Kuesa Music Box QML Example

 // ©2013-2016 Cameron Desrochers.
 // Distributed under the simplified BSD license (see the license file that
 // should have come with this header).

 #pragma once

 #include "atomicops.h"
 #include <type_traits>
 #include <utility>
 #include <cassert>
 #include <stdexcept>
 #include <new>
 #include <cstdint>
 #include <cstdlib>              // For malloc/free/abort & size_t
 #include <memory>
 #if __cplusplus > 199711L || _MSC_VER >= 1700 // C++11 or VS2012
 #include <chrono>
 #endif

 // A lock-free queue for a single-consumer, single-producer architecture.
 // The queue is also wait-free in the common path (except if more memory
 // needs to be allocated, in which case malloc is called).
 // Allocates memory sparingly (O(lg(n) times, amortized), and only once if
 // the original maximum size estimate is never exceeded.
 // Tested on x86/x64 processors, but semantics should be correct for all
 // architectures (given the right implementations in atomicops.h), provided
 // that aligned integer and pointer accesses are naturally atomic.
 // Note that there should only be one consumer thread and producer thread;
 // Switching roles of the threads, or using multiple consecutive threads for
 // one role, is not safe unless properly synchronized.
 // Using the queue exclusively from one thread is fine, though a bit silly.

 #ifndef MOODYCAMEL_CACHE_LINE_SIZE
 #define MOODYCAMEL_CACHE_LINE_SIZE 64
 #endif

 #ifndef MOODYCAMEL_EXCEPTIONS_ENABLED
 #if (defined(_MSC_VER) && defined(_CPPUNWIND)) || (defined(__GNUC__) && defined(__EXCEPTIONS)) || (!defined(_MSC_VER) && !defined(__GNUC__))
 #define MOODYCAMEL_EXCEPTIONS_ENABLED
 #endif
 #endif

 #ifndef MOODYCAMEL_HAS_EMPLACE
 #if !defined(_MSC_VER) || _MSC_VER >= 1800 // variadic templates: either a non-MS compiler or VS >= 2013
 #define MOODYCAMEL_HAS_EMPLACE    1
 #endif
 #endif

 #ifdef AE_VCPP
 #pragma warning(push)
 #pragma warning(disable: 4324)  // structure was padded due to __declspec(align())
 #pragma warning(disable: 4820)  // padding was added
 #pragma warning(disable: 4127)  // conditional expression is constant
 #endif

 namespace moodycamel {

 template<typename T, size_t MAX_BLOCK_SIZE = 512>
 class ReaderWriterQueue
 {
         // Design: Based on a queue-of-queues. The low-level queues are just
         // circular buffers with front and tail indices indicating where the
         // next element to dequeue is and where the next element can be enqueued,
         // respectively. Each low-level queue is called a "block". Each block
         // wastes exactly one element's worth of space to keep the design simple
         // (if front == tail then the queue is empty, and can't be full).
         // The high-level queue is a circular linked list of blocks; again there
         // is a front and tail, but this time they are pointers to the blocks.
         // The front block is where the next element to be dequeued is, provided
         // the block is not empty. The back block is where elements are to be
         // enqueued, provided the block is not full.
         // The producer thread owns all the tail indices/pointers. The consumer
         // thread owns all the front indices/pointers. Both threads read each
         // other's variables, but only the owning thread updates them. E.g. After
         // the consumer reads the producer's tail, the tail may change before the
         // consumer is done dequeuing an object, but the consumer knows the tail
         // will never go backwards, only forwards.
         // If there is no room to enqueue an object, an additional block (of
         // equal size to the last block) is added. Blocks are never removed.

 public:
         typedef T value_type;

         // Constructs a queue that can hold maxSize elements without further
         // allocations. If more than MAX_BLOCK_SIZE elements are requested,
         // then several blocks of MAX_BLOCK_SIZE each are reserved (including
         // at least one extra buffer block).
         AE_NO_TSAN explicit ReaderWriterQueue(size_t maxSize = 15)
 #ifndef NDEBUG
                 : enqueuing(false)
                 ,dequeuing(false)
 #endif
         {
                 assert(maxSize > 0);
                 assert(MAX_BLOCK_SIZE == ceilToPow2(MAX_BLOCK_SIZE) && "MAX_BLOCK_SIZE must be a power of 2");
                 assert(MAX_BLOCK_SIZE >= 2 && "MAX_BLOCK_SIZE must be at least 2");

