atomicops.h

// ©2013-2016 Cameron Desrochers.
// Distributed under the simplified BSD license (see the license file that
// should have come with this header).
// Uses Jeff Preshing's semaphore implementation (under the terms of its
// separate zlib license, embedded below).

#pragma once

// Provides portable (VC++2010+, Intel ICC 13, GCC 4.7+, and anything C++11 compliant) implementation
// of low-level memory barriers, plus a few semi-portable utility macros (for inlining and alignment).
// Also has a basic atomic type (limited to hardware-supported atomics with no memory ordering guarantees).
// Uses the AE_* prefix for macros (historical reasons), and the "moodycamel" namespace for symbols.

#include <cerrno>
#include <cassert>
#include <type_traits>
#include <cerrno>
#include <cstdint>
#include <ctime>

// Platform detection
#if defined(__INTEL_COMPILER)
#define AE_ICC
#elif defined(_MSC_VER)
#define AE_VCPP
#elif defined(__GNUC__)
#define AE_GCC
#endif

#if defined(_M_IA64) || defined(__ia64__)
#define AE_ARCH_IA64
#elif defined(_WIN64) || defined(__amd64__) || defined(_M_X64) || defined(__x86_64__)
#define AE_ARCH_X64
#elif defined(_M_IX86) || defined(__i386__)
#define AE_ARCH_X86
#elif defined(_M_PPC) || defined(__powerpc__)
#define AE_ARCH_PPC
#else
#define AE_ARCH_UNKNOWN
#endif


// AE_UNUSED
#define AE_UNUSED(x) ((void)x)

// AE_NO_TSAN/AE_TSAN_ANNOTATE_*
// For GCC
#if defined(__SANITIZE_THREAD__)
#define AE_TSAN_IS_ENABLED
#endif
// For clang
#if defined(__has_feature)
#if __has_feature(thread_sanitizer) && !defined(AE_TSAN_IS_ENABLED)
#define AE_TSAN_IS_ENABLED
#endif
#endif

#ifdef AE_TSAN_IS_ENABLED
#if __cplusplus >= 201703L  // inline variables require C++17
namespace moodycamel { inline int ae_tsan_global; }
#define AE_TSAN_ANNOTATE_RELEASE() AnnotateHappensBefore(__FILE__, __LINE__, (void *)(&::moodycamel::ae_tsan_global))
#define AE_TSAN_ANNOTATE_ACQUIRE() AnnotateHappensAfter(__FILE__, __LINE__, (void *)(&::moodycamel::ae_tsan_global))
extern "C" void AnnotateHappensBefore(const char*, int, void*);
extern "C" void AnnotateHappensAfter(const char*, int, void*);
#else  // when we can't work with tsan, attempt to disable its warnings
#define AE_NO_TSAN __attribute__((no_sanitize("thread")))
#endif
#endif

#ifndef AE_NO_TSAN
#define AE_NO_TSAN
#endif

#ifndef AE_TSAN_ANNOTATE_RELEASE
#define AE_TSAN_ANNOTATE_RELEASE()
#define AE_TSAN_ANNOTATE_ACQUIRE()
#endif


// AE_FORCEINLINE
#if defined(AE_VCPP) || defined(AE_ICC)
#define AE_FORCEINLINE __forceinline
#elif defined(AE_GCC)
//#define AE_FORCEINLINE __attribute__((always_inline)) 
#define AE_FORCEINLINE inline
#else
#define AE_FORCEINLINE inline
#endif


// AE_ALIGN
#if defined(AE_VCPP) || defined(AE_ICC)
#define AE_ALIGN(x) __declspec(align(x))
#elif defined(AE_GCC)
#define AE_ALIGN(x) __attribute__((aligned(x)))
#else
// Assume GCC compliant syntax...
#define AE_ALIGN(x) __attribute__((aligned(x)))
#endif


// Portable atomic fences implemented below:

namespace moodycamel {

enum memory_order {
	memory_order_relaxed,
	memory_order_acquire,
	memory_order_release,
	memory_order_acq_rel,
	memory_order_seq_cst,

	// memory_order_sync: Forces a full sync:
	// #LoadLoad, #LoadStore, #StoreStore, and most significantly, #StoreLoad
	memory_order_sync = memory_order_seq_cst
};

}    // end namespace moodycamel

#if (defined(AE_VCPP) && (_MSC_VER < 1700 || defined(__cplusplus_cli))) || (defined(AE_ICC) && __INTEL_COMPILER < 1600)
// VS2010 and ICC13 don't support std::atomic_*_fence, implement our own fences

#include <intrin.h>

#if defined(AE_ARCH_X64) || defined(AE_ARCH_X86)
#define AeFullSync _mm_mfence
#define AeLiteSync _mm_mfence
#elif defined(AE_ARCH_IA64)
#define AeFullSync __mf
#define AeLiteSync __mf
#elif defined(AE_ARCH_PPC)
#include <ppcintrinsics.h>
#define AeFullSync __sync
#define AeLiteSync __lwsync
#endif


#ifdef AE_VCPP
#pragma warning(push)
#pragma warning(disable: 4365)		// Disable erroneous 'conversion from long to unsigned int, signed/unsigned mismatch' error when using `assert`
#ifdef __cplusplus_cli
#pragma managed(push, off)
#endif
#endif

namespace moodycamel {

AE_FORCEINLINE void compiler_fence(memory_order order) AE_NO_TSAN
{
	switch (order) {
		case memory_order_relaxed: break;
		case memory_order_acquire: _ReadBarrier(); break;
		case memory_order_release: _WriteBarrier(); break;
		case memory_order_acq_rel: _ReadWriteBarrier(); break;
		case memory_order_seq_cst: _ReadWriteBarrier(); break;
		default: assert(false);
	}
}

// x86/x64 have a strong memory model -- all loads and stores have
// acquire and release semantics automatically (so only need compiler
// barriers for those).
#if defined(AE_ARCH_X86) || defined(AE_ARCH_X64)
AE_FORCEINLINE void fence(memory_order order) AE_NO_TSAN
{
	switch (order) {
		case memory_order_relaxed: break;
		case memory_order_acquire: _ReadBarrier(); break;
		case memory_order_release: _WriteBarrier(); break;
		case memory_order_acq_rel: _ReadWriteBarrier(); break;
		case memory_order_seq_cst:
			_ReadWriteBarrier();
			AeFullSync();
			_ReadWriteBarrier();
			break;
		default: assert(false);
	}
}
#else
AE_FORCEINLINE void fence(memory_order order) AE_NO_TSAN
{
	// Non-specialized arch, use heavier memory barriers everywhere just in case :-(
	switch (order) {
		case memory_order_relaxed:
			break;
		case memory_order_acquire:
			_ReadBarrier();
			AeLiteSync();
			_ReadBarrier();
			break;
		case memory_order_release:
			_WriteBarrier();
			AeLiteSync();
			_WriteBarrier();
			break;
		case memory_order_acq_rel:
			_ReadWriteBarrier();
			AeLiteSync();
			_ReadWriteBarrier();
			break;
		case memory_order_seq_cst:
			_ReadWriteBarrier();
			AeFullSync();
			_ReadWriteBarrier();
			break;
		default: assert(false);
	}
}
#endif
}    // end namespace moodycamel
#else
// Use standard library of atomics
#include <atomic>

namespace moodycamel {

AE_FORCEINLINE void compiler_fence(memory_order order) AE_NO_TSAN
{
	switch (order) {
		case memory_order_relaxed: break;
		case memory_order_acquire: std::atomic_signal_fence(std::memory_order_acquire); break;
		case memory_order_release: std::atomic_signal_fence(std::memory_order_release); break;
		case memory_order_acq_rel: std::atomic_signal_fence(std::memory_order_acq_rel); break;
		case memory_order_seq_cst: std::atomic_signal_fence(std::memory_order_seq_cst); break;
		default: assert(false);
	}
}

