ilya-biryukov added a comment.
In https://reviews.llvm.org/D51475#1219184, @ioeric wrote:
> The index loading can be slow. When using LLVM YAML index, I need to wait for
> >10s before clangd starts giving me anything useful. We could potentially
> speed up loading (e.g. replacing yaml), but the index can be arbitrary large.
> I think it's an improvement in general to be able to get clangd running
> before index is loaded.
I would trade-off those 10 seconds for giving consistent experience (i.e.
avoiding confusing the users with different modes of completion (with and
without index, etc.)).
But not terribly opposed to that.
================
Comment at: clangd/tool/ClangdMain.cpp:86
+ return nullptr;
+ Index = AsyncLoad.get();
+ return Index.get();
----------------
ioeric wrote:
> ilya-biryukov wrote:
> > I believe is a data race (multiple threads may run this line concurrently).
> > You would want some synchronization around this, `std::shared_future` could
> > be a good fit
> Nice catch.
>
> I am a bit hesitated about using `shared_future` though. It could potentially
> get rid of the mutex but would require much more careful use. For example,
> `Index` can be set to the same value repeatedly, which makes me a bit nervous.
The following pattern should give proper results:
```
class AsyncIndex : public Index {
public:
AsyncIndex(std::shared_future<Index> IndexFut);
//....
private;
const SymbolIndex *index() const {
if (IndexFut.wait(0) != ready)
return nullptr;
return &IndexFut.get();
}
std::shared_future<Index>IndexFut;
};
AsyncIndex AI(std::async([]() { /* load the index here */ return Index; });
```
Repository:
rCTE Clang Tools Extra
https://reviews.llvm.org/D51475
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