                 Block* firstBlock = nullptr;

                 largestBlockSize = ceilToPow2(maxSize + 1);             // We need a spare slot to fit maxSize elements in the block
                 if (largestBlockSize > MAX_BLOCK_SIZE * 2) {
                         // We need a spare block in case the producer is writing to a different block the consumer is reading from, and
                         // wants to enqueue the maximum number of elements. We also need a spare element in each block to avoid the ambiguity
                         // between front == tail meaning "empty" and "full".
                         // So the effective number of slots that are guaranteed to be usable at any time is the block size - 1 times the
                         // number of blocks - 1. Solving for maxSize and applying a ceiling to the division gives us (after simplifying):
                         size_t initialBlockCount = (maxSize + MAX_BLOCK_SIZE * 2 - 3) / (MAX_BLOCK_SIZE - 1);
                         largestBlockSize = MAX_BLOCK_SIZE;
                         Block* lastBlock = nullptr;
                         for (size_t i = 0; i != initialBlockCount; ++i) {
                                 auto block = make_block(largestBlockSize);
                                 if (block == nullptr) {
 #ifdef MOODYCAMEL_EXCEPTIONS_ENABLED
                                         throw std::bad_alloc();
 #else
                                         abort();
 #endif
                                 }
                                 if (firstBlock == nullptr) {
                                         firstBlock = block;
                                 }
                                 else {
                                         lastBlock->next = block;
                                 }
                                 lastBlock = block;
                                 block->next = firstBlock;
                         }
                 }
                 else {
                         firstBlock = make_block(largestBlockSize);
                         if (firstBlock == nullptr) {
 #ifdef MOODYCAMEL_EXCEPTIONS_ENABLED
                                 throw std::bad_alloc();
 #else
                                 abort();
 #endif
                         }
                         firstBlock->next = firstBlock;
                 }
                 frontBlock = firstBlock;
                 tailBlock = firstBlock;

                 // Make sure the reader/writer threads will have the initialized memory setup above:
                 fence(memory_order_sync);
         }

         // Note: The queue should not be accessed concurrently while it's
         // being moved. It's up to the user to synchronize this.
         AE_NO_TSAN ReaderWriterQueue(ReaderWriterQueue&& other)
                 : frontBlock(other.frontBlock.load()),
                 tailBlock(other.tailBlock.load()),
                 largestBlockSize(other.largestBlockSize)
 #ifndef NDEBUG
                 ,enqueuing(false)
                 ,dequeuing(false)
 #endif
         {
                 other.largestBlockSize = 32;
                 Block* b = other.make_block(other.largestBlockSize);
                 if (b == nullptr) {
 #ifdef MOODYCAMEL_EXCEPTIONS_ENABLED
                         throw std::bad_alloc();
 #else
                         abort();
 #endif
                 }
                 b->next = b;
                 other.frontBlock = b;
                 other.tailBlock = b;
         }

         // Note: The queue should not be accessed concurrently while it's
         // being moved. It's up to the user to synchronize this.
         ReaderWriterQueue& operator=(ReaderWriterQueue&& other) AE_NO_TSAN
         {
                 Block* b = frontBlock.load();
                 frontBlock = other.frontBlock.load();
                 other.frontBlock = b;
                 b = tailBlock.load();
                 tailBlock = other.tailBlock.load();
                 other.tailBlock = b;
                 std::swap(largestBlockSize, other.largestBlockSize);
                 return *this;
         }

         // Note: The queue should not be accessed concurrently while it's
         // being deleted. It's up to the user to synchronize this.
         AE_NO_TSAN ~ReaderWriterQueue()
         {
                 // Make sure we get the latest version of all variables from other CPUs:
                 fence(memory_order_sync);

                 // Destroy any remaining objects in queue and free memory
                 Block* frontBlock_ = frontBlock;
                 Block* block = frontBlock_;
                 do {
                         Block* nextBlock = block->next;
                         size_t blockFront = block->front;
                         size_t blockTail = block->tail;

