blockingconcurrentqueue.h

Go to the documentation of this file.

// Provides an efficient blocking version of moodycamel::ConcurrentQueue.
// ©2015-2016 Cameron Desrochers. Distributed under the terms of the simplified
// BSD license, available at the top of concurrentqueue.h.
// Uses Jeff Preshing's semaphore implementation (under the terms of its
// separate zlib license, embedded below).

#ifndef DMLC_BLOCKINGCONCURRENTQUEUE_H_
#define DMLC_BLOCKINGCONCURRENTQUEUE_H_

#pragma once

#include "concurrentqueue.h"
#include <type_traits>
#include <cerrno>
#include <memory>
#include <chrono>
#include <ctime>

#if defined(_WIN32)
// Avoid including windows.h in a header; we only need a handful of
// items, so we'll redeclare them here (this is relatively safe since
// the API generally has to remain stable between Windows versions).
// I know this is an ugly hack but it still beats polluting the global
// namespace with thousands of generic names or adding a .cpp for nothing.
extern "C" {
        struct _SECURITY_ATTRIBUTES;
        __declspec(dllimport) void* __stdcall CreateSemaphoreW(_SECURITY_ATTRIBUTES* lpSemaphoreAttributes, long lInitialCount, long lMaximumCount, const wchar_t* lpName);
        __declspec(dllimport) int __stdcall CloseHandle(void* hObject);
        __declspec(dllimport) unsigned long __stdcall WaitForSingleObject(void* hHandle, unsigned long dwMilliseconds);
        __declspec(dllimport) int __stdcall ReleaseSemaphore(void* hSemaphore, long lReleaseCount, long* lpPreviousCount);
}
#elif defined(__MACH__)
#include <mach/mach.h>
#elif defined(__unix__)
#include <semaphore.h>
#endif

namespace dmlc {

namespace moodycamel
{
namespace details
{
        // Code in the mpmc_sema namespace below is an adaptation of Jeff Preshing's
        // portable + lightweight semaphore implementations, originally from
        // https://github.com/preshing/cpp11-on-multicore/blob/master/common/sema.h
        // LICENSE:
        // Copyright (c) 2015 Jeff Preshing
        //
        // This software is provided 'as-is', without any express or implied
        // warranty. In no event will the authors be held liable for any damages
        // arising from the use of this software.
        //
        // Permission is granted to anyone to use this software for any purpose,
        // including commercial applications, and to alter it and redistribute it
        // freely, subject to the following restrictions:
        //
        // 1. The origin of this software must not be misrepresented; you must not
        //      claim that you wrote the original software. If you use this software
        //      in a product, an acknowledgement in the product documentation would be
        //      appreciated but is not required.
        // 2. Altered source versions must be plainly marked as such, and must not be
        //      misrepresented as being the original software.
        // 3. This notice may not be removed or altered from any source distribution.
        namespace mpmc_sema
        {
#if defined(_WIN32)
                class Semaphore
                {
                private:
                        void* m_hSema;

                        Semaphore(const Semaphore& other) MOODYCAMEL_DELETE_FUNCTION;
                        Semaphore& operator=(const Semaphore& other) MOODYCAMEL_DELETE_FUNCTION;

                public:
                        Semaphore(int initialCount = 0)
                        {
                                assert(initialCount >= 0);
                                const long maxLong = 0x7fffffff;
                                m_hSema = CreateSemaphoreW(nullptr, initialCount, maxLong, nullptr);
                        }

                        ~Semaphore()
                        {
                                CloseHandle(m_hSema);
                        }

                        void wait()
                        {
                                const unsigned long infinite = 0xffffffff;
                                WaitForSingleObject(m_hSema, infinite);
                        }

                        bool try_wait()
                        {
                                const unsigned long RC_WAIT_TIMEOUT = 0x00000102;
                                return WaitForSingleObject(m_hSema, 0) != RC_WAIT_TIMEOUT;
                        }

                        bool timed_wait(std::uint64_t usecs)
                        {
                                const unsigned long RC_WAIT_TIMEOUT = 0x00000102;
                                return WaitForSingleObject(m_hSema, (unsigned long)(usecs / 1000)) != RC_WAIT_TIMEOUT;
                        }

