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3476 lines (3045 loc) · 135 KB
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// Provides a C++11 implementation of a multi-producer, multi-consumer lock-free queue.
// An overview, including benchmark results, is provided here:
// http://moodycamel.com/blog/2014/a-fast-general-purpose-lock-free-queue-for-c++
// The full design is also described in excruciating detail at:
// http://moodycamel.com/blog/2014/detailed-design-of-a-lock-free-queue
// Simplified BSD license:
// Copyright (c) 2013-2015, 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.
#pragma once
#if defined(__GNUC__)
// Disable -Wconversion warnings (spuriously triggered when Traits::size_t and
// Traits::index_t are set to < 32 bits, causing integer promotion, causing warnings
// upon assigning any computed values)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wconversion"
#ifdef MCDBGQ_USE_RELACY
#pragma GCC diagnostic ignored "-Wint-to-pointer-cast"
#endif
#endif
#ifdef MCDBGQ_USE_RELACY
#include "relacy/relacy_std.hpp"
#include "relacy_shims.h"
// We only use malloc/free anyway, and the delete macro messes up `= delete` method declarations.
// We'll override the default trait malloc ourselves without a macro.
#undef new
#undef delete
#undef malloc
#undef free
#else
#include <atomic> // Requires C++11. Sorry VS2010.
#include <cassert>
#endif
#include <cstdint>
#include <cstdlib>
#include <type_traits>
#include <algorithm>
#include <utility>
#include <limits>
#include <climits> // for CHAR_BIT
#include <array>
#ifndef __runtime_js__
#include <thread> // for __WINPTHREADS_VERSION if on MinGW-w64 w/ POSIX threading
#endif
// Platform-specific definitions of a numeric thread ID type and an invalid value
#if defined(MCDBGQ_USE_RELACY)
namespace moodycamel { namespace details {
typedef std::uint32_t thread_id_t;
static const thread_id_t invalid_thread_id = 0xFFFFFFFFU;
static const thread_id_t invalid_thread_id2 = 0xFFFFFFFEU;
static inline thread_id_t thread_id() { return rl::thread_index(); }
} }
#elif defined(_WIN32) || defined(__WINDOWS__) || defined(__WIN32__)
// No sense pulling in windows.h in a header, we'll manually declare the function
// we use and rely on backwards-compatibility for this not to break
extern "C" __declspec(dllimport) unsigned long __stdcall GetCurrentThreadId(void);
namespace moodycamel { namespace details {
static_assert(sizeof(unsigned long) == sizeof(std::uint32_t), "Expected size of unsigned long to be 32 bits on Windows");
typedef std::uint32_t thread_id_t;
static const thread_id_t invalid_thread_id = 0; // See http://blogs.msdn.com/b/oldnewthing/archive/2004/02/23/78395.aspx
static const thread_id_t invalid_thread_id2 = 0xFFFFFFFFU; // Not technically guaranteed to be invalid, but is never used in practice. Note that all Win32 thread IDs are presently multiples of 4.
static inline thread_id_t thread_id() { return static_cast<thread_id_t>(::GetCurrentThreadId()); }
} }
#elif defined(__runtime_js__)
#include <kernel/cpu.h>
namespace moodycamel { namespace details {
typedef std::uintptr_t thread_id_t;
static const thread_id_t invalid_thread_id = 0; // Address can't be nullptr
static inline thread_id_t thread_id() { return static_cast<thread_id_t>(1 + rt::Cpu::id()); }
} }
#else
// Use a nice trick from this answer: http://stackoverflow.com/a/8438730/21475
// In order to get a numeric thread ID in a platform-independent way, we use a thread-local
// static variable's address as a thread identifier :-)
#if defined(__GNUC__) || defined(__INTEL_COMPILER)
#define MOODYCAMEL_THREADLOCAL __thread
#elif defined(_MSC_VER)
#define MOODYCAMEL_THREADLOCAL __declspec(thread)
#else
// Assume C++11 compliant compiler
#define MOODYCAMEL_THREADLOCAL thread_local
#endif
namespace moodycamel { namespace details {
typedef std::uintptr_t thread_id_t;
static const thread_id_t invalid_thread_id = 0; // Address can't be nullptr
static const thread_id_t invalid_thread_id2 = 1; // Member accesses off a null pointer are also generally invalid. Plus it's not aligned.