                         for (size_t i = blockFront; i != blockTail; i = (i + 1) & block->sizeMask) {
                                 auto element = reinterpret_cast<T*>(block->data + i * sizeof(T));
                                 element->~T();
                                 (void)element;
                         }

                         auto rawBlock = block->rawThis;
                         block->~Block();
                         std::free(rawBlock);
                         block = nextBlock;
                 } while (block != frontBlock_);
         }

         // Enqueues a copy of element if there is room in the queue.
         // Returns true if the element was enqueued, false otherwise.
         // Does not allocate memory.
         AE_FORCEINLINE bool try_enqueue(T const& element) AE_NO_TSAN
         {
                 return inner_enqueue<CannotAlloc>(element);
         }

         // Enqueues a moved copy of element if there is room in the queue.
         // Returns true if the element was enqueued, false otherwise.
         // Does not allocate memory.
         AE_FORCEINLINE bool try_enqueue(T&& element) AE_NO_TSAN
         {
                 return inner_enqueue<CannotAlloc>(std::forward<T>(element));
         }

 #if MOODYCAMEL_HAS_EMPLACE
         // Like try_enqueue() but with emplace semantics (i.e. construct-in-place).
         template<typename... Args>
         AE_FORCEINLINE bool try_emplace(Args&&... args) AE_NO_TSAN
         {
                 return inner_enqueue<CannotAlloc>(std::forward<Args>(args)...);
         }
 #endif

         // Enqueues a copy of element on the queue.
         // Allocates an additional block of memory if needed.
         // Only fails (returns false) if memory allocation fails.
         AE_FORCEINLINE bool enqueue(T const& element) AE_NO_TSAN
         {
                 return inner_enqueue<CanAlloc>(element);
         }

         // Enqueues a moved copy of element on the queue.
         // Allocates an additional block of memory if needed.
         // Only fails (returns false) if memory allocation fails.
         AE_FORCEINLINE bool enqueue(T&& element) AE_NO_TSAN
         {
                 return inner_enqueue<CanAlloc>(std::forward<T>(element));
         }

 #if MOODYCAMEL_HAS_EMPLACE
         // Like enqueue() but with emplace semantics (i.e. construct-in-place).
         template<typename... Args>
         AE_FORCEINLINE bool emplace(Args&&... args) AE_NO_TSAN
         {
                 return inner_enqueue<CanAlloc>(std::forward<Args>(args)...);
         }
 #endif

         // Attempts to dequeue an element; if the queue is empty,
         // returns false instead. If the queue has at least one element,
         // moves front to result using operator=, then returns true.
         template<typename U>
         bool try_dequeue(U& result) AE_NO_TSAN
         {
 #ifndef NDEBUG
                 ReentrantGuard guard(this->dequeuing);
 #endif

                 // High-level pseudocode:
                 // Remember where the tail block is
                 // If the front block has an element in it, dequeue it
                 // Else
                 //     If front block was the tail block when we entered the function, return false
                 //     Else advance to next block and dequeue the item there

                 // Note that we have to use the value of the tail block from before we check if the front
                 // block is full or not, in case the front block is empty and then, before we check if the
                 // tail block is at the front block or not, the producer fills up the front block *and
                 // moves on*, which would make us skip a filled block. Seems unlikely, but was consistently
                 // reproducible in practice.
                 // In order to avoid overhead in the common case, though, we do a double-checked pattern
                 // where we have the fast path if the front block is not empty, then read the tail block,
                 // then re-read the front block and check if it's not empty again, then check if the tail
                 // block has advanced.

                 Block* frontBlock_ = frontBlock.load();
                 size_t blockTail = frontBlock_->localTail;
                 size_t blockFront = frontBlock_->front.load();

                 if (blockFront != blockTail || blockFront != (frontBlock_->localTail = frontBlock_->tail.load())) {
                         fence(memory_order_acquire);

                 non_empty_front_block:
                         // Front block not empty, dequeue from here
                         auto element = reinterpret_cast<T*>(frontBlock_->data + blockFront * sizeof(T));
                         result = std::move(*element);
                         element->~T();

                         blockFront = (blockFront + 1) & frontBlock_->sizeMask;

                         fence(memory_order_release);
                         frontBlock_->front = blockFront;
                 }
                 else if (frontBlock_ != tailBlock.load()) {
                         fence(memory_order_acquire);

