[PATCH] Speculatively instantiate archive members

[Simon Atanasyan]

================
Comment at: lib/ReaderWriter/FileArchive.cpp:274
@@ +273,3 @@
+  mutable std::map<const char *, std::future<const File *>> _preloaded;
+  mutable std::vector<std::unique_ptr<std::promise<const File *>>> _promises;
+  mutable std::mutex _mutex;
----------------
ruiu wrote:
> atanasyan wrote:
> > Can we store promises directly and do not use `unique_ptr` wrapper? Though I did not test the following code, it compiled successfully. Does it have a sense?
> > 
> > ```
> > // Instantiate the member
> > _promises.emplace_back();
> > auto &promise = _promises.back();
> > _preloaded[memberStart] = promise.get_future();
> >                                                
> > group.spawn([this, &promise, ci] {
> >   std::unique_ptr<File> result;
> >   if (instantiateMember(ci, result)) {
> >     promise.set_value(nullptr);
> >     return;
> >   }
> >   promise.set_value(result.release());
> > });
> > 
> > [...]
> > 
> > mutable std::vector<std::promise<const File *>> _promises;
> > ```
> I think promises created here need to be deleted when it's no longer needed. Your code wouldn't delete promises, no?
They will be destroyed at the same time with the `_promises` container as any other types own destructor and stored in the `std::vector`.

http://reviews.llvm.org/D7015

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