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1-1. Executing a New Program

1-1. Executing a New Program. Exec : replaces the current process with the new program. execlp. execl. execle. create argv. create argv. create argv. execvp. execv. execve. convert file to path. add envp. system call. 1-2. 프로세스의 종료 : exit(). _exit. user functions.

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1-1. Executing a New Program

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  1. 1-1. Executing a New Program Exec : replaces the current process with the new program execlp execl execle create argv create argv create argv execvp execv execve convert file to path add envp system call

  2. 1-2. 프로세스의 종료 : exit() _exit user functions exit handler return exit . . . call return call return exit function _exit main function exit handler exit call user process return call call exit return C start-up routine _exit standard I/O cleanup exec Kernel

  3. 1-3. Exiting and Waiting Values returned by the wait system call Process called exit argument to exit 0x00 Signal terminated process 0x00 signal number core flag(0/1) Process stopped signal number 0x7f Posix.1 specifies termination status as the Macro. Macro Description WIFEXITED WEXITSTATUS(status) (status) WIFSIGNALED WTERMSIG(status) (status) WCOREDUMP(status) WIFSTOPPED WSTOPSIG(status) (status)

  4. 2-1. File systems Ⅰ disk drive partition partition partition file system i-list Directory blocks & Data blocks boot block super block i-node i-node i-node i-node

  5. 2-2. File systems Ⅱ directory blocks and data blocks i-list data block1 data block directory block(dirA) data block2 directory block(mydir) i-node i-node i-node i-node i-node number filename (fileA) i-node number filename (filleB.ln) i-node number dirname (dirA) mydir dirA fileB i-node number filename (filleB) fileA fileB.ln

  6. 3-1. Blocking Signals & Manipulate Signal Sets <sigpending.c> <sigprocmask.c> #include <stdio.h> #include <signal.h> #include <sys/types.h> int main() { sigset_t toblock, checkblock; sigemptyset(&toblock); sigemptyset(&checkblock); sigaddset(&toblock, SIGINT); sigprocmask(SIG_BLOCK, &toblock, (sigset_t *)NULL); sleep(5); sigpending(&checkblock); if (sigismember(&checkblock, SIGINT)) printf("^C pressed!!!\n"); sleep(5); sigprocmask(SIG_UNBLOCK, &toblock, (sigset_t *)NULL); printf("a SIGINT is ignored!!!\n"); return 0; } #include <stdio.h> #include <signal.h> #include <sys/types.h> int main() { sigset_t toblock; sigemptyset(&toblock); sigaddset(&toblock, SIGINT); sigprocmask(SIG_BLOCK, &toblock, (sigset_t *)NULL); sleep(10); sigprocmask(SIG_UNBLOCK, &toblock, (sigset_t *)NULL); printf("a SIGINT is ignored!!!\n"); return 0; }

  7. 3-2. Interrupting System Calls <testrestart.c> #include <stdio.h> #include <signal.h> #include <sys/types.h> #include <unistd.h> void handler(int); main() { struct sigaction act; int len; char line[100]; act.sa_handler=handler; act.sa_flags=SA_RESTART; (void)sigemptyset(&act.sa_mask); if (sigaction(SIGINT, &act, 0)==-1) { perror(“sigaction error”); exit(1); } write(1, “Input the string:”, 18); len=read(0, line, sizeof(line)); write(1, “string read :”, 13); write(1, line, len); } void handler(int signo) { write(1, “caught signal -> INT\n”, 21); write(1, “Input the string:”, 18); }

  8. 3-3. Non-Local GOTO - setjmp <setjmp.c> while (1) { if (setjmp(env)) if(count<2) count++; else break; alarm(10); write(1, “Input data :”, 12); if ((n=read(0, buf, sizeof(buf)) < 0) { perror(“read error”); exit(1); } alarm(0); break; } } void handler(int signo) { write(1, “Time expired!\n”, 15); longjmp(env, 1); } #include <stdio.h> #include <setjmp.h> #include <unistd.h> #include <signal.h> void handler(int); jmp_buf env; main() { struct sigaction act; char buf[100]; int n, count=0; act.sa_handler=handler; act.sa_flags=0; (void)sigemptyset(&act.sa_mask); if (sigaction(SIGALRM, &act, 0)==-1) { perror(“sigaction”); exit(1); }

