// 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) 2013-2016, 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
#if defined(__APPLE__)
#include "TargetConditionals.h"
#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 // Requires C++11. Sorry VS2010.
#include
#endif
#include // for max_align_t
#include
#include
#include
#include
#include
#include
#include // for CHAR_BIT
#include
#include // partly for __WINPTHREADS_VERSION if on MinGW-w64 w/ POSIX threading
// Platform-specific definitions of a numeric thread ID type and an invalid value
namespace moodycamel { namespace details {
template struct thread_id_converter {
typedef thread_id_t thread_id_numeric_size_t;
typedef thread_id_t thread_id_hash_t;
static thread_id_hash_t prehash(thread_id_t const& x) { return x; }
};
} }
#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(::GetCurrentThreadId()); }
} }
#elif defined(__APPLE__) && TARGET_OS_IPHONE
namespace moodycamel { namespace details {
static_assert(sizeof(std::thread::id) == 4 || sizeof(std::thread::id) == 8, "std::thread::id is expected to be either 4 or 8 bytes");
typedef std::thread::id thread_id_t;
static const thread_id_t invalid_thread_id; // Default ctor creates invalid ID
// Note we don't define a invalid_thread_id2 since std::thread::id doesn't have one; it's
// only used if MOODYCAMEL_CPP11_THREAD_LOCAL_SUPPORTED is defined anyway, which it won't
// be.
static inline thread_id_t thread_id() { return std::this_thread::get_id(); }
template struct thread_id_size { };
template<> struct thread_id_size<4> { typedef std::uint32_t numeric_t; };
template<> struct thread_id_size<8> { typedef std::uint64_t numeric_t; };
template<> struct thread_id_converter {
typedef thread_id_size::numeric_t thread_id_numeric_size_t;
#ifndef __APPLE__
typedef std::size_t thread_id_hash_t;
#else
typedef thread_id_numeric_size_t thread_id_hash_t;
#endif
static thread_id_hash_t prehash(thread_id_t const& x)
{
#ifndef __APPLE__
return std::hash()(x);
#else
return *reinterpret_cast(&x);
#endif
}
};
} }
#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(&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
#define MOODYCAMEL_THROW(expr) throw (expr)
#else
#define MOODYCAMEL_TRY if (true)
#define MOODYCAMEL_CATCH(...) else if (false)
#define MOODYCAMEL_RETHROW
#define MOODYCAMEL_THROW(expr)
#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 < 1800
// VS2012's std::is_nothrow_[move_]constructible is broken and returns true when it shouldn't :-(
// We have to assume *all* non-trivial constructors may throw on VS2012!
#define MOODYCAMEL_NOEXCEPT _NOEXCEPT
#define MOODYCAMEL_NOEXCEPT_CTOR(type, valueType, expr) (std::is_rvalue_reference::value && std::is_move_constructible::value ? std::is_trivially_move_constructible::value : std::is_trivially_copy_constructible::value)
#define MOODYCAMEL_NOEXCEPT_ASSIGN(type, valueType, expr) ((std::is_rvalue_reference::value && std::is_move_assignable::value ? std::is_trivially_move_assignable::value || std::is_nothrow_move_assignable::value : std::is_trivially_copy_assignable::value || std::is_nothrow_copy_assignable::value) && MOODYCAMEL_NOEXCEPT_CTOR(type, valueType, expr))
#elif defined(_MSC_VER) && defined(_NOEXCEPT) && _MSC_VER < 1900
#define MOODYCAMEL_NOEXCEPT _NOEXCEPT
#define MOODYCAMEL_NOEXCEPT_CTOR(type, valueType, expr) (std::is_rvalue_reference::value && std::is_move_constructible::value ? std::is_trivially_move_constructible::value || std::is_nothrow_move_constructible::value : std::is_trivially_copy_constructible::value || std::is_nothrow_copy_constructible::value)
#define MOODYCAMEL_NOEXCEPT_ASSIGN(type, valueType, expr) ((std::is_rvalue_reference::value && std::is_move_assignable::value ? std::is_trivially_move_assignable::value || std::is_nothrow_move_assignable::value : std::is_trivially_copy_assignable::value || std::is_nothrow_copy_assignable::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.
Finally, iOS/ARM doesn't have support for it either.
//#if (!defined(_MSC_VER) || _MSC_VER >= 1900) && (!defined(__MINGW32__) && !defined(__MINGW64__) || !defined(__WINPTHREADS_VERSION)) && (!defined(__GNUC__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 8)) && (!defined(__APPLE__) || !TARGET_OS_IPHONE)
Assume `thread_local` is fully supported in all other C++11 compilers/runtimes
//#define MOODYCAMEL_CPP11_THREAD_LOCAL_SUPPORTED
//#endif
#endif
#endif
// VS2012 doesn't support deleted functions.
// In this case, we declare the function normally but don't define it. A link error will be generated if the function is called.
