c++ 多线程 条件变量问题

Question

c++ 多线程： 请问为什么我在主线程里使用条件变量唤醒子线程没有反应，子线程不打印信息

#include <iostream>
#include <thread>
#include <mutex>
#include <vector>
#include <Windows.h>

using namespace std;

mutex mymutex;
condition_variable mCond;
bool f = false;

class Thread { // 自定义线程类
public:
    typedef void (*CallBackFunc) (void*);
    bool start(void* arg);
    bool detach();
    bool join();
    thread::id id;
    Thread() :mArg(nullptr), mIsStart(false), mIsDetach(false) {};
    Thread(CallBackFunc c) :mArg(nullptr), mIsStart(false), mIsDetach(false), c(c) {};
    ~Thread();
    void handle(void* arg) { c(arg); };
private:
    void run(void* arg);
    void* threadRun(void*);
    void* mArg;
    bool mIsStart;
    bool mIsDetach;
    thread mThreadId;
    CallBackFunc c;
};

bool Thread::start(void* arg)
{
    mArg = arg;
    mThreadId = thread(&Thread::threadRun, this, this);
    mIsStart = true;
    id = this_thread::get_id();
    return true;
}

bool Thread::detach()
{
    if (!mIsStart) { return false; }
    if (mIsDetach) { return true; }
    mThreadId.detach();
    mIsDetach = true;
    return true;
}

bool Thread::join()
{
    if (!mIsStart || mIsDetach) { return false; }
    mThreadId.join();
    return true;
}

Thread::~Thread()
{
    if (mIsStart && !mIsDetach) { detach(); }
}

void* Thread::threadRun(void* arg)
{
    Thread* t = (Thread*)arg;
    t->run(t->mArg);
    return nullptr;
}

void Thread::run(void* arg) {
    handle(arg);

}

void action1(void* arg) {
    while (!f)
    {
        unique_lock<mutex> sb(mymutex);
        mCond.wait(sb, [&]() {
            return f;
        });
        int* x = (int*)arg;
        cout << "thread id: " << this_thread::get_id() << " x: " << x << endl;
    }
}


int main() {
    
    int x = 1;
    vector<Thread*> v;
    for (int i = 0; i < 5; i++) {
        v.push_back(new Thread(action1));
        v[i]->start((void*)x++);
    }
    while (true)
    {
        f = !f;
        mCond.notify_one();
        Sleep(1000);
    }

    return 0;
}

Answer 1

#include <iostream>
#include <mutex>
#include <thread>
#include <vector>
#include <windows.h>

using std::condition_variable;
using std::mutex;
using std::thread;

mutex mymutex;
condition_variable mCond;
bool flag = false;

class Thread
{ // 自定义线程类
  public:
    using CallBackFunc = void (*)(void *);
    thread::id threadId;

    auto start(void *arg) -> bool;
    auto detach() -> bool;
    auto join() -> bool;
    void handle(void *arg)
    {
        callBackF(arg);
    };

    Thread()
        : mArg(nullptr)
        , mIsStart(false)
        , mIsDetach(false){};

    explicit Thread(CallBackFunc callBackFunc)
        : mArg(nullptr)
        , mIsStart(false)
        , mIsDetach(false)
        , callBackF(callBackFunc){};

    ~Thread();

  private:
    void run(void *arg);
    auto threadRun(void * /*arg*/) -> void *;
    void *mArg;
    bool mIsStart;
    bool mIsDetach;
    thread mThreadId;
    CallBackFunc callBackF;
};

auto Thread::start(void *arg) -> bool
{
    mArg = arg;
    mThreadId = thread(&Thread::threadRun, this, this);
    mIsStart = true;
    threadId = std::this_thread::get_id();
    return true;
}

auto Thread::detach() -> bool
{
    if (!mIsStart)
    {
        return false;
    }
    if (mIsDetach)
    {
        return true;
    }
    mThreadId.detach();
    mIsDetach = true;
    return true;
}

auto Thread::join() -> bool
{
    if (!mIsStart || mIsDetach)
    {
        return false;
    }
    mThreadId.join();
    return true;
}

Thread::~Thread()
{
    if (mIsStart && !mIsDetach)
    {
        detach();
        printf("detach");
    }
}

auto Thread::threadRun(void *arg) -> void *
{
    Thread *t = static_cast<Thread *>(arg);
    t->run(t->mArg);
    return nullptr;
}

void Thread::run(void *arg)
{
    handle(arg);
}

void action1(void *arg)
{
    std::unique_lock<mutex> sb(mymutex);
    mCond.wait(sb, []() -> bool { return !flag; });
    int *x = static_cast<int *>(arg);
    std::cout << "thread id: " << std::this_thread::get_id() << " x: " << x
              << std::endl;
}

int main()
{
    int x = 1;
    std::vector<Thread *> v;
    for (int i = 0; i < 5; i++)
    {
        v.push_back(new Thread(action1));
        v[i]->start((void *)&++x);
    }
    for (int i = 0; i != 10; ++i)
    {
        flag = !flag;
        mCond.notify_one();
        Sleep(1000);
    }
    for (int i = 0; i != 5; ++i)
    {
        delete v[i];
    }

    return 0;
}