Chapter 11

1. Whenever a thread needs to access a non-thread-safe resource, it takes a monitor on this resource. Monitor guarantees that only the thread that owns this monitor can work with his resource.
2. A Deadlock is a situation when two threads depend on the progress of one another, and neither of them can't progress until the other thread does. So both threads stagnate. See chapter 11 for an example of how a deadlock can occur.
3. An actor is a concurrency primitive. It has a mailbox where it can accept messages from other actors. It can send messages to other actors. It is defined in terms of reactions to the messages of other actors. Only one message can be processed at a time by a given actor. It is guaranteed that if an actor owns a non-thread-safe resource, no other actor is allowed to own it.

 

4. Since only one actor controls a non-thread safe resource, there is no danger of race conditions or deadlocks. Whenever other actors need access to the resource in question, they do so by asking the owner actor. The operation is performed indirectly by the owner actor of the resource, and the resource itself is never exposed to the outer world.