static inline thread_id_t thread_id() { static MOODYCAMEL_THREADLOCAL int x; return reinterpret_cast<thread_id_t>(&x); }
} }
#endif
// Exceptions
#ifndef MOODYCAMEL_EXCEPTIONS_ENABLED
#if (defined(_MSC_VER) && defined(_CPPUNWIND)) || (defined(__GNUC__) && defined(__EXCEPTIONS)) || (!defined(_MSC_VER) && !defined(__GNUC__))
#define MOODYCAMEL_EXCEPTIONS_ENABLED
#define MOODYCAMEL_TRY try
#define MOODYCAMEL_CATCH(...) catch(__VA_ARGS__)
#define MOODYCAMEL_RETHROW throw
#else
#define MOODYCAMEL_TRY if (true)
#define MOODYCAMEL_CATCH(...) else if (false)
#define MOODYCAMEL_RETHROW
#endif
#endif
#ifndef MOODYCAMEL_NOEXCEPT
#if !defined(MOODYCAMEL_EXCEPTIONS_ENABLED)
#define MOODYCAMEL_NOEXCEPT
#define MOODYCAMEL_NOEXCEPT_CTOR(type, valueType, expr) true
#define MOODYCAMEL_NOEXCEPT_ASSIGN(type, valueType, expr) true
#elif defined(_MSC_VER) && defined(_NOEXCEPT) && _MSC_VER < 1900
#define MOODYCAMEL_NOEXCEPT _NOEXCEPT
#define MOODYCAMEL_NOEXCEPT_CTOR(type, valueType, expr) (std::is_rvalue_reference<valueType>::value && std::is_move_constructible<type>::value ? std::is_trivially_move_constructible<type>::value || std::is_nothrow_move_constructible<type>::value : std::is_trivially_copy_constructible<type>::value || std::is_nothrow_copy_constructible<type>::value)
#define MOODYCAMEL_NOEXCEPT_ASSIGN(type, valueType, expr) ((std::is_rvalue_reference<valueType>::value && std::is_move_assignable<type>::value ? std::is_trivially_move_assignable<type>::value || std::is_nothrow_move_assignable<type>::value : std::is_trivially_copy_assignable<type>::value || std::is_nothrow_copy_assignable<type>::value) && MOODYCAMEL_NOEXCEPT_CTOR(type, valueType, expr))
#else
#define MOODYCAMEL_NOEXCEPT noexcept
#define MOODYCAMEL_NOEXCEPT_CTOR(type, valueType, expr) noexcept(expr)
#define MOODYCAMEL_NOEXCEPT_ASSIGN(type, valueType, expr) noexcept(expr)
#endif
#endif
#ifndef MOODYCAMEL_CPP11_THREAD_LOCAL_SUPPORTED
#ifdef MCDBGQ_USE_RELACY
#define MOODYCAMEL_CPP11_THREAD_LOCAL_SUPPORTED
#else
//// VS2013 doesn't support `thread_local`, and MinGW-w64 w/ POSIX threading has a crippling bug: http://sourceforge.net/p/mingw-w64/bugs/445
//// g++ <=4.7 doesn't support thread_local either
//#if (!defined(_MSC_VER) || _MSC_VER >= 1900) && (!defined(__MINGW32__) && !defined(__MINGW64__) || !defined(__WINPTHREADS_VERSION)) && (!defined(__GNUC__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 8))
//// Assume `thread_local` is fully supported in all other C++11 compilers/runtimes
//#define MOODYCAMEL_CPP11_THREAD_LOCAL_SUPPORTED
//#endif
#endif
#endif
// Compiler-specific likely/unlikely hints
namespace moodycamel { namespace details {
#if defined(__GNUC__)
inline bool likely(bool x) { return __builtin_expect((x), true); }
inline bool unlikely(bool x) { return __builtin_expect((x), false); }
#else
inline bool likely(bool x) { return x; }
inline bool unlikely(bool x) { return x; }
#endif
} }
#ifdef MOODYCAMEL_QUEUE_INTERNAL_DEBUG
#include "internal/concurrentqueue_internal_debug.h"
#endif
namespace moodycamel {
namespace details {
template<typename T>
struct const_numeric_max {
static_assert(std::is_integral<T>::value, "const_numeric_max can only be used with integers");
static const T value = std::numeric_limits<T>::is_signed
? (static_cast<T>(1) << (sizeof(T) * CHAR_BIT - 1)) - static_cast<T>(1)
: static_cast<T>(-1);
};
}
// Default traits for the ConcurrentQueue. To change some of the
// traits without re-implementing all of them, inherit from this
// struct and shadow the declarations you wish to be different;
// since the traits are used as a template type parameter, the
// shadowed declarations will be used where defined, and the defaults
// otherwise.
struct ConcurrentQueueDefaultTraits
{
// General-purpose size type. std::size_t is strongly recommended.
typedef std::size_t size_t;
// The type used for the enqueue and dequeue indices. Must be at least as
// large as size_t. Should be significantly larger than the number of elements
// you expect to hold at once, especially if you have a high turnover rate;
// for example, on 32-bit x86, if you expect to have over a hundred million
// elements or pump several million elements through your queue in a very
// short space of time, using a 32-bit type *may* trigger a race condition.
// A 64-bit int type is recommended in that case, and in practice will
// prevent a race condition no matter the usage of the queue. Note that
// whether the queue is lock-free with a 64-int type depends on the whether
// std::atomic<std::uint64_t> is lock-free, which is platform-specific.
typedef std::size_t index_t;
// Internally, all elements are enqueued and dequeued from multi-element
// blocks; this is the smallest controllable unit. If you expect few elements
// but many producers, a smaller block size should be favoured. For few producers
// and/or many elements, a larger block size is preferred. A sane default
// is provided. Must be a power of 2.
static const size_t BLOCK_SIZE = 32;
// For explicit producers (i.e. when using a producer token), the block is
// checked for being empty by iterating through a list of flags, one per element.
// For large block sizes, this is too inefficient, and switching to an atomic
// counter-based approach is faster. The switch is made for block sizes strictly
// larger than this threshold.
static const size_t EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD = 32;
// How many full blocks can be expected for a single explicit producer? This should
// reflect that number's maximum for optimal performance. Must be a power of 2.
static const size_t EXPLICIT_INITIAL_INDEX_SIZE = 32;
// How many full blocks can be expected for a single implicit producer? This should
// reflect that number's maximum for optimal performance. Must be a power of 2.
static const size_t IMPLICIT_INITIAL_INDEX_SIZE = 32;
// The initial size of the hash table mapping thread IDs to implicit producers.
