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--- at:tutorial:actors [2007/04/07 17:27] – tvcutsem
+++ at:tutorial:actors [2007/04/07 18:06] – added tvcutsem
@@ Line 169: / Line 169: @@
 === The Concept ===
-The most well-known language feature to reconcile return values with asynchronous message sends is the notion of a //future//. Futures are objects that represent return values that may not yet have been computed. Once the asynchronously invoked method has completed, the future is replaced with the actual return value, and objects that referred to the future transparently refer to the return value.
+The most well-known language feature to reconcile return values with asynchronous message sends is the notion of a [[Wp>Future_(programming)|future]]. Futures are objects that represent return values that may not yet have been computed. Once the asynchronously invoked method has completed, the future is replaced with the actual return value, and objects that referred to the future transparently refer to the return value.
 Using futures, it is possible to re-implement the previous example of requesting our calculator actor to add two numbers as follows:
@@ Line 254: / Line 254: @@
 </code>
-The ''when:*'' functions are a very easy mechanism to synchronise on the value of a future without actually making an actor block: remember that all the ''when:becomes:'' function does is register the closure with the future. After that, the actor simply continues processing the statement following ''when:becomes:''. Also, even if the future is already resolved at the time the closure observer is registered, the closure is guaranteed to be applied asynchronously. This ensures that the code following a ''when:becomes:'' block is guaranteed to be executed before the registered closure itself:
+The ''when:*'' functions are a very easy mechanism to synchronise on the value of a future without actually making an actor block: remember that all the ''when:becomes:'' function does is register the closure with the future. After that, the actor simply continues processing the statement following ''when:becomes:''. Also, even if the future is already resolved at the time the closure observer is registered, the closure is guaranteed to be applied asynchronously. This guarantees that the code following a ''when:becomes:'' block is executed before the registered closure itself:
 <code>
@@ Line 266: / Line 266: @@
 === Futures and Striped Messages ===
-Explain:
+As previously explained, there are two modes for enabling futures in AmbientTalk. Invoking ''enableFutures(true)'' makes asynchronous sends return a future by default. Invoking ''enableFutures(false)'' returns ''nil'' by default. No matter how you enabled futures, you can always override the default setting by explicitly //annotating// the message send itself by means of two stripes exported by the futures module, as explained below.
-''o<-m()@FutureMessage''
-''o<-m()@OneWayMessage''
+When a message send is striped with the ''OneWayMessage'' stripe, it will never attach a future to the message. This is primarily useful if you have enabled futures by default, but want to send a one-way message requiring no result. In this case, simply send the message as follows:
+<code>
+o<-m()@OneWayMessage
+</code>
+When a message send is striped with the ''FutureMessage'' stripe, a future is attached to the message, but //only if futures have been enabled//! This is primarily useful if you have enabled futures, but not by default, because you don't want to incur the overhead of future-type message sends on each of the messages sent. In cases where futures become useful, simply send the message as follows:
+<code>
+o<-m()@FutureMessage
+</code>
 === Conditional Synchronisation with Futures ===