Hi, On 30 September 2015 at 16:59, Derek Foreman <der...@osg.samsung.com> wrote: > Having an invalid serial number is quite useful - for example, we can > have protocol requests that optionally take a serial number or 0 > instead of having two similar requests. > > Signed-off-by: Derek Foreman <der...@osg.samsung.com> > --- > > Well, let's see where this goes ;) > > I've seen a few times now when having an invalid serial number would be > helpful, is it too late to do this? Are we going to break anything? > > Anything currently doing math on serial numbers can be wrong by one if one > of the serial numbers has wrapped around - this probably doesn't matter? > > I do wonder if we should have a wl_serial_compare() as part of wayland > but the semantics are tricky (a big serial and a small serial may actually > have happened quite close to eachother if the small happened after a > wrap around). > > I think the usual comparisons of interest are equality and "is A less than B > within (arbitrary distance to compensate for wrap-around)". I think strcmp() > like semantics won't necessarily be good here because we don't usually need > something to tell us "b happened before a", more "these almost certainly > happened in the order specified in the function call". > > Where do we go from here?
From the IRC discussion way back when: 20:27 < krh> if we do need to make a new serial, I'd much prefer to have it be 1 << 31 20:27 < krh> and then just restrict normal serial numbers space to 0 - (1<<31 - 1) 20:28 < krh> so that serial number increment is just serial = (serial + 1) & 0x7fffffff I have no relevant opinion on the matter, but I guess that 0x80000000 (or 0xffffffff) is a much more obviously invalid serial number than 0, which could also just be the victim of something uninitialised. A helper would be nice, though like you say I think it has to be directional/multi-return (older inc. wraparound? identical? newer/error? invalid?). It'd probably be best to do that inside an active user and only then shuffle it into Wayland. So, with the change to a different serial, and a note in documentation somewhere that any extension relying on the invalid-serial behaviour must itself explicitly document that: Acked-by: Daniel Stone <dani...@collabora.com> Cheers, Daniel _______________________________________________ wayland-devel mailing list wayland-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/wayland-devel
