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--- at:tutorial:actors [2007/04/01 11:32] – added tvcutsem
+++ at:tutorial:actors [2007/04/01 11:54] – finished tvcutsem
@@ Line 16: / Line 16: @@
 === Actors and Far References ===
+In AmbientTalk, concurrency is spawned by creating actors: each actor is an autonomous processor. AmbientTalk's actors are based on the [[Wp>E_programming_language|vat model]] of the [[http://www.erights.org|E programming language]]. In AmbientTalk, an actor consists of a message queue (to store incoming messages), a thread of control (to execute the incoming messages) and a number of regular objects that are said to be //hosted// by the actor.
+When an actor is created, it hosts a single object which is said to be the actor's //behaviour//: it is the "public interface" to the actor. The object that created the new actor gets a reference to this behaviour object, such that it can start sending messages to the new actor. An actor can be created in AmbientTalk as follows:
+<code>
+>def a := actor: {
+  def sayHello() {
+    system.println("Hello World")
+  };
+};
+>><far ref to:<object:1555668>>
+</code>
+As you can see, actors are created similar to objects. The ''actor:'' method, defined in the global lexical scope, takes a closure as its sole argument and uses that closure to initialize the behaviour of the new actor. The creator of the actor immediately receives a so-called //far reference// to this behaviour object, and from that moment on the creating actor and the created actor run in parallel, each capable of processing incoming messages autonomously.
+So what exactly is a far reference to an object? The terminology stems from the E language: it is an object reference that refers to an object hosted by another actor. The main difference between regular object references and far references is that regular references allow direct, synchronous access to an object, while far references disallow such access. This is enforced by the kind of messages that these references can carry, as will be explained below.
 === Asynchronous Message Sending ===