用C++實現(xiàn)數(shù)據(jù)總線的方法系列(上)：基本概念&同步隊列

視頻教程：https://www.bilibili.com/video/av94487439

本文主要介紹多線程中數(shù)據(jù)同步的方法，技術(shù)包括：線程鎖，同步變量，原子變量，消息處理等；以及三種同步隊列的實現(xiàn)方法。

std::unique_lock

  • 與std:::lock_gurad基本一致，但更加靈活的鎖管理類模板，構(gòu)造時是否加鎖是可選的，在對象析構(gòu)時如果持有鎖會自動釋放鎖，所有權(quán)可以轉(zhuǎn)移。對象生命期內(nèi)允許手動加鎖和釋放鎖。但提供了更好的上鎖和解鎖控制接口(lock，try_lock，try_lock_for，try_lock_until 和unlock)

條件變量

  • 條件變量可以阻塞一個或多個線程，直到收到另外一個線程發(fā)出的通知，或者超時了才會喚醒當(dāng)前阻塞的線程。

類型

  • condition_variable，配合std::unique_lock<std::mutex>進行操作
  • condition_variable_any，配合任意帶有l(wèi)ock，unlock語義的mutex進行操作
    • 比較靈活，更通用，對所有的鎖都適用
    • 效率比condition_variable差

成員函數(shù)

  • notify_one 通知一個等待線程(public)
  • notify_all 通知所有等待線程(public)

notify_one()和notify_all()都是Object對象用于通知處在等待該對象的線程的方法，但notify_one是通知一個線程獲取鎖，notify_all是通知所有相關(guān)的線程去競爭鎖。

  • wait 阻塞當(dāng)前線程直至條件變量被喚醒(public)
  • wait_for 阻塞當(dāng)前線程直至條件變量被喚醒或超時(public)
  • wait_until 阻塞當(dāng)前線程直至條件變量被喚醒或直到指定的時間點(public)

執(zhí)行過程

  • 擁有條件變量的線程首先獲取互斥量
  • 然后循環(huán)檢查某個條件，如果條件不滿足，釋放互斥量，同時阻塞該線程直到條件滿足；如果條件滿足，則向下執(zhí)行。
  • 另一個線程獲取互斥量，執(zhí)行完成后調(diào)用條件變量的notify_one或notify_all喚醒一個或者所有等待線程。

簡潔寫法及wait機制

std::unique_lock<std::mutex> lck(m_mtRun);
m_cvRun.wait(lck, [this]{ return m_runDown; });
  • 條件變量首先檢查判斷式是否滿足條件，例如上例中的m_runDown是否為true
  • 如果不滿足條件，釋放mutex，將線程置為wait狀態(tài)，繼續(xù)等待喚醒
  • 如果滿足條件，重新獲取mutex，線程結(jié)束wait狀態(tài)，繼續(xù)向下執(zhí)行
  • 這里需要注意的是，wait狀態(tài)的線程被喚醒，但判斷式不滿足條件，****即假喚醒****，條件變量將繼續(xù)釋放mutex，將線程置為wait狀態(tài)，繼續(xù)等待下一次的喚醒

基本示例-wait, wait_for和假喚醒

#include <iostream>                
#include <thread>               
#include <mutex>         
#include <list>
#include <condition_variable>   
#include <windows.h>

bool                     completed;
std::mutex               mtRun;
std::condition_variable  cvRun;

void Wait()
{
    std::unique_lock<std::mutex> lck(mtRun);

    std::cout <<"Thread_"<<std::this_thread::get_id() << " is waiting..." << std::endl;
    cvRun.wait(lck, []() {
        return completed;
    });

    std::cout << "Thread_" << std::this_thread::get_id() << " is completed" << std::endl;
}

void Wait_For()
{
    std::unique_lock<std::mutex> lck(mtRun);

    std::cout << "Thread_" << std::this_thread::get_id() << " is waiting..." << std::endl;
    if (!cvRun.wait_for(lck, std::chrono::seconds(4), []() {
    //if (!cvRun.wait_for(lck, std::chrono::seconds(2), []() {
        return completed;
    }))
    {
        std::cout << "Thread_" << std::this_thread::get_id() << " time out!" << std::endl;
    }
    else
    {
        std::cout << "Thread_" << std::this_thread::get_id() << " is completed" << std::endl;
    }
}

void Completed()
{
    {
        std::cout << "Thread_" << std::this_thread::get_id() << " set completed" << std::endl;
        std::unique_lock<std::mutex> lck(mtRun);
        completed = true;
    }
    cvRun.notify_all();
}

void FakeCompleted()
{
    {
        std::cout << "Thread_" << std::this_thread::get_id() << " not set completed" << std::endl;
        std::unique_lock<std::mutex> lck(mtRun);
        completed = false;
    }
    cvRun.notify_all();
}

