Actor model an approach to concurrency 1.0 (freiburg)
Post on 11-Jan-2017
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The Actor Model
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An alternative approach to concurrency
Lorenzo Nicora Senior Consultant @ OpenCredo
@nicusX https://opencredo.com/author/lorenzo/
✓ (1973) Carl Hewitt: “A Universal Modular Actor Formalism for Artificial Intelligence”
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A bit of History…
1973
2009
✓ (2009) Akka toolkit, Scala/Java✓ (1986) Ericsson: Erlang
Lorenzo Nicora Actor Model
According to Alan Kay, author of Smalltalk and inventor of the “Object-Orientation”:
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The original idea of Object
An “Object”
✓ Is the basic unit of object-oriented system
✓ Has its own state
✓ Communicate with others
by sending and receiving messages*
* in Java, C++, C# (derived from Simula, not Smalltalk) Objects interact by invoking methods
1980
Lorenzo Nicora Actor Model
An “Actor” is a computational entity that, in response to a message it receives, can concurrently:
a) Send a finite number of messages to other actors
b) Create a finite number of new actors
c) Designate the behaviour to be used for the next message it receives. [implies a state]
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The Actor
Actor
Actor
Actor
Mailbox Mailbox
Mailbox
Lorenzo Nicora Actor Model
Actors interacts only by messaging
Actors react to messages
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Actors are Reactive
Lorenzo Nicora Actor Model
An Actor handles one message a timeNever concurrently
An Actor has a state State cannot be modified from outside the actor
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Thread-safe
An Actor is inherently thread-safeNo Lock/Synchronisation on State
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Supervision
Actors are created by Actors
Parent -> Child
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Supervision
Failure Handling • If a Child throws an Exception, the Supervisor get notified • Supervision Strategy: e.g. relaunch, abandon…
Failure is always handled consistently
Parent = Supervisor
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Lightweight
Actor is lightweight
Creating an Actor has little overhead beyond creating an Object
Lorenzo Nicora Actor Model
Non-blocking implementation of Request/Response pattern
with multiple downstream collaborators
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Example: Non-blocking Request/Response
• One-Actor-per-Request pattern
• Enterprise Integration Patterns: ✴ Request/Reply ✴ Return Address ✴ Scatter-Gather, Aggregators ✴ Round-robin Message Router
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Example: Non-blocking Request/Response
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Example: Non-blocking Request/Response
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Example: Non-blocking Request/Response
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Example: Non-blocking Request/Response
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Example: Non-blocking Request/Response
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Example: Non-blocking Request/Response
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Example: Non-blocking Request/Response
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Example: Non-blocking Request/Response
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Example: Non-blocking Request/Response
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Example: Non-blocking Request/Response
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Example: Non-blocking Request/Response
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Conclusions
Actor model: an alternative approach to concurrency
Actors, Threads
+ Business logic implementation + inherently thread-safe
- A new programming paradigm - to learn
Lorenzo Nicora Actor Model
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