Set SO_REUSEPORT on multicast input sockets for Apple platforms#6471
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Set SO_REUSEPORT on multicast input sockets for Apple platforms#6471keskinonur wants to merge 1 commit into
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OpenAndBindInputSocket() only enabled SO_REUSEPORT for QNX (eProsima#272, eProsima#350). On Darwin, SO_REUSEADDR alone is not enough for two processes to share a UDP multicast port: the second bind fails with EADDRINUSE, the failure is not surfaced, and that DomainParticipant never receives SPDP multicast. Extend the existing QNX conditional to __APPLE__ in UDPv4 and UDPv6 transports. Linux intentionally unchanged: SO_REUSEPORT there load-balances datagrams instead of duplicating delivery. Signed-off-by: Onur Keskin <onur@bilims.com>
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Description
OpenAndBindInputSocket()setsSO_REUSEPORTon multicast input sockets only for QNX (#272, #350). Apple platforms (macOS/Darwin) have the same BSD requirement: withSO_REUSEADDRalone, the second process on a host that binds the SPDP multicast port getsEADDRINUSE, the failure is swallowed, and that participant never receives discovery multicast — it silently sees an empty domain while unicast ports bind fine.This PR extends the existing QNX conditional to
__APPLE__in bothUDPv4Transport.cppandUDPv6Transport.cpp.Linux intentionally unchanged:
SO_REUSEPORTon Linux load-balances datagrams across sockets rather than duplicating them, which would break multi-process discovery instead of fixing it.Fixes #6470
Motivation
Real-world failure: two librealsense processes using an Intel RealSense D555 Ethernet camera on macOS — whichever process binds the multicast port second never discovers the camera. Socket-level repro (no DDS needed) in the linked issue shows
EADDRINUSEfor the second bind withoutSO_REUSEPORTand full duplicate delivery to both sockets with it.Verified on macOS / Apple Silicon with a live D555 (RealSense PoE camera): without this patch a second concurrently-running process never discovers the remote participant; with it, second-process discovery works.
Full disclosure: our downstream stack also serializes near-simultaneous participant creation — a separate, rarer effect noted in #6470 as out of scope; an end-to-end 22/22 dual-process figure we report elsewhere was measured with both measures in place. The socket-level repro in the issue isolates what this patch alone fixes.
Contributor Checklist
Signed-off-by: Onur Keskin <keskinonur@me.com>)Backport
Please consider backporting to maintained 2.x branches (librealsense currently pins
v2.10.4/v2.10.4-realsense). The change is a one-line platform guard extension plus a short comment.