int main()
{
    //Wait
    completed = false;
    std::thread thWait(Wait);
    thWait.detach();
    Sleep(3000);
    std::thread thCompleted(Completed);
    thCompleted.join();
    Sleep(3000);
    //Waitfor
    //completed = false;
    //std::thread thWait(Wait_For);
    //thWait.detach();
    //Sleep(3000);
    //std::thread thCompleted(Completed);
    //thCompleted.join();
    //Sleep(3000);
    //Fake
    /*completed = false;
    std::thread thWait(Wait_For);
    thWait.detach();
    Sleep(3000);
    std::thread thCompleted(FakeCompleted);
    thCompleted.join();
    Sleep(3000);*/
    return 0;
}

原子變量

  • 使用原子變量不需要使用互斥量來保護這個變量，使用更簡潔。
  • C++11提供個原子類型std::atomic<T>, 可以使用任意類型作為參數(shù)模板，同時也內(nèi)置了基礎(chǔ)類型的原子變量。
typedef atomic<bool> atomic_bool;
typedef atomic<char> atomic_char;
typedef atomic<signed char> atomic_schar;
typedef atomic<unsigned char> atomic_uchar;
typedef atomic<short> atomic_short;
typedef atomic<unsigned short> atomic_ushort;
typedef atomic<int> atomic_int;
typedef atomic<unsigned int> atomic_uint;
typedef atomic<long> atomic_long;
typedef atomic<unsigned long> atomic_ulong;
typedef atomic<long long> atomic_llong;
typedef atomic<unsigned long long> atomic_ullong;
typedef atomic<char16_t> atomic_char16_t;
typedef atomic<char32_t> atomic_char32_t;
typedef atomic<wchar_t> atomic_wchar_t;
typedef atomic<int8_t> atomic_int8_t;
typedef atomic<uint8_t> atomic_uint8_t;
typedef atomic<int16_t> atomic_int16_t;
typedef atomic<uint16_t> atomic_uint16_t;
typedef atomic<int32_t> atomic_int32_t;
typedef atomic<uint32_t> atomic_uint32_t;
typedef atomic<int64_t> atomic_int64_t;
typedef atomic<uint64_t> atomic_uint64_t;
typedef atomic<int_least8_t> atomic_int_least8_t;
typedef atomic<uint_least8_t> atomic_uint_least8_t;
typedef atomic<int_least16_t> atomic_int_least16_t;
typedef atomic<uint_least16_t> atomic_uint_least16_t;
typedef atomic<int_least32_t> atomic_int_least32_t;
typedef atomic<uint_least32_t> atomic_uint_least32_t;
typedef atomic<int_least64_t> atomic_int_least64_t;
typedef atomic<uint_least64_t> atomic_uint_least64_t;
typedef atomic<int_fast8_t> atomic_int_fast8_t;
typedef atomic<uint_fast8_t> atomic_uint_fast8_t;
typedef atomic<int_fast16_t> atomic_int_fast16_t;
typedef atomic<uint_fast16_t> atomic_uint_fast16_t;
typedef atomic<int_fast32_t> atomic_int_fast32_t;
typedef atomic<uint_fast32_t> atomic_uint_fast32_t;
typedef atomic<int_fast64_t> atomic_int_fast64_t;
typedef atomic<uint_fast64_t> atomic_uint_fast64_t;

typedef atomic<intptr_t> atomic_intptr_t;
typedef atomic<uintptr_t> atomic_uintptr_t;
typedef atomic<size_t> atomic_size_t;
typedef atomic<ptrdiff_t> atomic_ptrdiff_t;
typedef atomic<intmax_t> atomic_intmax_t;
typedef atomic<uintmax_t> atomic_uintmax_t;
//
typedef signed char        int8_t;
typedef short              int16_t;
typedef int                int32_t;
typedef long long          int64_t;
typedef unsigned char      uint8_t;
typedef unsigned short     uint16_t;
typedef unsigned int       uint32_t;
typedef unsigned long long uint64_t;

typedef signed char        int_least8_t;
typedef short              int_least16_t;
typedef int                int_least32_t;
typedef long long          int_least64_t;
typedef unsigned char      uint_least8_t;
typedef unsigned short     uint_least16_t;
typedef unsigned int       uint_least32_t;
typedef unsigned long long uint_least64_t;

typedef signed char        int_fast8_t;
typedef int                int_fast16_t;
typedef int                int_fast32_t;
typedef long long          int_fast64_t;
typedef unsigned char      uint_fast8_t;
typedef unsigned int       uint_fast16_t;
typedef unsigned int       uint_fast32_t;
typedef unsigned long long uint_fast64_t;

typedef long long          intmax_t;
typedef unsigned long long uintmax_t;
  • 以下寫法是一樣
std::atomic_int                             m_standbyIdIndex;
std::atomic<int>                            m_standbyIdIndex;

call_once&once_flag

  • 如果多個線程需要同時調(diào)用某個函數(shù)，std::call_once 可以保證多個線程對該函數(shù)只調(diào)用一次。
  • 需要一個std::once_flag作為std::call_once的入?yún)?/li> 
std::once_flag m_flag;
std::call_once(m_flag, [this](){StopExecute(); });

