Sample - Linux下演示pthread、fork等函数

    #include <stdio.h>
    #include <pthread.h>
    #include <sys/types.h>
    #include <unistd.h>
    #include <signal.h>
    #include <sys/param.h>
    #include <sys/sysinfo.h>
    void command_thread(void *arg);
    void setup_daemon();
    void message_log(char *text);
    void command_thread(void *arg)
    {
        char str_command[120];
        sprintf(str_command, "This is command_thread.");
        fprintf(stdout, "we start to fork ......\n");
        //message_log(str_command);
        pid_t pid = fork();
        if (pid < 0){
            //message_log("failed to vfork child process.");
            pthread_exit(NULL);
            return ;
        }

        if (pid == 0){ // child process
           
            fprintf(stdout, "enter child process.\n");
            message_log("enter child process.");
            //setuid();
            //execlp("");
            //int r = chdir("work");
            //if (r == -1)
            //    message_log("failed to run chdir()");
            FILE *fp = fopen("/tmp/a.txt", "a+");
            if (fp == NULL){
                message_log("failed to open file /tmp/a.txt");
            }else{
                fputs("#!/bin/sh\n", fp);
                fputs("echo PATH\n", fp);
                fclose(fp);
            }

            char *cmd_str[] = {"ls", "-l",  NULL};
            char *env[] = {"PATH=$PATH:/usr/bin:/bin", NULL};
            int ret = execve("/bin/ls", cmd_str, env);
           
            fprintf(stdout, "after exec().\n");
            message_log("ret: ");
            exit(0);
        }
        waitpid(pid, NULL, 0);
        fprintf(stdout, "main precess.\n");
        message_log("main precess.\n");
        pthread_exit(NULL);   
    }

    void setup_daemon()
    {
        int i;
        // close all open file descriptors
        for (i=0; i<NOFILE; i++){
            close(i);
        }

        // 1st fork() call
        switch (fork()){
            case -1: // error in 1st fork()
                message_log("setup_daemon():  1st fork()");
                exit(-1);
            case 0:{  // continue in 1st child (2nd parent process)
                if (setsid() == -1){   // start new session , exit() on error
                    message_log("setup_daemon():  setsid()");
                    exit(-2);
                }
               
                // 2nd fork() call
                switch (fork()){
                case -1:
                    message_log("setup_daemon():  2nd fork()");
                    exit(-1);
                case 0:// continue in 2nd child
                    // reset file creation mask for LOG file
                    chdir("/tmp");
                    umask(0);
                    return;
                default: // exit 2nd parent process
                    exit(0);
                }
                }   // case 0:
            default: // exit 1st parent process
                exit(0);

        }
    }

    void message_log(char *text)
    {
        time_t sec;
        sec = time(NULL);
        struct tm *pt = localtime(&sec);
        char logfile[80];
        sprintf(logfile, "easy%04d%02d%02d.log", pt->tm_year+1900, pt->tm_mon+1, pt->tm_mday);
        FILE *fp = fopen(logfile, "a+");
        if (fp == NULL)
            return;

        char mesg[256];
        sprintf(mesg, "%02d:%02d:%02d ", pt->tm_hour, pt->tm_min, pt->tm_sec);
        fputs(mesg, fp);
        fputs(text, fp);
        fputs("\n", fp);
        fclose(fp);
    }
    int main(int argc, char *argv[])
    {
        setup_daemon();
        pthread_t my_th;
        int my_id = pthread_create(&my_th, NULL, (void *)&command_thread, NULL);
        pthread_join(my_th, NULL);
        /*chdir("work");
        char *cmd_str[] = {"ls", "-l",  NULL};
        char *env[] = {"PATH=$PATH:/usr/bin:/bin", NULL};
        int ret = execve("/bin/ls", cmd_str, env);
        fprintf(stdout, "ret: %d\n", ret);*/
        return 1;
    }