X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=folly%2FIndexedMemPool.h;h=275d441cc0e646746bd1f142f257853050d17d7e;hb=c5184205d39da8e99b3f61b53b38e873f4d06c7c;hp=1fa430823b4bc9bded795054e7bcb067dd4e2557;hpb=41365ea66d92749ba78f73d60325e5447beb04ab;p=folly.git diff --git a/folly/IndexedMemPool.h b/folly/IndexedMemPool.h index 1fa43082..275d441c 100644 --- a/folly/IndexedMemPool.h +++ b/folly/IndexedMemPool.h @@ -22,13 +22,14 @@ #include #include #include +#include #include #include #include // Ignore shadowing warnings within this file, so includers can use -Wshadow. -#pragma GCC diagnostic push -#pragma GCC diagnostic ignored "-Wshadow" +FOLLY_PUSH_WARNING +FOLLY_GCC_DISABLE_WARNING("-Wshadow") namespace folly { @@ -37,6 +38,65 @@ template struct IndexedMemPoolRecycler; } +template < + typename T, + bool EagerRecycleWhenTrivial = false, + bool EagerRecycleWhenNotTrivial = true> +struct IndexedMemPoolTraits { + static constexpr bool eagerRecycle() { + return std::is_trivial::value ? EagerRecycleWhenTrivial + : EagerRecycleWhenNotTrivial; + } + + /// Called when the element pointed to by ptr is allocated for the + /// first time. + static void initialize(T* ptr) { + if (!eagerRecycle()) { + new (ptr) T(); + } + } + + /// Called when the element pointed to by ptr is freed at the pool + /// destruction time. + static void cleanup(T* ptr) { + if (!eagerRecycle()) { + ptr->~T(); + } + } + + /// Called when the element is allocated with the arguments forwarded from + /// IndexedMemPool::allocElem. + template + static void onAllocate(T* ptr, Args&&... args) { + static_assert( + sizeof...(Args) == 0 || eagerRecycle(), + "emplace-style allocation requires eager recycle, " + "which is defaulted only for non-trivial types"); + if (eagerRecycle()) { + new (ptr) T(std::forward(args)...); + } + } + + /// Called when the element is recycled. + static void onRecycle(T* ptr) { + if (eagerRecycle()) { + ptr->~T(); + } + } +}; + +/// IndexedMemPool traits that implements the lazy lifecycle strategy. In this +/// strategy elements are default-constructed the first time they are allocated, +/// and destroyed when the pool itself is destroyed. +template +using IndexedMemPoolTraitsLazyRecycle = IndexedMemPoolTraits; + +/// IndexedMemPool traits that implements the eager lifecycle strategy. In this +/// strategy elements are constructed when they are allocated from the pool and +/// destroyed when recycled. +template +using IndexedMemPoolTraitsEagerRecycle = IndexedMemPoolTraits; + /// Instances of IndexedMemPool dynamically allocate and then pool their /// element type (T), returning 4-byte integer indices that can be passed /// to the pool's operator[] method to access or obtain pointers to the @@ -54,13 +114,17 @@ struct IndexedMemPoolRecycler; /// there won't be an ABA match due to the element being overwritten with /// a different type that has the same bit pattern. /// -/// IndexedMemPool has two object lifecycle strategies. The first -/// is to construct objects when they are allocated from the pool and -/// destroy them when they are recycled. In this mode allocIndex and -/// allocElem have emplace-like semantics. In the second mode, objects -/// are default-constructed the first time they are removed from the pool, -/// and deleted when the pool itself is deleted. By default the first -/// mode is used for non-trivial T, and the second is used for trivial T. +/// The object lifecycle strategy is controlled by the Traits parameter. +/// One strategy, implemented by IndexedMemPoolTraitsEagerRecycle, is