                        void signal(int count = 1)
                        {
                                ReleaseSemaphore(m_hSema, count, nullptr);
                        }
                };
#elif defined(__MACH__)
                //---------------------------------------------------------
                // Semaphore (Apple iOS and OSX)
                // Can't use POSIX semaphores due to http://lists.apple.com/archives/darwin-kernel/2009/Apr/msg00010.html
                //---------------------------------------------------------
                class Semaphore
                {
                private:
                        semaphore_t m_sema;

                        Semaphore(const Semaphore& other) MOODYCAMEL_DELETE_FUNCTION;
                        Semaphore& operator=(const Semaphore& other) MOODYCAMEL_DELETE_FUNCTION;

                public:
                        Semaphore(int initialCount = 0)
                        {
                                assert(initialCount >= 0);
                                semaphore_create(mach_task_self(), &m_sema, SYNC_POLICY_FIFO, initialCount);
                        }

                        ~Semaphore()
                        {
                                semaphore_destroy(mach_task_self(), m_sema);
                        }

                        void wait()
                        {
                                semaphore_wait(m_sema);
                        }

                        bool try_wait()
                        {
                                return timed_wait(0);
                        }

                        bool timed_wait(std::uint64_t timeout_usecs)
                        {
                                mach_timespec_t ts;
                                ts.tv_sec = static_cast<unsigned int>(timeout_usecs / 1000000);
                                ts.tv_nsec = (timeout_usecs % 1000000) * 1000;

                                // added in OSX 10.10: https://developer.apple.com/library/prerelease/mac/documentation/General/Reference/APIDiffsMacOSX10_10SeedDiff/modules/Darwin.html
                                kern_return_t rc = semaphore_timedwait(m_sema, ts);

                                return rc != KERN_OPERATION_TIMED_OUT;
                        }

                        void signal()
                        {
                                semaphore_signal(m_sema);
                        }

                        void signal(int count)
                        {
                                while (count-- > 0)
                                {
                                        semaphore_signal(m_sema);
                                }
                        }
                };
#elif defined(__unix__)
                //---------------------------------------------------------
                // Semaphore (POSIX, Linux)
                //---------------------------------------------------------
                class Semaphore
                {
                private:
                        sem_t m_sema;

                        Semaphore(const Semaphore& other) MOODYCAMEL_DELETE_FUNCTION;
                        Semaphore& operator=(const Semaphore& other) MOODYCAMEL_DELETE_FUNCTION;

                public:
                        Semaphore(int initialCount = 0)
                        {
                                assert(initialCount >= 0);
                                sem_init(&m_sema, 0, initialCount);
                        }

                        ~Semaphore()
                        {
                                sem_destroy(&m_sema);
                        }

                        void wait()
                        {
                                // http://stackoverflow.com/questions/2013181/gdb-causes-sem-wait-to-fail-with-eintr-error
                                int rc;
                                do {
                                        rc = sem_wait(&m_sema);
                                } while (rc == -1 && errno == EINTR);
                        }

                        bool try_wait()
                        {
                                int rc;
                                do {
                                        rc = sem_trywait(&m_sema);
                                } while (rc == -1 && errno == EINTR);
                                return !(rc == -1 && errno == EAGAIN);
                        }

                        bool timed_wait(std::uint64_t usecs)
                        {
                                struct timespec ts;
                                const int usecs_in_1_sec = 1000000;
                                const int nsecs_in_1_sec = 1000000000;
                                clock_gettime(CLOCK_REALTIME, &ts);
                                ts.tv_sec += usecs / usecs_in_1_sec;
                                ts.tv_nsec += (usecs % usecs_in_1_sec) * 1000;
                                // sem_timedwait bombs if you have more than 1e9 in tv_nsec
                                // so we have to clean things up before passing it in
                                if (ts.tv_nsec >= nsecs_in_1_sec) {
                                        ts.tv_nsec -= nsecs_in_1_sec;
                                        ++ts.tv_sec;
                                }

                                int rc;
                                do {
                                        rc = sem_timedwait(&m_sema, &ts);
                                } while (rc == -1 && errno == EINTR);
                                return !(rc == -1 && errno == ETIMEDOUT);
                        }

                        void signal()
                        {
                                sem_post(&m_sema);
                        }

                        void signal(int count)
                        {
                                while (count-- > 0)
                                {
                                        sem_post(&m_sema);
                                }
                        }
                };
#else
#error Unsupported platform! (No semaphore wrapper available)
#endif

                //---------------------------------------------------------
                // LightweightSemaphore
                //---------------------------------------------------------
                class LightweightSemaphore
                {
                public:
                        typedef std::make_signed<std::size_t>::type ssize_t;

                private:
                        std::atomic<ssize_t> m_count;
                        Semaphore m_sema;