#ifndef MOODYCAMEL_DELETE_FUNCTION
#if defined(_MSC_VER) && _MSC_VER < 1800
#define MOODYCAMEL_DELETE_FUNCTION
#else
#define MOODYCAMEL_DELETE_FUNCTION = delete
#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
struct const_numeric_max {
static_assert(std::is_integral::value, "const_numeric_max can only be used with integers");
static const T value = std::numeric_limits::is_signed
? (static_cast(1) << (sizeof(T) * CHAR_BIT - 1)) - static_cast(1)
: static_cast(-1);
};
#ifdef __GNUC__
typedef ::max_align_t max_align_t; // GCC forgot to add it to std:: for a while
#else
typedef std::max_align_t max_align_t; // Others (e.g. MSVC) insist it can *only* be accessed via std::
#endif
}
// 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 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::value;
#ifndef MCDBGQ_USE_RELACY
// Memory allocation can be customized if needed.
// malloc should return nullptr on failure, and handle alignment like std::malloc.
#if defined(malloc) || defined(free)
// Gah, this is 2015, stop defining macros that break standard code already!
// Work around malloc/free being special macros:
static inline void* WORKAROUND_malloc(size_t size) { return malloc(size); }
static inline void WORKAROUND_free(void* ptr) { return free(ptr); }
static inline void* (malloc)(size_t size) { return WORKAROUND_malloc(size); }
static inline void (free)(void* ptr) { return WORKAROUND_free(ptr); }
#else
static inline void* malloc(size_t size) { return std::malloc(size); }
static inline void free(void* ptr) { return std::free(ptr); }
#endif
#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 class ConcurrentQueue;
template class BlockingConcurrentQueue;
class ConcurrentQueueTests;
namespace details
{
struct ConcurrentQueueProducerTypelessBase
{
ConcurrentQueueProducerTypelessBase* next;
std::atomic inactive;
ProducerToken* token;
ConcurrentQueueProducerTypelessBase()
: next(nullptr), inactive(false), token(nullptr)
{
}
};
template 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 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(hash_32_or_64::thread_id_hash_t)>::hash(
thread_id_converter::prehash(id)));
}
template
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::value && !std::numeric_limits::is_signed, "circular_less_than is intended to be used only with unsigned integer types");
return static_cast(a - b) > static_cast(static_cast(1) << static_cast(sizeof(T) * CHAR_BIT - 1));
#ifdef _MSC_VER
#pragma warning(pop)
#endif
}
template
static inline char* align_for(char* ptr)
{
const std::size_t alignment = std::alignment_of::value;
return ptr + (alignment - (reinterpret_cast(ptr) % alignment)) % alignment;
}
template
static inline T ceil_to_pow_2(T x)
{
static_assert(std::is_integral::value && !std::numeric_limits::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
static inline void swap_relaxed(std::atomic& left, std::atomic& 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
static inline T const& nomove(T const& x)
{
return x;
}
template
struct nomove_if
{
template
static inline T const& eval(T const& x)
{
return x;
}
};
template<>
struct nomove_if
{
template
static inline auto eval(U&& x)
-> decltype(std::forward(x))
{
return std::forward(x);
}
};
template
static inline auto deref_noexcept(It& it) MOODYCAMEL_NOEXCEPT -> decltype(*it)
{
return *it;
}
#if defined(__clang__) || !defined(__GNUC__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 8)
template struct is_trivially_destructible : std::is_trivially_destructible { };
#else
template struct is_trivially_destructible : std::has_trivial_destructor { };
#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&) MOODYCAMEL_DELETE_FUNCTION;
ThreadExitNotifier& operator=(ThreadExitNotifier const&) MOODYCAMEL_DELETE_FUNCTION;
~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 struct static_is_lock_free_num { enum { value = 0 }; };
template<> struct static_is_lock_free_num { enum { value = ATOMIC_CHAR_LOCK_FREE }; };
template<> struct static_is_lock_free_num { enum { value = ATOMIC_SHORT_LOCK_FREE }; };
template<> struct static_is_lock_free_num { enum { value = ATOMIC_INT_LOCK_FREE }; };
template<> struct static_is_lock_free_num { enum { value = ATOMIC_LONG_LOCK_FREE }; };
template<> struct static_is_lock_free_num { enum { value = ATOMIC_LLONG_LOCK_FREE }; };
template struct static_is_lock_free : static_is_lock_free_num::type> { };
template<> struct static_is_lock_free { enum { value = ATOMIC_BOOL_LOCK_FREE }; };
template struct static_is_lock_free { enum { value = ATOMIC_POINTER_LOCK_FREE }; };
}
struct ProducerToken
{
template
explicit ProducerToken(ConcurrentQueue& queue);
template
explicit ProducerToken(BlockingConcurrentQueue& queue);
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&) MOODYCAMEL_DELETE_FUNCTION;
ProducerToken& operator=(ProducerToken const&) MOODYCAMEL_DELETE_FUNCTION;
private:
template friend class ConcurrentQueue;
friend class ConcurrentQueueTests;
protected:
details::ConcurrentQueueProducerTypelessBase* producer;
};
struct ConsumerToken
{
template
explicit ConsumerToken(ConcurrentQueue& q);
template
explicit ConsumerToken(BlockingConcurrentQueue& q);
