struct IndexedMemPoolRecycler;
}
+template <
+ typename T,
+ bool EagerRecycleWhenTrivial = false,
+ bool EagerRecycleWhenNotTrivial = true>
+struct IndexedMemPoolTraits {
+ static constexpr bool eagerRecycle() {
+ return std::is_trivial<T>::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 <typename... Args>
+ 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>(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 <typename T>
+using IndexedMemPoolTraitsLazyRecycle = IndexedMemPoolTraits<T, false, false>;
+
+/// 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 <typename T>
+using IndexedMemPoolTraitsEagerRecycle = IndexedMemPoolTraits<T, true, true>;
+
/// 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
/// 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
uint32_t NumLocalLists_ = 32,
uint32_t LocalListLimit_ = 200,
template <typename> class Atom = std::atomic,
- bool EagerRecycleWhenTrivial = false,
- bool EagerRecycleWhenNotTrivial = true>
+ typename Traits = IndexedMemPoolTraits<T>>
struct IndexedMemPool : boost::noncopyable {
typedef T value_type;
LocalListLimit = LocalListLimit_
};
-
- static constexpr bool eagerRecycle() {
- return std::is_trivial<T>::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
/// Destroys all of the contained elements
~IndexedMemPool() {
- if (!eagerRecycle()) {
- // Take the minimum since it is possible that size_ > actualCapacity_.
- // This can happen if there are multiple concurrent requests
- // when size_ == actualCapacity_ - 1.
- uint32_t last = std::min(uint32_t(size_), uint32_t(actualCapacity_));
- for (uint32_t i = last; i > 0; --i) {
- slots_[i].~Slot();
- }
+ for (uint32_t i = maxAllocatedIndex(); i > 0; --i) {
+ Traits::cleanup(&slots_[i].elem);
}
munmap(slots_, mmapLength_);
}
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 <typename ...Args>
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>(args)...);
+ if (idx != 0) {
+ Slot& s = slot(idx);
+ Traits::onAllocate(&s.elem, std::forward<Args>(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 <typename ...Args>
UniquePtr allocElem(Args&&... args) {
auto idx = allocIndex(std::forward<Args>(args)...);
/// Gives up ownership previously granted by alloc()
void recycleIndex(uint32_t idx) {
assert(isAllocated(idx));
- if (eagerRecycle()) {
- slot(idx).elem.~T();
- }
+ Traits::onRecycle(&slot(idx).elem);
localPush(localHead(), idx);
}
/// Returns true iff idx has been alloc()ed and not recycleIndex()ed
bool isAllocated(uint32_t idx) const {
- return slot(idx).localNext.load(std::memory_order_relaxed) == uint32_t(-1);
+ return slot(idx).localNext.load(std::memory_order_acquire) == uint32_t(-1);
}
auto next = s.localNext.load(std::memory_order_relaxed);
if (head.compare_exchange_strong(h, h.withIdx(next).withSizeDecr())) {
// success
- s.localNext.store(uint32_t(-1), std::memory_order_relaxed);
return h.idx;
}
continue;
// 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.store(uint32_t(-1), std::memory_order_relaxed);
+ Traits::initialize(&slot(idx).elem);
return idx;
}
if (head.compare_exchange_strong(
h, h.withIdx(next).withSize(LocalListLimit))) {
// global list moved to local list, keep head for us
- s.localNext.store(uint32_t(-1), std::memory_order_relaxed);
return idx;
}
// local bulk push failed, return idx to the global list and try again
auto stripe = detail::AccessSpreader<Atom>::current(NumLocalLists);
return local_[stripe].head;
}
+
+ void markAllocated(Slot& slot) {
+ slot.localNext.store(uint32_t(-1), std::memory_order_release);
+ }
};
namespace detail {
projects / folly.git / blobdiff