// Note that the hash is resized every time it becomes half full.
// Must be a power of two, and either 0 or at least 1. If 0, implicit production
// (using the enqueue methods without an explicit producer token) is disabled.
static const size_t INITIAL_IMPLICIT_PRODUCER_HASH_SIZE = 32;
// Controls the number of items that an explicit consumer (i.e. one with a token)
// must consume before it causes all consumers to rotate and move on to the next
// internal queue.
static const std::uint32_t EXPLICIT_CONSUMER_CONSUMPTION_QUOTA_BEFORE_ROTATE = 256;
// The maximum number of elements (inclusive) that can be enqueued to a sub-queue.
// Enqueue operations that would cause this limit to be surpassed will fail. Note
// that this limit is enforced at the block level (for performance reasons), i.e.
// it's rounded up to the nearest block size.
static const size_t MAX_SUBQUEUE_SIZE = details::const_numeric_max<size_t>::value;
#ifndef MCDBGQ_USE_RELACY
// Memory allocation can be customized if needed.
// malloc should return nullptr on failure, and handle alignment like std::malloc.
static inline void* malloc(size_t size) { return std::malloc(size); }
static inline void free(void* ptr) { return std::free(ptr); }
#else
// Debug versions when running under the Relacy race detector (ignore
// these in user code)
static inline void* malloc(size_t size) { return rl::rl_malloc(size, $); }
static inline void free(void* ptr) { return rl::rl_free(ptr, $); }
#endif
};
// When producing or consuming many elements, the most efficient way is to:
// 1) Use one of the bulk-operation methods of the queue with a token
// 2) Failing that, use the bulk-operation methods without a token
// 3) Failing that, create a token and use that with the single-item methods
// 4) Failing that, use the single-parameter methods of the queue
// Having said that, don't create tokens willy-nilly -- ideally there should be
// a maximum of one token per thread (of each kind).
struct ProducerToken;
struct ConsumerToken;
template<typename T, typename Traits> class ConcurrentQueue;
class ConcurrentQueueTests;
namespace details
{
struct ConcurrentQueueProducerTypelessBase
{
ConcurrentQueueProducerTypelessBase* next;
std::atomic<bool> inactive;
ProducerToken* token;
ConcurrentQueueProducerTypelessBase()
: inactive(false), token(nullptr)
{
}
};
template<bool use32> struct _hash_32_or_64 {
static inline std::uint32_t hash(std::uint32_t h)
{
// MurmurHash3 finalizer -- see https://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
// Since the thread ID is already unique, all we really want to do is propagate that
// uniqueness evenly across all the bits, so that we can use a subset of the bits while
// reducing collisions significantly
h ^= h >> 16;
h *= 0x85ebca6b;
h ^= h >> 13;
h *= 0xc2b2ae35;
return h ^ (h >> 16);
}
};
template<> struct _hash_32_or_64<1> {
static inline std::uint64_t hash(std::uint64_t h)
{
h ^= h >> 33;
h *= 0xff51afd7ed558ccd;
h ^= h >> 33;
h *= 0xc4ceb9fe1a85ec53;
return h ^ (h >> 33);
}
};
template<std::size_t size> struct hash_32_or_64 : public _hash_32_or_64<(size > 4)> { };
static inline size_t hash_thread_id(thread_id_t id)
{
static_assert(sizeof(thread_id_t) <= 8, "Expected a platform where thread IDs are at most 64-bit values");
return static_cast<size_t>(hash_32_or_64<sizeof(thread_id_t)>::hash(id));
}
template<typename T>
static inline bool circular_less_than(T a, T b)
{
#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable: 4554)
#endif
static_assert(std::is_integral<T>::value && !std::numeric_limits<T>::is_signed, "circular_less_than is intended to be used only with unsigned integer types");
return static_cast<T>(a - b) > static_cast<T>(static_cast<T>(1) << static_cast<T>(sizeof(T) * CHAR_BIT - 1));
#ifdef _MSC_VER
#pragma warning(pop)
#endif
}
template<typename U>
static inline 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;
}
template<typename T>
static inline T ceil_to_pow_2(T x)
{
static_assert(std::is_integral<T>::value && !std::numeric_limits<T>::is_signed, "ceil_to_pow_2 is intended to be used only with unsigned integer types");
// Adapted from http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
--x;
x |= x >> 1;
x |= x >> 2;
x |= x >> 4;
for (std::size_t i = 1; i < sizeof(T); i <<= 1) {
x |= x >> (i << 3);
}
++x;
return x;
}
template<typename T>
static inline void swap_relaxed(std::atomic<T>& left, std::atomic<T>& right)
