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

[Manuel Klimek]

Yep that addresses my concerns...
On Mar 3, 2014 4:47 PM, "Ben Langmuir" <blangmuir at apple.com> wrote:

>
> On Feb 27, 2014, at 8:00 AM, Argyrios Kyrtzidis <kyrtzidis at apple.com>
> wrote:
>
>
> On Feb 27, 2014, at 4:43 AM, Manuel Klimek <klimek at google.com> wrote:
>
> 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.
>
>
> I propose we introduce a RefCountedBase that is using atomic reference
> count (either change RefCountedBase or add a new class), and have
> FileSystem use that.
>
>
> Makes sense to me.  Manuel, does this address your concern?
>
> Ben
>
> Cheers,
> /Manuel
>
>
>
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