                        bool waitWithPartialSpinning(std::int64_t timeout_usecs = -1)
                        {
                                ssize_t oldCount;
                                // Is there a better way to set the initial spin count?
                                // If we lower it to 1000, testBenaphore becomes 15x slower on my Core i7-5930K Windows PC,
                                // as threads start hitting the kernel semaphore.
                                int spin = 10000;
                                while (--spin >= 0)
                                {
                                        oldCount = m_count.load(std::memory_order_relaxed);
                                        if ((oldCount > 0) && m_count.compare_exchange_strong(oldCount, oldCount - 1, std::memory_order_acquire, std::memory_order_relaxed))
                                                return true;
                                        std::atomic_signal_fence(std::memory_order_acquire);     // Prevent the compiler from collapsing the loop.
                                }
                                oldCount = m_count.fetch_sub(1, std::memory_order_acquire);
                                if (oldCount > 0)
                                        return true;
                                if (timeout_usecs < 0)
                                {
                                        m_sema.wait();
                                        return true;
                                }
                                if (m_sema.timed_wait((std::uint64_t)timeout_usecs))
                                        return true;
                                // At this point, we've timed out waiting for the semaphore, but the
                                // count is still decremented indicating we may still be waiting on
                                // it. So we have to re-adjust the count, but only if the semaphore
                                // wasn't signaled enough times for us too since then. If it was, we
                                // need to release the semaphore too.
                                while (true)
                                {
                                        oldCount = m_count.load(std::memory_order_acquire);
                                        if (oldCount >= 0 && m_sema.try_wait())
                                                return true;
                                        if (oldCount < 0 && m_count.compare_exchange_strong(oldCount, oldCount + 1, std::memory_order_relaxed, std::memory_order_relaxed))
                                                return false;
                                }
                        }

                        ssize_t waitManyWithPartialSpinning(ssize_t max, std::int64_t timeout_usecs = -1)
                        {
                                assert(max > 0);
                                ssize_t oldCount;
                                int spin = 10000;
                                while (--spin >= 0)
                                {
                                        oldCount = m_count.load(std::memory_order_relaxed);
                                        if (oldCount > 0)
                                        {
                                                ssize_t newCount = oldCount > max ? oldCount - max : 0;
                                                if (m_count.compare_exchange_strong(oldCount, newCount, std::memory_order_acquire, std::memory_order_relaxed))
                                                        return oldCount - newCount;
                                        }
                                        std::atomic_signal_fence(std::memory_order_acquire);
                                }
                                oldCount = m_count.fetch_sub(1, std::memory_order_acquire);
                                if (oldCount <= 0)
                                {
                                        if (timeout_usecs < 0)
                                                m_sema.wait();
                                        else if (!m_sema.timed_wait((std::uint64_t)timeout_usecs))
                                        {
                                                while (true)
                                                {
                                                        oldCount = m_count.load(std::memory_order_acquire);
                                                        if (oldCount >= 0 && m_sema.try_wait())
                                                                break;
                                                        if (oldCount < 0 && m_count.compare_exchange_strong(oldCount, oldCount + 1, std::memory_order_relaxed, std::memory_order_relaxed))
                                                                return 0;
                                                }
                                        }
                                }
                                if (max > 1)
                                        return 1 + tryWaitMany(max - 1);
                                return 1;
                        }

                public:
                        LightweightSemaphore(ssize_t initialCount = 0) : m_count(initialCount)
                        {
                                assert(initialCount >= 0);
                        }

                        bool tryWait()
                        {
                                ssize_t oldCount = m_count.load(std::memory_order_relaxed);
                                while (oldCount > 0)
                                {
                                        if (m_count.compare_exchange_weak(oldCount, oldCount - 1, std::memory_order_acquire, std::memory_order_relaxed))
                                                return true;
                                }
                                return false;
                        }

                        void wait()
                        {
                                if (!tryWait())
                                        waitWithPartialSpinning();
                        }

                        bool wait(std::int64_t timeout_usecs)
                        {
                                return tryWait() || waitWithPartialSpinning(timeout_usecs);
                        }

