[azakai]

Message passing can be very efficient for some tasks. But there are cases where it is hard to optimize out copying.

For example, let's say you're running a raytracer, and you have several web workers each render a slice of the frame. Then each worker can transfer back their output to the "main" thread (using existing typed array transfer). But the main thread now has several separate typed arrays, one from each worker. If it wants to combine them all into one contiguous typed array, it needs to do a copy of the data, which is something we'd like to avoid.

In this case, what you really want is to have a single contiguous typed array, and let each worker write to a slice of it. Something similar to that would be possible in what is proposed in the blogpost.

[justincormack]

Copying in cache is very fast now. Spending time aboiding copies is no longer always a win like it used to be.

[bzbarsky]

In cache is key, though.

Decoded image data is 4 bytes per pixel, so a raytraced image of any sort of reasonable size would barely (if at all) fit in L3 cache even on modern processors. And you need to fit both the source and the destination, right?