                         frontBlock_ = frontBlock.load();
                         blockTail = frontBlock_->localTail = frontBlock_->tail.load();
                         blockFront = frontBlock_->front.load();
                         fence(memory_order_acquire);

                         if (blockFront != blockTail) {
                                 // Oh look, the front block isn't empty after all
                                 goto non_empty_front_block;
                         }

                         // Front block is empty but there's another block ahead, advance to it
                         Block* nextBlock = frontBlock_->next;
                         // Don't need an acquire fence here since next can only ever be set on the tailBlock,
                         // and we're not the tailBlock, and we did an acquire earlier after reading tailBlock which
                         // ensures next is up-to-date on this CPU in case we recently were at tailBlock.

                         size_t nextBlockFront = nextBlock->front.load();
                         size_t nextBlockTail = nextBlock->localTail = nextBlock->tail.load();
                         fence(memory_order_acquire);

                         // Since the tailBlock is only ever advanced after being written to,
                         // we know there's for sure an element to dequeue on it
                         assert(nextBlockFront != nextBlockTail);
                         AE_UNUSED(nextBlockTail);

                         // We're done with this block, let the producer use it if it needs
                         fence(memory_order_release);            // Expose possibly pending changes to frontBlock->front from last dequeue
                         frontBlock = frontBlock_ = nextBlock;

                         compiler_fence(memory_order_release);   // Not strictly needed

                         auto element = reinterpret_cast<T*>(frontBlock_->data + nextBlockFront * sizeof(T));

                         result = std::move(*element);
                         element->~T();

                         nextBlockFront = (nextBlockFront + 1) & frontBlock_->sizeMask;

                         fence(memory_order_release);
                         frontBlock_->front = nextBlockFront;
                 }
                 else {
                         // No elements in current block and no other block to advance to
                         return false;
                 }

                 return true;
         }

         // Returns a pointer to the front element in the queue (the one that
         // would be removed next by a call to `try_dequeue` or `pop`). If the
         // queue appears empty at the time the method is called, nullptr is
         // returned instead.
         // Must be called only from the consumer thread.
         T* peek() AE_NO_TSAN
         {
 #ifndef NDEBUG
                 ReentrantGuard guard(this->dequeuing);
 #endif
                 // See try_dequeue() for reasoning

                 Block* frontBlock_ = frontBlock.load();
                 size_t blockTail = frontBlock_->localTail;
                 size_t blockFront = frontBlock_->front.load();

                 if (blockFront != blockTail || blockFront != (frontBlock_->localTail = frontBlock_->tail.load())) {
                         fence(memory_order_acquire);
                 non_empty_front_block:
                         return reinterpret_cast<T*>(frontBlock_->data + blockFront * sizeof(T));
                 }
                 else if (frontBlock_ != tailBlock.load()) {
                         fence(memory_order_acquire);
                         frontBlock_ = frontBlock.load();
                         blockTail = frontBlock_->localTail = frontBlock_->tail.load();
                         blockFront = frontBlock_->front.load();
                         fence(memory_order_acquire);

                         if (blockFront != blockTail) {
                                 goto non_empty_front_block;
                         }

                         Block* nextBlock = frontBlock_->next;

                         size_t nextBlockFront = nextBlock->front.load();
                         fence(memory_order_acquire);

                         assert(nextBlockFront != nextBlock->tail.load());
                         return reinterpret_cast<T*>(nextBlock->data + nextBlockFront * sizeof(T));
                 }

                 return nullptr;
         }

         // Removes the front element from the queue, if any, without returning it.
         // Returns true on success, or false if the queue appeared empty at the time
         // `pop` was called.
         bool pop() AE_NO_TSAN
         {
 #ifndef NDEBUG
                 ReentrantGuard guard(this->dequeuing);
 #endif
                 // See try_dequeue() for reasoning

                 Block* frontBlock_ = frontBlock.load();
                 size_t blockTail = frontBlock_->localTail;
                 size_t blockFront = frontBlock_->front.load();

                 if (blockFront != blockTail || blockFront != (frontBlock_->localTail = frontBlock_->tail.load())) {
                         fence(memory_order_acquire);

                 non_empty_front_block:
                         auto element = reinterpret_cast<T*>(frontBlock_->data + blockFront * sizeof(T));
                         element->~T();

