Differences

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--- at:tutorial:actors [2008/11/04 10:11] – added tvcutsem
+++ at:tutorial:actors [2009/01/29 16:48] – elisag
@@ Line 317: / Line 317: @@
 o<-m()@FutureMessage
 </code>
+When a message send is annotated with the ''Due'' type tag, the attached future is expected to be resolved before a specified deadline. As shown below, the annotation takes as parameter a timeout value (in milliseconds) relative to the time at which a message is sent. The future is automatically ruined with a ''TimeoutException'' if the timeout elapses before the return value was received. This is primarily useful to have time-based delivery policy guarantees on asynchronous messages.
+<code>
+o<-m()@Due(timeout);
+</code>
+<note>
+More details about the ''Due'' annotation can be found in the section about [[distribution#dealing_with_permanent_failures|leased object references]] within the chapter about distributed programming.
+</note>
 Finally, it is possible to first invoke ''enableFutures(false)'' and later enable it by default anyway by invoking ''enableFutures(true)''. However, once futures have been enabled by default, they can no longer be "turned off" by default. The reason for this is that if two separate files load the futures module and one enables futures by default and the other does not, then the net result is that they will be enabled by default, which will make both applications work correctly. If futures could be disabled, this can cause one object to unexpectedly make other objects crash because they depend on futures.
@@ Line 469: / Line 479: @@
 </code>
-If both the ''outer'' and ''inner'' actors lexically see ''x'', they could modify it concurrently, reintroducing race conditions on the internal state of an actor. Therefore, when defining an actor using a block of code, we disallow access to the enclosing lexical scope by the new actor. It is as if it was defined at top-level. Hence, actors behave similarly to [[#isolates|isolates]] in this respect. The above example is incorrect in that ''inner'' will not be able to read or modify ''x''.
+If both the ''outer'' and ''inner'' actors lexically see ''x'', they could modify it concurrently, reintroducing race conditions on the internal state of an actor. Therefore, when defining an actor using a block of code, we disallow direct access to the enclosing lexical scope by the new actor. Actors behave similarly to [[#isolates|isolates]] in this respect. The above example code will work, but the programmer has to keep in mind that the ''x'' variable accessed by ''inner'' is a //copy// of the ''x'' variable of ''outer''. Hence, assignments to ''x'' by ''inner'' will not affect ''outer'' and vice versa.
-Recall that isolates could be given selective access to their enclosing lexical scope by specifying accessed variables as formal parameters to their initializing closure, which gave rise to copying the variable into the isolate. We allow actors to do the same. Hence, the above example can be written properly as:
+Recall that isolates could be given access to their enclosing lexical scope either by specifying accessed variables as formal parameters to their initializing closure or by having the interpreter derive the lexically free variables automatically. If the programmer wants to make explicit the fact that ''x'' is copied, the example can also be rewritten as:
 <code>