提升线程问题，当一个线程与另一个线程没有相同的副本时如何共享变量？

Boost thread issue, how to share variable when one thread doesn't have the same copy as another?

本文关键字：线程 副本 共享变量 问题 一个 另一个      更新时间：2023-10-16
这可能是

一个愚蠢的问题，但我确实在互联网上搜索了变量，并找到了与互斥体和赛车条件、锁等相关的所有内容;但似乎没有什么能解决这个简单的问题。

基本上下面的代码创建两个线程，在每个线程中更改变量shared_int以表示使用它的线程。线程单独运行，类本身似乎在两个不同的线程中shared_int具有同一变量的两个实例？我遇到的问题是我希望这个变量在任一线程中被更改并且也是可读的，但我也希望从一个线程中看到的shared_int值在第二个线程中相同。这是代码

#include <boost/thread.hpp>
template <typename I>
class threaded
{
    private:
        I volatile shared_int;
    public:
        threaded();
        virtual ~threaded();
        bool inputAvailable();
        void thread_1();
        void thread_2();
};
template <typename I>
threaded<I>::threaded(){}
template <typename I>
threaded<I>::~threaded(){}
template <typename I>
bool threaded<I>::inputAvailable()
{
      struct timeval tv;
      fd_set fds;
      tv.tv_sec = 0;
      tv.tv_usec = 0;
      FD_ZERO(&fds);
      FD_SET(STDIN_FILENO, &fds);
      select(STDIN_FILENO + 1, &fds, NULL, NULL, &tv);
      return (FD_ISSET(0, &fds));
}
template <typename I>
void threaded<I>::thread_1()
{
    shared_int = 1;
    while(!inputAvailable())
    {
        std::cout<<"threaded::thread_1 shared_int "<<this->shared_int<<std::endl;
        boost::this_thread::sleep_for( boost::chrono::milliseconds{ 9000});
    };
}
template <typename I>
void threaded<I>::thread_2()
{
    shared_int = 2;
    while(!inputAvailable())
    {
        std::cout<<"threaded::thread_2 shared_int "<<this->shared_int<<std::endl;
        boost::this_thread::sleep_for( boost::chrono::milliseconds{ 10000});
    };
}
int main()
{
    boost::thread_group thread;
    threaded< int> threads;
    thread.add_thread( new boost::thread( boost::bind( &threaded<int>::thread_1, threads)));
    thread.add_thread( new boost::thread( boost::bind( &threaded<int>::thread_2, threads)));
    thread.join_all();
    return 0;
}

下面的代码似乎确实解决了这个问题。它使用boost::shared_ptr但也适用于常规指针;无论哪种方式！我仍然想要一个按值而不是指针传递对象的解决方案，但指针现在有效。

#include <boost/thread.hpp>
#include <boost/shared_ptr.hpp>
template <typename I>
class threaded
{
    private:
        I volatile shared_int;
    public:
        threaded();
        virtual ~threaded();
        bool inputAvailable();
        void thread_1();
        void thread_2();
};
template <typename I>
threaded<I>::threaded(){}
template <typename I>
threaded<I>::~threaded(){}
template <typename I>
bool threaded<I>::inputAvailable()
{
      struct timeval tv;
      fd_set fds;
      tv.tv_sec = 0;
      tv.tv_usec = 0;
      FD_ZERO(&fds);
      FD_SET(STDIN_FILENO, &fds);
      select(STDIN_FILENO + 1, &fds, NULL, NULL, &tv);
      return (FD_ISSET(0, &fds));
}
template <typename I>
void threaded<I>::thread_1()
{
    shared_int = 1;
    while(!inputAvailable())
    {
        std::cout<<"threaded::thread_1 shared_int "<<this->shared_int<<std::endl;
        boost::this_thread::sleep_for( boost::chrono::milliseconds{ 9000});
    };
}
template <typename I>
void threaded<I>::thread_2()
{
    shared_int = 2;
    while(!inputAvailable())
    {
        std::cout<<"threaded::thread_2 shared_int "<<this->shared_int<<std::endl;
        boost::this_thread::sleep_for( boost::chrono::milliseconds{ 10000});
    };
}
int main()
{
    boost::thread_group thread;
    boost::shared_ptr< threaded <int> > threads{ new threaded <int>};
    thread.add_thread( new boost::thread( boost::bind( &threaded<int>::thread_1, threads)));
    thread.add_thread( new boost::thread( boost::bind( &threaded<int>::thread_2, threads)));
    thread.join_all();
    threads.reset();
    return 0;
}
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