Differences

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--- at:tutorial:distribution [2007/05/04 08:35] – * elisag
+++ at:tutorial:distribution [2007/05/04 09:05] – * elisag
@@ Line 92: / Line 92: @@
 This code illustrate how the instant messenger application notifies when a buddy goes online or offline. In the above code, ''messenger'' is a remote reference to another remote buddy discovered. Note that installing disconnected observers also allows developers to clean certain resources when a remote reference becomes disconnected. However, when an instant messengers disconnects, the remote object referred to by ''messenger'' remains exported. This implies that remote objects remains pointed by a disconnected remote reference which prevents them from being garbage collected. In fact, ''messenger'' are never garbage unlesss explicit cancelation of the subscription. But other types of objects which are only relevant within the context of an interaction should become eventually candidates for garbage collection. In the next section, we detail how AmbientTalk deals with distributed memory management.
+In other to cope with partial failures, AmbientTalk also allows developers to retract all currently unsent messages from the far reference outbox by means of the ''retract'' language construct. This is specially useful in the context of distribution, since developers can have explicit control on the messages that are buffered but have not been sent while the remote far reference is disconnected. Any undelivered messages accumulated by the remote reference can be then for example forwarded to another remote object or simply cancelled.
+The ''retract'' language construct takes as argument the far reference of which to retract outgoing message send. One can store the unsent messages upon disconnection of a service type ''Service'' as follows:
+<code>
+when: Service discovered: { | reference |
+    when: reference disconnected: {
+         messages := retract: reference;
+    }
+}
+</code>
+The construct returns a table containing copies of all messenges that were sent to this far reference, but not yet transmitted by the far reference to the remote object pointed to. Note that this has the side effect that the returned messages will not be sent automatically anymore; the programmer is thus responsible to explicitly resend all messages that were retracted but still need to be sent.
 ===== Garbage collecting remote references =====
@@ Line 121: / Line 135: @@
 <note>
-The complete implementation of the instant messenger application explained along this chapter can be found in the file at/demo/InstantMessenger.at.
+The complete implementation of the instant messenger application explained along this chapter can be found in the file ''at/demo/InstantMessenger.at''.
 </note>