to +/// construct objects when they are allocated from the pool and destroy +/// them when they are recycled. In this mode allocIndex and allocElem +/// have emplace-like semantics. In another strategy, implemented by +/// IndexedMemPoolTraitsLazyRecycle, objects are default-constructed the +/// first time they are removed from the pool, and deleted when the pool +/// itself is deleted. By default the first mode is used for non-trivial +/// T, and the second is used for trivial T. Clients can customize the +/// object lifecycle by providing their own Traits implementation. +/// See IndexedMemPoolTraits for a Traits example. /// /// IMPORTANT: Space for extra elements is allocated to account for those /// that are inaccessible because they are in other local lists, so the @@ -89,8 +153,7 @@ template < uint32_t NumLocalLists_ = 32, uint32_t LocalListLimit_ = 200, template class Atom = std::atomic, - bool EagerRecycleWhenTrivial = false, - bool EagerRecycleWhenNotTrivial = true> + typename Traits = IndexedMemPoolTraits> struct IndexedMemPool : boost::noncopyable { typedef T value_type; @@ -103,12 +166,6 @@ struct IndexedMemPool : boost::noncopyable { LocalListLimit = LocalListLimit_ }; - - static constexpr bool eagerRecycle() { - return std::is_trivial::value - ? EagerRecycleWhenTrivial : EagerRecycleWhenNotTrivial; - } - // these are public because clients may need to reason about the number // of bits required to hold indices from a pool, given its capacity @@ -149,10 +206,8 @@ struct IndexedMemPool : boost::noncopyable { /// Destroys all of the contained elements ~IndexedMemPool() { - if (!eagerRecycle()) { - for (uint32_t i = size_; i > 0; --i) { - slots_[i].~Slot(); - } + for (uint32_t i = maxAllocatedIndex(); i > 0; --i) { + Traits::cleanup(&slots_[i].elem); } munmap(slots_, mmapLength_); } @@ -165,25 +220,35 @@ struct IndexedMemPool : boost::noncopyable { return capacityForMaxIndex(actualCapacity_); } + /// Returns the maximum index of elements ever allocated in this pool + /// including elements that have been recycled. + uint32_t maxAllocatedIndex() const { + // Take the minimum since it is possible that size_ > actualCapacity_. + // This can happen if there are multiple concurrent requests + // when size_ == actualCapacity_ - 1. + return std::min(uint32_t(size_), uint32_t(actualCapacity_)); + } + /// Finds a slot with a non-zero index, emplaces a T there if we're /// using the eager recycle lifecycle mode, and returns the index, - /// or returns 0 if no elements are available. + /// or returns 0 if no elements are available. Passes a pointer to + /// the element to Traits::onAllocate before the slot is marked as + /// allocated. template uint32_t allocIndex(Args&&... args) { - static_assert(sizeof...(Args) == 0 || eagerRecycle(), - "emplace-style allocation requires eager recycle, " - "which is defaulted only for non-trivial types"); auto idx = localPop(localHead()); - if (idx != 0 && eagerRecycle()) { - T* ptr = &slot(idx).elem; - new (ptr) T(std::forward(args)...); + if (idx != 0) { + Slot& s = slot(idx); + Traits::onAllocate(&s.elem, std::forward(args)...); + markAllocated(s); } return idx; } /// If an element is available, returns a std::unique_ptr to it that will /// recycle the element to the pool when it is reclaimed, otherwise returns - /// a null (falsy) std::unique_ptr + /// a null (falsy) std::unique_ptr. Passes a pointer to the element to + /// Traits::onAllocate before the slot is marked as allocated. template UniquePtr allocElem(Args&&... args) { auto idx = allocIndex(std::forward(args)...); @@ -194,9 +259,6 @@ struct IndexedMemPool : boost::noncopyable { /// Gives up ownership previously granted by alloc() void recycleIndex(uint32_t idx) { assert(isAllocated(idx)); - if (eagerRecycle()) { - slot(idx).elem.