// Simplified BSD License: // // Copyright (c) 2013-2021, Cameron Desrochers // All rights reserved. // // Redistribution and use in source and binary forms, with or without modification, // are permitted provided that the following conditions are met: // // - Redistributions of source code must retain the above copyright notice, this list of // conditions and the following disclaimer. // - Redistributions in binary form must reproduce the above copyright notice, this list of // conditions and the following disclaimer in the documentation and/or other materials // provided with the distribution. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY // EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF // MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL // THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT // OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) // HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR // TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, // EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. // ©2013-2020 Cameron Desrochers. // Distributed under the simplified BSD license (see the license file that // should have come with this header). // atomicops.h // ©2013-2016 Cameron Desrochers. // Distributed under the simplified BSD license (see the license file that // should have come with this header). #pragma once // Provides portable (VC++2010+, Intel ICC 13, GCC 4.7+, and anything C++11 compliant) implementation // of low-level memory barriers, plus a few semi-portable utility macros (for inlining and alignment). // Also has a basic atomic type (limited to hardware-supported atomics with no memory ordering guarantees). // Uses the AE_* prefix for macros (historical reasons), and the "moodycamel" namespace for symbols. #include #include #include #include #include #include // Platform detection #if defined(__INTEL_COMPILER) #define AE_ICC #elif defined(_MSC_VER) #define AE_VCPP #elif defined(__GNUC__) #define AE_GCC #endif #if defined(_M_IA64) || defined(__ia64__) #define AE_ARCH_IA64 #elif defined(_WIN64) || defined(__amd64__) || defined(_M_X64) || defined(__x86_64__) #define AE_ARCH_X64 #elif defined(_M_IX86) || defined(__i386__) #define AE_ARCH_X86 #elif defined(_M_PPC) || defined(__powerpc__) #define AE_ARCH_PPC #else #define AE_ARCH_UNKNOWN #endif // AE_UNUSED #define AE_UNUSED(x) ((void)x) // AE_NO_TSAN #if defined(__has_feature) #if __has_feature(thread_sanitizer) #define AE_NO_TSAN __attribute__((no_sanitize("thread"))) #else #define AE_NO_TSAN #endif #else #define AE_NO_TSAN #endif // AE_FORCEINLINE #if defined(AE_VCPP) || defined(AE_ICC) #define AE_FORCEINLINE __forceinline #elif defined(AE_GCC) //#define AE_FORCEINLINE __attribute__((always_inline)) #define AE_FORCEINLINE inline #else #define AE_FORCEINLINE inline #endif // AE_ALIGN #if defined(AE_VCPP) || defined(AE_ICC) #define AE_ALIGN(x) __declspec(align(x)) #elif defined(AE_GCC) #define AE_ALIGN(x) __attribute__((aligned(x))) #else // Assume GCC compliant syntax... #define AE_ALIGN(x) __attribute__((aligned(x))) #endif // Portable atomic fences implemented below: namespace tracy { enum memory_order { memory_order_relaxed, memory_order_acquire, memory_order_release, memory_order_acq_rel, memory_order_seq_cst, // memory_order_sync: Forces a full sync: // #LoadLoad, #LoadStore, #StoreStore, and most significantly, #StoreLoad memory_order_sync = memory_order_seq_cst }; } // end namespace moodycamel #if (defined(AE_VCPP) && (_MSC_VER < 1700 || defined(__cplusplus_cli))) || (defined(AE_ICC) && __INTEL_COMPILER < 1600) // VS2010 and ICC13 don't support std::atomic_*_fence, implement our own fences #include #if defined(AE_ARCH_X64) || defined(AE_ARCH_X86) #define AeFullSync _mm_mfence #define AeLiteSync _mm_mfence #elif defined(AE_ARCH_IA64) #define AeFullSync __mf #define AeLiteSync __mf #elif defined(AE_ARCH_PPC) #include #define AeFullSync __sync #define AeLiteSync __lwsync #endif #ifdef AE_VCPP #pragma warning(push) #pragma warning(disable: 4365) // Disable erroneous 'conversion from long to unsigned int, signed/unsigned mismatch' error when using `assert` #ifdef __cplusplus_cli #pragma managed(push, off) #endif #endif namespace tracy { AE_FORCEINLINE void compiler_fence(memory_order order) AE_NO_TSAN { switch (order) { case memory_order_relaxed: break; case memory_order_acquire: _ReadBarrier(); break; case memory_order_release: _WriteBarrier(); break; case memory_order_acq_rel: _ReadWriteBarrier(); break; case memory_order_seq_cst: _ReadWriteBarrier(); break; default: assert(false); } } // x86/x64 have a strong memory model -- all loads and stores have // acquire and