                        // Acquires between 0 and (greedily) max, inclusive
                        ssize_t tryWaitMany(ssize_t max)
                        {
                                assert(max >= 0);
                                ssize_t oldCount = m_count.load(std::memory_order_relaxed);
                                while (oldCount > 0)
                                {
                                        ssize_t newCount = oldCount > max ? oldCount - max : 0;
                                        if (m_count.compare_exchange_weak(oldCount, newCount, std::memory_order_acquire, std::memory_order_relaxed))
                                                return oldCount - newCount;
                                }
                                return 0;
                        }

                        // Acquires at least one, and (greedily) at most max
                        ssize_t waitMany(ssize_t max, std::int64_t timeout_usecs)
                        {
                                assert(max >= 0);
                                ssize_t result = tryWaitMany(max);
                                if (result == 0 && max > 0)
                                        result = waitManyWithPartialSpinning(max, timeout_usecs);
                                return result;
                        }

                        ssize_t waitMany(ssize_t max)
                        {
                                ssize_t result = waitMany(max, -1);
                                assert(result > 0);
                                return result;
                        }

                        void signal(ssize_t count = 1)
                        {
                                assert(count >= 0);
                                ssize_t oldCount = m_count.fetch_add(count, std::memory_order_release);
                                ssize_t toRelease = -oldCount < count ? -oldCount : count;
                                if (toRelease > 0)
                                {
                                        m_sema.signal((int)toRelease);
                                }
                        }

                        ssize_t availableApprox() const
                        {
                                ssize_t count = m_count.load(std::memory_order_relaxed);
                                return count > 0 ? count : 0;
                        }
                };
        }       // end namespace mpmc_sema
}       // end namespace details


// This is a blocking version of the queue. It has an almost identical interface to
// the normal non-blocking version, with the addition of various wait_dequeue() methods
// and the removal of producer-specific dequeue methods.
template<typename T, typename Traits = ConcurrentQueueDefaultTraits>
class BlockingConcurrentQueue
{
private:
        typedef ::dmlc::moodycamel::ConcurrentQueue<T, Traits> ConcurrentQueue;
        typedef details::mpmc_sema::LightweightSemaphore LightweightSemaphore;

public:
        typedef typename ConcurrentQueue::producer_token_t producer_token_t;
        typedef typename ConcurrentQueue::consumer_token_t consumer_token_t;

        typedef typename ConcurrentQueue::index_t index_t;
        typedef typename ConcurrentQueue::size_t size_t;
        typedef typename std::make_signed<size_t>::type ssize_t;

        static const size_t BLOCK_SIZE = ConcurrentQueue::BLOCK_SIZE;
        static const size_t EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD = ConcurrentQueue::EXPLICIT_BLOCK_EMPTY_COUNTER_THRESHOLD;
        static const size_t EXPLICIT_INITIAL_INDEX_SIZE = ConcurrentQueue::EXPLICIT_INITIAL_INDEX_SIZE;
        static const size_t IMPLICIT_INITIAL_INDEX_SIZE = ConcurrentQueue::IMPLICIT_INITIAL_INDEX_SIZE;
        static const size_t INITIAL_IMPLICIT_PRODUCER_HASH_SIZE = ConcurrentQueue::INITIAL_IMPLICIT_PRODUCER_HASH_SIZE;
        static const std::uint32_t EXPLICIT_CONSUMER_CONSUMPTION_QUOTA_BEFORE_ROTATE = ConcurrentQueue::EXPLICIT_CONSUMER_CONSUMPTION_QUOTA_BEFORE_ROTATE;
        static const size_t MAX_SUBQUEUE_SIZE = ConcurrentQueue::MAX_SUBQUEUE_SIZE;

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 BlockingConcurrentQueue(size_t capacity = 6 * BLOCK_SIZE)
                : inner(capacity), sema(create<LightweightSemaphore>(), &BlockingConcurrentQueue::template destroy<LightweightSemaphore>)
        {
                assert(reinterpret_cast<ConcurrentQueue*>((BlockingConcurrentQueue*)1) == &((BlockingConcurrentQueue*)1)->inner && "BlockingConcurrentQueue must have ConcurrentQueue as its first member");
                if (!sema) {
                        MOODYCAMEL_THROW(std::bad_alloc());
                }
        }