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&) MOODYCAMEL_DELETE_FUNCTION;
ConsumerToken& operator=(ConsumerToken const&) MOODYCAMEL_DELETE_FUNCTION;
private:
template 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
inline void swap(typename ConcurrentQueue::ImplicitProducerKVP& a, typename ConcurrentQueue::ImplicitProducerKVP& b) MOODYCAMEL_NOEXCEPT;
template
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(Traits::BLOCK_SIZE);
static const size_t EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD = static_cast(Traits::EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD);
static const size_t EXPLICIT_INITIAL_INDEX_SIZE = static_cast(Traits::EXPLICIT_INITIAL_INDEX_SIZE);
static const size_t IMPLICIT_INITIAL_INDEX_SIZE = static_cast(Traits::IMPLICIT_INITIAL_INDEX_SIZE);
static const size_t INITIAL_IMPLICIT_PRODUCER_HASH_SIZE = static_cast(Traits::INITIAL_IMPLICIT_PRODUCER_HASH_SIZE);
static const std::uint32_t EXPLICIT_CONSUMER_CONSUMPTION_QUOTA_BEFORE_ROTATE = static_cast(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::value - static_cast(Traits::MAX_SUBQUEUE_SIZE) < BLOCK_SIZE) ? details::const_numeric_max::value : ((static_cast(Traits::MAX_SUBQUEUE_SIZE) + (BLOCK_SIZE - 1)) / BLOCK_SIZE * BLOCK_SIZE);
#ifdef _MSC_VER
#pragma warning(pop)
#endif
static_assert(!std::numeric_limits::is_signed && std::is_integral::value, "Traits::size_t must be an unsigned integral type");
static_assert(!std::numeric_limits::is_signed && std::is_integral::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
}
// Computes the correct amount of pre-allocated blocks for you based
// on the minimum number of elements you want available at any given
// time, and the maximum concurrent number of each type of producer.
ConcurrentQueue(size_t minCapacity, size_t maxExplicitProducers, size_t maxImplicitProducers)
: producerListTail(nullptr),
producerCount(0),
initialBlockPoolIndex(0),
nextExplicitConsumerId(0),
globalExplicitConsumerOffset(0)
{
implicitProducerHashResizeInProgress.clear(std::memory_order_relaxed);
populate_initial_implicit_producer_hash();
size_t blocks = ((((minCapacity + BLOCK_SIZE - 1) / BLOCK_SIZE) - 1) * (maxExplicitProducers + 1) + 2 * (maxExplicitProducers + maxImplicitProducers)) * BLOCK_SIZE;
populate_initial_block_list(blocks);
#ifdef MOODYCAMEL_QUEUE_INTERNAL_DEBUG
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&) MOODYCAMEL_DELETE_FUNCTION;
ConcurrentQueue& operator=(ConcurrentQueue const&) MOODYCAMEL_DELETE_FUNCTION;
// 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(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(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(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(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
bool enqueue_bulk(It itemFirst, size_t count)
{
if (INITIAL_IMPLICIT_PRODUCER_HASH_SIZE == 0) return false;
return inner_enqueue_bulk(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
bool enqueue_bulk(producer_token_t const& token, It itemFirst, size_t count)
{
return inner_enqueue_bulk(token, 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(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(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(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(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
bool try_enqueue_bulk(It itemFirst, size_t count)
{
if (INITIAL_IMPLICIT_PRODUCER_HASH_SIZE == 0) return false;
return inner_enqueue_bulk(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
bool try_enqueue_bulk(producer_token_t const& token, It itemFirst, size_t count)
{
return inner_enqueue_bulk(token, 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
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. This is mostly only useful for internal unit tests.
// Never allocates. Thread-safe.
template
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
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;
}
}
// 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 (static_cast(token.currentProducer)->dequeue(item)) {
if (++token.itemsConsumedFromCurrent == EXPLICIT_CONSUMER_CONSUMPTION_QUOTA_BEFORE_ROTATE) {
globalExplicitConsumerOffset.fetch_add(1, std::memory_order_relaxed);
}
return true;
}
auto tail = producerListTail.load(std::memory_order_acquire);
auto ptr = static_cast(token.currentProducer)->next_prod();
if (ptr == nullptr) {
ptr = tail;
}
while (ptr != static_cast(token.currentProducer)) {
if (ptr->dequeue(item)) {
token.currentProducer = ptr;
token.itemsConsumedFromCurrent = 1;
return true;
}
ptr = ptr->next_prod();
if (ptr == nullptr) {
ptr = tail;
}
}
return false;
}
// Attempts to dequeue several elements from the queue.
// Returns the number of items actually dequeued.
// Returns 0 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
size_t try_dequeue_bulk(It itemFirst, size_t max)
{
size_t count = 0;
for (auto ptr = producerListTail.load(std::memory_order_acquire); ptr != nullptr; ptr = ptr->next_prod()) {
count += ptr->dequeue_bulk(itemFirst, max - count);
if (count == max) {
break;
}
}
return count;
}
// Attempts to dequeue several elements from the queue using an explicit consumer token.