{
T temp = std::move(left.load(std::memory_order_relaxed));
left.store(std::move(right.load(std::memory_order_relaxed)), std::memory_order_relaxed);
right.store(std::move(temp), std::memory_order_relaxed);
}
template<typename T>
static inline T const& nomove(T const& x)
{
return x;
}
template<bool Enable>
struct nomove_if
{
template<typename T>
static inline T const& eval(T const& x)
{
return x;
}
};
template<>
struct nomove_if<false>
{
template<typename U>
static inline auto eval(U&& x)
-> decltype(std::forward<U>(x))
{
return std::forward<U>(x);
}
};
template<typename It>
static inline auto deref_noexcept(It& it) MOODYCAMEL_NOEXCEPT -> decltype(*it)
{
return *it;
}
#if defined(__APPLE__) || !defined(__GNUC__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 8)
template<typename T> struct is_trivially_destructible : std::is_trivially_destructible<T> { };
#else
template<typename T> struct is_trivially_destructible : std::has_trivial_destructor<T> { };
#endif
#ifdef MOODYCAMEL_CPP11_THREAD_LOCAL_SUPPORTED
#ifdef MCDBGQ_USE_RELACY
typedef RelacyThreadExitListener ThreadExitListener;
typedef RelacyThreadExitNotifier ThreadExitNotifier;
#else
struct ThreadExitListener
{
typedef void (*callback_t)(void*);
callback_t callback;
void* userData;
ThreadExitListener* next; // reserved for use by the ThreadExitNotifier
};
class ThreadExitNotifier
{
public:
static void subscribe(ThreadExitListener* listener)
{
auto& tlsInst = instance();
listener->next = tlsInst.tail;
tlsInst.tail = listener;
}
static void unsubscribe(ThreadExitListener* listener)
{
auto& tlsInst = instance();
ThreadExitListener** prev = &tlsInst.tail;
for (auto ptr = tlsInst.tail; ptr != nullptr; ptr = ptr->next) {
if (ptr == listener) {
*prev = ptr->next;
break;
}
prev = &ptr->next;
}
}
private:
ThreadExitNotifier() : tail(nullptr) { }
ThreadExitNotifier(ThreadExitNotifier const&) = delete;
ThreadExitNotifier& operator=(ThreadExitNotifier const&) = delete;
~ThreadExitNotifier()
{
// This thread is about to exit, let everyone know!
assert(this == &instance() && "If this assert fails, you likely have a buggy compiler! Change the preprocessor conditions such that MOODYCAMEL_CPP11_THREAD_LOCAL_SUPPORTED is no longer defined.");
for (auto ptr = tail; ptr != nullptr; ptr = ptr->next) {
ptr->callback(ptr->userData);
}
}
// Thread-local
static inline ThreadExitNotifier& instance()
{
static thread_local ThreadExitNotifier notifier;
return notifier;
}
private:
ThreadExitListener* tail;
};
#endif
#endif
template<typename T> struct static_is_lock_free_num { enum { value = 0 }; };
template<> struct static_is_lock_free_num<signed char> { enum { value = ATOMIC_CHAR_LOCK_FREE }; };
template<> struct static_is_lock_free_num<short> { enum { value = ATOMIC_SHORT_LOCK_FREE }; };
template<> struct static_is_lock_free_num<int> { enum { value = ATOMIC_INT_LOCK_FREE }; };
template<> struct static_is_lock_free_num<long> { enum { value = ATOMIC_LONG_LOCK_FREE }; };
template<> struct static_is_lock_free_num<long long> { enum { value = ATOMIC_LLONG_LOCK_FREE }; };
template<typename T> struct static_is_lock_free : static_is_lock_free_num<typename std::make_signed<T>::type> { };
template<> struct static_is_lock_free<bool> { enum { value = ATOMIC_BOOL_LOCK_FREE }; };
template<typename U> struct static_is_lock_free<U*> { enum { value = ATOMIC_POINTER_LOCK_FREE }; };
}
struct ProducerToken
{
template<typename T, typename Traits>
explicit ProducerToken(ConcurrentQueue<T, Traits>& queue);
explicit ProducerToken(ProducerToken&& other) MOODYCAMEL_NOEXCEPT
: producer(other.producer)
{
other.producer = nullptr;
if (producer != nullptr) {
producer->token = this;
}
}
inline ProducerToken& operator=(ProducerToken&& other) MOODYCAMEL_NOEXCEPT
{
swap(other);
return *this;
}
void swap(ProducerToken& other) MOODYCAMEL_NOEXCEPT
{
std::swap(producer, other.producer);
if (producer != nullptr) {
producer->token = this;
}
if (other.producer != nullptr) {
other.producer->token = &other;
}
}
// A token is always valid unless:
// 1) Memory allocation failed during construction
// 2) It was moved via the move constructor
// (Note: assignment does a swap, leaving both potentially valid)
// 3) The associated queue was destroyed
// Note that if valid() returns true, that only indicates
// that the token is valid for use with a specific queue,
// but not which one; that's up to the user to track.
