articles on asynchronous communications with a focus on Javascript. Minimizing Code Paths In Asynchronous Code, a recent post of his, is about a lesson that I learned the hard way with GWT that applies to all RIA systems that use asynchronous calls. His example is the same case I encountered, where a function might return a value from a cache or might query the server to get the value: an obvious way to do this in psuedocode is: function getData(...arguments...,callback) { if (... data in cache...) { callback(...cached data...); } cacheCallback=anonymousFunction(...return value...) { ... store value in cache... callback(...cached data...); } getDataFromServer(...arguments...,cacheCallback) } At first glance this code looks innocuous, but there’s a major difference between what happens in the cached and uncached case. In the cached case, the callback() function gets called before getData() returns — in the uncached case, the opposite happens. What happens in this function has a global impact on the execution of the program, opening up two code paths that complicate concurrency control and introduce bugs that can be frustrating to debug. This function can be made more reliable if it schedules callback() to run after the thread it is running in completes. In Javascript, this can be done with setTimeout(). In Silverlight use System.Windows.Threading.Dispatcher. to schedule the callback

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Oliver Steele writes an excellent blog about coding style, and has written some good
articles on asynchronous communications with a focus on Javascript.
Minimizing Code Paths In Asynchronous Code, a recent post of his, is about a lesson
that I learned the hard way with GWT that applies to all RIA systems that use
asynchronous calls. His example is the same case I encountered, where a function
might return a value from a cache or might query the server to get the value: an
obvious way to do this in psuedocode is:
function getData(...arguments...,callback) {
if (... data in cache...) {
callback(...cached data...);
}
cacheCallback=anonymousFunction(...return value...) {
... store value in cache...
callback(...cached data...);
}
getDataFromServer(...arguments...,cacheCallback)
}
At first glance this code looks innocuous, but there’s a major difference between
what happens in the cached and uncached case. In the cached case, the callback()
function gets called before getData() returns — in the uncached case, the opposite
happens. What happens in this function has a global impact on the execution of the
program, opening up two code paths that complicate concurrency control and
introduce bugs that can be frustrating to debug.
This function can be made more reliable if it schedules callback() to run after the
thread it is running in completes. In Javascript, this can be done with setTimeout().
In Silverlight use System.Windows.Threading.Dispatcher. to schedule the callback to
run in the UI thread.
Paul Houle on April 21st 2008 in Asynchronous Communications, GWT,
Silverlight
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Generation 5 » The Multiton Design Pattern
[...] (In a more developed application, the BlogPosting could keep a cache of the latest BlogPostingData:
this could improve responsiveness by updating the BlogPostingViewer at the moment it registers, or by
doing a timestamp or checksum stamp against the server to reduce the bandwidth requirements of a
Fetch(), just watch out for the unintended consequences of multiple code paths.) [...]
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