Race Condition in SunshineRepository.getInstance

[ronykrell]

There is a race condition in the getInstance method in SunshineRepository.java.

Imagine there are 2 threads - A and B - both calling getInstance() and that sInstance is null to start with

Thread A
Checks if sInstance is null. Returns True

Thread B
Checks if sInstance is null. Returns True

Thread A
Obtains the lock and creates a new instance for sInstance. Releases lock

Thread B
Remember Thread B already checked if sInstance was null earlier.
Obtains the lock and creates a new instance for sInstance. Releases lock

There should be a second null check inside the synchronized block.