inline bool valid() const { return producer != nullptr; }
~ProducerToken()
{
if (producer != nullptr) {
producer->token = nullptr;
producer->inactive.store(true, std::memory_order_release);
}
}
// Disable copying and assignment
ProducerToken(ProducerToken const&) = delete;
ProducerToken& operator=(ProducerToken const&) = delete;
private:
template<typename T, typename Traits> friend class ConcurrentQueue;
friend class ConcurrentQueueTests;
protected:
details::ConcurrentQueueProducerTypelessBase* producer;
};
struct ConsumerToken
{
template<typename T, typename Traits>
explicit ConsumerToken(ConcurrentQueue<T, Traits>& q);
explicit ConsumerToken(ConsumerToken&& other) MOODYCAMEL_NOEXCEPT
: initialOffset(other.initialOffset), lastKnownGlobalOffset(other.lastKnownGlobalOffset), itemsConsumedFromCurrent(other.itemsConsumedFromCurrent), currentProducer(other.currentProducer), desiredProducer(other.desiredProducer)
{
}
inline ConsumerToken& operator=(ConsumerToken&& other) MOODYCAMEL_NOEXCEPT
{
swap(other);
return *this;
}
void swap(ConsumerToken& other) MOODYCAMEL_NOEXCEPT
{
std::swap(initialOffset, other.initialOffset);
std::swap(lastKnownGlobalOffset, other.lastKnownGlobalOffset);
std::swap(itemsConsumedFromCurrent, other.itemsConsumedFromCurrent);
std::swap(currentProducer, other.currentProducer);
std::swap(desiredProducer, other.desiredProducer);
}
// Disable copying and assignment
ConsumerToken(ConsumerToken const&) = delete;
ConsumerToken& operator=(ConsumerToken const&) = delete;
private:
template<typename T, typename Traits> friend class ConcurrentQueue;
friend class ConcurrentQueueTests;
private: // but shared with ConcurrentQueue
std::uint32_t initialOffset;
std::uint32_t lastKnownGlobalOffset;
std::uint32_t itemsConsumedFromCurrent;
details::ConcurrentQueueProducerTypelessBase* currentProducer;
details::ConcurrentQueueProducerTypelessBase* desiredProducer;
};
// Need to forward-declare this swap because it's in a namespace.
// See http://stackoverflow.com/questions/4492062/why-does-a-c-friend-class-need-a-forward-declaration-only-in-other-namespaces
template<typename T, typename Traits>
inline void swap(typename ConcurrentQueue<T, Traits>::ImplicitProducerKVP& a, typename ConcurrentQueue<T, Traits>::ImplicitProducerKVP& b) MOODYCAMEL_NOEXCEPT;
template<typename T, typename Traits = ConcurrentQueueDefaultTraits>
class ConcurrentQueue
{
public:
typedef ::moodycamel::ProducerToken producer_token_t;
typedef ::moodycamel::ConsumerToken consumer_token_t;
typedef typename Traits::index_t index_t;
typedef typename Traits::size_t size_t;
static const size_t BLOCK_SIZE = static_cast<size_t>(Traits::BLOCK_SIZE);
static const size_t EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD = static_cast<size_t>(Traits::EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD);
static const size_t EXPLICIT_INITIAL_INDEX_SIZE = static_cast<size_t>(Traits::EXPLICIT_INITIAL_INDEX_SIZE);
static const size_t IMPLICIT_INITIAL_INDEX_SIZE = static_cast<size_t>(Traits::IMPLICIT_INITIAL_INDEX_SIZE);
static const size_t INITIAL_IMPLICIT_PRODUCER_HASH_SIZE = static_cast<size_t>(Traits::INITIAL_IMPLICIT_PRODUCER_HASH_SIZE);
static const std::uint32_t EXPLICIT_CONSUMER_CONSUMPTION_QUOTA_BEFORE_ROTATE = static_cast<std::uint32_t>(Traits::EXPLICIT_CONSUMER_CONSUMPTION_QUOTA_BEFORE_ROTATE);
#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable: 4307) // + integral constant overflow (that's what the ternary expression is for!)
#pragma warning(disable: 4309) // static_cast: Truncation of constant value
#endif
static const size_t MAX_SUBQUEUE_SIZE = (details::const_numeric_max<size_t>::value - static_cast<size_t>(Traits::MAX_SUBQUEUE_SIZE) < BLOCK_SIZE) ? details::const_numeric_max<size_t>::value : ((static_cast<size_t>(Traits::MAX_SUBQUEUE_SIZE) + (BLOCK_SIZE - 1)) / BLOCK_SIZE * BLOCK_SIZE);
#ifdef _MSC_VER
#pragma warning(pop)
#endif
static_assert(!std::numeric_limits<size_t>::is_signed && std::is_integral<size_t>::value, "Traits::size_t must be an unsigned integral type");
static_assert(!std::numeric_limits<index_t>::is_signed && std::is_integral<index_t>::value, "Traits::index_t must be an unsigned integral type");
static_assert(sizeof(index_t) >= sizeof(size_t), "Traits::index_t must be at least as wide as Traits::size_t");
static_assert((BLOCK_SIZE > 1) && !(BLOCK_SIZE & (BLOCK_SIZE - 1)), "Traits::BLOCK_SIZE must be a power of 2 (and at least 2)");
static_assert((EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD > 1) && !(EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD & (EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD - 1)), "Traits::EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD must be a power of 2 (and greater than 1)");
static_assert((EXPLICIT_INITIAL_INDEX_SIZE > 1) && !(EXPLICIT_INITIAL_INDEX_SIZE & (EXPLICIT_INITIAL_INDEX_SIZE - 1)), "Traits::EXPLICIT_INITIAL_INDEX_SIZE must be a power of 2 (and greater than 1)");
static_assert((IMPLICIT_INITIAL_INDEX_SIZE > 1) && !(IMPLICIT_INITIAL_INDEX_SIZE & (IMPLICIT_INITIAL_INDEX_SIZE - 1)), "Traits::IMPLICIT_INITIAL_INDEX_SIZE must be a power of 2 (and greater than 1)");
static_assert((INITIAL_IMPLICIT_PRODUCER_HASH_SIZE == 0) || !(INITIAL_IMPLICIT_PRODUCER_HASH_SIZE & (INITIAL_IMPLICIT_PRODUCER_HASH_SIZE - 1)), "Traits::INITIAL_IMPLICIT_PRODUCER_HASH_SIZE must be a power of 2");
static_assert(INITIAL_IMPLICIT_PRODUCER_HASH_SIZE == 0 || INITIAL_IMPLICIT_PRODUCER_HASH_SIZE >= 1, "Traits::INITIAL_IMPLICIT_PRODUCER_HASH_SIZE must be at least 1 (or 0 to disable implicit enqueueing)");
public:
// Creates a queue with at least `capacity` element slots; note that the
// actual number of elements that can be inserted without additional memory
// allocation depends on the number of producers and the block size (e.g. if
// the block size is equal to `capacity`, only a single block will be allocated
// up-front, which means only a single producer will be able to enqueue elements
// without an extra allocation -- blocks aren't shared between producers).
