[信息与通信]第四讲UNIX进程环境、进程控制和进程关系.ppt

Lecture four: the environment of a Unix process、process control and processes relationship Ren Liyong Computer Science of UESTC Contents Process status transition diagram Process start and termination Non local jump Create and terminate process Race condition Process relationship Process status Linux的进程组织 Linux的进程结构 Linux的进程结构 Linux的进程结构 Process start A C program starts execution with a function main. When a C program is started by the kernel, a special start-up routine is called before main function is called, which obtains address of main and arguments from main. It would copy these information to u-area of process control block . int main ( int argc, char *argv[] ); Command-line arguments int main(int argc, char **argv) { int i; printf(argument number is %d\n,argc); for(i=0;iargc;i++) printf(argv[%d] : %s\n,i,argv[i]); exit(0); } Process termination There are five ways for process to terminate Normal termination Return from main； Calling exit Calling _exit Abnormal termination Calling abort; Terminated by a signal. exit and _exit Function void exit( int status ); /* stdlib.h */ void _exit (int status ); /* unistd.h */ Two functions terminate a program normally: _exit ,which returns to the kernel immediately, and exit which performs certain cleanup processing and then returns to the kernel. The exit function has always performs a clean shutdown of the standard I/O library: the fclose function is called for all open stream. This causes all buffered output data to be flushed. atexit Function #include stdlib.h int atexit ( void ( *func )(void) ); Int on_exit ( void (*func)( int, void * ), void *arg ); With ANSI C a process can register up to 32 functions that are automatically called by exit. These are registered by atexit or on_exit function The exit function calls these functions in reverse order of their registration. Example: (doatexit) static void my_exit1(void), my_exit2(void); int main(void) { if (a