[PATCH] Some infrastructure work for virtual file system (now on phab)

[Manuel Klimek]

On Thu, Feb 27, 2014 at 1:37 PM, Manuel Klimek <klimek at google.com> wrote:

> On Wed, Feb 12, 2014 at 11:22 PM, Douglas Gregor <dgregor at apple.com>wrote:
>
>>
>> On Feb 12, 2014, at 2:21 PM, Rafael Ávila de Espíndola <
>> rafael.espindola at gmail.com> wrote:
>>
>> >
>> >
>> > ================
>> > Comment at: include/clang/Basic/FileManager.h:122
>> > @@ -121,2 +121,3 @@
>> > class FileManager : public RefCountedBase<FileManager> {
>> > +  IntrusiveRefCntPtr<AbstractFileSystem> FS;
>> >   FileSystemOptions FileSystemOpts;
>> > ----------------
>> > Why is the reference count necessary? Given its nature I would expect
>> the FS to outlive the file manger, in which case the FileManager could have
>> just a pointer to the FileSystem.
>>
>>
>> The FS is likely to get shared among a number of FileManagers in
>> different compiler instances within a thread. Yes, we could try to
>> establish and maintain relationships among these, but it’s simpler and
>> costs us effectively nothing to make this ref-counted.
>>
>
> Just to follow up:
> I found one more argument against making this ref-counted:
> The constructor of FileManager that uses the default "real" file system is
> now actively thread hostile (you cannot create a FileManager per thread
> without locking). I think that's rather unexpected.
>

And even worse, because RealFileSystem is an implementation detail, and
getRealFileSystem returns a ref counted pointer by value, I cannot see any
way to get me a RealFileSystem without locking.

Cheers,
/Manuel
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