        BlockingConcurrentQueue(size_t minCapacity, size_t maxExplicitProducers, size_t maxImplicitProducers)
                : inner(minCapacity, maxExplicitProducers, maxImplicitProducers), sema(create<LightweightSemaphore>(), &BlockingConcurrentQueue::template destroy<LightweightSemaphore>)
        {
                assert(reinterpret_cast<ConcurrentQueue*>((BlockingConcurrentQueue*)1) == &((BlockingConcurrentQueue*)1)->inner && "BlockingConcurrentQueue must have ConcurrentQueue as its first member");
                if (!sema) {
                        MOODYCAMEL_THROW(std::bad_alloc());
                }
        }

        // Disable copying and copy assignment
        BlockingConcurrentQueue(BlockingConcurrentQueue const&) MOODYCAMEL_DELETE_FUNCTION;
        BlockingConcurrentQueue& operator=(BlockingConcurrentQueue 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).
        BlockingConcurrentQueue(BlockingConcurrentQueue&& other) MOODYCAMEL_NOEXCEPT
                : inner(std::move(other.inner)), sema(std::move(other.sema))
        { }

        inline BlockingConcurrentQueue& operator=(BlockingConcurrentQueue&& 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(BlockingConcurrentQueue& other) MOODYCAMEL_NOEXCEPT
        {
                swap_internal(other);
        }

private:
        BlockingConcurrentQueue& swap_internal(BlockingConcurrentQueue& other)
        {
                if (this == &other) {
                        return *this;
                }

                inner.swap(other.inner);
                sema.swap(other.sema);
                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 (details::likely(inner.enqueue(item))) {
                        sema->signal();
                        return true;
                }
                return false;
        }

        // 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 (details::likely(inner.enqueue(std::move(item)))) {
                        sema->signal();
                        return true;
                }
                return false;
        }

        // 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)
        {
                if (details::likely(inner.enqueue(token, item))) {
                        sema->signal();
                        return true;
                }
                return false;
        }

        // 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)
        {
                if (details::likely(inner.enqueue(token, std::move(item)))) {
                        sema->signal();
                        return true;
                }
                return false;
        }

        // 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>
        inline bool enqueue_bulk(It itemFirst, size_t count)
        {
                if (details::likely(inner.enqueue_bulk(std::forward<It>(itemFirst), count))) {
                        sema->signal((LightweightSemaphore::ssize_t)(ssize_t)count);
                        return true;
                }
                return false;
        }

        // 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>
        inline bool enqueue_bulk(producer_token_t const& token, It itemFirst, size_t count)
        {
                if (details::likely(inner.enqueue_bulk(token, std::forward<It>(itemFirst), count))) {
                        sema->signal((LightweightSemaphore::ssize_t)(ssize_t)count);
                        return true;
                }
                return false;
        }

        // 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 (inner.try_enqueue(item)) {
                        sema->signal();
                        return true;
                }
                return false;
        }

        // 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 (inner.try_enqueue(std::move(item))) {
                        sema->signal();
                        return true;
                }
                return false;
        }

        // 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)
        {
                if (inner.try_enqueue(token, item)) {
                        sema->signal();
                        return true;
                }
                return false;
        }

        // 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)
        {
                if (inner.try_enqueue(token, std::move(item))) {
                        sema->signal();
                        return true;
                }
                return false;
        }

        // 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>
        inline bool try_enqueue_bulk(It itemFirst, size_t count)
        {
                if (inner.try_enqueue_bulk(std::forward<It>(itemFirst), count)) {
                        sema->signal((LightweightSemaphore::ssize_t)(ssize_t)count);
                        return true;
                }
                return false;
        }

        // 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>
        inline bool try_enqueue_bulk(producer_token_t const& token, It itemFirst, size_t count)
        {
                if (inner.try_enqueue_bulk(token, std::forward<It>(itemFirst), count)) {
                        sema->signal((LightweightSemaphore::ssize_t)(ssize_t)count);
                        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).
        // Never allocates. Thread-safe.
        template<typename U>
        inline bool try_dequeue(U& item)
        {
                if (sema->tryWait()) {
                        while (!inner.try_dequeue(item)) {
                                continue;
                        }
                        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>
        inline bool try_dequeue(consumer_token_t& token, U& item)
        {
                if (sema->tryWait()) {
                        while (!inner.try_dequeue(token, item)) {
                                continue;
                        }
                        return true;
                }
                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<typename It>
        inline size_t try_dequeue_bulk(It itemFirst, size_t max)
        {
                size_t count = 0;
                max = (size_t)sema->tryWaitMany((LightweightSemaphore::ssize_t)(ssize_t)max);
                while (count != max) {
                        count += inner.template try_dequeue_bulk<It&>(itemFirst, max - count);
                }
                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<typename It>
        inline size_t try_dequeue_bulk(consumer_token_t& token, It itemFirst, size_t max)
        {
                size_t count = 0;
                max = (size_t)sema->tryWaitMany((LightweightSemaphore::ssize_t)(ssize_t)max);
                while (count != max) {
                        count += inner.template try_dequeue_bulk<It&>(token, itemFirst, max - count);
                }
                return count;
        }