// Returns the number of items actually dequeued.
// Returns 0 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
size_t try_dequeue_bulk(consumer_token_t& token, It itemFirst, size_t max)
{
if (token.desiredProducer == nullptr || token.lastKnownGlobalOffset != globalExplicitConsumerOffset.load(std::memory_order_relaxed)) {
if (!update_current_producer_after_rotation(token)) {
return 0;
}
}
size_t count = static_cast(token.currentProducer)->dequeue_bulk(itemFirst, max);
if (count == max) {
if ((token.itemsConsumedFromCurrent += static_cast(max)) >= EXPLICIT_CONSUMER_CONSUMPTION_QUOTA_BEFORE_ROTATE) {
globalExplicitConsumerOffset.fetch_add(1, std::memory_order_relaxed);
}
return max;
}
token.itemsConsumedFromCurrent += static_cast(count);
max -= count;
auto tail = producerListTail.load(std::memory_order_acquire);
auto ptr = static_cast(token.currentProducer)->next_prod();
if (ptr == nullptr) {
ptr = tail;
}
while (ptr != static_cast(token.currentProducer)) {
auto dequeued = ptr->dequeue_bulk(itemFirst, max);
count += dequeued;
if (dequeued != 0) {
token.currentProducer = ptr;
token.itemsConsumedFromCurrent = static_cast(dequeued);
}
if (dequeued == max) {
break;
}
max -= dequeued;
ptr = ptr->next_prod();
if (ptr == nullptr) {
ptr = tail;
}
}
return count;
}
// Attempts to dequeue from a specific producer's inner queue.
// If you happen to know which producer you want to dequeue from, this
// is significantly faster than using the general-case try_dequeue methods.
// Returns false if the producer's queue appeared empty at the time it
// was checked (so, the queue is likely but not guaranteed to be empty).
// Never allocates. Thread-safe.
template
inline bool try_dequeue_from_producer(producer_token_t const& producer, U& item)
{
return static_cast(producer.producer)->dequeue(item);
}
// Attempts to dequeue several elements from a specific producer's inner queue.
// Returns the number of items actually dequeued.
// If you happen to know which producer you want to dequeue from, this
// is significantly faster than using the general-case try_dequeue methods.
// Returns 0 if the producer's queue appeared empty at the time it
// was checked (so, the queue is likely but not guaranteed to be empty).
// Never allocates. Thread-safe.
template
inline size_t try_dequeue_bulk_from_producer(producer_token_t const& producer, It itemFirst, size_t max)
{
return static_cast(producer.producer)->dequeue_bulk(itemFirst, max);
}
// Returns an estimate of the total number of elements currently in the queue. This
// estimate is only accurate if the queue has completely stabilized before it is called
// (i.e. all enqueue and dequeue operations have completed and their memory effects are
// visible on the calling thread, and no further operations start while this method is
// being called).
// Thread-safe.
size_t size_approx() const
{
size_t size = 0;
for (auto ptr = producerListTail.load(std::memory_order_acquire); ptr != nullptr; ptr = ptr->next_prod()) {
size += ptr->size_approx();
}
return size;
}
// Returns true if the underlying atomic variables used by
// the queue are lock-free (they should be on most platforms).
// Thread-safe.
static bool is_lock_free()
{
return
details::static_is_lock_free::value == 2 &&
details::static_is_lock_free::value == 2 &&
details::static_is_lock_free::value == 2 &&
details::static_is_lock_free::value == 2 &&
details::static_is_lock_free::value == 2 &&
details::static_is_lock_free::thread_id_numeric_size_t>::value == 2;
}
private:
friend struct ProducerToken;
friend struct ConsumerToken;
friend struct ExplicitProducer;
friend class ConcurrentQueueTests;
enum AllocationMode { CanAlloc, CannotAlloc };
///
// Queue methods
///
template
inline bool inner_enqueue(producer_token_t const& token, U&& element)
{
return static_cast(token.producer)->ConcurrentQueue::ExplicitProducer::template enqueue(std::forward(element));
}
template
inline bool inner_enqueue(U&& element)
{
auto producer = get_or_add_implicit_producer();
return producer == nullptr ? false : producer->ConcurrentQueue::ImplicitProducer::template enqueue(std::forward(element));
}
template
inline bool inner_enqueue_bulk(producer_token_t const& token, It itemFirst, size_t count)
{
return static_cast(token.producer)->ConcurrentQueue::ExplicitProducer::template enqueue_bulk(itemFirst, count);
}
template
inline bool inner_enqueue_bulk(It itemFirst, size_t count)
{
auto producer = get_or_add_implicit_producer();
return producer == nullptr ? false : producer->ConcurrentQueue::ImplicitProducer::template enqueue_bulk(itemFirst, count);
}
inline bool update_current_producer_after_rotation(consumer_token_t& token)
{
// Ah, there's been a rotation, figure out where we should be!
auto tail = producerListTail.load(std::memory_order_acquire);
if (token.desiredProducer == nullptr && tail == nullptr) {
return false;
}
auto prodCount = producerCount.load(std::memory_order_relaxed);
auto globalOffset = globalExplicitConsumerOffset.load(std::memory_order_relaxed);
if (details::unlikely(token.desiredProducer == nullptr)) {
// Aha, first time we're dequeueing anything.
