Synchronously Wait for Message in Web-Worker

问题

Is there some way to synchronously wait for or check for a new message in a web-worker?

I have a large complicated body of code (compiled LLVM from emscripten) that I cannot refactor around callbacks.

I need to make sure that code after a certain line doesn't execute until I receive and handle a message from the UI-thread. If I block with a while-loop, the event-loop never runs so I can't receive messages.

回答1:

No, unfortunately. There was some discussion of adding a way to block on a message from the parent page, but it went nowhere. I'll see if I can dig up the relevant mailing list thread.

回答2:

Can you break the sequence as follow without refactoring?

wrk.onmessage = function(e) {
    if (e.data.step === 'initial input') {
        doInitialWork(e.data.inputs)
    } else if (e.data.step === 'ui input') {
        doTheRest(e.data.uiData)
    }
}

The onmessage event will be blocked until the initial step execution stack is complete and the critical ui bits will only launch when and if the info is available.

回答3:

A crude hack to do this could be to use a synchronous API, such as the FileSystem API, and use a temporary file as a synchronising mechanism.

In your example, the emscripten code could issue a synchronous read on a file, while the UI thread writes to the same file, effectively unblocking the worker.

来源：https://stackoverflow.com/questions/10590213/synchronously-wait-for-message-in-web-worker