/*
- * Copyright 2016 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
#pragma once
#include <type_traits>
-#include <stdint.h>
#include <assert.h>
+#include <errno.h>
+#include <stdint.h>
#include <boost/noncopyable.hpp>
#include <folly/AtomicStruct.h>
+#include <folly/Portability.h>
#include <folly/detail/CacheLocality.h>
#include <folly/portability/SysMman.h>
#include <folly/portability/Unistd.h>
// 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 {
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
/// constructed, but delays element construction. This means that only
/// elements that are actually returned to the caller get paged into the
/// process's resident set (RSS).
-template <typename T,
- int NumLocalLists_ = 32,
- int LocalListLimit_ = 200,
- template<typename> class Atom = std::atomic,
- bool EagerRecycleWhenTrivial = false,
- bool EagerRecycleWhenNotTrivial = true>
+template <
+ typename T,
+ uint32_t NumLocalLists_ = 32,
+ uint32_t LocalListLimit_ = 200,
+ template <typename> class Atom = std::atomic,
+ 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
static constexpr uint32_t maxIndexForCapacity(uint32_t capacity) {
- // index of uint32_t(-1) == UINT32_MAX is reserved for isAllocated tracking
+ // index of std::numeric_limits<uint32_t>::max() is reserved for isAllocated
+ // tracking
return uint32_t(std::min(
uint64_t(capacity) + (NumLocalLists - 1) * LocalListLimit,
- uint64_t(uint32_t(-1) - 1)));
+ uint64_t(std::numeric_limits<uint32_t>::max() - 1)));
}
static constexpr uint32_t capacityForMaxIndex(uint32_t maxIndex) {
, globalHead_(TaggedPtr{})
{
const size_t needed = sizeof(Slot) * (actualCapacity_ + 1);
- size_t pagesize = sysconf(_SC_PAGESIZE);
+ size_t pagesize = size_t(sysconf(_SC_PAGESIZE));
mmapLength_ = ((needed - 1) & ~(pagesize - 1)) + pagesize;
assert(needed <= mmapLength_ && mmapLength_ < needed + pagesize);
assert((mmapLength_ % pagesize) == 0);
/// Destroys all of the contained elements
~IndexedMemPool() {
- if (!eagerRecycle()) {
- for (size_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_);
}
/// simultaneously allocated and not yet recycled. Because of the
/// local lists it is possible that more elements than this are returned
/// successfully
- size_t capacity() {
+ uint32_t capacity() {
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 == uint32_t(-1);
+ return slot(idx).localNext.load(std::memory_order_acquire) == uint32_t(-1);
}
struct Slot {
T elem;
- uint32_t localNext;
- uint32_t globalNext;
+ Atom<uint32_t> localNext;
+ Atom<uint32_t> globalNext;
Slot() : localNext{}, globalNext{} {}
};
////////// fields
+ /// the number of bytes allocated from mmap, which is a multiple of
+ /// the page size of the machine
+ size_t mmapLength_;
+
/// the actual number of slots that we will allocate, to guarantee
/// that we will satisfy the capacity requested at construction time.
/// They will be numbered 1..actualCapacity_ (note the 1-based counting),
/// and occupy slots_[1..actualCapacity_].
- size_t actualCapacity_;
-
- /// the number of bytes allocated from mmap, which is a multiple of
- /// the page size of the machine
- size_t mmapLength_;
+ uint32_t actualCapacity_;
/// this records the number of slots that have actually been constructed.
/// To allow use of atomic ++ instead of CAS, we let this overflow.
///////////// private methods
- size_t slotIndex(uint32_t idx) const {
+ uint32_t slotIndex(uint32_t idx) const {
assert(0 < idx &&
idx <= actualCapacity_ &&
idx <= size_.load(std::memory_order_acquire));
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;
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_relaxed);
if (h.size() == LocalListLimit) {
// push will overflow local list, steal it instead
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;
}
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;
// 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
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 {
} // namespace folly
-# pragma GCC diagnostic pop
+FOLLY_POP_WARNING
projects / folly.git / blobdiff