                         blockFront = (blockFront + 1) & frontBlock_->sizeMask;

                         fence(memory_order_release);
                         frontBlock_->front = blockFront;
                 }
                 else if (frontBlock_ != tailBlock.load()) {
                         fence(memory_order_acquire);
                         frontBlock_ = frontBlock.load();
                         blockTail = frontBlock_->localTail = frontBlock_->tail.load();
                         blockFront = frontBlock_->front.load();
                         fence(memory_order_acquire);

                         if (blockFront != blockTail) {
                                 goto non_empty_front_block;
                         }

                         // Front block is empty but there's another block ahead, advance to it
                         Block* nextBlock = frontBlock_->next;

                         size_t nextBlockFront = nextBlock->front.load();
                         size_t nextBlockTail = nextBlock->localTail = nextBlock->tail.load();
                         fence(memory_order_acquire);

                         assert(nextBlockFront != nextBlockTail);
                         AE_UNUSED(nextBlockTail);

                         fence(memory_order_release);
                         frontBlock = frontBlock_ = nextBlock;

                         compiler_fence(memory_order_release);

                         auto element = reinterpret_cast<T*>(frontBlock_->data + nextBlockFront * sizeof(T));
                         element->~T();

                         nextBlockFront = (nextBlockFront + 1) & frontBlock_->sizeMask;

                         fence(memory_order_release);
                         frontBlock_->front = nextBlockFront;
                 }
                 else {
                         // No elements in current block and no other block to advance to
                         return false;
                 }

                 return true;
         }

         // Returns the approximate number of items currently in the queue.
         // Safe to call from both the producer and consumer threads.
         inline size_t size_approx() const AE_NO_TSAN
         {
                 size_t result = 0;
                 Block* frontBlock_ = frontBlock.load();
                 Block* block = frontBlock_;
                 do {
                         fence(memory_order_acquire);
                         size_t blockFront = block->front.load();
                         size_t blockTail = block->tail.load();
                         result += (blockTail - blockFront) & block->sizeMask;
                         block = block->next.load();
                 } while (block != frontBlock_);
                 return result;
         }

 private:
         enum AllocationMode { CanAlloc, CannotAlloc };

 #if MOODYCAMEL_HAS_EMPLACE
         template<AllocationMode canAlloc, typename... Args>
         bool inner_enqueue(Args&&... args) AE_NO_TSAN
 #else
         template<AllocationMode canAlloc, typename U>
         bool inner_enqueue(U&& element) AE_NO_TSAN
 #endif
         {
 #ifndef NDEBUG
                 ReentrantGuard guard(this->enqueuing);
 #endif

                 // High-level pseudocode (assuming we're allowed to alloc a new block):
                 // If room in tail block, add to tail
                 // Else check next block
                 //     If next block is not the head block, enqueue on next block
                 //     Else create a new block and enqueue there
                 //     Advance tail to the block we just enqueued to

                 Block* tailBlock_ = tailBlock.load();
                 size_t blockFront = tailBlock_->localFront;
                 size_t blockTail = tailBlock_->tail.load();

                 size_t nextBlockTail = (blockTail + 1) & tailBlock_->sizeMask;
                 if (nextBlockTail != blockFront || nextBlockTail != (tailBlock_->localFront = tailBlock_->front.load())) {
                         fence(memory_order_acquire);
                         // This block has room for at least one more element
                         char* location = tailBlock_->data + blockTail * sizeof(T);
 #if MOODYCAMEL_HAS_EMPLACE
                         new (location) T(std::forward<Args>(args)...);
 #else
                         new (location) T(std::forward<U>(element));
 #endif

                         fence(memory_order_release);
                         tailBlock_->tail = nextBlockTail;
                 }
                 else {
                         fence(memory_order_acquire);
                         if (tailBlock_->next.load() != frontBlock) {
                                 // Note that the reason we can't advance to the frontBlock and start adding new entries there
                                 // is because if we did, then dequeue would stay in that block, eventually reading the new values,
                                 // instead of advancing to the next full block (whose values were enqueued first and so should be
                                 // consumed first).

