On Feb 12, 2014, at 2:41 PM, Rafael Espíndola <[email protected]>
wrote:
>> Look at CompilerInstance. It has a number of IntrusiveRefCntPtr’s that exist
>> because we consistently ran into problems with other clients needing to hold
>> onto these core, cooperating objects for longer than the given
>> CompilerInstance. ASTUnit is one of the major culprits here, but it’s not
>> the only one.
>
> Yes. I am not suggesting for CompilerInstance to own the FS. That
> would be really odd.
Unique ownership would be odd; shared ownership is not.
>>> But is it not the case that
>>> * A clang process will always use a single FS.
>>> * The decision as to which to use can happen just after parsing the
>>> command line arguments?
>>
>>
>> We may spawn a number of Clang invocations within the same thread to build
>> modules from headers, and they all need to share the same FS.
>
> Which perfectly matches to having a FS being constructed before any
> CompilerInstance and each CompilerInstance has a pointer to the same
> FS. In other words, a FS is a singleton in a clang process, no?
I have no idea what you mean by “clang process”. You don’t actually mean the
whole process itself, because FS isn’t thread-safe and therefore isn’t some
kind of global singleton. Plus, different invocations of the compiler may have
different FS, so making this a global singleton is completely wrong . Any
thread-specific “singleton” would be wrong for the same reasons.
I guess we could toss the responsibility for managing the FS instance up to
“the client”, but which clients are those? Some clients will want to
pre-populate and widely share a FS, while others just want CompilerInvocation
to create the FS if the command-line arguments passed through to it require the
FS. We want to support the former without complicating the latter.
IntrusiveRefCntPtr makes that easy to do with completely acceptable overhead.
- Doug
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