// Figure out our local position
// Note: offset is from start, not end, but we're traversing from end -- subtract from count first
std::uint32_t offset = prodCount - 1 - (token.initialOffset % prodCount);
token.desiredProducer = tail;
for (std::uint32_t i = 0; i != offset; ++i) {
token.desiredProducer = static_cast(token.desiredProducer)->next_prod();
if (token.desiredProducer == nullptr) {
token.desiredProducer = tail;
}
}
}
std::uint32_t delta = globalOffset - token.lastKnownGlobalOffset;
if (delta >= prodCount) {
delta = delta % prodCount;
}
for (std::uint32_t i = 0; i != delta; ++i) {
token.desiredProducer = static_cast(token.desiredProducer)->next_prod();
if (token.desiredProducer == nullptr) {
token.desiredProducer = tail;
}
}
token.lastKnownGlobalOffset = globalOffset;
token.currentProducer = token.desiredProducer;
token.itemsConsumedFromCurrent = 0;
return true;
}
///
// Free list
///
template
struct FreeListNode
{
FreeListNode() : freeListRefs(0), freeListNext(nullptr) { }
std::atomic freeListRefs;
std::atomic freeListNext;
};
// A simple CAS-based lock-free free list. Not the fastest thing in the world under heavy contention, but
// simple and correct (assuming nodes are never freed until after the free list is destroyed), and fairly
// speedy under low contention.
template // N must inherit FreeListNode or have the same fields (and initialization of them)
struct FreeList
{
FreeList() : freeListHead(nullptr) { }
FreeList(FreeList&& other) : freeListHead(other.freeListHead.load(std::memory_order_relaxed)) { other.freeListHead.store(nullptr, std::memory_order_relaxed); }
void swap(FreeList& other) { details::swap_relaxed(freeListHead, other.freeListHead); }
FreeList(FreeList const&) MOODYCAMEL_DELETE_FUNCTION;
FreeList& operator=(FreeList const&) MOODYCAMEL_DELETE_FUNCTION;
inline void add(N* node)
{
#if MCDBGQ_NOLOCKFREE_FREELIST
debug::DebugLock lock(mutex);
#endif
// We know that the should-be-on-freelist bit is 0 at this point, so it's safe to
// set it using a fetch_add
if (node->freeListRefs.fetch_add(SHOULD_BE_ON_FREELIST, std::memory_order_acq_rel) == 0) {
// Oh look! We were the last ones referencing this node, and we know
// we want to add it to the free list, so let's do it!
add_knowing_refcount_is_zero(node);
}
}
inline N* try_get()
{
#if MCDBGQ_NOLOCKFREE_FREELIST
debug::DebugLock lock(mutex);
#endif
auto head = freeListHead.load(std::memory_order_acquire);
while (head != nullptr) {
auto prevHead = head;
auto refs = head->freeListRefs.load(std::memory_order_relaxed);
if ((refs & REFS_MASK) == 0 || !head->freeListRefs.compare_exchange_strong(refs, refs + 1, std::memory_order_acquire, std::memory_order_relaxed)) {
head = freeListHead.load(std::memory_order_acquire);
continue;
}
// Good, reference count has been incremented (it wasn't at zero), which means we can read the
// next and not worry about it changing between now and the time we do the CAS
auto next = head->freeListNext.load(std::memory_order_relaxed);
if (freeListHead.compare_exchange_strong(head, next, std::memory_order_acquire, std::memory_order_relaxed)) {
// Yay, got the node. This means it was on the list, which means shouldBeOnFreeList must be false no
// matter the refcount (because nobody else knows it's been taken off yet, it can't have been put back on).
assert((head->freeListRefs.load(std::memory_order_relaxed) & SHOULD_BE_ON_FREELIST) == 0);
// Decrease refcount twice, once for our ref, and once for the list's ref
head->freeListRefs.fetch_add(-2, std::memory_order_release);
return head;
}
// OK, the head must have changed on us, but we still need to decrease the refcount we increased.
