Thread Safe list in python
works in 3 modes:
dirty: Allows concurrent reads and concurrent writers to the access the list. No lock mode.
safe_write: Allows exactly one writer at a time, but reader threads can access without
having to acquire any lock.
Possibility of dirty reads. Writers need an exclusive lock.
safe_readwrite: Allows either exactly one writer or n readers concurrently accessing.
Readers and Writers
both need to acquire the lock before accessing the list.