同步隊列

基本同步隊列

#include <iostream>
#include <thread>  
#include <mutex>         
#include <list>
#include <condition_variable>  
#include <windows.h>

class SyncQueue
{
public:
    SyncQueue()
    {

    }

    void Push(const int& x)
    {
        {
            std::unique_lock<std::mutex> lck(m_mutex);
            m_queue.push_back(x);
        }
        m_notEmpty.notify_all();
    }

    void Pop(int& x)
    {
        std::unique_lock<std::mutex> lck(m_mutex);
        m_notEmpty.wait(lck, [this]() {
            return !m_queue.empty();
        });
        x = m_queue.front();
        m_queue.pop_front();
    }

    bool Empty()
    {
        std::lock_guard<std::mutex> lck(m_mutex);
        return m_queue.empty();
    }

    size_t Size()
    {
        std::lock_guard<std::mutex> lck(m_mutex);
        return m_queue.size();
    }

private:
    std::list<int>          m_queue;
    std::mutex              m_mutex;
    std::condition_variable m_notEmpty;
};

SyncQueue queue;

void GetData()
{
    int x = 0;
    while (queue.Empty())
    {
        queue.Pop(x);
        std::cout << "Thread_" << std::this_thread::get_id() << "---- Pop " << x << std::endl;
        if (x == 0)
        {
            break;
        }
    }
    std::cout << "Thread_" << std::this_thread::get_id() << "---- Pop End!" << std::endl;
}

void SetData()
{
    for (int i = 10; i >= 0; i--)
    {
        Sleep(1000);
        std::cout << "Thread_" << std::this_thread::get_id() << "---- Push " << i << std::endl;
        queue.Push(i);
    }
    Sleep(500);
    std::cout << "Thread_" << std::this_thread::get_id() << "---- Push End!" << std::endl;
}

int main()
{
    std::thread thGet(GetData);
    thGet.detach();
    std::thread thSet(SetData);
    thSet.join();
    return 0;
}
//output
Thread_27072---- Push 1
Thread_26712---- Pop 1
Thread_27072---- Push 2
Thread_26712---- Pop 2
Thread_27072---- Push 3
Thread_26712---- Pop 3
Thread_27072---- Push 4
Thread_26712---- Pop 4
Thread_27072---- Push 5
Thread_26712---- Pop 5
Thread_27072---- Push 6
Thread_26712---- Pop 6
Thread_27072---- Push 7
Thread_26712---- Pop 7
Thread_27072---- Push 8
Thread_26712---- Pop 8
Thread_27072---- Push 9
Thread_26712---- Pop 9
Thread_27072---- Push 10
Thread_26712---- Pop 10
Thread_26712---- Pop End!
Thread_27072---- Push End!

帶外部控制的同步隊列

#include <iostream>
#include <thread>  
#include <mutex>         
#include <list>
#include <condition_variable>  
#include <windows.h>
#include <atomic>

class SyncQueue
{
public:
    SyncQueue()
    {

    }

    void Push(const int& x)
    {
        {
            std::unique_lock<std::mutex> lck(m_mutex);
            m_queue.push_back(x);
        }
        m_notEmpty.notify_all();
    }

    void Pop(int& x)
    {
        std::unique_lock<std::mutex> lck(m_mutex);
        m_notEmpty.wait(lck, [this]() {
            return !m_queue.empty();
        });
        x = m_queue.front();
        m_queue.pop_front();
    }

    bool Empty()
    {
        std::lock_guard<std::mutex> lck(m_mutex);
        return m_queue.empty();
    }

    size_t Size()
    {
        std::lock_guard<std::mutex> lck(m_mutex);
        return m_queue.size();
    }

private:
    std::list<int>          m_queue;
    std::mutex              m_mutex;
    std::condition_variable m_notEmpty;
};

