linux C：多进程嵌套多线程的例子

以下是一个简单的多进程嵌套多线程的例子，其中父进程创建两个子进程，每个子进程再创建两个线程：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>

void *thread_func(void *arg) {
    int tid = *(int *)arg;
    printf("Thread %d is running in Process %d\n", tid, getpid());
    return NULL;
}

int main() {
    pid_t pid;
    int i, j, k;
    for (i = 0; i < 2; i++) {
        pid = fork();
        if (pid < 0) {
            perror("fork error");
            exit(EXIT_FAILURE);
        } else if (pid == 0) {
            printf("Child Process %d is running\n", getpid());
            for (j = 0; j < 2; j++) {
                pthread_t tid;
                int ret;
                int *arg = (int *)malloc(sizeof(int));
                *arg = j;
                ret = pthread_create(&tid, NULL, thread_func, arg);
                if (ret != 0) {
                    perror("pthread_create error");
                    exit(EXIT_FAILURE);
                }
            }
            for (k = 0; k < 2; k++) {
                pthread_join(tid, NULL);
            }
            printf("Child Process %d is exiting\n", getpid());
            exit(EXIT_SUCCESS);
        }
    }
    for (i = 0; i < 2; i++) {
        wait(NULL);
    }
    printf("Parent Process %d is exiting\n", getpid());
    exit(EXIT_SUCCESS);
}

在这个例子中，父进程创建两个子进程，每个子进程再创建两个线程。每个线程打印出它所属的进程和线程编号。父进程在两个子进程都结束后退出。运行程序，可以看到输出结果类似于：

Child Process 13063 is running
Thread 0 is running in Process 13063
Thread 1 is running in Process 13063
Child Process 13064 is running
Thread 0 is running in Process 13064
Thread 1 is running in Process 13064
Child Process 13063 is exiting
Thread 0 is running in Process 13064
Thread 1 is running in Process 13064
Child Process 13064 is exiting
Parent Process 13062 is exiting

可以看到，每个进程都创建了两个线程，并且线程运行的顺序是不确定的。