Question

I am aware that Action Script does not provide multithreading so when writing flex application we are limited to work on one thread. which is ok for rendering my UI.

However some questions arise when preferring flex over silverlight:

1. As a UI layer single thread is good enough but is it fair to assume that for Aync httpservice like operations in flex , internally it would use some worker threads to manage the async operation and then come back to the main thread ? it looks like it does since my UI does not freeze.
2. Can the flex/flash player deal with multiple httpservice calls in parallel ? ( e.g more than one section of the UI loading data at the same time.)
3. How about the animation stuff ( e.g the parallel animation ) – does flash player internally leverages some threading for accelerating graphics or is it all done on the UI thread ?

Answer 1

but is it fair to assume that for Aync httpservice like operations in flex , internally it would use some worker threads to manage the async operation and then come back to the main thread

No.
Processing of the response data occurs in the same thread as updating the UI. For example, if you return 5,000 AMF objects in a single call, the Flash Player will deserialize these on the thread, which will cause the UI to freeze.

Internally, the browser may be using threads to manage the loading of the response from the end URL. However, once the response has been returned, and handed off from the browser to the Flash player plugin, the deserialization and processing of that data occurs on the main thread.

Can the flex/flash player deal with multiple httpservice calls in parallel ? ( e.g more than one section of the UI loading data at the same time.)

Yes.
The limitation here is enforced from the browser, in the maximum number of concurrent HTTP requests that the browser. This varies from browser-to-browser, but generally speaking, it’s fine (and encouraged) to send multiple requests to backend services.

It’s worth familiarizing yourself with AsyncToken, which is Flex’s main class used when handling concurrent calls, ensuring that the request and response are matched together.

Be aware that most classes in Flex which are used for communciating with remote services (eg., HttpService and RemoteObject) expose a concurrency property, which defines how the object should react to multiple concurrent requests. (Allowing the developer to explicilty allow or prohibit it).

How about the animation stuff ( e.g the parallel animation ) – does flash player internally leverages some threading for accelerating graphics or is it all done on the UI thread ?

This is not my area of speciality, and someone may correct me. However, I believe that Flex creates animations by generating a series of KeyFrames which change the properties of values on a UIComponent over time, and then executing them. (The execution occurs in the same thread as everything else).
Therefore, Parallal animations are generated by aggregating the targets for the keyframes, and executing them together.

eg: Keyframe n at ms300 = { UIComponent1.x = 300; UIComponent2.y = 300 }