~T(); - } localPush(localHead(), idx); } @@ -230,7 +292,7 @@ struct IndexedMemPool : boost::noncopyable { /// Returns true iff idx has been alloc()ed and not recycleIndex()ed bool isAllocated(uint32_t idx) const { - return slot(idx).localNext == uint32_t(-1); + return slot(idx).localNext.load(std::memory_order_acquire) == uint32_t(-1); } @@ -239,8 +301,8 @@ struct IndexedMemPool : boost::noncopyable { struct Slot { T elem; - uint32_t localNext; - uint32_t globalNext; + Atom localNext; + Atom globalNext; Slot() : localNext{}, globalNext{} {} }; @@ -346,7 +408,7 @@ struct IndexedMemPool : boost::noncopyable { void globalPush(Slot& s, uint32_t localHead) { while (true) { TaggedPtr gh = globalHead_.load(std::memory_order_acquire); - s.globalNext = gh.idx; + s.globalNext.store(gh.idx, std::memory_order_relaxed); if (globalHead_.compare_exchange_strong(gh, gh.withIdx(localHead))) { // success return; @@ -359,7 +421,8 @@ struct IndexedMemPool : boost::noncopyable { Slot& s = slot(idx); TaggedPtr h = head.load(std::memory_order_acquire); while (true) { - s.localNext = h.idx; + s.localNext.store(h.idx, std::memory_order_release); + Traits::onRecycle(&slot(idx).elem); if (h.size() == LocalListLimit) { // push will overflow local list, steal it instead @@ -383,8 +446,11 @@ struct IndexedMemPool : boost::noncopyable { uint32_t globalPop() { while (true) { TaggedPtr gh = globalHead_.load(std::memory_order_acquire); - if (gh.idx == 0 || globalHead_.compare_exchange_strong( - gh, gh.withIdx(slot(gh.idx).globalNext))) { + if (gh.idx == 0 || + globalHead_.compare_exchange_strong( + gh, + gh.withIdx( + slot(gh.idx).globalNext.load(std::memory_order_relaxed)))) { // global list is empty, or pop was successful return gh.idx; } @@ -398,10 +464,9 @@ struct IndexedMemPool : boost::noncopyable { if (h.idx != 0) { // local list is non-empty, try to pop Slot& s = slot(h.idx); - if (head.compare_exchange_strong( - h, h.withIdx(s.localNext).withSizeDecr())) { + auto next = s.localNext.load(std::memory_order_relaxed); + if (head.compare_exchange_strong(h, h.withIdx(next).withSizeDecr())) { // success - s.localNext = uint32_t(-1); return h.idx; } continue; @@ -415,21 +480,15 @@ struct IndexedMemPool : boost::noncopyable { // allocation failed return 0; } - // default-construct it now if we aren't going to construct and - // destroy on each allocation - if (!eagerRecycle()) { - T* ptr = &slot(idx).elem; - new (ptr) T(); - } - slot(idx).localNext = uint32_t(-1); + Traits::initialize(&slot(idx).elem); return idx; } Slot& s = slot(idx); + auto next = s.localNext.load(std::memory_order_relaxed); if (head.compare_exchange_strong( - h, h.withIdx(s.localNext).withSize(LocalListLimit))) { + h, h.withIdx(next).withSize(LocalListLimit))) { // global list moved to local list, keep head for us - s.localNext = uint32_t(-1); return idx; } // local bulk push failed, return idx to the global list and try again @@ -441,6 +500,10 @@ struct IndexedMemPool : boost::noncopyable { auto stripe = detail::AccessSpreader::current(NumLocalLists); return local_[stripe].head; } + + void markAllocated(Slot& slot) { + slot.localNext.store(uint32_t(-1), std::memory_order_release); + } }; namespace detail { @@ -468,4 +531,4 @@ struct IndexedMemPoolRecycler { } // namespace folly -# pragma GCC diagnostic pop +FOLLY_POP_WARNING