AE_FORCEINLINE void fence(memory_order order) AE_NO_TSAN
{
	switch (order) {
		case memory_order_relaxed: break;
		case memory_order_acquire: AE_TSAN_ANNOTATE_ACQUIRE(); std::atomic_thread_fence(std::memory_order_acquire); break;
		case memory_order_release: AE_TSAN_ANNOTATE_RELEASE(); std::atomic_thread_fence(std::memory_order_release); break;
		case memory_order_acq_rel: AE_TSAN_ANNOTATE_ACQUIRE(); AE_TSAN_ANNOTATE_RELEASE(); std::atomic_thread_fence(std::memory_order_acq_rel); break;
		case memory_order_seq_cst: AE_TSAN_ANNOTATE_ACQUIRE(); AE_TSAN_ANNOTATE_RELEASE(); std::atomic_thread_fence(std::memory_order_seq_cst); break;
		default: assert(false);
	}
}

}    // end namespace moodycamel

#endif


#if !defined(AE_VCPP) || (_MSC_VER >= 1700 && !defined(__cplusplus_cli))
#define AE_USE_STD_ATOMIC_FOR_WEAK_ATOMIC
#endif

#ifdef AE_USE_STD_ATOMIC_FOR_WEAK_ATOMIC
#include <atomic>
#endif
#include <utility>

// WARNING: *NOT* A REPLACEMENT FOR std::atomic. READ CAREFULLY:
// Provides basic support for atomic variables -- no memory ordering guarantees are provided.
// The guarantee of atomicity is only made for types that already have atomic load and store guarantees
// at the hardware level -- on most platforms this generally means aligned pointers and integers (only).
namespace moodycamel {
template<typename T>
class weak_atomic
{
public:
	AE_NO_TSAN weak_atomic() : value() { }
#ifdef AE_VCPP
#pragma warning(push)
#pragma warning(disable: 4100)		// Get rid of (erroneous) 'unreferenced formal parameter' warning
#endif
	template<typename U> AE_NO_TSAN weak_atomic(U&& x) : value(std::forward<U>(x)) {  }
#ifdef __cplusplus_cli
	// Work around bug with universal reference/nullptr combination that only appears when /clr is on
	AE_NO_TSAN weak_atomic(nullptr_t) : value(nullptr) {  }
#endif
	AE_NO_TSAN weak_atomic(weak_atomic const& other) : value(other.load()) {  }
	AE_NO_TSAN weak_atomic(weak_atomic&& other) : value(std::move(other.load())) {  }
#ifdef AE_VCPP
#pragma warning(pop)
#endif

	AE_FORCEINLINE operator T() const AE_NO_TSAN { return load(); }

	
#ifndef AE_USE_STD_ATOMIC_FOR_WEAK_ATOMIC
	template<typename U> AE_FORCEINLINE weak_atomic const& operator=(U&& x) AE_NO_TSAN { value = std::forward<U>(x); return *this; }
	AE_FORCEINLINE weak_atomic const& operator=(weak_atomic const& other) AE_NO_TSAN { value = other.value; return *this; }
	
	AE_FORCEINLINE T load() const AE_NO_TSAN { return value; }
	
	AE_FORCEINLINE T fetch_add_acquire(T increment) AE_NO_TSAN
	{
#if defined(AE_ARCH_X64) || defined(AE_ARCH_X86)
		if (sizeof(T) == 4) return _InterlockedExchangeAdd((long volatile*)&value, (long)increment);
#if defined(_M_AMD64)
		else if (sizeof(T) == 8) return _InterlockedExchangeAdd64((long long volatile*)&value, (long long)increment);
#endif
#else
#error Unsupported platform
#endif
		assert(false && "T must be either a 32 or 64 bit type");
		return value;
	}
	
	AE_FORCEINLINE T fetch_add_release(T increment) AE_NO_TSAN
	{
#if defined(AE_ARCH_X64) || defined(AE_ARCH_X86)
		if (sizeof(T) == 4) return _InterlockedExchangeAdd((long volatile*)&value, (long)increment);
#if defined(_M_AMD64)
		else if (sizeof(T) == 8) return _InterlockedExchangeAdd64((long long volatile*)&value, (long long)increment);
#endif
#else
#error Unsupported platform
#endif
		assert(false && "T must be either a 32 or 64 bit type");
		return value;
	}
#else
	template<typename U>
	AE_FORCEINLINE weak_atomic const& operator=(U&& x) AE_NO_TSAN
	{
		value.store(std::forward<U>(x), std::memory_order_relaxed);
		return *this;
	}
	
