// SPDX-FileCopyrightText: 2013-2020 Cameron Desrochers
// SPDX-License-Identifier: BSD-2-Clause
#pragma once
#include <cassert>
#include <cstdint>
#include <cstdlib> // For malloc/free/abort & size_t
#include <memory>
#include <new>
#include <stdexcept>
#include <type_traits>
#include <utility>
#include "common/atomic_helpers.h"
#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, 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
#ifndef MOODYCAMEL_MAYBE_ALIGN_TO_CACHELINE
#if defined(__APPLE__) && defined(__MACH__) && __cplusplus >= 201703L
// This is required to find out what deployment target we are using
#include <CoreFoundation/CoreFoundation.h>
#if !defined(MAC_OS_X_VERSION_MIN_REQUIRED) || \
MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_14
// C++17 new(size_t, align_val_t) is not backwards-compatible with older versions of macOS, so we
// can't support over-alignment in this case
#define MOODYCAMEL_MAYBE_ALIGN_TO_CACHELINE
#endif
#endif
#endif
#ifndef MOODYCAMEL_MAYBE_ALIGN_TO_CACHELINE
#define MOODYCAMEL_MAYBE_ALIGN_TO_CACHELINE AE_ALIGN(MOODYCAMEL_CACHE_LINE_SIZE)
#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 Common {
template <typename T, size_t MAX_BLOCK_SIZE = 512>
class MOODYCAMEL_MAYBE_ALIGN_TO_CACHELINE 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 at least `size` 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 size = 15)
#ifndef NDEBUG
: enqueuing(false), dequeuing(false)
#endif
{
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(size + 1); // We need a spare slot to fit size 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 size and applying a ceiling to the division gives us (after simplifying):
size_t initialBlockCount = (size + 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() const 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;
}
// Returns the total number of items that could be enqueued without incurring
// an allocation when this queue is empty.
// Safe to call from both the producer and consumer threads.
//
// NOTE: The actual capacity during usage may be different depending on the consumer.
// If the consumer is removing elements concurrently, the producer cannot add to
// the block the consumer is removing from until it's completely empty, except in
// the case where the producer was writing to the same block the consumer was
// reading from the whole time.
inline size_t max_capacity() const {
size_t result = 0;
Block* frontBlock_ = frontBlock.load();
Block* block = frontBlock_;
do {
fence(memory_order_acquire);
result += 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(weak_atomic<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:
weak_atomic<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(0UL), localTail(0), tail(0UL), 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 dequeued from this block
char cachelineFiller[MOODYCAMEL_CACHE_LINE_SIZE - sizeof(weak_atomic<Block*>)];
weak_atomic<Block*> tailBlock; // (Atomic) Elements are enqueued to this block
size_t largestBlockSize;
#ifndef NDEBUG
weak_atomic<bool> enqueuing;
mutable weak_atomic<bool> dequeuing;
#endif
};
// Like ReaderWriterQueue, but also providees blocking operations
template <typename T, size_t MAX_BLOCK_SIZE = 512>
class BlockingReaderWriterQueue {
private:
typedef ::Common::ReaderWriterQueue<T, MAX_BLOCK_SIZE> ReaderWriterQueue;
public:
explicit BlockingReaderWriterQueue(size_t size = 15) AE_NO_TSAN
: inner(size),
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;
}
#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 {
if (inner.try_emplace(std::forward<Args>(args)...)) {
sema->signal();
return true;
}
return false;
}
#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 {
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;
}
#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 {
if (inner.emplace(std::forward<Args>(args)...)) {
sema->signal();
return true;
}
return false;
}
#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 {
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 {
while (!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() const 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();
}
// Returns the total number of items that could be enqueued without incurring
// an allocation when this queue is empty.
// Safe to call from both the producer and consumer threads.
//
// NOTE: The actual capacity during usage may be different depending on the consumer.
// If the consumer is removing elements concurrently, the producer cannot add to
// the block the consumer is removing from until it's completely empty, except in
// the case where the producer was writing to the same block the consumer was
// reading from the whole time.
AE_FORCEINLINE size_t max_capacity() const {
return inner.max_capacity();
}
private:
// Disable copying & assignment
BlockingReaderWriterQueue(BlockingReaderWriterQueue const&) {}
BlockingReaderWriterQueue& operator=(BlockingReaderWriterQueue const&) {}
private:
ReaderWriterQueue inner;
std::unique_ptr<spsc_sema::LightweightSemaphore> sema;
};
} // namespace Common
#ifdef AE_VCPP
#pragma warning(pop)
#endif
