Actor Model - Revision history

Miranda ricardo at 19:03, 30 November 2014

2014-11-30T19:03:33Z

Miranda ricardo at 19:02, 30 November 2014

2014-11-30T19:02:51Z

Miranda ricardo at 10:57, 14 October 2014

2014-10-14T10:57:36Z

Miranda ricardo at 10:57, 14 October 2014

2014-10-14T10:57:13Z

Miranda ricardo at 18:00, 2 October 2014

2014-10-02T18:00:55Z

Miranda ricardo at 18:00, 2 October 2014

2014-10-02T18:00:18Z

Miranda ricardo: /* Notes on the Actor Model */

2014-10-02T17:45:07Z

‎Notes on the Actor Model

Miranda ricardo: /* Relevance of the Actor Model for the Mohid system */

2014-01-24T13:55:26Z

‎Relevance of the Actor Model for the Mohid system

Miranda ricardo: /* Relevance of the Actor Model for the Mohid system */

2014-01-24T13:54:30Z

‎Relevance of the Actor Model for the Mohid system

Miranda ricardo: /* Relevance of the Actor Model for the Mohid system */

2014-01-24T13:51:00Z

‎Relevance of the Actor Model for the Mohid system

@@ Line 31: / Line 31: @@
 Here a [[Fortran implementation of the Actor Model using MPI]] is discussed.
-The program to consolidate results from [[Domain Decomposition]]runs, [[Consolidate Domain Decomposition]], is the first using the actor model approach. It is a simple and small program, the perfect test bed before expanding to Mohid.
+The program to consolidate results from [[Domain Decomposition]] runs, [[Consolidate Domain Decomposition]], is the first using the actor model approach. It is a simple and small program, the perfect test bed before expanding to Mohid.
 == Relevance of the Actor Model for the Mohid system ==

← Older revision		Revision as of 19:02, 30 November 2014
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	Here a [[Fortran implementation of the Actor Model using MPI]] is discussed.		Here a [[Fortran implementation of the Actor Model using MPI]] is discussed.
		+
		+	The program to consolidate results from [[Domain Decomposition]]runs, [[Consolidate Domain Decomposition]], is the first using the actor model approach. It is a simple and small program, the perfect test bed before expanding to Mohid.

	== Relevance of the Actor Model for the Mohid system ==		== Relevance of the Actor Model for the Mohid system ==

← Older revision		Revision as of 10:57, 14 October 2014
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−	According to the Wikipedia[http://en.wikipedia.org/wiki/Actor_model] "the actor model in computer science 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" (changing state). The actor model is a special form of Reactive Programming.	+	According to the Wikipedia[http://en.wikipedia.org/wiki/Actor_model] "the actor model in computer science 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" (changing state). The actor model is a special form of [[Reactive Programming]].

	There are several resources in the Internet explaining the Actor Model and Reactive Programing. Some videos and interesting interviews:		There are several resources in the Internet explaining the Actor Model and Reactive Programing. Some videos and interesting interviews:

@@ Line 1: / Line 1: @@
-According to the Wikipedia[http://en.wikipedia.org/wiki/Actor_model] "the actor model in computer science 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" (changing state).
+According to the Wikipedia[http://en.wikipedia.org/wiki/Actor_model] "the actor model in computer science 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" (changing state). The actor model is a special form of Reactive Programming.
 There are several resources in the Internet explaining the Actor Model and Reactive Programing. Some videos and interesting interviews:
@@ Line 22: / Line 22: @@
 </ul>
-When an actor recieves a message it reacts:
+When an actor receives a message it reacts:
 <ul>
      <li>sending messages to actors it knows (finite number);</li>
@@ Line 33: / Line 33: @@
 == Relevance of the Actor Model for the Mohid system ==
-Mohid is a large system with complex memory management. With the comodization of multi-core machines and access to fast local networks MPI is becoming the de facto way of running Mohid. MPI (Message Passing Interface) is a very powerfull, standardized and portable message-passing system.
+Mohid is a large system with complex memory management. With the commoditization of multi-core machines and access to fast local networks MPI is becoming the de facto way of running Mohid. MPI (Message Passing Interface) is a very powerful, standardized and portable message-passing system.
 The way MPI is currently used in Mohid is difficult to implement, hard to understand and complex to maintain. It is essential to use MPI in such a way that it becomes easier to reason about:
@@ Line 45: / Line 45: @@
 == Actor Model in Mohid ==
-[[File:am.01.png|thumb|left|alt=Domain in decomposed in 3 subdomains creates 3 instances of MohidWater (MW1, MW2 and MW3).|Domain in decomposed in 3 subdomains.]]Suppose a domain is decomposed in 3 sub-domains according to the first image. Each sub-dmain is an actor that sends messages to other actors and reacts to messages it receives. Each model has a Main Loop that progresses in time-steps. Each model sends messages with information (for example border conditions) to actors that need it.
+[[File:am.01.png|thumb|left|alt=Domain in decomposed in 3 subdomains creates 3 instances of MohidWater (MW1, MW2 and MW3).|Domain in decomposed in 3 subdomains.]]Suppose a domain is decomposed in 3 sub-domains according to the first image. Each subdomain is an actor that sends messages to other actors and reacts to messages it receives. Each model has a Main Loop that progresses in time-steps. Each model sends messages with information (for example border conditions) to actors that need it.
@@ Line 53: / Line 53: @@
-[[File:am.02.png|thumb|left|alt=Actor MW3 is the first actor to terminate its time-step.|(1) Actor MW3 is the first actor to terminate its time-step.]]Suppose Actor MW3 is the first actor to terminate its timestep. It sends messages to other actors with border conditions. MW3 has no messages in its mailbox so it is idle. Actor MW2 has a message in its mailbox but it can not process it yet so the message stays there.
+[[File:am.02.png|thumb|left|alt=Actor MW3 is the first actor to terminate its time-step.|(1) Actor MW3 is the first actor to terminate its time-step.]]Suppose Actor MW3 is the first actor to terminate its time-step. It sends messages to other actors with border conditions. MW3 has no messages in its mailbox so it is idle. Actor MW2 has a message in its mailbox but it can not process it yet so the message stays there.
-MW3 will react when a message arrives to its mailbox. When it gathers enough information to strat a new time-step it will react triggering some computations. There is no central authority ordering it to start, stay idle, etc.
+MW3 will react when a message arrives to its mailbox. When it gathers enough information to start a new time-step it will react triggering some computations. There is no central authority ordering it to start, stay idle, etc.
@@ Line 65: / Line 65: @@
-[[File:am.04.png|thumb|right|alt=All actors are working.|(4) All actors are working.]]All actors are computing a new timestep
+[[File:am.04.png|thumb|right|alt=All actors are working.|(4) All actors are working.]]All actors are computing a new time-step.
 == Notes on the Actor Model ==

