多线程常识相关

https://blog.csdn.net/dxyt2002/article/details/130209169

#include <iostream>
#include <unistd.h>
#include <pthread.h>
using std::cout;
using std::endl;

int tickets = 10000;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;		// 定义全局锁, 并用宏来初始化

void* grabTicket(void* args) {
    const char* name = static_cast<const char*>(args);

    while (true) {
        pthread_mutex_lock(&mutex); // 在即将进入临界区时加锁
        if (tickets > 0) {
            printf("%s: %lu 抢到票了, 编号为: %d\n", name, pthread_self(), tickets--);
            pthread_mutex_unlock(&mutex); // 在即将离开临界区时解锁
            usleep(10);
        }
        else {
            printf("没有票了, %s: %lu 放弃抢票\n", name, pthread_self());
            pthread_mutex_unlock(&mutex); // 在线程即将退出时解锁
            break;
        }
    }

    return nullptr;
}

int main() {
    pthread_t tid1, tid2, tid3, tid4;

    pthread_create(&tid1, nullptr, grabTicket, (void*)"thread_1");
    pthread_create(&tid2, nullptr, grabTicket, (void*)"thread_2");
    pthread_create(&tid3, nullptr, grabTicket, (void*)"thread_3");
    pthread_create(&tid4, nullptr, grabTicket, (void*)"thread_4");

    pthread_join(tid1, nullptr);
    cout << "main thread join thread_1" << endl;
    pthread_join(tid2, nullptr);
    cout << "main thread join thread_2" << endl;
    pthread_join(tid3, nullptr);
    cout << "main thread join thread_3" << endl;
    pthread_join(tid4, nullptr);
    cout << "main thread join thread_4" << endl;

    return 0;
}

这里运行的结果是：
所有票被抢完以后，才依次输出
cout << “main thread join thread_1” << endl;
cout << “main thread join thread_2” << endl;
cout << “main thread join thread_3” << endl;
cout << “main thread join thread_4” << endl;
因为join 限制了一个线程退出以后，才会执行join以后的代码。
但是pthread_create以后，每个线程都已经开始了。他们和主线程是并行的。
如果是detach，那么
cout << “main thread join thread_1” << endl;
cout << “main thread join thread_2” << endl;
cout << “main thread join thread_3” << endl;
cout << “main thread join thread_4” << endl;
这几句话会交错掺杂在抢票结果过程中。抢票未结束的时候主线程就已经退出了。因为进程结束，所以所有线程都杀死。