BlockInfo has a StorageLevel,
size attribute is the size of the memory block. It starts with
readerCount counter is the number of readers of the memory block, i.e. the number of read locks. It starts with
readerCount is incremented when a read lock is acquired and decreases when the following happens:
writerTask attribute is the task that owns the write lock for the memory block.
A writer task can be one of the three possible identifiers:
The writer task is assigned in the following scenarios: