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428 lines
12 KiB
C++
428 lines
12 KiB
C++
// Provides an efficient implementation of a semaphore (LightweightSemaphore).
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// This is an extension of Jeff Preshing's sempahore implementation (licensed
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// under the terms of its separate zlib license) that has been adapted and
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// extended by Cameron Desrochers.
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#pragma once
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#include <cstddef> // For std::size_t
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#include <atomic>
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#include <type_traits> // For std::make_signed<T>
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#if defined(_WIN32)
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// Avoid including windows.h in a header; we only need a handful of
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// items, so we'll redeclare them here (this is relatively safe since
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// the API generally has to remain stable between Windows versions).
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// I know this is an ugly hack but it still beats polluting the global
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// namespace with thousands of generic names or adding a .cpp for nothing.
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extern "C" {
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struct _SECURITY_ATTRIBUTES;
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__declspec(dllimport) void* __stdcall CreateSemaphoreW(_SECURITY_ATTRIBUTES* lpSemaphoreAttributes, long lInitialCount, long lMaximumCount, const wchar_t* lpName);
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__declspec(dllimport) int __stdcall CloseHandle(void* hObject);
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__declspec(dllimport) unsigned long __stdcall WaitForSingleObject(void* hHandle, unsigned long dwMilliseconds);
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__declspec(dllimport) int __stdcall ReleaseSemaphore(void* hSemaphore, long lReleaseCount, long* lpPreviousCount);
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}
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#elif defined(__MACH__)
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#include <mach/mach.h>
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#elif defined(__MVS__)
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#include <zos-semaphore.h>
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#elif defined(__unix__)
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#include <semaphore.h>
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#if defined(__GLIBC_PREREQ) && defined(_GNU_SOURCE)
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#if __GLIBC_PREREQ(2,30)
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#define MOODYCAMEL_LIGHTWEIGHTSEMAPHORE_MONOTONIC
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#endif
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#endif
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#endif
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namespace moodycamel
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{
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namespace details
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{
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// Code in the mpmc_sema namespace below is an adaptation of Jeff Preshing's
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// portable + lightweight semaphore implementations, originally from
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// https://github.com/preshing/cpp11-on-multicore/blob/master/common/sema.h
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// LICENSE:
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// Copyright (c) 2015 Jeff Preshing
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//
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// This software is provided 'as-is', without any express or implied
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// warranty. In no event will the authors be held liable for any damages
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// arising from the use of this software.
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//
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// Permission is granted to anyone to use this software for any purpose,
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// including commercial applications, and to alter it and redistribute it
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// freely, subject to the following restrictions:
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//
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// 1. The origin of this software must not be misrepresented; you must not
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// claim that you wrote the original software. If you use this software
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// in a product, an acknowledgement in the product documentation would be
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// appreciated but is not required.
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// 2. Altered source versions must be plainly marked as such, and must not be
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// misrepresented as being the original software.
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// 3. This notice may not be removed or altered from any source distribution.
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#if defined(_WIN32)
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class Semaphore
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{
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private:
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void* m_hSema;
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Semaphore(const Semaphore& other) MOODYCAMEL_DELETE_FUNCTION;
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Semaphore& operator=(const Semaphore& other) MOODYCAMEL_DELETE_FUNCTION;
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public:
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Semaphore(int initialCount = 0)
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{
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assert(initialCount >= 0);
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const long maxLong = 0x7fffffff;
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m_hSema = CreateSemaphoreW(nullptr, initialCount, maxLong, nullptr);
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assert(m_hSema);
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}
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~Semaphore()
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{
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CloseHandle(m_hSema);
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}
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bool wait()
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{
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const unsigned long infinite = 0xffffffff;
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return WaitForSingleObject(m_hSema, infinite) == 0;
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}
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bool try_wait()
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{
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return WaitForSingleObject(m_hSema, 0) == 0;
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}
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bool timed_wait(std::uint64_t usecs)
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{
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return WaitForSingleObject(m_hSema, (unsigned long)(usecs / 1000)) == 0;
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}
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void signal(int count = 1)
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{
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while (!ReleaseSemaphore(m_hSema, count, nullptr));
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}
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};
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#elif defined(__MACH__)
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//---------------------------------------------------------
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// Semaphore (Apple iOS and OSX)
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// Can't use POSIX semaphores due to http://lists.apple.com/archives/darwin-kernel/2009/Apr/msg00010.html
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//---------------------------------------------------------
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class Semaphore
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{
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private:
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semaphore_t m_sema;
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Semaphore(const Semaphore& other) MOODYCAMEL_DELETE_FUNCTION;
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Semaphore& operator=(const Semaphore& other) MOODYCAMEL_DELETE_FUNCTION;
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public:
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Semaphore(int initialCount = 0)
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{
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assert(initialCount >= 0);
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kern_return_t rc = semaphore_create(mach_task_self(), &m_sema, SYNC_POLICY_FIFO, initialCount);
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assert(rc == KERN_SUCCESS);
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(void)rc;
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}
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~Semaphore()
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{
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semaphore_destroy(mach_task_self(), m_sema);
