The document discusses the actor programming model, which involves lightweight processes communicating through messaging rather than sharing data or memory. It focuses on actors in Erlang and how they use message-passing instead of shared state. Actors react to received messages asynchronously and communicate through message-passing rather than shared memory.

1. Actors
Reidar Sollid
The actor programming model
Drammen
25.10.2012

2. Erlang
• The world is concurrent
• Things in the world don't share data
• Things communicate with messages
• Things fail
• - Joe Armstrong
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3. Original problem
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4. New problem
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5. Shared memory
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6. Shared memory model
Shared
memory
Process Process
thread thread
Process
thread
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7. Concurrency and shared memory
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8. What is the Actor Model
• Light weight processes/tasks/agents
communicating through messaging
• Messages are buffered in a “mailbox”
• No shared state
• Isolated from other processes
• Normally event systems are inversion of
control
• Adding a listener to an object
• Hard to maintain in large systems
• Humans do not share memory, we
communicate through messages
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9. React or receive
• React is the “normal” actor, lightweight
process
• Receive spins out a new Java thread
• In the paper *
• 5000 threads
• 1 200 000 actors
• React uses partial functions to send the
process to the heap
• Receive runs on the stack and is
heavyweight JVM threads (like Java)
• *Actors That Unify Threads and Events P. Haller, M.
Odersky
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10. Pattern matching
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11. Pattern matching
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12. Tail optimized recursion
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13. Tail recursion
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14. F# Agent
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15. Scala actor
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16. Application security
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