1 files changed, 772 insertions, 0 deletions

diff --git a/src/common/atomic_helpers.h b/src/common/atomic_helpers.h
new file mode 100644
index 000000000..6d912b52e
--- /dev/null
+++ b/src/common/atomic_helpers.h
@@ -0,0 +1,772 @@
+// ©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 <cassert>
+#include <cerrno>
+#include <cstdint>
+#include <ctime>
+#include <type_traits>
+
+// 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_*
+#if defined(__has_feature)
+#if __has_feature(thread_sanitizer)
+#if __cplusplus >= 201703L // inline variables require C++17
+namespace Common {
+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
+#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 Common {
+
+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
+};
+
+} // namespace Common
+
+#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 Common {
+
+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
+} // namespace Common
+#else
+// Use standard library of atomics
+#include <atomic>
+
+namespace Common {
+
+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);
+    }
+}
+
+} // namespace Common
+
+#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 Common {
+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
+};
+
+} // namespace Common
+
+// 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 Common {
+// 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;
+    }
+};
+} // namespace spsc_sema
+} // namespace Common
+
+#if defined(AE_VCPP) && (_MSC_VER < 1700 || defined(__cplusplus_cli))
+#pragma warning(pop)
+#ifdef __cplusplus_cli
+#pragma managed(pop)
+#endif
+#endif