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IPC Programming (cont) Faculty of Computer Science and Engineering Ho chi Minh city University of Technology SinhVienZone.com https://fb.com/sinhvienzonevn IPC  Communication Transferring message Sharing information Mechanisms: Pipe Signal Message queue Shared memory Socket RPC/RMI SinhVienZone.com Synchronization Solving confliction Processing order Mechanisms: Lock file Semaphore Mutex (pthread) https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT IPC Programming  Shared memory  Semaphore SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT SystemV IPC $ipcs Shared Memory Segments -key shmid owner perms bytes 0x00000000 65536 root 644 110592 nattch 11 Semaphore Arrays -key semid owner perms nsems Message Queues -key msqid owner perms used-bytes SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT status dest messages Shared memory xy Process Process Process Process xy xy SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Shared memory  See all shared memory segments  ipcs  ipcs –a  ipcs -m  Remove a shared memory segment  ipcrm shm shm_id  ipcrm -m shm_id SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Shared memory  Allow a lot of processes using the same memory segment  Minimum/Maximum shared memory segment size is 1byte/4MB  Maximum number of shared memory segments: 4096  Usage  Shared memory segment must be created first  Attach shared memory segment to process’s address space before using  Detach shared memory segment from process’s address space after finishing using it SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Operations on shared memory  shmget()  shmat()  shmdt()  shmctl() SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT shmget() #include #include #include int shmget(key_t key,int size,int shmflg);  key: key of shared memory segment  size: size of shared memory segment (bytes)  shmflg: IPC_CREAT, IPC_EXCL or with its permission  Example shm_id = shmget(123, 4096, IPC_CREAT | 0660) SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Create IPC object key #include #include key_t ftok(const char *path, int id);  path: refer to an existing, accessible file  id: project identifier Return value:  key_t value: if successful  -1: if fail  Example key = ftok(“/tmp/file_123”, 321); SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Example else { /*parent*/ sleep(1); printf("Process %d writes to shared memory \n", getpid()); shm[2]=shm[0]+shm[1]; shmdt((void *)shm); } return(0); } SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT IPC Programming  Shared memory  Semaphore SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT SystemV IPC $ipcs Shared Memory Segments -key shmid owner perms bytes 0x00000000 65536 root 644 110592 nattch 11 Semaphore Arrays -key semid owner perms nsems Message Queues -key msqid owner perms used-bytes SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT status dest messages Semaphore  See all shared semaphore  ipcs  ipcs –a  ipcs -s  Remove a semaphore  ipcrm sem semid  ipcrm -s semid SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Operations on semaphore  semget()  semop()  semctl() SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT semget() #include #include #include int semget(key_t key, int nsems, int semflg);  key: key of semaphore  nsems: number of semaphore in the semaphore set  semflag: IPC_CREAT, IPC_EXCL or with its permission  Example sem_id1=semget(IPC_PRIVATE,8,IPC_CREAT|0600); sem_id2=semget(123,1,IPC_CREAT|IPC_EXCL|0660); SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Hàm semop() #include #include #include int semop(int semid, struct sembuf *sops, size_t nsops);  semid: semaphore set ID returned from semget() function  sops: a pointer to an array of nsops sembuf structures, each sembuf specifies an operation on a specific semaphore  nsops: number of struct sembuf to be performed SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT struct sembuf struct sembuf { ushort sem_num; short sem_op; short sem_flg; } /* semaphore number */ /* semaphore operation */ /* operation flags */  sem_num: the order of this semaphore in the semaphore set  sem_op: change the semaphore value  sem_flg:   IPC_NOWAIT: non-blocking mode SEM_UNDO: undo operation SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT semctl() #include #include #include int semctl(int semid, int semnum, int cmd); int semctl(int semid, int semnum, int cmd, union semun arg); union semun{ int val; struct semid_ds *buf; ushort *array; }; SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT semctl() - cmd argument  Commands on semaphore set  IPC_STAT: get semaphore information  IPC_SET : set semaphore’s ownership and permissions  IPC_RMID: remove the semaphore set immediately  Commands on individual semaphore  GETVAL: get the value of the semnum-th semaphore  SETVAL: set value of the semnum-th semaphore to arg.val  GETPID: get PID of process that executed the last semop call for the semnum-th semaphore of the set  GETNCNT : get number of processes waiting for semval to increase  GETZCNT: get number of processes waiting for semval to become zero  Commands on all semaphores  SETALL: set values for all semaphores of the set  GETALL: get values of all semaphores of the set SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Example  Implement semaphore functions  seminit(): create a semaphore  p (): decrease value of semaphore by  v (): increase value of semaphore by  semrel(): remove semaphore  Write a program using semaphore to solve confliction on critical sections SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT #include #include #include #include #include union { int val; struct semid_ds *buf; ushort *array; } carg; int seminit() { int i, semid; if (semid=semget(IPC_PRIVATE,1,IPC_EXCL|0666)==-1) return(-1); carg.val=1; if (semctl(semid,0,SETVAL,carg)==-1) return(-1); return semid; } SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT void p(int sem){ struct sembuf pbuf; pbuf.sem_num=0; pbuf.sem_op=-1; /* decrease semaphore’s value */ pbuf.sem_flg=SEM_UNDO; if (semop(sem,&pbuf,1)==-1) { perror("semop"); exit(1); } } void v(int sem){ struct sembuf vbuf; vbuf.sem_num=0; vbuf.sem_op=1; vbuf.sem_flg=SEM_UNDO; if (semop(sem,&vbuf,1)==-1) { perror("semop"); exit(1); } } SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT int semrel(int semid){ return semctl(semid,0,IPC_RMID,0); } void func(int sem) { while(1) { p(sem); /* enter critical section */ printf("%d Do something in CS\n",getpid()); sleep(5); v(sem); /* exit critical section */ printf("%d Out of CS\n",getpid()); sleep(1); } } void main() { int sem=seminit();; if (fork()==0) func(sem); else func(sem); semrel(sem); } SinhVienZone.com https://fb.com/sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Questions??? SinhVienZone.com https://fb.com/sinhvienzonevn ... func(sem); semrel(sem); } SinhVienZone. com https://fb .com/ sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Questions??? SinhVienZone. com https://fb .com/ sinhvienzonevn ... https://fb .com/ sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT IPC Programming  Shared memory  Semaphore SinhVienZone. com https://fb .com/ sinhvienzonevn Faculty of Computer Science... https://fb .com/ sinhvienzonevn Faculty of Computer Science and Engineering - HCMUT Operations on semaphore  semget()  semop()  semctl() SinhVienZone. com https://fb .com/ sinhvienzonevn Faculty of Computer