README.md

Tyrion Lock Profiler

A Java agent that extracts runtime locking information from a JVM.

Goals

The main goal of Tyrion is to give a clear view on how an application uses locks. For instance, the following questions should be answered easily :

• In my application, which locks are never used ?
• In my application, which locks are used only by one thread ?
• In my application, which locks are contended ?
• How much time does my threads spend in critical sections ?
• ...

Components

Tyrion is composed by two main components :

• A java agent that collects information in a JVM and produces a log file
• A GUI that takes this log file and produce reports on it

The Java agent has been created with a "low overhead" policy in mind, so that it can be added to a JVM and then forgotten, until its data are really needed. This policy is comparable to the GC logs one : always enabled, almost invisible, VERY useful.

Bytecode instrumentation

The agent transforms bytecode so that every synchronized block starts and ends with a call to Tyrion. Consider, for example, the following method :

public void foo() {
  synchronized(bar) {
    //...
  }
}

After being instrumented, it will be the following :

public void foo() {
  synchronized(bar) {
    LocksInterceptor.enteredSynchronizedBlock(bar);
    //...
    LocksInterceptor.leavingSynchronizedBlock(bar);
  }
}

The same rule applies for synchronzied methods.