// Note that we don't need to release any memory effects, but we do need to ensure that the reference
// count decrement happens-after the CAS on the head.
refs = prevHead->freeListRefs.fetch_add(-1, std::memory_order_acq_rel);
if (refs == SHOULD_BE_ON_FREELIST + 1) {
add_knowing_refcount_is_zero(prevHead);
}
}
return nullptr;
}
// Useful for traversing the list when there's no contention (e.g. to destroy remaining nodes)
N* head_unsafe() const { return freeListHead.load(std::memory_order_relaxed); }
private:
inline void add_knowing_refcount_is_zero(N* node)
{
// Since the refcount is zero, and nobody can increase it once it's zero (except us, and we run
// only one copy of this method per node at a time, i.e. the single thread case), then we know
// we can safely change the next pointer of the node; however, once the refcount is back above
// zero, then other threads could increase it (happens under heavy contention, when the refcount
// goes to zero in between a load and a refcount increment of a node in try_get, then back up to
// something non-zero, then the refcount increment is done by the other thread) -- so, if the CAS
// to add the node to the actual list fails, decrease the refcount and leave the add operation to
// the next thread who puts the refcount back at zero (which could be us, hence the loop).
auto head = freeListHead.load(std::memory_order_relaxed);
while (true) {
node->freeListNext.store(head, std::memory_order_relaxed);
node->freeListRefs.store(1, std::memory_order_release);
if (!freeListHead.compare_exchange_strong(head, node, std::memory_order_release, std::memory_order_relaxed)) {
// Hmm, the add failed, but we can only try again when the refcount goes back to zero
if (node->freeListRefs.fetch_add(SHOULD_BE_ON_FREELIST - 1, std::memory_order_release) == 1) {
continue;
}
}
return;
}
}
private:
// Implemented like a stack, but where node order doesn't matter (nodes are inserted out of order under contention)
std::atomic freeListHead;
static const std::uint32_t REFS_MASK = 0x7FFFFFFF;
static const std::uint32_t SHOULD_BE_ON_FREELIST = 0x80000000;
#if MCDBGQ_NOLOCKFREE_FREELIST
debug::DebugMutex mutex;
#endif
};
///
// Block
///
enum InnerQueueContext { implicit_context = 0, explicit_context = 1 };
struct Block
{
Block()
: next(nullptr), elementsCompletelyDequeued(0), freeListRefs(0), freeListNext(nullptr), shouldBeOnFreeList(false), dynamicallyAllocated(true)
{
#if MCDBGQ_TRACKMEM
owner = nullptr;
#endif
}
template
inline bool is_empty() const
{
if (context == explicit_context && BLOCK_SIZE <= EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD) {
// Check flags
for (size_t i = 0; i < BLOCK_SIZE; ++i) {
if (!emptyFlags[i].load(std::memory_order_relaxed)) {
return false;
}
}
// Aha, empty; make sure we have all other memory effects that happened before the empty flags were set
std::atomic_thread_fence(std::memory_order_acquire);
return true;
}
else {
// Check counter
if (elementsCompletelyDequeued.load(std::memory_order_relaxed) == BLOCK_SIZE) {
std::atomic_thread_fence(std::memory_order_acquire);
return true;
}
assert(elementsCompletelyDequeued.load(std::memory_order_relaxed) <= BLOCK_SIZE);
return false;
}
}
// Returns true if the block is now empty (does not apply in explicit context)
template
inline bool set_empty(index_t i)
{
if (context == explicit_context && BLOCK_SIZE <= EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD) {
// Set flag
assert(!emptyFlags[BLOCK_SIZE - 1 - static_cast(i & static_cast(BLOCK_SIZE - 1))].load(std::memory_order_relaxed));
emptyFlags[BLOCK_SIZE - 1 - static_cast(i & static_cast(BLOCK_SIZE - 1))].store(true, std::memory_order_release);
return false;
}
else {
// Increment counter
auto prevVal = elementsCompletelyDequeued.fetch_add(1, std::memory_order_release);
assert(prevVal < BLOCK_SIZE);
return prevVal == BLOCK_SIZE - 1;
}
}
// Sets multiple contiguous item statuses to 'empty' (assumes no wrapping and count > 0).
// Returns true if the block is now empty (does not apply in explicit context).
template
inline bool set_many_empty(index_t i, size_t count)
{
if (context == explicit_context && BLOCK_SIZE <= EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD) {
// Set flags
std::atomic_thread_fence(std::memory_order_release);
i = BLOCK_SIZE - 1 - static_cast(i & static_cast(BLOCK_SIZE - 1)) - count + 1;
for (size_t j = 0; j != count; ++j) {
assert(!emptyFlags[i + j].load(std::memory_order_relaxed));
emptyFlags[i + j].store(true, std::memory_order_relaxed);
}
return false;
}
else {
// Increment counter
auto prevVal = elementsCompletelyDequeued.fetch_add(count, std::memory_order_release);
assert(prevVal + count <= BLOCK_SIZE);
return prevVal + count == BLOCK_SIZE;
}
}
template
inline void set_all_empty()
{
if (context == explicit_context && BLOCK_SIZE <= EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD) {
// Set all flags
for (size_t i = 0; i != BLOCK_SIZE; ++i) {
emptyFlags[i].store(true, std::memory_order_relaxed);
}
}
else {
// Reset counter
elementsCompletelyDequeued.store(BLOCK_SIZE, std::memory_order_relaxed);
}
}
template
inline void reset_empty()
{
if (context == explicit_context && BLOCK_SIZE <= EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD) {
// Reset flags
for (size_t i = 0; i != BLOCK_SIZE; ++i) {
emptyFlags[i].store(false, std::memory_order_relaxed);
}
}
else {
// Reset counter
elementsCompletelyDequeued.store(0, std::memory_order_relaxed);
}
}
inline T* operator[](index_t idx) MOODYCAMEL_NOEXCEPT { return static_cast(static_cast(elements)) + static_cast(idx & static_cast(BLOCK_SIZE - 1)); }
inline T const* operator[](index_t idx) const MOODYCAMEL_NOEXCEPT { return static_cast(static_cast(elements)) + static_cast(idx & static_cast(BLOCK_SIZE - 1)); }
private:
// IMPORTANT: This must be the first member in Block, so that if T depends on the alignment of
// addresses returned by malloc, that alignment will be preserved. Apparently clang actually
// generates code that uses this assumption for AVX instructions in some cases. Ideally, we
// should also align Block to the alignment of T in case it's higher than malloc's 16-byte
// alignment, but this is hard to do in a cross-platform way. Assert for this case:
static_assert(std::alignment_of::value <= std::alignment_of::value, "The queue does not support super-aligned types at this time");
// Additionally, we need the alignment of Block itself to be a multiple of max_align_t since
// otherwise the appropriate padding will not be added at the end of Block in order to make
// arrays of Blocks all be properly aligned (not just the first one). We use a union to force
// this.
