text: // ©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
  #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
  
  #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:
  		// 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).
  		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.
  		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)
  		{
  			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.
  		~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)
  		{
  			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)
  		{
  			return inner_enqueue<CannotAlloc>(std::forward<T>(element));
  		}
  
  
  		// 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)
  		{
  			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)
  		{
  			return inner_enqueue<CanAlloc>(std::forward<T>(element));
  		}
  
  
  		// 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)
  		{
  #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()
  		{
  #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()
  		{
  #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
  		{
  			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 };
  
  		template<AllocationMode canAlloc, typename U>
  		bool inner_enqueue(U&& element)
  		{
  #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);
  				new (location) T(std::forward<U>(element));
  
  				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);
  					new (location) T(std::forward<U>(element));
  
  					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;
  
  					new (newBlock->data) T(std::forward<U>(element));
  
  					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)
  		{
  			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
  		{
  			ReentrantGuard(bool& _inSection)
  				: inSection(_inSection)
  			{
  				assert(!inSection && "ReaderWriterQueue does not support enqueuing or dequeuing elements from other elements' ctors and dtors");
  				inSection = true;
  			}
  
  			~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)
  			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)
  		{
  			// 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)
  			: inner(maxSize)
  		{ }
  
  
  		// 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)
  		{
  			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)
  		{
  			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)
  		{
  			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)
  		{
  			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)
  		{
  			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)
  		{
  			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)
  		{
  			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)
  		{
  			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()
  		{
  			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()
  		{
  			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
  		{
  			return sema.availableApprox();
  		}
  
  
  	private:
  		// Disable copying & assignment
  		BlockingReaderWriterQueue(ReaderWriterQueue const&) {  }
  		BlockingReaderWriterQueue& operator=(ReaderWriterQueue const&) {  }
  
  	private:
  		ReaderWriterQueue inner;
  		spsc_sema::LightweightSemaphore sema;
  	};
  
  }    // end namespace moodycamel
  
  #ifdef AE_VCPP
  #pragma warning(pop)
  #endif