	AE_FORCEINLINE weak_atomic const& operator=(weak_atomic const& other) AE_NO_TSAN
	{
		value.store(other.value.load(std::memory_order_relaxed), std::memory_order_relaxed);
		return *this;
	}

	AE_FORCEINLINE T load() const AE_NO_TSAN { return value.load(std::memory_order_relaxed); }
	
	AE_FORCEINLINE T fetch_add_acquire(T increment) AE_NO_TSAN
	{
		return value.fetch_add(increment, std::memory_order_acquire);
	}
	
	AE_FORCEINLINE T fetch_add_release(T increment) AE_NO_TSAN
	{
		return value.fetch_add(increment, std::memory_order_release);
	}
#endif
	

private:
#ifndef AE_USE_STD_ATOMIC_FOR_WEAK_ATOMIC
	// No std::atomic support, but still need to circumvent compiler optimizations.
	// `volatile` will make memory access slow, but is guaranteed to be reliable.
	volatile T value;
#else
	std::atomic<T> value;
#endif
};

}	// end namespace moodycamel



// Portable single-producer, single-consumer semaphore below:

#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>
#elif defined(FREERTOS)
#include <FreeRTOS.h>
#include <semphr.h>
#include <task.h>
#endif

namespace moodycamel
{
	// Code in the spsc_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 spsc_sema
	{
#if defined(_WIN32)
		class Semaphore
		{
		private:
		    void* m_hSema;
		    
		    Semaphore(const Semaphore& other);
		    Semaphore& operator=(const Semaphore& other);

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

		    AE_NO_TSAN ~Semaphore()
		    {
		        CloseHandle(m_hSema);
		    }

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

			bool try_wait() AE_NO_TSAN
			{
				return WaitForSingleObject(m_hSema, 0) == 0;
			}

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

		    void signal(int count = 1) AE_NO_TSAN
		    {
		        while (!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);
		    Semaphore& operator=(const Semaphore& other);

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

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

		    bool wait() AE_NO_TSAN
		    {
		        return semaphore_wait(m_sema) == KERN_SUCCESS;
		    }

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

			bool timed_wait(std::uint64_t timeout_usecs) AE_NO_TSAN
			{
				mach_timespec_t ts;
				ts.tv_sec = static_cast<unsigned int>(timeout_usecs / 1000000);
				ts.tv_nsec = static_cast<int>((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_SUCCESS;
			}

		    void signal() AE_NO_TSAN
		    {
		        while (semaphore_signal(m_sema) != KERN_SUCCESS);
		    }

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

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

		public:
		    AE_NO_TSAN Semaphore(int initialCount = 0) : m_sema()
		    {
		        assert(initialCount >= 0);
		        int rc = sem_init(&m_sema, 0, static_cast<unsigned int>(initialCount));
		        assert(rc == 0);
		        AE_UNUSED(rc);
		    }

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

		    bool wait() AE_NO_TSAN
		    {
		        // 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);
		        return rc == 0;
		    }

			bool try_wait() AE_NO_TSAN
			{
				int rc;
				do {
					rc = sem_trywait(&m_sema);
				} while (rc == -1 && errno == EINTR);
				return rc == 0;
			}

			bool timed_wait(std::uint64_t usecs) AE_NO_TSAN
			{
				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 += static_cast<time_t>(usecs / usecs_in_1_sec);
				ts.tv_nsec += static_cast<long>(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 == 0;
			}

		    void signal() AE_NO_TSAN
		    {
		        while (sem_post(&m_sema) == -1);
		    }

		    void signal(int count) AE_NO_TSAN
		    {
		        while (count-- > 0)
		        {
		            while (sem_post(&m_sema) == -1);
		        }
		    }
		};
#elif defined(FREERTOS)
		//---------------------------------------------------------
		// Semaphore (FreeRTOS)
		//---------------------------------------------------------
		class Semaphore
		{
		private:
			SemaphoreHandle_t m_sema;

