Hi,
I'm dealing with code refactoring from a synchronous system to an
asynchronous one, using OSGi Promises. One pattern we have goes as follows:
public void handleNodeAddition(Object element, Set<Node> addedNodes) {
Node node = diagram.getNode(element);
if (node == null) {
node = actionProvider.createNode(element, diagram);
addedNodes.add(node);
}
actionProvider.synchronize(node);
}
The problem I'm facing is that *actionProvider.createNode()* now returns a
Promise<Node> due to asynchronous execution. This means we can no longer
just add nodes to the Set, but not only this, we have to make sure that
each createNode() call from this thread happens after the previous one is
resolved.
Would there be a best practice for this kind of process? If I were to keep
the pattern as-is but implement support for asynchronous node creation,
here's how I would do it:
public void handleNodeAddition(Object element,
AtomicReference<Promise<Set<Node>>> addedNodes) {
Promises.resolved(diagram.getNode(element))
.then(existingNode -> {
Node node = existingNode.getValue();
Promise<Node> nodePromise;
if (node == null) {
// Using an AtomicReference so the Promise chain can be updated
Promise<Set<Node>> addedNodesPromise =
addedNodesPromiseRef.get();
nodePromise = addedNodesPromise // wait for previous node to be
added
.then(previousNodeAdded ->
actionProvider.createNode(element, diagram))
.onSuccess(createdNode ->
createdNode.setLocation(location));
addedNodesPromiseRef.set(createNodePromise
.then(createdNode -> {
addedNodesPromise.getValue().add(createdNode.getValue());
return addedNodesPromise; // still holds the Set
})
);
}
else {
nodePromise = Promises.resolved(node);
}
return nodePromise;
})
.onSuccess(nodeToSync -> actionProvider.synchronize(nodeToSync));
}
Any and all advice is much appreciated, thank you!
-Olivier Labrosse
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