        // Blocks the current thread until there's something to dequeue, then
        // dequeues it.
        // Never allocates. Thread-safe.
        template<typename U>
        inline void wait_dequeue(U& item)
        {
                sema->wait();
                while (!inner.try_dequeue(item)) {
                        continue;
                }
        }

        // Blocks the current thread until either there's something to dequeue
        // or the timeout (specified in microseconds) expires. Returns false
        // without setting `item` if the timeout expires, otherwise assigns
        // to `item` and returns true.
        // Using a negative timeout indicates an indefinite timeout,
        // and is thus functionally equivalent to calling wait_dequeue.
        // Never allocates. Thread-safe.
        template<typename U>
        inline bool wait_dequeue_timed(U& item, std::int64_t timeout_usecs)
        {
                if (!sema->wait(timeout_usecs)) {
                        return false;
                }
                while (!inner.try_dequeue(item)) {
                        continue;
                }
                return true;
        }

    // Blocks the current thread until either there's something to dequeue
        // or the timeout expires. Returns false without setting `item` if the
    // timeout expires, otherwise assigns to `item` and returns true.
        // Never allocates. Thread-safe.
        template<typename U, typename Rep, typename Period>
        inline bool wait_dequeue_timed(U& item, std::chrono::duration<Rep, Period> const& timeout)
    {
        return wait_dequeue_timed(item, std::chrono::duration_cast<std::chrono::microseconds>(timeout).count());
    }

        // Blocks the current thread until there's something to dequeue, then
        // dequeues it using an explicit consumer token.
        // Never allocates. Thread-safe.
        template<typename U>
        inline void wait_dequeue(consumer_token_t& token, U& item)
        {
                sema->wait();
                while (!inner.try_dequeue(token, item)) {
                        continue;
                }
        }

        // Blocks the current thread until either there's something to dequeue
        // or the timeout (specified in microseconds) expires. Returns false
        // without setting `item` if the timeout expires, otherwise assigns
        // to `item` and returns true.
        // Using a negative timeout indicates an indefinite timeout,
        // and is thus functionally equivalent to calling wait_dequeue.
        // Never allocates. Thread-safe.
        template<typename U>
        inline bool wait_dequeue_timed(consumer_token_t& token, U& item, std::int64_t timeout_usecs)
        {
                if (!sema->wait(timeout_usecs)) {
                        return false;
                }
                while (!inner.try_dequeue(token, item)) {
                        continue;
                }
                return true;
        }

    // Blocks the current thread until either there's something to dequeue
        // or the timeout expires. Returns false without setting `item` if the
    // timeout expires, otherwise assigns to `item` and returns true.
        // Never allocates. Thread-safe.
        template<typename U, typename Rep, typename Period>
        inline bool wait_dequeue_timed(consumer_token_t& token, U& item, std::chrono::duration<Rep, Period> const& timeout)
    {
        return wait_dequeue_timed(token, item, std::chrono::duration_cast<std::chrono::microseconds>(timeout).count());
    }

        // Attempts to dequeue several elements from the queue.
        // Returns the number of items actually dequeued, which will
        // always be at least one (this method blocks until the queue
        // is non-empty) and at most max.
        // Never allocates. Thread-safe.
        template<typename It>
        inline size_t wait_dequeue_bulk(It itemFirst, size_t max)
        {
                size_t count = 0;
                max = (size_t)sema->waitMany((LightweightSemaphore::ssize_t)(ssize_t)max);
                while (count != max) {
                        count += inner.template try_dequeue_bulk<It&>(itemFirst, max - count);
                }
                return count;
        }

        // Attempts to dequeue several elements from the queue.
        // Returns the number of items actually dequeued, which can
        // be 0 if the timeout expires while waiting for elements,
        // and at most max.
        // Using a negative timeout indicates an indefinite timeout,
        // and is thus functionally equivalent to calling wait_dequeue_bulk.
        // Never allocates. Thread-safe.
        template<typename It>
        inline size_t wait_dequeue_bulk_timed(It itemFirst, size_t max, std::int64_t timeout_usecs)
        {
                size_t count = 0;
                max = (size_t)sema->waitMany((LightweightSemaphore::ssize_t)(ssize_t)max, timeout_usecs);
                while (count != max) {
                        count += inner.template try_dequeue_bulk<It&>(itemFirst, max - count);
                }
                return count;
        }