                                 fence(memory_order_acquire);            // Ensure we get latest writes if we got the latest frontBlock

                                 // tailBlock is full, but there's a free block ahead, use it
                                 Block* tailBlockNext = tailBlock_->next.load();
                                 size_t nextBlockFront = tailBlockNext->localFront = tailBlockNext->front.load();
                                 nextBlockTail = tailBlockNext->tail.load();
                                 fence(memory_order_acquire);

                                 // This block must be empty since it's not the head block and we
                                 // go through the blocks in a circle
                                 assert(nextBlockFront == nextBlockTail);
                                 tailBlockNext->localFront = nextBlockFront;

                                 char* location = tailBlockNext->data + nextBlockTail * sizeof(T);
 #if MOODYCAMEL_HAS_EMPLACE
                                 new (location) T(std::forward<Args>(args)...);
 #else
                                 new (location) T(std::forward<U>(element));
 #endif

                                 tailBlockNext->tail = (nextBlockTail + 1) & tailBlockNext->sizeMask;

                                 fence(memory_order_release);
                                 tailBlock = tailBlockNext;
                         }
                         else if (canAlloc == CanAlloc) {
                                 // tailBlock is full and there's no free block ahead; create a new block
                                 auto newBlockSize = largestBlockSize >= MAX_BLOCK_SIZE ? largestBlockSize : largestBlockSize * 2;
                                 auto newBlock = make_block(newBlockSize);
                                 if (newBlock == nullptr) {
                                         // Could not allocate a block!
                                         return false;
                                 }
                                 largestBlockSize = newBlockSize;

 #if MOODYCAMEL_HAS_EMPLACE
                                 new (newBlock->data) T(std::forward<Args>(args)...);
 #else
                                 new (newBlock->data) T(std::forward<U>(element));
 #endif
                                 assert(newBlock->front == 0);
                                 newBlock->tail = newBlock->localTail = 1;

                                 newBlock->next = tailBlock_->next.load();
                                 tailBlock_->next = newBlock;

                                 // Might be possible for the dequeue thread to see the new tailBlock->next
                                 // *without* seeing the new tailBlock value, but this is OK since it can't
                                 // advance to the next block until tailBlock is set anyway (because the only
                                 // case where it could try to read the next is if it's already at the tailBlock,
                                 // and it won't advance past tailBlock in any circumstance).

                                 fence(memory_order_release);
                                 tailBlock = newBlock;
                         }
                         else if (canAlloc == CannotAlloc) {
                                 // Would have had to allocate a new block to enqueue, but not allowed
                                 return false;
                         }
                         else {
                                 assert(false && "Should be unreachable code");
                                 return false;
                         }
                 }

                 return true;
         }

         // Disable copying
         ReaderWriterQueue(ReaderWriterQueue const&) {  }

         // Disable assignment
         ReaderWriterQueue& operator=(ReaderWriterQueue const&) {  }

         AE_FORCEINLINE static size_t ceilToPow2(size_t x)
         {
                 // From http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
                 --x;
                 x |= x >> 1;
                 x |= x >> 2;
                 x |= x >> 4;
                 for (size_t i = 1; i < sizeof(size_t); i <<= 1) {
                         x |= x >> (i << 3);
                 }
                 ++x;
                 return x;
         }

         template<typename U>
         static AE_FORCEINLINE char* align_for(char* ptr) AE_NO_TSAN
         {
                 const std::size_t alignment = std::alignment_of<U>::value;
                 return ptr + (alignment - (reinterpret_cast<std::uintptr_t>(ptr) % alignment)) % alignment;
         }
 private:
 #ifndef NDEBUG
         struct ReentrantGuard
         {
                 AE_NO_TSAN ReentrantGuard(bool& _inSection)
                         : inSection(_inSection)
                 {
                         assert(!inSection && "Concurrent (or re-entrant) enqueue or dequeue operation detected (only one thread at a time may hold the producer or consumer role)");
                         inSection = true;
                 }

