contain all the symbolic information of the given class: methods, fields and byte code instructions, in particular.

Nov The Deadlock Hunter Main code flow Get the Client class file Create new Instruction list for each method Insert the “enter” function call where needed Update exception table handler Loop over its methods Deal with branch instructions Dump new class file

Nov Statistics Before code instrumentation, 0 deadlocks occurred in 100 runs. After adding all waits randomly (probability 70%) in one function only, 65 deadlocks occurred in 100 runs. After adding all waits randomly (probability 20%) in one function only, 35 deadlocks occurred in 100 runs. Adding waits randomly in all functions resulted in 100 deadlocks in 100 runs !