SyncQueue queue;
std::atomic_bool getStop = false;

void GetData()
{
    int x = 0;
    while (queue.Empty())
    {
        if (getStop)
        {
            break;
        }
        queue.Pop(x);
        std::cout << "Thread_" << std::this_thread::get_id() << "---- Pop " << x << std::endl;
    }
    std::cout << "Thread_" << std::this_thread::get_id() << "---- Pop End!" << std::endl;
}

void SetData()
{
    for (int i = 10; i >= 0; i--)
    {
        Sleep(1000);
        std::cout << "Thread_" << std::this_thread::get_id() << "---- Push " << i << std::endl;
        queue.Push(i);
        if (i == 5)
        {
            getStop = true;
        }
    }

    std::cout << "Thread_" << std::this_thread::get_id() << "---- Push End!" << std::endl;
}

int main()
{
    std::thread thGet(GetData);
    thGet.detach();
    std::thread thSet(SetData);
    thSet.join();
    return 0;
}
//output
Thread_29616---- Push 10
Thread_30076---- Pop 10
Thread_29616---- Push 9
Thread_30076---- Pop 9
Thread_29616---- Push 8
Thread_30076---- Pop 8
Thread_29616---- Push 7
Thread_30076---- Pop 7
Thread_29616---- Push 6
Thread_30076---- Pop 6
Thread_29616---- Push 5
Thread_30076---- Pop 5
Thread_30076---- Pop End!
Thread_29616---- Push 4
Thread_29616---- Push 3
Thread_29616---- Push 2
Thread_29616---- Push 1
Thread_29616---- Push 0
Thread_29616---- Push End!

帶超時的同步隊列

#include <iostream>
#include <thread>  
#include <mutex>         
#include <list>
#include <condition_variable>  
#include <windows.h>
#include <atomic>


class SyncQueue
{
public:
    SyncQueue()
    {


    }


    void Push(const int& x)
    {
        {
            std::unique_lock<std::mutex> lck(m_mutex);
            m_queue.push_back(x);
        }
        m_notEmpty.notify_all();
    }


    bool Pop(int& x)
    {
        std::unique_lock<std::mutex> lck(m_mutex);


        if (m_notEmpty.wait_for(lck, std::chrono::seconds(1), [this]() {
            return !m_queue.empty();
        }))
        {
            x = m_queue.front();
            m_queue.pop_front();
            return true;
        }
        else
        {
            return false;
        }
        
    }


    bool Empty()
    {
        std::lock_guard<std::mutex> lck(m_mutex);
        return m_queue.empty();
    }


    size_t Size()
    {
        std::lock_guard<std::mutex> lck(m_mutex);
        return m_queue.size();
    }


private:
    std::list<int>          m_queue;
    std::mutex              m_mutex;
    std::condition_variable m_notEmpty;
};


SyncQueue queue;
std::atomic_bool getStop = false;


void GetData()
{
    int x = 0;
    while (queue.Empty())
    {
        if (getStop)
        {
            break;
        }
        if (queue.Pop(x))
        {
            std::cout << "Thread_" << std::this_thread::get_id() << "---- Pop " << x << std::endl;
        }
        else
        {
            std::cout << "Thread_" << std::this_thread::get_id() << "---- Get Data Time out" << std::endl;
        }
    }
        
    std::cout << "Thread_" << std::this_thread::get_id() << "---- Pop End!" << std::endl;
}


void SetData()
{
    for (int i = 10; i >= 0; i--)
    {
        Sleep(100);
        std::cout << "Thread_" << std::this_thread::get_id() << "---- Push " << i << std::endl;
        queue.Push(i);
        if (i <= 5)
        {
            Sleep(2000);
        }
    }
    getStop = true;
    Sleep(500);
    std::cout << "Thread_" << std::this_thread::get_id() << "---- Push End!" << std::endl;
}


int main()
{
    std::thread thGet(GetData);
    thGet.detach();


    std::thread thSet(SetData);
    thSet.join();


    return 0;
}

//output
Thread_18908---- Push 10
Thread_2204---- Pop 10
Thread_18908---- Push 9
Thread_2204---- Pop 9
Thread_18908---- Push 8
Thread_2204---- Pop 8
Thread_18908---- Push 7
Thread_2204---- Pop 7
Thread_18908---- Push 6
Thread_2204---- Pop 6
Thread_18908---- Push 5
Thread_2204---- Pop 5
Thread_2204---- Get Data Time out
Thread_2204---- Get Data Time out
Thread_18908---- Push 4
Thread_2204---- Pop 4
Thread_2204---- Get Data Time out
Thread_2204---- Get Data Time out
Thread_18908---- Push 3
Thread_2204---- Pop 3
Thread_2204---- Get Data Time out
Thread_2204---- Get Data Time out
Thread_18908---- Push 2
Thread_2204---- Pop 2
Thread_2204---- Get Data Time out
Thread_2204---- Get Data Time out
Thread_18908---- Push 1
Thread_2204---- Pop 1
Thread_2204---- Get Data Time out
Thread_2204---- Get Data Time out
Thread_18908---- Push 0
Thread_2204---- Pop 0
Thread_2204---- Get Data Time out
Thread_2204---- Get Data Time out
Thread_2204---- Pop End!
Thread_18908---- Push End!
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