union {
char elements[sizeof(T) * BLOCK_SIZE];
details::max_align_t dummy;
};
public:
Block* next;
std::atomic elementsCompletelyDequeued;
std::atomic emptyFlags[BLOCK_SIZE <= EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD ? BLOCK_SIZE : 1];
public:
std::atomic freeListRefs;
std::atomic freeListNext;
std::atomic shouldBeOnFreeList;
bool dynamicallyAllocated; // Perhaps a better name for this would be 'isNotPartOfInitialBlockPool'
#if MCDBGQ_TRACKMEM
void* owner;
#endif
};
static_assert(std::alignment_of::value >= std::alignment_of::value, "Internal error: Blocks must be at least as aligned as the type they are wrapping");
#if MCDBGQ_TRACKMEM
public:
struct MemStats;
private:
#endif
///
// Producer base
///
struct ProducerBase : public details::ConcurrentQueueProducerTypelessBase
{
ProducerBase(ConcurrentQueue* parent, bool isExplicit) :
tailIndex(0),
headIndex(0),
dequeueOptimisticCount(0),
dequeueOvercommit(0),
tailBlock(nullptr),
isExplicit(isExplicit),
parent(parent)
{
}
virtual ~ProducerBase() { };
template
inline bool dequeue(U& element)
{
if (isExplicit) {
return static_cast(this)->dequeue(element);
}
else {
return static_cast(this)->dequeue(element);
}
}
template
inline size_t dequeue_bulk(It& itemFirst, size_t max)
{
if (isExplicit) {
return static_cast(this)->dequeue_bulk(itemFirst, max);
}
else {
return static_cast(this)->dequeue_bulk(itemFirst, max);
}
}
inline ProducerBase* next_prod() const { return static_cast(next); }
inline size_t size_approx() const
{
auto tail = tailIndex.load(std::memory_order_relaxed);
auto head = headIndex.load(std::memory_order_relaxed);
return details::circular_less_than(head, tail) ? static_cast(tail - head) : 0;
}
inline index_t getTail() const { return tailIndex.load(std::memory_order_relaxed); }
protected:
std::atomic tailIndex; // Where to enqueue to next
std::atomic headIndex; // Where to dequeue from next
std::atomic dequeueOptimisticCount;
std::atomic dequeueOvercommit;
Block* tailBlock;
public:
bool isExplicit;
ConcurrentQueue* parent;
protected:
#if MCDBGQ_TRACKMEM
friend struct MemStats;
#endif
};
///
// Explicit queue
///
struct ExplicitProducer : public ProducerBase
{
explicit ExplicitProducer(ConcurrentQueue* parent) :
ProducerBase(parent, true),
blockIndex(nullptr),
pr_blockIndexSlotsUsed(0),
pr_blockIndexSize(EXPLICIT_INITIAL_INDEX_SIZE >> 1),
pr_blockIndexFront(0),
pr_blockIndexEntries(nullptr),
pr_blockIndexRaw(nullptr)
{
size_t poolBasedIndexSize = details::ceil_to_pow_2(parent->initialBlockPoolSize) >> 1;
if (poolBasedIndexSize > pr_blockIndexSize) {
pr_blockIndexSize = poolBasedIndexSize;
}
new_block_index(0); // This creates an index with double the number of current entries, i.e. EXPLICIT_INITIAL_INDEX_SIZE
}
~ExplicitProducer()
{
// Destruct any elements not yet dequeued.
