upb_msg was trying to be general enough that it could either live in
an arena or be allocated with malloc()/free(). This was too much
complexity for too little benefit. We should commit to just saying
that upb_msg is arena-only.
I also ripped out the code to glue upb_msg to the existing
handlers-based encoder/decoder. upb_msg has its own, small, simple
encoder/decoder. I'm trying to whittle down upb_msg to a small
and simple core.
I updated the Lua extension for these changes. Lua needs some more
work to properly create arenas per message. For now I just created
a single global arena.
Also includes an implementation of the conformance tests
to display what the API usage will be like.
There is still a lot to do, and things that are broken (oneofs,
repeated fields, etc), but it's a good start.
This involves:
- remove upb_msglayout -> upb_msgfactory dependency.
- remove upb_msglayout -> upb_msgdef dependency (in progress).
- make upb_msglayout use a representation that can be
statically initialized by generated code.
The goal here is that upb_msglayout becomes a kind of "descriptor
lite": it contains enough data to parser and serialize protobufs
and manipulate a upb_msg in memory, while being far smaller and
simpler than a full descriptor. It also does not include field
names, which can be a benefit for applications that do not want
to leak field names.
Generated code can then create a upb_msglayout, and do most things
without ever needing to construct full descriptors/defs if they
don't want to.
Many things have changed and been simplified.
The memory-management story for upb_def and upb_handlers
is much more robust; upb_def and upb_handlers should be
fairly stable interfaces now. There is still much work
to do for the runtime component (upb_sink).
Many improvements, too many to mention. One significant
perf regression warrants investigation:
omitfp.parsetoproto2_googlemessage1.upb_jit: 343 -> 252 (-26.53)
plain.parsetoproto2_googlemessage1.upb_jit: 334 -> 251 (-24.85)
25% regression for this benchmark is bad, but since I don't think
there's any fundamental design issue that caused it I'm going to
go ahead with the commit anyway. Can investigate and fix later.
Other benchmarks were neutral or showed slight improvement.
Includes are now via upb/foo.h.
Files specific to the protobuf format are
now in upb/pb (the core library is concerned
with message definitions, handlers, and
byte streams, but knows nothing about any
particular serializationf format).
I'm realizing that basically all upb objects
will need to be refcounted to be sharable
across languages, but *not* messages which
are on their way out so we can get out of
the business of data representations.
Things which must be refcounted:
- encoders, decoders
- handlers objects
- defs
Startseq/endseq handlers are called at the beginning
and end of a sequence of repeated values. Protobuf
does not really have direct support for this (repeated
primitive fields do not delimit "begin" and "end" of
the sequence) but we can infer them from the bytestream.
The benefit of supporting them explicitly is that they
get their own stack frame and closure, so we can avoid
having to find the array's address over and over and
deciding if we need to initialize it.
This will also pave the way for better support of JSON,
which does have explicit "startseq/endseq" markers: [].
This doesn't reflect any material change in
how I will be working on upb, and I have no
problem making this change. It's still open
source under the BSD license, and I'll still
be working on it well beyond the hours that
constitute a normal job.
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)
Joshua Haberman
Bo Yang
Josh Haberman
Joshua Haberman