Parallel programming / Synchronization using JavaS

问题:

Are there any synchronization primitives like Barriers, Semaphors, Locks, Monitors, ... available in JavaScript / Web Workers or is there some library available empowering me to make use of such things (I'm thinking of something like java.util.concurrent in Java)?

Do Workers have obscure properties which differentiate them from Threads (can they share memory with the main thread, for example)? Is there some kind of limit how many workers can be spawned (like, for security reasons or something...)? Do I have to take special care of something?

回答1:

Web workers don't have a concept of shared memory; all messages that are passed between threads are copied. With that being said, you don't have Barriers, Semaphores, Locks, and Monitors, because you don't need them in the web worker model.

The concept of shared memory was proposed back in Feb 2011 but the status is now wontfix due to developer complexity => https://lists.webkit.org/pipermail/webkit-unassigned/2011-February/287595.html

There is also a nice blurb about web workers here. http://blogs.msdn.com/b/ie/archive/2011/07/01/web-workers-in-ie10-background-javascript-makes-web-apps-faster.aspx

Hope this helps

回答2:

In short: no there aren't any synchronization primitives in javascript but there is also no need for them since JavaScript is inherently single threaded :). Workers can only access there own scope (no dom manipulation just calculations) and send messages to the main ui thread where the normal js resides. I'm not sure about the maximum count of workers but there sure is a limit, you could try it out in a browser :)

Hope this helps!

回答3:

Here you have a library based on jQuery made for that purpose: http://www.megiddo.ch/jcon-q-rency.

Of course the model is not really identical to java.util.concurrent since we are not dealing with the same environment, as explained in the other answers...