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}
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bool wait()
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{
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return semaphore_wait(m_sema) == KERN_SUCCESS;
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}
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bool try_wait()
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{
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return timed_wait(0);
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}
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bool timed_wait(std::uint64_t timeout_usecs)
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{
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mach_timespec_t ts;
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ts.tv_sec = static_cast<unsigned int>(timeout_usecs / 1000000);
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ts.tv_nsec = static_cast<int>((timeout_usecs % 1000000) * 1000);
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// added in OSX 10.10: https://developer.apple.com/library/prerelease/mac/documentation/General/Reference/APIDiffsMacOSX10_10SeedDiff/modules/Darwin.html
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kern_return_t rc = semaphore_timedwait(m_sema, ts);
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return rc == KERN_SUCCESS;
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}
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void signal()
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{
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while (semaphore_signal(m_sema) != KERN_SUCCESS);
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}
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void signal(int count)
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{
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while (count-- > 0)
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{
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while (semaphore_signal(m_sema) != KERN_SUCCESS);
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}
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}
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};
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#elif defined(__unix__) || defined(__MVS__)
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//---------------------------------------------------------
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// Semaphore (POSIX, Linux, zOS)
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//---------------------------------------------------------
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class Semaphore
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{
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private:
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sem_t m_sema;
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Semaphore(const Semaphore& other) MOODYCAMEL_DELETE_FUNCTION;
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Semaphore& operator=(const Semaphore& other) MOODYCAMEL_DELETE_FUNCTION;
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public:
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Semaphore(int initialCount = 0)
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{
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assert(initialCount >= 0);
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int rc = sem_init(&m_sema, 0, static_cast<unsigned int>(initialCount));
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assert(rc == 0);
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(void)rc;
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}
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~Semaphore()
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{
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sem_destroy(&m_sema);
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}
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bool wait()
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{
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// http://stackoverflow.com/questions/2013181/gdb-causes-sem-wait-to-fail-with-eintr-error
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int rc;
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do {
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rc = sem_wait(&m_sema);
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} while (rc == -1 && errno == EINTR);
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return rc == 0;
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}
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bool try_wait()
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{
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int rc;
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do {
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rc = sem_trywait(&m_sema);
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} while (rc == -1 && errno == EINTR);
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return rc == 0;
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}
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bool timed_wait(std::uint64_t usecs)
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{
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struct timespec ts;
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const int usecs_in_1_sec = 1000000;
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const int nsecs_in_1_sec = 1000000000;
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#ifdef MOODYCAMEL_LIGHTWEIGHTSEMAPHORE_MONOTONIC
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clock_gettime(CLOCK_MONOTONIC, &ts);
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#else
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clock_gettime(CLOCK_REALTIME, &ts);
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#endif
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ts.tv_sec += (time_t)(usecs / usecs_in_1_sec);
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ts.tv_nsec += (long)(usecs % usecs_in_1_sec) * 1000;
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// sem_timedwait bombs if you have more than 1e9 in tv_nsec
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// so we have to clean things up before passing it in
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if (ts.tv_nsec >= nsecs_in_1_sec) {
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ts.tv_nsec -= nsecs_in_1_sec;
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++ts.tv_sec;
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}
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int rc;
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do {
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#ifdef MOODYCAMEL_LIGHTWEIGHTSEMAPHORE_MONOTONIC
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rc = sem_clockwait(&m_sema, CLOCK_MONOTONIC, &ts);
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#else
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rc = sem_timedwait(&m_sema, &ts);
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#endif
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} while (rc == -1 && errno == EINTR);
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return rc == 0;
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}
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void signal()
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{
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while (sem_post(&m_sema) == -1);
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}
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void signal(int count)
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{
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while (count-- > 0)
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{
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while (sem_post(&m_sema) == -1);
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}
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}
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};
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#else
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#error Unsupported platform! (No semaphore wrapper available)
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#endif
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} // end namespace details
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//---------------------------------------------------------
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// LightweightSemaphore
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//---------------------------------------------------------
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class LightweightSemaphore
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{
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public:
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typedef std::make_signed<std::size_t>::type ssize_t;
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private:
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std::atomic<ssize_t> m_count;
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details::Semaphore m_sema;
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int m_maxSpins;
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bool waitWithPartialSpinning(std::int64_t timeout_usecs = -1)
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{
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ssize_t oldCount;
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int spin = m_maxSpins;
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while (--spin >= 0)
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{
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oldCount = m_count.load(std::memory_order_relaxed);
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if ((oldCount > 0) && m_count.compare_exchange_strong(oldCount, oldCount - 1, std::memory_order_acquire, std::memory_order_relaxed))
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return true;
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std::atomic_signal_fence(std::memory_order_acquire); // Prevent the compiler from collapsing the loop.
