Kuesa Music Box QML Example

 // ©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 <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
 #if defined(__has_feature)
 #if __has_feature(thread_sanitizer)
 #define AE_NO_TSAN __attribute__((no_sanitize("thread")))
 #else
 #define AE_NO_TSAN
 #endif
 #else
 #define AE_NO_TSAN
 #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: std::atomic_thread_fence(std::memory_order_acquire); break;
                 case memory_order_release: std::atomic_thread_fence(std::memory_order_release); break;
                 case memory_order_acq_rel: std::atomic_thread_fence(std::memory_order_acq_rel); break;
                 case memory_order_seq_cst: 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() { }
 #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>
 #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)
                     {
                         assert(initialCount >= 0);
                         const long maxLong = 0x7fffffff;
                         m_hSema = CreateSemaphoreW(nullptr, initialCount, maxLong, nullptr);
                     }

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

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

                         bool try_wait() AE_NO_TSAN
                         {
                                 const unsigned long RC_WAIT_TIMEOUT = 0x00000102;
                                 return WaitForSingleObject(m_hSema, 0) != RC_WAIT_TIMEOUT;
                         }

                         bool timed_wait(std::uint64_t usecs) AE_NO_TSAN
                         {
                                 const unsigned long RC_WAIT_TIMEOUT = 0x00000102;
                                 return WaitForSingleObject(m_hSema, (unsigned long)(usecs / 1000)) != RC_WAIT_TIMEOUT;
                         }

                     void signal(int count = 1) AE_NO_TSAN
                     {
                         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)
                     {
                         assert(initialCount >= 0);
                         semaphore_create(mach_task_self(), &m_sema, SYNC_POLICY_FIFO, initialCount);
                     }

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

                     void wait() AE_NO_TSAN
                     {
                         semaphore_wait(m_sema);
                     }

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

                         bool timed_wait(std::int64_t timeout_usecs) AE_NO_TSAN
                         {
                                 mach_timespec_t ts;
                                 ts.tv_sec = static_cast<unsigned int>(timeout_usecs / 1000000);
                                 ts.tv_nsec = (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_OPERATION_TIMED_OUT && rc != KERN_ABORTED;
                         }

                     void signal() AE_NO_TSAN
                     {
                         semaphore_signal(m_sema);
                     }

                     void signal(int count) AE_NO_TSAN
                     {
                         while (count-- > 0)
                         {
                             semaphore_signal(m_sema);
                         }
                     }
                 };
 #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)
                     {
                         assert(initialCount >= 0);
                         sem_init(&m_sema, 0, initialCount);
                     }

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

                     void 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);
                     }

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

                         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 += usecs / usecs_in_1_sec;
                                 ts.tv_nsec += (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 == -1 && errno == ETIMEDOUT);
                         }

                     void signal() AE_NO_TSAN
                     {
                         sem_post(&m_sema);
                     }

                     void signal(int count) AE_NO_TSAN
                     {
                         while (count-- > 0)
                         {
                             sem_post(&m_sema);
                         }
                     }
                 };
 #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 = 10000;
                         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)
                                 {
                                         m_sema.wait();
                                         return true;
                                 }
                                 if (m_sema.timed_wait(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)
                     {
                         assert(initialCount >= 0);
                     }

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

                     void wait() AE_NO_TSAN
                     {
                         if (!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);
                         }
                     }

                     ssize_t availableApprox() const AE_NO_TSAN
                     {
                         ssize_t count = m_count.load();
                         return count > 0 ? 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