release semantics automatically (so only need compiler // barriers for those). #if defined(AE_ARCH_X86) || defined(AE_ARCH_X64) AE_FORCEINLINE void fence(memory_order order) AE_NO_TSAN { switch (order) { case memory_order_relaxed: break; case memory_order_acquire: _ReadBarrier(); break; case memory_order_release: _WriteBarrier(); break; case memory_order_acq_rel: _ReadWriteBarrier(); break; case memory_order_seq_cst: _ReadWriteBarrier(); AeFullSync(); _ReadWriteBarrier(); break; default: assert(false); } } #else AE_FORCEINLINE void fence(memory_order order) AE_NO_TSAN { // Non-specialized arch, use heavier memory barriers everywhere just in case :-( switch (order) { case memory_order_relaxed: break; case memory_order_acquire: _ReadBarrier(); AeLiteSync(); _ReadBarrier(); break; case memory_order_release: _WriteBarrier(); AeLiteSync(); _WriteBarrier(); break; case memory_order_acq_rel: _ReadWriteBarrier(); AeLiteSync(); _ReadWriteBarrier(); break; case memory_order_seq_cst: _ReadWriteBarrier(); AeFullSync(); _ReadWriteBarrier(); break; default: assert(false); } } #endif } // end namespace moodycamel #else // Use standard library of atomics #include namespace tracy { AE_FORCEINLINE void compiler_fence(memory_order order) AE_NO_TSAN { switch (order) { case memory_order_relaxed: break; case memory_order_acquire: std::atomic_signal_fence(std::memory_order_acquire); break; case memory_order_release: std::atomic_signal_fence(std::memory_order_release); break; case memory_order_acq_rel: std::atomic_signal_fence(std::memory_order_acq_rel); break; case memory_order_seq_cst: std::atomic_signal_fence(std::memory_order_seq_cst); break; default: assert(false); } } AE_FORCEINLINE void fence(memory_order order) AE_NO_TSAN { switch (order) { case memory_order_relaxed: break; case memory_order_acquire: std::atomic_thread_fence(std::memory_order_acquire); break; case memory_order_release: std::atomic_thread_fence(std::memory_order_release); break; case memory_order_acq_rel: std::atomic_thread_fence(std::memory_order_acq_rel); break; case memory_order_seq_cst: std::atomic_thread_fence(std::memory_order_seq_cst); break; default: assert(false); } } } // end namespace moodycamel #endif #if !defined(AE_VCPP) || (_MSC_VER >= 1700 && !defined(__cplusplus_cli)) #define AE_USE_STD_ATOMIC_FOR_WEAK_ATOMIC #endif #ifdef AE_USE_STD_ATOMIC_FOR_WEAK_ATOMIC #include #endif #include // WARNING: *NOT* A REPLACEMENT FOR std::atomic. READ CAREFULLY: // Provides basic support for atomic variables -- no memory ordering guarantees are provided. // The guarantee of atomicity is only made for types that already have atomic load and store guarantees // at the hardware level -- on most platforms this generally means aligned pointers and integers (only). namespace tracy { template class weak_atomic { public: AE_NO_TSAN weak_atomic() : value() { } #ifdef AE_VCPP #pragma warning(push) #pragma warning(disable: 4100) // Get rid of (erroneous) 'unreferenced formal parameter' warning #endif template AE_NO_TSAN weak_atomic(U&& x) : value(std::forward(x)) { } #ifdef __cplusplus_cli // Work around bug with universal reference/nullptr combination that only appears when /clr is on AE_NO_TSAN weak_atomic(nullptr_t) : value(nullptr) { } #endif AE_NO_TSAN weak_atomic(weak_atomic const& other) : value(other.load()) { } AE_NO_TSAN weak_atomic(weak_atomic&& other) : value(std::move(other.load())) { } #ifdef AE_VCPP #pragma warning(pop) #endif AE_FORCEINLINE operator T() const AE_NO_TSAN { return load(); } #ifndef AE_USE_STD_ATOMIC_FOR_WEAK_ATOMIC template AE_FORCEINLINE weak_atomic const& operator=(U&& x) AE_NO_TSAN { value = std::forward(x); return *this; } AE_FORCEINLINE weak_atomic const& operator=(weak_atomic const& other) AE_NO_TSAN { value = other.value; return *this; } AE_FORCEINLINE T load() const AE_NO_TSAN { return value; } AE_FORCEINLINE T fetch_add_acquire(T increment) AE_NO_TSAN { #if defined(AE_ARCH_X64) || defined(AE_ARCH_X86) if (sizeof(T) == 4) return _InterlockedExchangeAdd((long volatile*)&value, (long)increment); #if defined(_M_AMD64) else if (sizeof(T) == 8) return _InterlockedExchangeAdd64((long long volatile*)&value, (long long)increment); #endif #else #error Unsupported platform #endif assert(false && "T must be either a 32 or 64 bit type"); return value; } AE_FORCEINLINE T fetch_add_release(T increment) AE_NO_TSAN { #if defined(AE_ARCH_X64) || defined(AE_ARCH_X86) if (sizeof(T) == 4) return _InterlockedExchangeAdd((long volatile*)&value, (long)increment); #if defined(_M_AMD64) else if (sizeof(T) == 8) return _InterlockedExchangeAdd64((long long volatile*)&value, (long long)increment); #endif #else #error Unsupported platform #endif assert(false && "T must be either a 32 or 64 bit type"); return value; } #else template AE_FORCEINLINE weak_atomic const& operator=(U&& x) AE_NO_TSAN { value.store(std::forward(x), std::memory_order_relaxed); return *this; } AE_FORCEINLINE weak_atomic const& operator=(weak_atomic const& other) AE_NO_TSAN { value.store(other.value.load(std::memory_order_relaxed), std::memory_order_relaxed); return *this; } AE_FORCEINLINE T load() const AE_NO_TSAN { return value.load(std::memory_order_relaxed); } AE_FORCEINLINE T fetch_add_acquire(T increment) AE_NO_TSAN { return value.fetch_add(increment, std::memory_order_acquire); } AE_FORCEINLINE T fetch_add_release(T increment) AE_NO_TSAN { return value.fetch_add(increment, std::memory_order_release); } #endif private: #ifndef AE_USE_STD_ATOMIC_FOR_WEAK_ATOMIC // No std::atomic support, but still need to circumvent compiler optimizations. // `volatile` will make memory access slow, but is guaranteed to be reliable. volatile T value; #else std::atomic value; #endif }; } // end namespace moodycamel #if defined(AE_VCPP) && (_MSC_VER < 1700 || defined(__cplusplus_cli)) #pragma warning(pop) #ifdef __cplusplus_cli #pragma managed(pop) #endif #endif // end of atomicops.h #include #include #include #include #include #include #include #include // For malloc/free/abort & size_t #include #if __cplusplus > 199711L || _MSC_VER >= 1700 // C++11 or VS2012 #include #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 #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 tracy { template 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(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(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(std::forward(element)); } #if MOODYCAMEL_HAS_EMPLACE // Like try_enqueue() but with emplace semantics (i.e. construct-in-place). template AE_FORCEINLINE bool try_emplace(Args&&... args) AE_NO_TSAN { return inner_enqueue(std::forward(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(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(std::forward(element)); } #if MOODYCAMEL_HAS_EMPLACE // Like enqueue() but with emplace semantics (i.e. construct-in-place). template AE_FORCEINLINE bool emplace(Args&&... args) AE_NO_TSAN { return inner_enqueue(std::forward(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 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(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(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(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(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(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(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 bool inner_enqueue(Args&&... args) AE_NO_TSAN #else template 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)...); #else new (location) T(std::forward(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)...); #else new (location) T(std::forward(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)...); #else new (newBlock->data) T(std::forward(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 static AE_FORCEINLINE char* align_for(char* ptr) AE_NO_TSAN { const std::size_t alignment = std::alignment_of::value; return ptr + (alignment - (reinterpret_cast(ptr) % alignment)) % alignment; } private: #ifndef NDEBUG struct ReentrantGuard { AE_NO_TSAN ReentrantGuard(weak_atomic& _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& inSection; }; #endif struct Block { // Avoid false-sharing by putting highly contended variables on their own cache lines weak_atomic 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) - sizeof(size_t)]; weak_atomic tail; // (Atomic) Elements are enqueued here size_t localFront; char cachelineFiller1[MOODYCAMEL_CACHE_LINE_SIZE - sizeof(weak_atomic) - 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 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::value - 1; size += sizeof(T) * capacity + std::alignment_of::value - 1; auto newBlockRaw = static_cast(std::malloc(size)); if (newBlockRaw == nullptr) { return nullptr; } auto newBlockAligned = align_for(newBlockRaw); auto newBlockData = align_for(newBlockAligned + sizeof(Block)); return new (newBlockAligned) Block(capacity, newBlockRaw, newBlockData); } private: weak_atomic frontBlock; // (Atomic) Elements are dequeued from this block char cachelineFiller[MOODYCAMEL_CACHE_LINE_SIZE - sizeof(weak_atomic)]; weak_atomic tailBlock; // (Atomic) Elements are enqueued to this block size_t largestBlockSize; #ifndef NDEBUG weak_atomic enqueuing; mutable weak_atomic dequeuing; #endif }; } // end namespace moodycamel #ifdef AE_VCPP #pragma warning(pop) #endif