On Mon, Aug 19, 2019 at 10:25 AM Yusuke Suzuki <ysuz...@apple.com> wrote:
> Hello WebKit folks! > > I would like to announce that I’ve just landed the patch which introduces > `WTF::makeUnique<T>` and `WTF::makeUniqueWithoutFastMallocCheck<T>` in > https://trac.webkit.org/changeset/248846. > They are drop-in-replacement to std::make_unique<T>, and we should not use > std::make_unique<T> after that patch is introduced. > I’m planning to add cpplint check for `std::make_unique` to avoid the use > of that. > > The motivation behind this change is the following. > > 1. Our typical way of allocating heap memory is three-fold. Using > containers (Vector etc.), RefCounted, and std::unique_ptr. > 2. Containers and RefCounted are covered well by FastMalloc. > 3. But std::unique_ptr case, we missed using FastMalloc in many places so > far. > > Even in very recently written code, we missed FastMalloc annotation. For > example, we sometimes create a data structure just like a struct, and > allocate it with make_unique. > > struct XXXData { > ... > }; > > m_data = std::make_unique<XXXData>(); > > We missed WTF_MAKE_STRUCT_FAST_ALLOCATED annotation in XXXData so > frequently so that the allocation of XXXData ends up being allocated from > system-malloc. > > This WTF::makeUnique adds one `static_assert` over std::make_unique: the > static_assert ensures T is FastMalloced or IsoHeap-allocated. > Otherwise, we see compile-error. > Could WTF::makeUnique simply use FastMalloc by default? We could then remove most of these messy annotations. This would require replacing std::unique_ptr with a type that knows how to free the objects correctly (bring back OwnPtr!) but that doesn't seem like a big deal. It wouldn't play well with mixed use of OwnPtr and new/delete but that should be avoided in any case. antti > This mechanism surprisingly found so many classes that do not have > WTF_MAKE_FAST_ALLOCATED / WTF_MAKE_STRUCT_FAST_ALLOCATED in our code base. > > If the type T comes from ThirdParty and if we cannot annotate T with > FAST_ALLOCATED, we can use WTF::makeUniqueWithoutFastMallocCheck explicitly > as a fallback. > > More detailed explanation behind why we took this design (instead of > allocating FastMalloced-memory automatically when using makeUnique<T>() > etc.) is described in ChangeLog in > https://trac.webkit.org/changeset/248846/webkit. > I already annotated missed structs / classes with WTF_MAKE_FAST_ALLOCATED > in https://trac.webkit.org/changeset/248762. So, now I think 99% of > allocations in WebKit-itself are handled well by FastMalloc. > > -Yusuke > _______________________________________________ > webkit-dev mailing list > webkit-dev@lists.webkit.org > https://lists.webkit.org/mailman/listinfo/webkit-dev >
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