This matches an API already present in proto2
(const DescriptorPool* FileDescriptor::pool()).
However there is a slightly subtle implication here.
In proto2, the relationship between Descriptor and
MessageFactory is 1:many. You can create as many
DynamicMessageFactory instances as you want, and
each one will have its own independent DynamicMessage
prototype and computed layout for the same underlying
Descriptor. In practice the layouts will all be the same,
but one thing that could be distinct is that each can
have its own extension pool, which is a DescriptorPool
that will be searched for extensions when parsing.
In contrast, upb does not have a separate "message
factory" abstraction. That means that each upb_msgdef
has a single distinct layout, in other words a 1:1
correspondence between descriptor and layout. This means
that there is no way to create multiple message types
for the same descriptor that have distinct extension
pools. If you want a different set of extensions, you
must create a separate upb_symtab with a distinct set
of descriptors.
This change further entrenches that upb_filedef:upb_symtab
is a 1:1 relationship. A single upb_filedef cannot be a
member of multiple symbol tables. In practice this was
already true (there is no way to add a single filedef to
multiple symbol tables) but this change codifies this
1:1 relationship.
We used to use a separate "add table" during the upb_symtab_addfile()
operation to make it easier to back out the file if it contained
errors. But this created unnecessary work of re-adding the same symbols
to the main symtab once everything was validated.
Instead we directly add symbols to the main symbols table. If there is
an error in validation, we remove precisely the set of symbols that
were already added.
This also requires using a separate arena for each file. We can fuse
it with the symtab's main arena if the operation is successful.
LoadDescriptor_Upb 61.2µs ± 4% 53.5µs ± 1% -12.50% (p=0.000 n=12+12)
LoadAdsDescriptor_Upb 4.43ms ± 1% 3.06ms ± 0% -31.00% (p=0.000 n=12+12)
LoadDescriptor_Proto2 257µs ± 0% 259µs ± 0% +1.00% (p=0.000 n=12+12)
LoadAdsDescriptor_Proto2 13.9ms ± 1% 13.9ms ± 1% ~ (p=0.128 n=12+12)
* WIP.
* WIP.
* Tests are passing.
* Recover some perf: LIKELY doesn't propagate through functions. :(
* Added some more benchmarks.
* Simplify & optimize upb_arena_realloc().
* Only add owned blocks to the freelist.
* More optimization/simplification.
* Re-fixed the bug.
* Revert unintentional changes to parser.rl.
* Revert Lua changes for now.
* Revert the arena fuse changes for now.
* Added last_size to the arena representation.
* Re-applied Lua changes.
* Implemented upb_arena_fuse().
* Fix the compile by re-ordering statements.
* Improve comments.
* [textformat]: added missing newline when a message opens.
* Added tostring() support to Lua that prints to text format.
Also fixed a gnarly bug that this exposed.
Map parsing/serializing relies on map entries always
having a predictable order. The code that generates
layout was not respecting this in the case of string
keys and primitive values.
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.
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.
* Put oneofs in the same table as fields.
Oneofs and fields are not allowed to have names that conflict,
so we might as well put them all in the same table. This also
allows an efficient operation that looks for both fields and
oneofs in a single lookup.
Added support for OneofDef to Lua to allow testing of this.
* Addressed PR comments.
Joshua Haberman