Fb question answer roundtrip

Session roundtrip interaction with api client
Maybe something like: 
```java
Map<String, Lock> lockMap = new MapMaker().makeComputingMap(new Function<String, Lock>() {
  @Override public Lock apply(String input) {
    return new ReentrantLock();
  }
});
```

http://stackoverflow.com/questions/5639870/simple-java-name-based-locks/5639920#5639920