The DAL plugin-based virtualcamera shares data between OBS and the
plugin using an IOSurface. IOSurface locks are necessary to ensure
race conditions between data generation (OBS side) and consumption
(virtual camera side) and also that an IOSurface is not offloaded to
GPU memory when it is indeed needed in CPU memory.
Also moves the invalidation of the NSMachPort for the frames to after
the IOSurface data has been converted into a pixelbuffer and added to
the frame queue of the virtual camera, as an early invalidation will
cut off access to the pixel data shared with the DAL plugin.
Apple Silicon-based Macs have a unified memory architecture, as such
an IOSurface will always be available in memory accessible to the CPU
and GPU (and an off-load of the IOSurface will not take place).
eGPUs are not supported on Apple Silicon-based Macs either, so an
IOSurface lock to ensure data is copied back to CPU memory is not
necessary.
Without invalidating the mach port used for sharing the IOSurface
between OBS and the application displaying the virtual camera output,
IOKit seems to run into the issue of receiving "shared" mach ports,
possibly because of port exhaustion. IOKit requires a "new" port
however and crashes upon that error otherwise.
Co-authored-by: Steven Michaud <smichaud@pobox.com>
This issue primarily seems to affect Intel-based Macs without unified
memory: While an IOSurface is supposed to be shared via a mach port
with other processes, each process needs to lock the surface during
access (as is common with other shared resources).
Apple Silicon-based Macs seem to be less affected as a switch between
GPU and CPU memory (which can happen dynamically for IOSurfaces) would
still point to the same unified memory.
This change fixes a memory leak in the mac-virtualcam plugin that causes
OBS to not release the CVPixelBuffers (and underlying IOSurfaces)
it emits to the virtual camera consumers.
Pull request https://github.com/obsproject/obs-studio/pull/6573 (Avoid
transcoding where possible) updated the mac-virtualcam to share the
virtual camera feed with other processes via IOSurfaces.
Although the changes work correctly, users have observed that OBS memory
usage keeps increasing when the virtual camera is active until OBS runs
out of memory or the consuming application is closed.
See the report by @SciTechNick for more information:
https://github.com/obsproject/obs-studio/pull/6573#issuecomment-1161979765
After some debugging, I have found that the plugin is leaking Mach ports
associated with IOSurfaces, preventing them from being re-used. The
previous approach using `NSMachPort` does not seem to properly release
the Mach port allocated via `CVPixelBufferGetIOSurface` and
`IOSurfaceLookupFromMachPort`. Instead, we must explicitly deallocate
the port using `mach_port_deallocate`.
I have tested the changes on a Macbook Pro (M1) running macOS Monterey with
Google Chrome, Zoom, and Cameo. OBS shows no signs of memory leakage
after multiple minutes.
This change updates the virtual camera implementation on macOS to
utilize IOSurface to share the output feed with the virtual cameras.
By using IOSurface, we remove the need for copying the frames across
multiple buffers, since they can be shared across Mach connections using
zero-copy.
