atomicops.h

Go to the documentation of this file.

// ©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