// Since we're in the destructor, we can assume all elements
// are either completely dequeued or completely not (no halfways).
if (this->tailBlock != nullptr) { // Note this means there must be a block index too
// First find the block that's partially dequeued, if any
Block* halfDequeuedBlock = nullptr;
if ((this->headIndex.load(std::memory_order_relaxed) & static_cast(BLOCK_SIZE - 1)) != 0) {
// The head's not on a block boundary, meaning a block somewhere is partially dequeued
// (or the head block is the tail block and was fully dequeued, but the head/tail are still not on a boundary)
size_t i = (pr_blockIndexFront - pr_blockIndexSlotsUsed) & (pr_blockIndexSize - 1);
while (details::circular_less_than(pr_blockIndexEntries[i].base + BLOCK_SIZE, this->headIndex.load(std::memory_order_relaxed))) {
i = (i + 1) & (pr_blockIndexSize - 1);
}
assert(details::circular_less_than(pr_blockIndexEntries[i].base, this->headIndex.load(std::memory_order_relaxed)));
halfDequeuedBlock = pr_blockIndexEntries[i].block;
}
// Start at the head block (note the first line in the loop gives us the head from the tail on the first iteration)
auto block = this->tailBlock;
do {
block = block->next;
if (block->ConcurrentQueue::Block::template is_empty()) {
continue;
}
size_t i = 0; // Offset into block
if (block == halfDequeuedBlock) {
i = static_cast(this->headIndex.load(std::memory_order_relaxed) & static_cast(BLOCK_SIZE - 1));
}
// Walk through all the items in the block; if this is the tail block, we need to stop when we reach the tail index
auto lastValidIndex = (this->tailIndex.load(std::memory_order_relaxed) & static_cast(BLOCK_SIZE - 1)) == 0 ? BLOCK_SIZE : static_cast(this->tailIndex.load(std::memory_order_relaxed) & static_cast(BLOCK_SIZE - 1));
while (i != BLOCK_SIZE && (block != this->tailBlock || i != lastValidIndex)) {
(*block)[i++]->~T();
}
} while (block != this->tailBlock);
}
// Destroy all blocks that we own
if (this->tailBlock != nullptr) {
auto block = this->tailBlock;
do {
auto nextBlock = block->next;
if (block->dynamicallyAllocated) {
destroy(block);
}
else {
this->parent->add_block_to_free_list(block);
}
block = nextBlock;
} while (block != this->tailBlock);
}
// Destroy the block indices
auto header = static_cast(pr_blockIndexRaw);
while (header != nullptr) {
auto prev = static_cast(header->prev);
header->~BlockIndexHeader();
(Traits::free)(header);
header = prev;
}
}
template
inline bool enqueue(U&& element)
{
index_t currentTailIndex = this->tailIndex.load(std::memory_order_relaxed);
index_t newTailIndex = 1 + currentTailIndex;
if ((currentTailIndex & static_cast(BLOCK_SIZE - 1)) == 0) {
// We reached the end of a block, start a new one
auto startBlock = this->tailBlock;
auto originalBlockIndexSlotsUsed = pr_blockIndexSlotsUsed;
if (this->tailBlock != nullptr && this->tailBlock->next->ConcurrentQueue::Block::template is_empty()) {
// We can re-use the block ahead of us, it's empty!
this->tailBlock = this->tailBlock->next;
this->tailBlock->ConcurrentQueue::Block::template reset_empty();
// We'll put the block on the block index (guaranteed to be room since we're conceptually removing the
// last block from it first -- except instead of removing then adding, we can just overwrite).
// Note that there must be a valid block index here, since even if allocation failed in the ctor,
// it would have been re-attempted when adding the first block to the queue; since there is such
// a block, a block index must have been successfully allocated.
}
else {
// Whatever head value we see here is >= the last value we saw here (relatively),
// and <= its current value. Since we have the most recent tail, the head must be
// <= to it.
auto head = this->headIndex.load(std::memory_order_relaxed);
assert(!details::circular_less_than(currentTailIndex, head));
if (!details::circular_less_than(head, currentTailIndex + BLOCK_SIZE)
|| (MAX_SUBQUEUE_SIZE != details::const_numeric_max::value && (MAX_SUBQUEUE_SIZE == 0 || MAX_SUBQUEUE_SIZE - BLOCK_SIZE < currentTailIndex - head))) {
// We can't enqueue in another block because there's not enough leeway -- the
// tail could surpass the head by the time the block fills up! (Or we'll exceed
// the size limit, if the second part of the condition was true.)
return false;
}
// We're going to need a new block; check that the block index has room
if (pr_blockIndexRaw == nullptr || pr_blockIndexSlotsUsed == pr_blockIndexSize) {
// Hmm, the circular block index is already full -- we'll need
// to allocate a new index. Note pr_blockIndexRaw can only be nullptr if
// the initial allocation failed in the constructor.
if (allocMode == CannotAlloc || !new_block_index(pr_blockIndexSlotsUsed)) {
return false;
}
}
// Insert a new block in the circular linked list
auto newBlock = this->parent->ConcurrentQueue::template requisition_block();
if (newBlock == nullptr) {
return false;
}
#if MCDBGQ_TRACKMEM
newBlock->owner = this;
#endif
newBlock->ConcurrentQueue::Block::template reset_empty
