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+// ©2013-2015 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 <cstdint>
+#include <cstdlib> // For malloc/free & size_t
+
+
+// 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.
+
+#define CACHE_LINE_SIZE 64
+
+#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) {
+ throw std::bad_alloc();
+ }
+ if (firstBlock == nullptr) {
+ firstBlock = block;
+ }
+ else {
+ lastBlock->next = block;
+ }
+ lastBlock = block;
+ block->next = firstBlock;
+ }
+ }
+ else {
+ firstBlock = make_block(largestBlockSize);
+ if (firstBlock == nullptr) {
+ throw std::bad_alloc();
+ }
+ 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 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);
+ if (inSection) {
+ throw std::runtime_error("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[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[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[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);
+ }
+
+
+ // 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
generated by cgit v1.2.3 (git 2.25.1) at 2024-04-19 20:31:09 +0000