11.进程操作

1.创建子进程

#include<stdio.h>
#include<sys/types.h>
#include<unistd.h>
#define E_MSG(str, value) do{perror(str); return (value);} while(0)
int main(void){
    printf("getpid: %d\n", getpid());
    pid_t pid;
    pid = fork();
    if(pid == -1) E_MSG("fork", -1);
    if(pid == 0){ //子进程运行的代码
        printf("create child process OK\n pid = %d\n", getpid());
        printf("get parent pid %d\n", getppid());
    }
    else{ //父进程运行的代码
        printf("Run parent process code\n");
        printf("getpid: %d\n", getpid());
    }
    printf("Both run here\n");
    return 0;
}

运行结果：

zhongjun@eclipse:~/projects$ ./pr
getpid: 2345
Run parent process code
getpid: 2345
Both run here
create child process OK
 pid = 2346
get parent pid 2345
Both run here

2.进程终止

exit(int status)
------
echo $? //查看退出码

3.遗言函数，注册多次，运行多次。注册顺序和调用顺序相反。子进程继承父进程的遗言函数。

#include<stdio.h>
#include<stdlib.h>
void last(void){
   printf("last function");
   return;
}
int main(void){
    atexit(last);
    getchar();
    return 0;
}

on_exit调用方法

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

void bye(int n, void *arg){
    printf("bye...%d...%s\n", n, (char *)arg);
    return;
}

int main(void){
    on_exit(bye, "goodbye...");
    getchar();
    return 0;
}

4. 进程同步wait调用及信号。在该方法中，可以再bash终端运行kill -signal pid去测试

#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<wait.h>
#include<stdlib.h>

#define E_MSG(str, value) do{perror(str); return (value);} while(0)

int main(void){
    int signal;
    pid_t pid = fork();
    if(pid == -1) E_MSG("fork", -1);
    if(pid == 0){//运行子进程代码
        printf("Run child process %d\n", getpid());
        getchar();
        exit(-1);
    }
    else {//运行父进程代码
        //父进程回收子进程的资源，阻塞状态
        wait(&signal);
        if(WIFEXITED(signal)) //子进程正常终止
            printf("exit code: %d\n", WEXITSTATUS(signal));
        if(WIFSIGNALED(signal))//子进程被其他程序打断
            printf("Signum... %d \n", WTERMSIG(signal));
        printf("parent process...%d", getpid());
    }
    return 0;
}

waitpid用法

#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<wait.h>
#include<stdlib.h>

#define E_MSG(str, value) do{perror(str); return (value);} while(0)

int main(void){
    int signal;
    pid_t pid = fork();
    if(pid == -1) E_MSG("fork", -1);
    if(pid == 0){//运行子进程代码
        printf("Run child process %d\n", getpid());
        getchar();
        exit(-1);
    }
    else {//运行父进程代码
        int w = waitpid(-1, &signal, WNOHANG); //父进程回收子进程的资源，非阻塞
        if(w == 0){//没有子进程的终止
            printf("parent exit...");
            return 0;
        }
        if(WIFEXITED(signal)) //子进程正常终止
            printf("exit code: %d\n", WEXITSTATUS(signal));
        if(WIFSIGNALED(signal))//子进程被其他程序打断
            printf("Signum... %d \n", WTERMSIG(signal));
        printf("parent process...%d", getpid());
    }
    return 0;
}