// This method is not thread safe -- it is up to the user to ensure that the
// queue is fully constructed before it starts being used by other threads (this
// includes making the memory effects of construction visible, possibly with a
// memory barrier).
explicit ConcurrentQueue(size_t capacity = 6 * BLOCK_SIZE)
: producerListTail(nullptr),
producerCount(0),
initialBlockPoolIndex(0),
nextExplicitConsumerId(0),
globalExplicitConsumerOffset(0)
{
implicitProducerHashResizeInProgress.clear(std::memory_order_relaxed);
populate_initial_implicit_producer_hash();
populate_initial_block_list(capacity / BLOCK_SIZE + ((capacity & (BLOCK_SIZE - 1)) == 0 ? 0 : 1));
#ifdef MOODYCAMEL_QUEUE_INTERNAL_DEBUG
// Track all the producers using a fully-resolved typed list for
// each kind; this makes it possible to debug them starting from
// the root queue object (otherwise wacky casts are needed that
// don't compile in the debugger's expression evaluator).
explicitProducers.store(nullptr, std::memory_order_relaxed);
implicitProducers.store(nullptr, std::memory_order_relaxed);
#endif
}
// Note: The queue should not be accessed concurrently while it's
// being deleted. It's up to the user to synchronize this.
// This method is not thread safe.
~ConcurrentQueue()
{
// Destroy producers
auto ptr = producerListTail.load(std::memory_order_relaxed);
while (ptr != nullptr) {
auto next = ptr->next_prod();
if (ptr->token != nullptr) {
ptr->token->producer = nullptr;
}
destroy(ptr);
ptr = next;
}
// Destroy implicit producer hash tables
if (INITIAL_IMPLICIT_PRODUCER_HASH_SIZE != 0) {
auto hash = implicitProducerHash.load(std::memory_order_relaxed);
while (hash != nullptr) {
auto prev = hash->prev;
if (prev != nullptr) { // The last hash is part of this object and was not allocated dynamically
for (size_t i = 0; i != hash->capacity; ++i) {
hash->entries[i].~ImplicitProducerKVP();
}
hash->~ImplicitProducerHash();
Traits::free(hash);
}
hash = prev;
}
}
// Destroy global free list
auto block = freeList.head_unsafe();
while (block != nullptr) {
auto next = block->freeListNext.load(std::memory_order_relaxed);
if (block->dynamicallyAllocated) {
destroy(block);
}
block = next;
}
// Destroy initial free list
destroy_array(initialBlockPool, initialBlockPoolSize);
}
// Disable copying and copy assignment
ConcurrentQueue(ConcurrentQueue const&) = delete;
ConcurrentQueue& operator=(ConcurrentQueue const&) = delete;
// Moving is supported, but note that it is *not* a thread-safe operation.
// Nobody can use the queue while it's being moved, and the memory effects
// of that move must be propagated to other threads before they can use it.
// Note: When a queue is moved, its tokens are still valid but can only be
// used with the destination queue (i.e. semantically they are moved along
// with the queue itself).
ConcurrentQueue(ConcurrentQueue&& other) MOODYCAMEL_NOEXCEPT
: producerListTail(other.producerListTail.load(std::memory_order_relaxed)),
producerCount(other.producerCount.load(std::memory_order_relaxed)),
initialBlockPoolIndex(other.initialBlockPoolIndex.load(std::memory_order_relaxed)),
initialBlockPool(other.initialBlockPool),
initialBlockPoolSize(other.initialBlockPoolSize),
freeList(std::move(other.freeList)),
nextExplicitConsumerId(other.nextExplicitConsumerId.load(std::memory_order_relaxed)),
globalExplicitConsumerOffset(other.globalExplicitConsumerOffset.load(std::memory_order_relaxed))
{
// Move the other one into this, and leave the other one as an empty queue
implicitProducerHashResizeInProgress.clear(std::memory_order_relaxed);
populate_initial_implicit_producer_hash();
swap_implicit_producer_hashes(other);
other.producerListTail.store(nullptr, std::memory_order_relaxed);
other.producerCount.store(0, std::memory_order_relaxed);
other.nextExplicitConsumerId.store(0, std::memory_order_relaxed);
other.globalExplicitConsumerOffset.store(0, std::memory_order_relaxed);
#ifdef MOODYCAMEL_QUEUE_INTERNAL_DEBUG
explicitProducers.store(other.explicitProducers.load(std::memory_order_relaxed), std::memory_order_relaxed);
other.explicitProducers.store(nullptr, std::memory_order_relaxed);
implicitProducers.store(other.implicitProducers.load(std::memory_order_relaxed), std::memory_order_relaxed);
other.implicitProducers.store(nullptr, std::memory_order_relaxed);
#endif
other.initialBlockPoolIndex.store(0, std::memory_order_relaxed);
other.initialBlockPoolSize = 0;
other.initialBlockPool = nullptr;
reown_producers();
}
inline ConcurrentQueue& operator=(ConcurrentQueue&& other) MOODYCAMEL_NOEXCEPT
{
return swap_internal(other);
}
// Swaps this queue's state with the other's. Not thread-safe.
