This allows buffers to be shared between different asynchronous operations.
Once all users no longer need the buffer, it will be freed.
The motivation for this is being able to stream Wayland clipboard data
asynchronously to multiple clients. The buffer should only be freed after
the clipboard has changed and all ongoing transfer completes.
This changes the method of the memory copy from the host application to
the guest. Instead of performing a full copy from the capture device
into shared memory, and then flagging the new frame, we instead set a
write pointer, flag the client that there is a new frame and then copy
in chunks of 1024 bytes until the entire frame is copied. The client
upon seeing the new frame flag begins to poll at high frequency the
write pointer and upon each update copies as much as it can into the
texture.
This should improve latency but also slightly increase CPU usage on the
client due to the high frequency polling.
