This is a significant change to the upb_stream
protocol, and should hopefully be the last
significant change.
All callbacks are now registered ahead-of-time
instead of having delegated callbacks registered
at runtime, which makes it much easier to
aggressively optimize ahead-of-time (like with a
JIT).
Other impacts of this change:
- You no longer need to have loaded descriptor.proto
as a upb_def to load other descriptors! This means
the special-case code we used for bootstrapping is
no longer necessary, and we no longer need to link
the descriptor for descriptor.proto into upb.
- A client can now register any upb_value as what
will be delivered to their value callback, not
just a upb_fielddef*. This should allow for other
clients to get more bang out of the streaming
decoder.
This change unfortunately causes a bit of a performance
regression -- I think largely due to highly
suboptimal code that GCC generates when structs
are returned by value. See:
http://blog.reverberate.org/2011/03/19/when-a-compilers-slow-code-actually-bites-you/
On the other hand, once we have a JIT this should
no longer matter.
Performance numbers:
plain.parsestream_googlemessage1.upb_table: 374 -> 396 (5.88)
plain.parsestream_googlemessage2.upb_table: 616 -> 449 (-27.11)
plain.parsetostruct_googlemessage1.upb_table_byref: 268 -> 269 (0.37)
plain.parsetostruct_googlemessage1.upb_table_byval: 215 -> 204 (-5.12)
plain.parsetostruct_googlemessage2.upb_table_byref: 307 -> 281 (-8.47)
plain.parsetostruct_googlemessage2.upb_table_byval: 297 -> 272 (-8.42)
omitfp.parsestream_googlemessage1.upb_table: 423 -> 410 (-3.07)
omitfp.parsestream_googlemessage2.upb_table: 679 -> 483 (-28.87)
omitfp.parsetostruct_googlemessage1.upb_table_byref: 287 -> 282 (-1.74)
omitfp.parsetostruct_googlemessage1.upb_table_byval: 226 -> 219 (-3.10)
omitfp.parsetostruct_googlemessage2.upb_table_byref: 315 -> 298 (-5.40)
omitfp.parsetostruct_googlemessage2.upb_table_byval: 297 -> 287 (-3.37)
ParsePartial does not check that required fields are set, which upb
also currently does not do.
This sped up proto2 reflection by 40%, but upb is still 7x faster in
a comparable test (instead of 11x, like before).
The symtab that contains them is now hidden, and
you can look them up by name but there is no access
to the symtab itself, so there is no risk of
mutating it (by extending it, adding other defs
to it, etc).
Josh Haberman
Joshua Haberman