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 ;
    }