  9. 5-1. System V IPC Types : Message queue, Shared memory, Semaphore Each IPC structure in the kernel is refferred to by a nonnegative integer identifier. Permission structure (공통) struct ipc_perm { uid_t uid; /* owner’s effective user id */ gid_t gid; /* owner’s effective group id */ uid_t cuid; /* creator’s effective user id */ gid_t cgid; /* creator’s effective group id */ mode_t mode; /* access modes */ ulong seg; /* slot usage sequence number */ key_t key; /* key */ };

  10. 6-1. Shared Memory I Shared Memory allows two or more processes to share a given region of memory. Shared Memory is the fastest form of IPC (because the data does not need to be copied between the client and server) Movement of data between client and server client server client server Shared memory FIFO, PIPE or MQ Output file Input file Input file Output file kernel kernel

  11. 6-2. Shared Memory II System V struct shmid_ds { struct ipc_perm shm_perm; int shm_segsz; struct XXX shm_YYY; ushort shm_lkcnt; pid_t shm_lpid; pid_t shm_cpid; ulong shm_nattch; ulong shm_cattach; time_t shm_atime; time_t shm_dtime; time_t shm_ctime; } Page1 Process1 Page2 Shared Area A Real Shared Memory!! Page3 Page4 Process2 Page5 Shared Area Page6 Physical Memory page Virtual Memory Space

  12. 6-3. Shared Memory III Functions #include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> -. Getting : int shmget(key_t key, int size, int flag); -. Operating : void *shmat(int shmid, void *addr, int flag); void *shmdt(void *addr); -. Controlling : int shmctl(int shmid, int cmd, struct shmid_ds *buf); 0 , SHM_RDONLY IPC_STAT, IPC_SET, IPC_RMID, SHM_LOCK, SHM_UNLOCK

  13. shmlistener.c shmtalker.c void handler(int dummy) {;} int main() { int shmid; key_t key; void *shmaddr; sigset_t mask; char buf[1024]; key = ftok("/etc/passwd", 1); shmid = shmget(key, 1024, IPC_CREAT | 0666); sigfillset(&mask); sigdelset(&mask, SIGUSR1); sigset(SIGUSR1, handler); printf("listener wait for talker\n"); sigsuspend(&mask); shmaddr = shmat(shmid, NULL, 0); strcpy(buf, shmaddr); printf("listener received : %s\n", buf); strcpy(shmaddr, "Have a nice day."); msync(shmaddr, 1024, MS_SYNC); sleep(10); shmdt(shmaddr); shmctl(shmid, IPC_RMID, NULL); return 0; } int main(int argc, char **argv) { key_t key; int shmid; void *addr; void *shmaddr; char buf[1024]; if (argc != 2) { perror("argc"); exit(1); } key = ftok("/etc/passwd", 1); shmid = shmget(key, 1024, 0); shmaddr = shmat(shmid, NULL, 0); strcpy(shmaddr, "Hello, I'm talker\n"); kill(atoi(argv[1]), SIGUSR1); printf("mmap send.\n"); msync(shmaddr, 1024, MS_SYNC); strcpy(buf, shmaddr); printf("Listener said : %s\n", buf); sleep(3); system("ipcs"); shmdt(shmaddr); return 0; }

  14. 7-1. Semaphores I Semaphores are not used for exchanging large amounts of data. Semaphores are intended to let multiple processes synchronize their operations. A semaphore is a counter used to provide access to a shared data object for multiple processes. process A process B Semaphore 0 or 1 kernel

  15. 7-2. Semaphores II Kernel data structures for a semaphore set struct semid_ds semid sem_perm stucture struct sem { ushort semval; pid_t sempid; ushort semncnt; ushort semzcnt; }; struct semid_ds { struct ipc_perm sem_perm; struct sem *sem_base; ushort sem_nsems; time_t sem_otime; time_t sem_ctime; } sem_base [0] semval sem_nsems sempid [0] sem_otime semncnt [0] sem_ctime semzcnt [0] semval [1] sempid [1] semncnt [1] semzcnt [1] kernel

  16. 7-3. Semaphores III Functions -. Getting : int semget(key_t key, int nsems, int flag); -. Operating : int semop(int semid, struct sembuf *sops, size_t nops); struct sembuf { ushort sem_num; short sem_op; short sem_flg; } -. Controlling : int semctl(int semid, int semnum, int cmd, union semun arg); union semun { int val; struct semid_ds *buf; ushort *array; } IPC_NOWAIT, SEM_UNDO IPC_STAT, IPC_SET, IPC_RMID, GETVAL, SETVAL, GETALL, SETALL