// Swapping two queues does not invalidate their tokens, however
// the tokens that were created for one queue must be used with
// only the swapped queue (i.e. the tokens are tied to the
// queue's movable state, not the object itself).
inline void swap(ConcurrentQueue& other) MOODYCAMEL_NOEXCEPT
{
swap_internal(other);
}
private:
ConcurrentQueue& swap_internal(ConcurrentQueue& other)
{
if (this == &other) {
return *this;
}
details::swap_relaxed(producerListTail, other.producerListTail);
details::swap_relaxed(producerCount, other.producerCount);
details::swap_relaxed(initialBlockPoolIndex, other.initialBlockPoolIndex);
std::swap(initialBlockPool, other.initialBlockPool);
std::swap(initialBlockPoolSize, other.initialBlockPoolSize);
freeList.swap(other.freeList);
details::swap_relaxed(nextExplicitConsumerId, other.nextExplicitConsumerId);
details::swap_relaxed(globalExplicitConsumerOffset, other.globalExplicitConsumerOffset);
swap_implicit_producer_hashes(other);
reown_producers();
other.reown_producers();
#ifdef MOODYCAMEL_QUEUE_INTERNAL_DEBUG
details::swap_relaxed(explicitProducers, other.explicitProducers);
details::swap_relaxed(implicitProducers, other.implicitProducers);
#endif
return *this;
}
public:
// Enqueues a single item (by copying it).
// Allocates memory if required. Only fails if memory allocation fails (or implicit
// production is disabled because Traits::INITIAL_IMPLICIT_PRODUCER_HASH_SIZE is 0,
// or Traits::MAX_SUBQUEUE_SIZE has been defined and would be surpassed).
// Thread-safe.
inline bool enqueue(T const& item)
{
if (INITIAL_IMPLICIT_PRODUCER_HASH_SIZE == 0) return false;
return inner_enqueue<CanAlloc>(item);
}
// Enqueues a single item (by moving it, if possible).
// Allocates memory if required. Only fails if memory allocation fails (or implicit
// production is disabled because Traits::INITIAL_IMPLICIT_PRODUCER_HASH_SIZE is 0,
// or Traits::MAX_SUBQUEUE_SIZE has been defined and would be surpassed).
// Thread-safe.
inline bool enqueue(T&& item)
{
if (INITIAL_IMPLICIT_PRODUCER_HASH_SIZE == 0) return false;
return inner_enqueue<CanAlloc>(std::move(item));
}
// Enqueues a single item (by copying it) using an explicit producer token.
// Allocates memory if required. Only fails if memory allocation fails (or
// Traits::MAX_SUBQUEUE_SIZE has been defined and would be surpassed).
// Thread-safe.
inline bool enqueue(producer_token_t const& token, T const& item)
{
return inner_enqueue<CanAlloc>(token, item);
}
// Enqueues a single item (by moving it, if possible) using an explicit producer token.
// Allocates memory if required. Only fails if memory allocation fails (or
// Traits::MAX_SUBQUEUE_SIZE has been defined and would be surpassed).
// Thread-safe.
inline bool enqueue(producer_token_t const& token, T&& item)
{
return inner_enqueue<CanAlloc>(token, std::move(item));
}
// Enqueues several items.
// Allocates memory if required. Only fails if memory allocation fails (or
// implicit production is disabled because Traits::INITIAL_IMPLICIT_PRODUCER_HASH_SIZE
// is 0, or Traits::MAX_SUBQUEUE_SIZE has been defined and would be surpassed).
// Note: Use std::make_move_iterator if the elements should be moved instead of copied.
// Thread-safe.
template<typename It>
bool enqueue_bulk(It itemFirst, size_t count)
{
if (INITIAL_IMPLICIT_PRODUCER_HASH_SIZE == 0) return false;
return inner_enqueue_bulk<CanAlloc>(std::forward<It>(itemFirst), count);
}
// Enqueues several items using an explicit producer token.
// Allocates memory if required. Only fails if memory allocation fails
// (or Traits::MAX_SUBQUEUE_SIZE has been defined and would be surpassed).
// Note: Use std::make_move_iterator if the elements should be moved
// instead of copied.
// Thread-safe.
template<typename It>
bool enqueue_bulk(producer_token_t const& token, It itemFirst, size_t count)
{
return inner_enqueue_bulk<CanAlloc>(token, std::forward<It>(itemFirst), count);
}
// Enqueues a single item (by copying it).
// Does not allocate memory. Fails if not enough room to enqueue (or implicit
// production is disabled because Traits::INITIAL_IMPLICIT_PRODUCER_HASH_SIZE
// is 0).