                 AE_NO_TSAN ~ReentrantGuard() { inSection = false; }

         private:
                 ReentrantGuard& operator=(ReentrantGuard const&);

         private:
                 bool& inSection;
         };
 #endif

         struct Block
         {
                 // Avoid false-sharing by putting highly contended variables on their own cache lines
                 weak_atomic<size_t> front;      // (Atomic) Elements are read from here
                 size_t localTail;                       // An uncontended shadow copy of tail, owned by the consumer

                 char cachelineFiller0[MOODYCAMEL_CACHE_LINE_SIZE - sizeof(weak_atomic<size_t>) - sizeof(size_t)];
                 weak_atomic<size_t> tail;       // (Atomic) Elements are enqueued here
                 size_t localFront;

                 char cachelineFiller1[MOODYCAMEL_CACHE_LINE_SIZE - sizeof(weak_atomic<size_t>) - sizeof(size_t)];       // next isn't very contended, but we don't want it on the same cache line as tail (which is)
                 weak_atomic<Block*> next;       // (Atomic)

                 char* data;             // Contents (on heap) are aligned to T's alignment

                 const size_t sizeMask;

                 // size must be a power of two (and greater than 0)
                 AE_NO_TSAN Block(size_t const& _size, char* _rawThis, char* _data)
                         : front(0), localTail(0), tail(0), localFront(0), next(nullptr), data(_data), sizeMask(_size - 1), rawThis(_rawThis)
                 {
                 }

         private:
                 // C4512 - Assignment operator could not be generated
                 Block& operator=(Block const&);

         public:
                 char* rawThis;
         };

         static Block* make_block(size_t capacity) AE_NO_TSAN
         {
                 // Allocate enough memory for the block itself, as well as all the elements it will contain
                 auto size = sizeof(Block) + std::alignment_of<Block>::value - 1;
                 size += sizeof(T) * capacity + std::alignment_of<T>::value - 1;
                 auto newBlockRaw = static_cast<char*>(std::malloc(size));
                 if (newBlockRaw == nullptr) {
                         return nullptr;
                 }

                 auto newBlockAligned = align_for<Block>(newBlockRaw);
                 auto newBlockData = align_for<T>(newBlockAligned + sizeof(Block));
                 return new (newBlockAligned) Block(capacity, newBlockRaw, newBlockData);
         }

 private:
         weak_atomic<Block*> frontBlock;         // (Atomic) Elements are enqueued to this block

         char cachelineFiller[MOODYCAMEL_CACHE_LINE_SIZE - sizeof(weak_atomic<Block*>)];
         weak_atomic<Block*> tailBlock;          // (Atomic) Elements are dequeued from this block

         size_t largestBlockSize;

 #ifndef NDEBUG
         bool enqueuing;
         bool dequeuing;
 #endif
 };

 // Like ReaderWriterQueue, but also providees blocking operations
 template<typename T, size_t MAX_BLOCK_SIZE = 512>
 class BlockingReaderWriterQueue
 {
 private:
         typedef ::moodycamel::ReaderWriterQueue<T, MAX_BLOCK_SIZE> ReaderWriterQueue;

 public:
         explicit BlockingReaderWriterQueue(size_t maxSize = 15) AE_NO_TSAN
                 : inner(maxSize), sema(new spsc_sema::LightweightSemaphore())
         { }

         BlockingReaderWriterQueue(BlockingReaderWriterQueue&& other) AE_NO_TSAN
                 : inner(std::move(other.inner)), sema(std::move(other.sema))
         { }

         BlockingReaderWriterQueue& operator=(BlockingReaderWriterQueue&& other) AE_NO_TSAN
         {
                 std::swap(sema, other.sema);
                 std::swap(inner, other.inner);
                 return *this;
         }

         // Enqueues a copy of element if there is room in the queue.
         // Returns true if the element was enqueued, false otherwise.
         // Does not allocate memory.
         AE_FORCEINLINE bool try_enqueue(T const& element) AE_NO_TSAN
         {
                 if (inner.try_enqueue(element)) {
                         sema->signal();
                         return true;
                 }
                 return false;
         }

         // Enqueues a moved copy of element if there is room in the queue.
         // Returns true if the element was enqueued, false otherwise.
         // Does not allocate memory.
         AE_FORCEINLINE bool try_enqueue(T&& element) AE_NO_TSAN
         {
                 if (inner.try_enqueue(std::forward<T>(element))) {
                         sema->signal();
                         return true;
                 }
                 return false;
         }