@@ Line 29: / Line 29: @@
 </ul>
-Here a [[Fortran implementation of the Actor Model]] is discussed.
+Here a [[Fortran implementation of the Actor Model using MPI]] is discussed.
 == Relevance of the Actor Model for the Mohid system ==

@@ Line 28: / Line 28: @@
      <li>designating how it should handle the next message it receives (changing state).</li>
 </ul>
 == Relevance of the Actor Model for the Mohid system ==

@@ Line 72: / Line 72: @@
      <li>the sender does not verify if the message reaches its destination;</li>
      <li>the order of arrival is independent of the order of sending;</li>
      <li>there is no central point of control; and</li>
      <li>messages in mailbox are not processed in the order of arrival, there is a loop over the queue checking which messages the actor can react upon.</li>
 </ul>

@@ Line 38: / Line 38: @@
      <li>making explicit conventions on MPI usage of Mohid, for instance banning the use of semaphores and barriers;</li>
      <li>there will be a very limited number of modules where MPI directives are allowed; and</li>
-     <li>MPI will be used to create explicit APIs (Application programming interface) that can be easily expanded and refactored according to Mohid's needs.</li>
+     <li>MPI will be used to create explicit APIs (Application Programming Interface) that can be easily expanded and refactored according to Mohid's needs.</li>
 </ul>

@@ Line 31: / Line 31: @@
 == Relevance of the Actor Model for the Mohid system ==
-The actor model makes it easier to reason about distributed programming. All MPI directives will be packed up in a set of well defined modules. Communication among actors takes place through clear and standard interfaces with well defined behaviors. This software architecture is proven to provide scalability, resilience and responsiveness. There is no central management and no points of synchronism so actors just react to events; this is a simpler way of reasoning about concurrency and parallelism.
+Mohid is a large system with complex memory management. With the comodization of multi-core machines and access to fast local networks MPI is becoming the de facto way of running Mohid. MPI (Message Passing Interface) is a very powerfull, standardized and portable message-passing system.
-According to Carl Hewitts' definition (Carl Hewitt; Peter Bishop; Richard Steiger (1973). A Universal Modular Actor Formalism for Artificial Intelligence. IJCAI) an actor is the fundamental unit of computation that embodies:
+The way MPI is currently used in Mohid is dificult to implement, hard to undestand and complex to maintain. It is essential to use MPI in such a way that it becomes easier to reason about:
 <ul>
-     <li>processing (the behavior, the executable code);</li>
+     <li>standarizing MPI's implementation in Mohid, embeding it in the programming framework;</li>
-     <li>storage (its the state, the stuff on the heap, memory); and</li>
+     <li>making explicit convensions on the usage of Mohid, for instance banning the use of semaphors and barriers;</li>
-     <li>communication.</li>
+     <li>there will be a very limited number of modules whrere MPI directives are allowed; and</li>
-</ul>
+     <li>MPI will be used to create explicit APIs (Application programming interface) that can be eaily expand and refactored according to Mohid's needs.</li>
 </ul>