A few notes on message passing
The big problem nobody talks about with actors and message passing is non-determinism and state.<p>If two otherwise independent processes A and B are sending messages to a single process C, it&#x27;s non-deterministic which arrives at C first. This can create a race condition. C may respond differently depending on which messages arrives first - A&#x27;s or B&#x27;s. This is also effectively an example of shared mutable state - the state of C, which can be mutated whenever a message is received - is shared with A and B because they&#x27;re communicating with it and their messages work differently based on the current state.<p>Non-determinism, race-conditions, shared mutable state: the absolute opposite of what we want when dealing with concurrency and parallelism.