How to prevent HTML5 Web Workers from locking up thus correctly responding to messages from parent

Question

Hi guys,

I'm using web workers to do some CPU intensive work but have the requirement that the worker will respond to messages from the parent script while the worker is still processing.

The worker however will not respond to messages while it is locked in a processing loop, and I have not found a way to say poll the message queue. Thus it seems like the only solution is to break processing at an interval to allow any messages in the queue to be serviced.

The obvious options are to use a timer (say with setInterval) however I have read that the minimum delay between firings is quite long (http://ajaxian.com/archives/settimeout-delay) which is unfortunate as it will slow down processing alot.

What are other peoples thoughts on this? I'm going to try have the worker dispatch onmessage to itself at the end of each onmessage, thus effectively implementing one step of the processing loop per event received from itself, but just wanted to see if anyone had any ideas about this.

Thanks,

Answer 1

Hey Steve,

A worker can spawn sub workers. You can have your main worker act as your message queue, and when it receives a request for a long running operation, spawn a sub worker to process that data. The sub worker can then send the results back to the main worker to remove the event from the queue and return the results to the main thread. That way your main worker will always be free to listen for new messages and you have complete control over the queue.

--Nick

Answer 2

Having the same problem I searched the web workers draft and found something in the Processing model section, steps from 9 to 12. As far as I have understood, a worker that starts processing a task will not process another one until the first is completed. So, if you don't care about stopping and resuming a task, nciagra's answer should give better performances than rescheduling each iteration of the task.

Still investigating, though.