diff --git a/dep/concurrentqueue/blockingconcurrentqueue.h b/dep/concurrentqueue/blockingconcurrentqueue.h new file mode 100644 index 0000000..996c556 --- /dev/null +++ b/dep/concurrentqueue/blockingconcurrentqueue.h @@ -0,0 +1,760 @@ +// Provides an efficient blocking version of moodycamel::ConcurrentQueue. +// ©2015 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). + +#pragma once + +#include "concurrentqueue.h" +#include +#include + +#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 +#elif defined(__unix__) +#include +#endif + +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); + } + + 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); + } + + 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); + } + + 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::type ssize_t; + + private: + std::atomic m_count; + Semaphore m_sema; + + void waitWithPartialSpinning() + { + 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; + 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) + { + m_sema.wait(); + } + } + + ssize_t waitManyWithPartialSpinning(ssize_t max) + { + 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) + m_sema.wait(); + 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(); + } + + // 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) + { + assert(max >= 0); + ssize_t result = tryWaitMany(max); + if (result == 0 && max > 0) + result = waitManyWithPartialSpinning(max); + 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 +class BlockingConcurrentQueue +{ +private: + typedef ::moodycamel::ConcurrentQueue 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::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(), &BlockingConcurrentQueue::template destroy) + { + assert(reinterpret_cast((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(), &BlockingConcurrentQueue::template destroy) + { + assert(reinterpret_cast((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 + inline bool enqueue_bulk(It itemFirst, size_t count) + { + if (details::likely(inner.enqueue_bulk(std::forward(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 + inline bool enqueue_bulk(producer_token_t const& token, It itemFirst, size_t count) + { + if (details::likely(inner.enqueue_bulk(token, std::forward(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 + inline bool try_enqueue_bulk(It itemFirst, size_t count) + { + if (inner.try_enqueue_bulk(std::forward(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 + inline bool try_enqueue_bulk(producer_token_t const& token, It itemFirst, size_t count) + { + if (inner.try_enqueue_bulk(token, std::forward(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 + 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 + 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 + 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(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 + 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(token, itemFirst, max - count); + } + return count; + } + + + + // Blocks the current thread until there's something to dequeue, then + // dequeues it. + // Never allocates. Thread-safe. + template + inline void wait_dequeue(U& item) + { + sema->wait(); + while (!inner.try_dequeue(item)) { + continue; + } + } + + // Blocks the current thread until there's something to dequeue, then + // dequeues it using an explicit consumer token. + // Never allocates. Thread-safe. + template + inline void wait_dequeue(consumer_token_t& token, U& item) + { + sema->wait(); + while (!inner.try_dequeue(token, item)) { + continue; + } + } + + // 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 + 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(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 will + // always be at least one (this method blocks until the queue + // is non-empty) and at most max. + // Never allocates. Thread-safe. + template + 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(token, itemFirst, max - count); + } + return 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 + static inline U* create() + { + auto p = Traits::malloc(sizeof(U)); + return p != nullptr ? new (p) U : nullptr; + } + + template + static inline U* create(A1&& a1) + { + auto p = Traits::malloc(sizeof(U)); + return p != nullptr ? new (p) U(std::forward(a1)) : nullptr; + } + + template + static inline void destroy(U* p) + { + if (p != nullptr) { + p->~U(); + } + Traits::free(p); + } + +private: + ConcurrentQueue inner; + std::unique_ptr sema; +}; + + +template +inline void swap(BlockingConcurrentQueue& a, BlockingConcurrentQueue& b) MOODYCAMEL_NOEXCEPT +{ + a.swap(b); +} + +} // end namespace moodycamel diff --git a/test.cpp b/test.cpp index e87eb55..580dd5b 100644 --- a/test.cpp +++ b/test.cpp @@ -17,6 +17,7 @@ #include #include "concurrentqueue.h" +#include "blockingconcurrentqueue.h" #include @@ -283,7 +284,7 @@ class DispatcherPool std::condition_variable _condition; - moodycamel::ConcurrentQueue _queue; + moodycamel::BlockingConcurrentQueue _queue; public: DispatcherPool() : DispatcherPool(std::thread::hardware_concurrency()) { }