  17. if (creator) { if (semctl(semid, 0, SETVAL, 1) == -1) { perror(“semctl SETVAL failed”); exit(2); } } pid=getpid(); for(i=0; i<COUNT; i++) { if (semop(semid, &lock, 1)==-1) { perror(“semop lock failed”); exit(3); } printf(“\t[%d]locking\n”, pid); sleep(3); printf(“\t[%d]unlocking\n”, pid); if (semop(semid, &unlock, 1) == -1) { perror(“semop unlock failed”); exit(4); } } if (creator) { sleep(5); if (semctl(semid, DUMMY, IPC_RMID, DUMMY) == -1) { perror(“semctl IPC_RMID failed”); exit(5); } } } /* end of main */ mysem.c #include <stdio.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/sem.h> #include <stdio.h> #define DUMMY 0 #define COUNT 3 main(int argc, char *argv[]) { key_t ipckey; int semid, pid, creator, i; struct sembuf lock={0, -1, SEM_UNDO}; struct sembuf unlock={0, 1, SEM_UNDO}; setbuf(stdout, (char *)NULL); ipckey=ftok(argv[0], 1); if ((semid= semget(ipckey, 1,IPC_CREAT | IPC_EXCL | 0666)) != -1) creator=1; else if ((semid=semget(ipckey, 1, 0)) == -1) { perror(“semget failed”); exit(1); } else creator=0;

  18. 8-1. Message Queue I Linked list of message stored within the kernel and identified by message queue Identifier. Kernel data structures for a message queue struct msqid_ds struct msqid_ds { struct ipc_perm msg_perm; sturct msg *msg_first; struct msg *msg_last; ulong msg_cbytes; ulong msg_qnum; ulong msg_qbytes; pid_t msg_lspid; pid_t msg_lrpid; time_t msg_stime; time_t msg_rtime; time_t msg_ctime; }; msg_perm structure link link NULL msq_id type type type msg_first length length length msg_last data data data . . msg_ctime kernel

  19. 8-2. Message Queue II Functions #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> -. Getting : int msgget(key_t key, int flag); -. Operating : int msgsnd(int msqid, const void *ptr, size_t nbytes, int flag); int msgrcv(int msqid, void *ptr, size_t nbytes, long type, int flag); -. Controlling : int msgctl(int msqid, int cmd, struct msqid_ds *buf); IPC_CREAT, IPC_EXCL IPC_NOWAIT IPC_STAT, IPC_SET, IPC_RMID

  20. 8-3. Multiplexing Messages The purpose of having a type, associated with each message is to allow multiple processes to multiplex messages on to a single queue. client1 pid=123 client2 pid=456 client3 pid=789 type=1 type=123 type=1 type=456 type=1 type=789 Message queue type=1 type=123 or 456 or 789 Server

  21. 9-1. Memory Mapping Files - mmap Page1 Page2 Process1 Memory Mapped File Page3 Shared Area File Page4 Page5 File System Process2 Memory Mapped File Page6 Shared Area Page7 Physical Memory page Virtual Memory Space

  22. 9-2. Memory Mapping Files - Example #include <sys/types.h> #include <sys/mman.h> #include <sys/stat.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> main(int argc, char *argv[]) { int fd; caddr_t addr; struct stat statbuf; if (argc != 2) { fprintf(stderr, “Usage: mymmap filename\n”); exit(1); } if (stat(argv[1], &statbuf) == -1) { perror(“stat”); exit(1); } if ((fd=open(argv[1], O_RDONLY))==-1) { perror(“open”); exit(1); } addr=mmap(NULL, statbuf.st_size, PROT_READ, MAP_SHARED, fd (off_t)0); if (addr == MAP_FAILED) { perror(“mmap”); exit(1); } close(fd); write(1, addr, statbuf.st_size); return(0); } <mmap.c> Sizing a File #include <unistd.h> int truncate(const char *path, off_t length); int ftruncate(int fildes, off_t length);

  23. 10-1. Asynchronous I/O SIGIO : asynchronous I/O in 4.3 BSD 1) Establish a signal handler  sigaction(SIGIO, &act, 0); 2) Set the process ID to receive the signal for the descriptior.  ioctl(fd, FIOSETOWN, &pid); /* pid=getpid(); */ 3) Enable asynchronous I/O on the descriptor.  ioctl(fd, FIOASYNC, &arg); /* arg=1 */ SIGPOLL : asynchronous I/O in SVR4 1) Establish a signal handler  sigaction(SIGPOLL, &act, 0); 2) Enable asynchronous I/O for a stream device  ioctl(fd, I_SETSIG, S_RDNORM); Limitation : There is only one signal per process.