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

		public:
			AE_NO_TSAN Semaphore(int initialCount = 0) : m_sema()
			{
				assert(initialCount >= 0);
				m_sema = xSemaphoreCreateCounting(static_cast<UBaseType_t>(~0ull), static_cast<UBaseType_t>(initialCount));
				assert(m_sema);
			}

			AE_NO_TSAN ~Semaphore()
			{
				vSemaphoreDelete(m_sema);
			}

			bool wait() AE_NO_TSAN
			{
				return xSemaphoreTake(m_sema, portMAX_DELAY) == pdTRUE;
			}

			bool try_wait() AE_NO_TSAN
			{
				// Note: In an ISR context, if this causes a task to unblock,
				// the caller won't know about it
				if (xPortIsInsideInterrupt())
					return xSemaphoreTakeFromISR(m_sema, NULL) == pdTRUE;
				return xSemaphoreTake(m_sema, 0) == pdTRUE;
			}

			bool timed_wait(std::uint64_t usecs) AE_NO_TSAN
			{
				std::uint64_t msecs = usecs / 1000;
				TickType_t ticks = static_cast<TickType_t>(msecs / portTICK_PERIOD_MS);
				if (ticks == 0)
					return try_wait();
				return xSemaphoreTake(m_sema, ticks) == pdTRUE;
			}

			void signal() AE_NO_TSAN
			{
				// Note: In an ISR context, if this causes a task to unblock,
				// the caller won't know about it
				BaseType_t rc;
				if (xPortIsInsideInterrupt())
					rc = xSemaphoreGiveFromISR(m_sema, NULL);
				else
					rc = xSemaphoreGive(m_sema);
				assert(rc == pdTRUE);
				AE_UNUSED(rc);
			}

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

		//---------------------------------------------------------
		// LightweightSemaphore
		//---------------------------------------------------------
		class LightweightSemaphore
		{
		public:
			typedef std::make_signed<std::size_t>::type ssize_t;
			
		private:
		    weak_atomic<ssize_t> m_count;
		    Semaphore m_sema;

		    bool waitWithPartialSpinning(std::int64_t timeout_usecs = -1) AE_NO_TSAN
		    {
		        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 = 1024;
		        while (--spin >= 0)
		        {
		            if (m_count.load() > 0)
		            {
		                m_count.fetch_add_acquire(-1);
		                return true;
		            }
		            compiler_fence(memory_order_acquire);     // Prevent the compiler from collapsing the loop.
		        }
		        oldCount = m_count.fetch_add_acquire(-1);
				if (oldCount > 0)
					return true;
		        if (timeout_usecs < 0)
				{
					if (m_sema.wait())
						return true;
				}
				if (timeout_usecs > 0 && m_sema.timed_wait(static_cast<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.fetch_add_release(1);
					if (oldCount < 0)
						return false;    // successfully restored things to the way they were
					// Oh, the producer thread just signaled the semaphore after all. Try again:
					oldCount = m_count.fetch_add_acquire(-1);
					if (oldCount > 0 && m_sema.try_wait())
						return true;
				}
		    }

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

		    bool tryWait() AE_NO_TSAN
		    {
		        if (m_count.load() > 0)
		        {
		        	m_count.fetch_add_acquire(-1);
		        	return true;
		        }
		        return false;
		    }

		    bool wait() AE_NO_TSAN
		    {
		        return tryWait() || waitWithPartialSpinning();
		    }

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

		    void signal(ssize_t count = 1) AE_NO_TSAN
		    {
		    	assert(count >= 0);
		        ssize_t oldCount = m_count.fetch_add_release(count);
		        assert(oldCount >= -1);
		        if (oldCount < 0)
		        {
		            m_sema.signal(1);
		        }
		    }
		    
		    std::size_t availableApprox() const AE_NO_TSAN
		    {
		    	ssize_t count = m_count.load();
		    	return count > 0 ? static_cast<std::size_t>(count) : 0;
		    }
		};
	}	// end namespace spsc_sema
}	// end namespace moodycamel

#if defined(AE_VCPP) && (_MSC_VER < 1700 || defined(__cplusplus_cli))
#pragma warning(pop)
#ifdef __cplusplus_cli
#pragma managed(pop)
#endif
#endif