// Thread-safe.
inline bool try_enqueue(T const& item)
{
if (INITIAL_IMPLICIT_PRODUCER_HASH_SIZE == 0) return false;
return inner_enqueue<CannotAlloc>(item);
}
// Enqueues a single item (by moving it, if possible).
// Does not allocate memory (except for one-time implicit producer).
// Fails if not enough room to enqueue (or implicit production is
// disabled because Traits::INITIAL_IMPLICIT_PRODUCER_HASH_SIZE is 0).
// Thread-safe.
inline bool try_enqueue(T&& item)
{
if (INITIAL_IMPLICIT_PRODUCER_HASH_SIZE == 0) return false;
return inner_enqueue<CannotAlloc>(std::move(item));
}
// Enqueues a single item (by copying it) using an explicit producer token.
// Does not allocate memory. Fails if not enough room to enqueue.
// Thread-safe.
inline bool try_enqueue(producer_token_t const& token, T const& item)
{
return inner_enqueue<CannotAlloc>(token, item);
}
// Enqueues a single item (by moving it, if possible) using an explicit producer token.
// Does not allocate memory. Fails if not enough room to enqueue.
// Thread-safe.
inline bool try_enqueue(producer_token_t const& token, T&& item)
{
return inner_enqueue<CannotAlloc>(token, std::move(item));
}
// Enqueues several items.
// Does not allocate memory (except for one-time implicit producer).
// Fails if not enough room to enqueue (or implicit production is
// disabled because Traits::INITIAL_IMPLICIT_PRODUCER_HASH_SIZE is 0).
// Note: Use std::make_move_iterator if the elements should be moved
// instead of copied.
// Thread-safe.
template<typename It>
bool try_enqueue_bulk(It itemFirst, size_t count)
{
if (INITIAL_IMPLICIT_PRODUCER_HASH_SIZE == 0) return false;
return inner_enqueue_bulk<CannotAlloc>(std::forward<It>(itemFirst), count);
}
// Enqueues several items using an explicit producer token.
// Does not allocate memory. Fails if not enough room to enqueue.
// Note: Use std::make_move_iterator if the elements should be moved
// instead of copied.
// Thread-safe.
template<typename It>
bool try_enqueue_bulk(producer_token_t const& token, It itemFirst, size_t count)
{
return inner_enqueue_bulk<CannotAlloc>(token, std::forward<It>(itemFirst), count);
}
// Attempts to dequeue from the queue.
// Returns false if all producer streams appeared empty at the time they
// were checked (so, the queue is likely but not guaranteed to be empty).
// Never allocates. Thread-safe.
template<typename U>
bool try_dequeue(U& item)
{
// Instead of simply trying each producer in turn (which could cause needless contention on the first
// producer), we score them heuristically.
size_t nonEmptyCount = 0;
ProducerBase* best = nullptr;
size_t bestSize = 0;
for (auto ptr = producerListTail.load(std::memory_order_acquire); nonEmptyCount < 3 && ptr != nullptr; ptr = ptr->next_prod()) {
auto size = ptr->size_approx();
if (size > 0) {
if (size > bestSize) {
bestSize = size;
best = ptr;
}
++nonEmptyCount;
}
}
// If there was at least one non-empty queue but it appears empty at the time
// we try to dequeue from it, we need to make sure every queue's been tried
if (nonEmptyCount > 0) {
if (details::likely(best->dequeue(item))) {
return true;
}
for (auto ptr = producerListTail.load(std::memory_order_acquire); ptr != nullptr; ptr = ptr->next_prod()) {
if (ptr != best && ptr->dequeue(item)) {
return true;
}
}
}
return false;
}
// Attempts to dequeue from the queue.
// Returns false if all producer streams appeared empty at the time they
// were checked (so, the queue is likely but not guaranteed to be empty).
// This differs from the try_dequeue(item) method in that this one does
// not attempt to reduce contention by interleaving the order that producer
// streams are dequeued from. So, using this method can reduce overall throughput
// under contention, but will give more predictable results in single-threaded
// consumer scenarios.
// Never allocates. Thread-safe.
template<typename U>
bool try_dequeue_non_interleaved(U& item)
{
for (auto ptr = producerListTail.load(std::memory_order_acquire); ptr != nullptr; ptr = ptr->next_prod()) {
if (ptr->dequeue(item)) {
return true;
}
}
return false;
}
// Attempts to dequeue from the queue using an explicit consumer token.
// Returns false if all producer streams appeared empty at the time they
// were checked (so, the queue is likely but not guaranteed to be empty).
// Never allocates. Thread-safe.
template<typename U>
bool try_dequeue(consumer_token_t& token, U& item)
{
// The idea is roughly as follows:
// Every 256 items from one producer, make everyone rotate (increase the global offset) -> this means the highest efficiency consumer dictates the rotation speed of everyone else, more or less
// If you see that the global offset has changed, you must reset your consumption counter and move to your designated place
// If there's no items where you're supposed to be, keep moving until you find a producer with some items
// If the global offset has not changed but you've run out of items to consume, move over from your current position until you find an producer with something in it
if (token.desiredProducer == nullptr || token.lastKnownGlobalOffset != globalExplicitConsumerOffset.load(std::memory_order_relaxed)) {
if (!update_current_producer_after_rotation(token)) {
return false;
You can’t perform that action at this time.