         // Enqueues a copy of element on the queue.
         // Allocates an additional block of memory if needed.
         // Only fails (returns false) if memory allocation fails.
         AE_FORCEINLINE bool enqueue(T const& element) AE_NO_TSAN
         {
                 if (inner.enqueue(element)) {
                         sema->signal();
                         return true;
                 }
                 return false;
         }

         // Enqueues a moved copy of element on the queue.
         // Allocates an additional block of memory if needed.
         // Only fails (returns false) if memory allocation fails.
         AE_FORCEINLINE bool enqueue(T&& element) AE_NO_TSAN
         {
                 if (inner.enqueue(std::forward<T>(element))) {
                         sema->signal();
                         return true;
                 }
                 return false;
         }

         // Attempts to dequeue an element; if the queue is empty,
         // returns false instead. If the queue has at least one element,
         // moves front to result using operator=, then returns true.
         template<typename U>
         bool try_dequeue(U& result) AE_NO_TSAN
         {
                 if (sema->tryWait()) {
                         bool success = inner.try_dequeue(result);
                         assert(success);
                         AE_UNUSED(success);
                         return true;
                 }
                 return false;
         }

         // Attempts to dequeue an element; if the queue is empty,
         // waits until an element is available, then dequeues it.
         template<typename U>
         void wait_dequeue(U& result) AE_NO_TSAN
         {
                 sema->wait();
                 bool success = inner.try_dequeue(result);
                 AE_UNUSED(result);
                 assert(success);
                 AE_UNUSED(success);
         }

         // Attempts to dequeue an element; if the queue is empty,
         // waits until an element is available up to the specified timeout,
         // then dequeues it and returns true, or returns false if the timeout
         // expires before an element can be dequeued.
         // Using a negative timeout indicates an indefinite timeout,
         // and is thus functionally equivalent to calling wait_dequeue.
         template<typename U>
         bool wait_dequeue_timed(U& result, std::int64_t timeout_usecs) AE_NO_TSAN
         {
                 if (!sema->wait(timeout_usecs)) {
                         return false;
                 }
                 bool success = inner.try_dequeue(result);
                 AE_UNUSED(result);
                 assert(success);
                 AE_UNUSED(success);
                 return true;
         }

 #if __cplusplus > 199711L || _MSC_VER >= 1700
         // Attempts to dequeue an element; if the queue is empty,
         // waits until an element is available up to the specified timeout,
         // then dequeues it and returns true, or returns false if the timeout
         // expires before an element can be dequeued.
         // Using a negative timeout indicates an indefinite timeout,
         // and is thus functionally equivalent to calling wait_dequeue.
         template<typename U, typename Rep, typename Period>
         inline bool wait_dequeue_timed(U& result, std::chrono::duration<Rep, Period> const& timeout) AE_NO_TSAN
         {
         return wait_dequeue_timed(result, std::chrono::duration_cast<std::chrono::microseconds>(timeout).count());
         }
 #endif

         // Returns a pointer to the front element in the queue (the one that
         // would be removed next by a call to `try_dequeue` or `pop`). If the
         // queue appears empty at the time the method is called, nullptr is
         // returned instead.
         // Must be called only from the consumer thread.
         AE_FORCEINLINE T* peek() AE_NO_TSAN
         {
                 return inner.peek();
         }

         // Removes the front element from the queue, if any, without returning it.
         // Returns true on success, or false if the queue appeared empty at the time
         // `pop` was called.
         AE_FORCEINLINE bool pop() AE_NO_TSAN
         {
                 if (sema->tryWait()) {
                         bool result = inner.pop();
                         assert(result);
                         AE_UNUSED(result);
                         return true;
                 }
                 return false;
         }

         // Returns the approximate number of items currently in the queue.
         // Safe to call from both the producer and consumer threads.
         AE_FORCEINLINE size_t size_approx() const AE_NO_TSAN
         {
                 return sema->availableApprox();
         }

 private:
         // Disable copying & assignment
         BlockingReaderWriterQueue(BlockingReaderWriterQueue const&) {  }
         BlockingReaderWriterQueue& operator=(BlockingReaderWriterQueue const&) {  }

 private:
         ReaderWriterQueue inner;
         std::unique_ptr<spsc_sema::LightweightSemaphore> sema;
 };

 }    // end namespace moodycamel

 #ifdef AE_VCPP
 #pragma warning(pop)
 #endif