blockingconcurrentqueue.h

// Provides an efficient blocking version of moodycamel::ConcurrentQueue.
// ©2015-2020 Cameron Desrochers. Distributed under the terms of the simplified
// BSD license, available at the top of concurrentqueue.h.
// Also dual-licensed under the Boost Software License (see LICENSE.md)
// Uses Jeff Preshing's semaphore implementation (under the terms of its
// separate zlib license, see lightweightsemaphore.h).
 
#pragma once
 
#include "concurrentqueue.h"
#include "lightweightsemaphore.h"
 
#include <type_traits>
#include <cerrno>
#include <memory>
#include <chrono>
#include <ctime>
 
namespace moodycamel {
// 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 ::moodycamel::ConcurrentQueue<T, Traits> ConcurrentQueue;
    typedef ::moodycamel::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, ssize_t, int>(0, (int)Traits::MAX_SEMA_SPINS),
               &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, ssize_t, int>(0, (int)Traits::MAX_SEMA_SPINS),
               &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)
    {
        while (!sema->wait()) {
            continue;
        }
        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)
    {
        while (!sema->wait()) {
            continue;
        }
        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 constexpr bool is_lock_free() { return ConcurrentQueue::is_lock_free(); }
 
  private:
    template <typename U, typename A1, typename A2> static inline U* create(A1&& a1, A2&& a2)
    {
        void* p = (Traits::malloc)(sizeof(U));
        return p != nullptr ? new (p) U(std::forward<A1>(a1), std::forward<A2>(a2)) : 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