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}
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oldCount = m_count.fetch_sub(1, std::memory_order_acquire);
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if (oldCount > 0)
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return true;
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if (timeout_usecs < 0)
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{
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if (m_sema.wait())
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return true;
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}
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if (timeout_usecs > 0 && m_sema.timed_wait((std::uint64_t)timeout_usecs))
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return true;
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// At this point, we've timed out waiting for the semaphore, but the
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// count is still decremented indicating we may still be waiting on
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// it. So we have to re-adjust the count, but only if the semaphore
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// wasn't signaled enough times for us too since then. If it was, we
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// need to release the semaphore too.
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while (true)
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{
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oldCount = m_count.load(std::memory_order_acquire);
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if (oldCount >= 0 && m_sema.try_wait())
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return true;
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if (oldCount < 0 && m_count.compare_exchange_strong(oldCount, oldCount + 1, std::memory_order_relaxed, std::memory_order_relaxed))
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return false;
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}
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}
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ssize_t waitManyWithPartialSpinning(ssize_t max, std::int64_t timeout_usecs = -1)
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{
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assert(max > 0);
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ssize_t oldCount;
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int spin = m_maxSpins;
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while (--spin >= 0)
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{
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oldCount = m_count.load(std::memory_order_relaxed);
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if (oldCount > 0)
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{
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ssize_t newCount = oldCount > max ? oldCount - max : 0;
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if (m_count.compare_exchange_strong(oldCount, newCount, std::memory_order_acquire, std::memory_order_relaxed))
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return oldCount - newCount;
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}
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std::atomic_signal_fence(std::memory_order_acquire);
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}
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oldCount = m_count.fetch_sub(1, std::memory_order_acquire);
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if (oldCount <= 0)
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{
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if ((timeout_usecs == 0) || (timeout_usecs < 0 && !m_sema.wait()) || (timeout_usecs > 0 && !m_sema.timed_wait((std::uint64_t)timeout_usecs)))
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{
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while (true)
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{
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oldCount = m_count.load(std::memory_order_acquire);
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if (oldCount >= 0 && m_sema.try_wait())
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break;
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if (oldCount < 0 && m_count.compare_exchange_strong(oldCount, oldCount + 1, std::memory_order_relaxed, std::memory_order_relaxed))
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return 0;
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}
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}
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}
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if (max > 1)
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return 1 + tryWaitMany(max - 1);
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return 1;
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}
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public:
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LightweightSemaphore(ssize_t initialCount = 0, int maxSpins = 10000) : m_count(initialCount), m_maxSpins(maxSpins)
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{
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assert(initialCount >= 0);
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assert(maxSpins >= 0);
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}
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bool tryWait()
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{
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ssize_t oldCount = m_count.load(std::memory_order_relaxed);
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while (oldCount > 0)
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{
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if (m_count.compare_exchange_weak(oldCount, oldCount - 1, std::memory_order_acquire, std::memory_order_relaxed))
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return true;
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}
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return false;
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}
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bool wait()
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{
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return tryWait() || waitWithPartialSpinning();
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}
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bool wait(std::int64_t timeout_usecs)
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{
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return tryWait() || waitWithPartialSpinning(timeout_usecs);
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}
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// Acquires between 0 and (greedily) max, inclusive
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ssize_t tryWaitMany(ssize_t max)
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{
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assert(max >= 0);
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ssize_t oldCount = m_count.load(std::memory_order_relaxed);
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while (oldCount > 0)
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{
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ssize_t newCount = oldCount > max ? oldCount - max : 0;
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if (m_count.compare_exchange_weak(oldCount, newCount, std::memory_order_acquire, std::memory_order_relaxed))
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return oldCount - newCount;
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}
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return 0;
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}
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// Acquires at least one, and (greedily) at most max
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ssize_t waitMany(ssize_t max, std::int64_t timeout_usecs)
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{
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assert(max >= 0);
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ssize_t result = tryWaitMany(max);
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if (result == 0 && max > 0)
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result = waitManyWithPartialSpinning(max, timeout_usecs);
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return result;
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}
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ssize_t waitMany(ssize_t max)
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{
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ssize_t result = waitMany(max, -1);
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assert(result > 0);
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return result;
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}
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void signal(ssize_t count = 1)
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{
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assert(count >= 0);
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ssize_t oldCount = m_count.fetch_add(count, std::memory_order_release);
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ssize_t toRelease = -oldCount < count ? -oldCount : count;
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if (toRelease > 0)
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{
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m_sema.signal((int)toRelease);
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}
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}
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std::size_t availableApprox() const
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{
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ssize_t count = m_count.load(std::memory_order_relaxed);
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return count > 0 ? static_cast<std::size_t>(count) : 0;
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}
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};
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} // end namespace moodycamel
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