  24. 10-2. I/O Multiplexing #include <sys/types.h> #include <sys/time.h> #include <unistd.h> int select(int maxfdp1, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *tvptr);  FD_ZERO(&rset); FD_CLR(fd, &rset) FD_SET(fd, &rset); if (FD_ISSET(fd, &rset)) … #include <stropts.h> #include <poll.h> int poll(struct pollfd fdarray[], unsigned long nfds, int timeout); struct pollfd { int fd; /* file descriptor to check */ short event; /* events of interest on fd */ short revents; /* events that occurred on fd */ }; NULL :Wait forever fd0 fd1 fd2 0 0 0 …… readfds One bit per possible descriptor INFTIM(-1) : Wait forever 0 : Don’t wait positive : Wait timeout milliseconds

  25. 11-1. Treads Overview Definition : an independent sequence of execution of program code inside a UNIX process. Calling function vs creating thread funt_call(); Pthread_create(); Created thread Called function Creating program Calling program

  26. 11-2. Treads Overview II Single Thread vs Multi Threads Thread Thread Thread Registers Registers Registers Registers Memory Memory Stack Stack Stack Stack Heap Heap 정적자료 정적자료 Code Code <단일 Thread 형 Process> <멀티 Thread 형 Process>

  27. 11-3. Two model of Thread Control I User-level Thread : are not visible outside of the process User-level thread Kernel entity Runtime mapping -. Extremely low overhead -. The threads can share only processor resources allocated to their encapsulating process.

  28. 11-4. Two model of Thread Control II Kernel-level Thread : are scheduled just like individual process User-level thread Kernel entity -. The kernel is aware of thread as a schedulable entity  expensive -. This model can take advantage of the multi- processor.

  29. 11-5. Hybrid Thread Model This model have advantages of both user-level and kernel-level models by providing two levels of control User-level thread Kernel entity

  30. 11-6. Creating a Thread #include <pthread.h> int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void (*start_routine)(void *), void *arg); #include <pthread.h> void pthread_exit(void *value_ptr); int pthread_cancel(pthread_t target_thread); int pthread_join(pthread_t thread, void **value_ptr); pthread_create() pthread_t *thread –> thread_ID pthread_attr_t *attr –> thread attributes void *(*start_routine) (void *) –> function pointer void *arg –> pointer to the data to be passed to the call pthread_exit() ->Terminates thread itself pthread_cancel() ->Terminates thread specified tid pthread_join() ->Wait for specified thread are finished

  31. 11-7. Basic Example #include <pthread.h> #include <stdio.h> void *pthread1(void *dummy) { sleep(1); printf("Hello.. I'm pthread1\n"); pthread_exit(NULL); } void *pthread2(void *dummy) { sleep(2); printf("Hello.. I'm pthread2.. %d\n", (int)dummy); pthread_exit(NULL); } <pth_create.c> int main() { pthread_t tid1, tid2; pthread_create(&tid1, NULL, pthread1, NULL); pthread_create(&tid2, NULL, pthread2, (void *)3); pthread_join(tid1, NULL); pthread_join(tid2, NULL); return 0; }

  32. 11-8. Synchronization Synchronization methods • Mutual exclusion (mutex) locks • When another thread locks same mutex, my thread is suspended until another thread releases same mutex • Multiple-reader-single-writer (rwlock) locks • Same as mutex locks, but read-lock is more free access resources. • Semaphore locks • Enables two or more locks • Condition variable locks • Producer vs Consumer problem

  33. 11-9. Synchronization - Mutex #include <stdio.h> #include <pthread.h> pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; void *pthread1(void *dummy) { sleep(2); pthread_mutex_lock(&mutex); printf("Hello.. I'm pthread1\n"); sleep(2); pthread_mutex_unlock(&mutex); printf("unlocked.. (1)\n"); } void *pthread2(void *dummy) { sleep(1); pthread_mutex_lock(&mutex); printf("Hello.. I'm pthread2. I'll rest 3 seconds.\n"); sleep(3); pthread_mutex_unlock(&mutex); printf("unlocked.. (2)\n"); } int main() { <Same as ‘the Basic Example’> return 0; } <mutex.c> #include <pthread.h> int pthread_mutex_init(pthread_mutex_t *obj); int pthread_mutex_lock(pthread_mutex_t *obj); int pthread_mutex_unlock(pthread_mutex_t *obj); int pthread_mutex_trylock(pthread_mutex_t *obj);

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