问题
It seems that we can not get sensor data in the web workers. I wonder the reason behind it. The use case is that I am thinking about getting geolocation data in the worker thread and only send the processed version to the main thread.
For GPS, this post says it is not supported in the worker thread (no reason is given). And I double checked it, navigator.geolocation is not supported in web workers. For accelerator and gyroscope, we have DeviceOrientationEvent and DeviceMotionEvent. But we need to use them through the window object, which is not available to the worker thread. The same situation applies to ambient light event.
So my questions are:
- Why navigator.geolocation is not supported in web workers? I don't see any reason to prevent it in the worker thread. I think there should be no thread safety or security problems.
- Does navigator.geolocation belong to navigator? This looks like a silly question. But I cannot find a good explanation online quickly... Web workers have access to the navigator object. And I am confused why navigation.geolocation is not supported.
- Why don't we have raw sensor readings from accelerator and gyroscope? I understand that the abstracted event is useful. But there are cases we want to use the raw data for processing. I find that PhoneGap provides ways to access raw sensor data, e.g., through navigator.accelerometer. But my understanding is that such API does not belong to the standardized HTML specification.
- What are the related design decisions to decide whether general sensor reading should be supported in the worker thread or not? General sensor reading support in HTML is currently shelved according to W3C Device APIs Working Group. Seeing current sensor support (gps, accelerator, gyro), I think we will get abstracted DOM events. And it is likely to have raw sensor data readings through the navigator object.
回答1:
OK. After reading some Chromium code, I have the answer to my own question 2 now. I still have no answer to the other 3 questions...
Answer to question 2: Does navigator.geolocation belong to navigator?
navigator.geolocation belongs to navigator in the main thread only, but doesn't belong to navigator in the worker thread.
The main reason is that even though the navigator in worker thread looks exactly the same as the one in main thread, those two navigators have independent implementations on the C++ side. That is why navigator.geolocation is not supported in the worker thread.
The related code is in Navigator.idl and WorkerNavigator.idl in Chromium code. You can see that they are two independent interfaces in the .idl files. And they have independent implementations on the C++ side of the binding. Navigator is an attribute of DOMWindow, while WorkerNavigator is an attribute of WorkerGlobalScope.
However, on the JavaScript side, they have the same name: navigator. Well, I understand that the two navigators are in two different scopes, so there is no name conflict. But when I use the APIs in JavaScript, I expect similar behavior on both main and worker threads if they have the same name. That's how the ambiguity happens.
来源：https://stackoverflow.com/questions/21580944/sensor-reading-in-web-worker