The document discusses the actor model and how it relates to Erlang processes and fault tolerance. It introduces some key concepts of the actor model like actors communicating asynchronously via message passing. It also explains how Erlang processes are isolated with no shared memory, and how this helps enable fault tolerance since failures don't impact other processes. Finally, it mentions how OTP provides patterns like supervisors and state machines to help build robust and fault tolerant applications in Erlang.

1. Actor Oriented Programming, Fault Tolerance and OTP Dhananjay Nene #devcamp pune April 9 th , 2011

2. What is the Actor Model ?

3. “ In computer science, the Actor model is a mathematical model of concurrent computation that treats "actors" as the universal primitives of concurrent digital computation : in response to a message that it receives , an actor can make local decisions, create more actors, send more messages, and determine how to respond to the next message received.” – Wikipedia (Actor Model)

4. Erlang Process Model

5. In erlang parlance, each actor is a process

6. However thats not the same as an operating system process. A single OS process hosts many erlang processes. An erlang process is far lighter than even a thread.

7. Isolation : Processes are isolated. They do not share any memory between themselves. Garbage collection also works independently per processes

8. Since processes run concurrently, the inability to share memory between them reduces many of the difficulties associated with conventional multi threaded programming

9. Messages : Processes interact with each other by sending each other messages asynchronously

10. For asynchronous messaging to work each process has a mailbox of messages and it processes one message at a time from the mailbox

11. Introduction : Sleeping Barber Problem

12. OTP : Open Telecom Platform

13. OTP plays a somewhat similar role as JEE does for Java

14. OTP Design Patterns : Application

15. Server

16. Supervisor

17. State Machines

18. Event Handling

19. Philosophy : Let it crash

20. Let it crash actually encouraging higher availability initially seems like an oxymoron

21. But what it really emphasises is the ensured continued availability of the overall system rather than the robustness of every small piece that forms it.

22. So what features of erlang help fault tolerance?