    // Attempts to dequeue several elements from the queue.
        // Returns the number of items actually dequeued, which can
        // be 0 if the timeout expires while waiting for elements,
        // and at most max.
        // Never allocates. Thread-safe.
        template<typename It, typename Rep, typename Period>
        inline size_t wait_dequeue_bulk_timed(It itemFirst, size_t max, std::chrono::duration<Rep, Period> const& timeout)
    {
        return wait_dequeue_bulk_timed<It&>(itemFirst, max, std::chrono::duration_cast<std::chrono::microseconds>(timeout).count());
    }

        // Attempts to dequeue several elements from the queue using an explicit consumer token.
        // Returns the number of items actually dequeued, which will
        // always be at least one (this method blocks until the queue
        // is non-empty) and at most max.
        // Never allocates. Thread-safe.
        template<typename It>
        inline size_t wait_dequeue_bulk(consumer_token_t& token, It itemFirst, size_t max)
        {
                size_t count = 0;
                max = (size_t)sema->waitMany((LightweightSemaphore::ssize_t)(ssize_t)max);
                while (count != max) {
                        count += inner.template try_dequeue_bulk<It&>(token, itemFirst, max - count);
                }
                return count;
        }

        // Attempts to dequeue several elements from the queue using an explicit consumer token.
        // Returns the number of items actually dequeued, which can
        // be 0 if the timeout expires while waiting for elements,
        // and at most max.
        // Using a negative timeout indicates an indefinite timeout,
        // and is thus functionally equivalent to calling wait_dequeue_bulk.
        // Never allocates. Thread-safe.
        template<typename It>
        inline size_t wait_dequeue_bulk_timed(consumer_token_t& token, It itemFirst, size_t max, std::int64_t timeout_usecs)
        {
                size_t count = 0;
                max = (size_t)sema->waitMany((LightweightSemaphore::ssize_t)(ssize_t)max, timeout_usecs);
                while (count != max) {
                        count += inner.template try_dequeue_bulk<It&>(token, itemFirst, max - count);
                }
                return count;
        }

        // Attempts to dequeue several elements from the queue using an explicit consumer token.
        // Returns the number of items actually dequeued, which can
        // be 0 if the timeout expires while waiting for elements,
        // and at most max.
        // Never allocates. Thread-safe.
        template<typename It, typename Rep, typename Period>
        inline size_t wait_dequeue_bulk_timed(consumer_token_t& token, It itemFirst, size_t max, std::chrono::duration<Rep, Period> const& timeout)
    {
        return wait_dequeue_bulk_timed<It&>(token, itemFirst, max, std::chrono::duration_cast<std::chrono::microseconds>(timeout).count());
    }


        // 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.
        inline size_t size_approx() const
        {
                return (size_t)sema->availableApprox();
        }


        // 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 ConcurrentQueue::is_lock_free();
        }


private:
        template<typename U>
        static inline U* create()
        {
                auto p = (Traits::malloc)(sizeof(U));
                return p != nullptr ? new (p) U : nullptr;
        }

        template<typename U, typename A1>
        static inline U* create(A1&& a1)
        {
                auto p = (Traits::malloc)(sizeof(U));
                return p != nullptr ? new (p) U(std::forward<A1>(a1)) : nullptr;
        }

        template<typename U>
        static inline void destroy(U* p)
        {
                if (p != nullptr) {
                        p->~U();
                }
                (Traits::free)(p);
        }

private:
        ConcurrentQueue inner;
        std::unique_ptr<LightweightSemaphore, void (*)(LightweightSemaphore*)> sema;
};


template<typename T, typename Traits>
inline void swap(BlockingConcurrentQueue<T, Traits>& a, BlockingConcurrentQueue<T, Traits>& b) MOODYCAMEL_NOEXCEPT
{
        a.swap(b);
}

}       // end namespace moodycamel
}  // namespace dmlc

#endif  // DMLC_BLOCKINGCONCURRENTQUEUE_H_

---

Generated on Fri Sep 11 2020 03:38:03 for mxnet by   1.8.11