Allow IpcSharedMemory to support a take function that might be more efficient

[Narfinger]

IpcSharedMemory currently only supports deref to get the element out of it. This leads to a lot of potential copies.
On some platforms these copies seem to be unavoidable but for inprocess we can actually take the already allocated vector.

For an example in servo this decreases the overall time of copying bytes from roughly 2.5ms from 117ms.

Signed-off-by: Narfinger Narfinger@users.noreply.github.com

[glyn]

Any chance of adding a test(s)?

Also, I'd like to understand the context better. What are the non-development usecases for single process Servo?

[Narfinger]

Yes I can try to add a test.
Single process servo is used on small embedders. Some of them don't want to spend the resources on different processes, some of them make spawning different processes very difficult.

[glyn]

LGTM and thanks for the test.

[glyn]

IpcSharedMemory currently only supports deref to get the element out of it. This leads to a lot of potential copies. On some platforms these copies seem to be unavoidable but for inprocess we can actually take the already allocated vector.

For an example in servo this decreases the overall time of copying bytes from roughly 2.5ms from 117ms.

How many bytes were copied? Presumably the time reduced from 117ms to 2.5ms?

[Narfinger]

I don't have the report anymore and with the changes it would be a bit difficult to get the numbers again.
But the above was total time spend on the copying the bytes for this specific function over a run on servo for inprocess mode.