Linux semaphores (inter-process communication)

Linux semaphores (inter-process communication) will use a program to demonstrate the use of semaphores. The program uses PV to control semaphores, to operate the critical section, and P to reduce semaphores by 1, the V operation adds 1 to the Semaphore, and the code between PV operations is the key code in the critical section. Only one process can be accessed at a time. Program...
Linux semaphores (inter-process communication) will use a program to demonstrate the use of semaphores. The program uses PV to control semaphores, to operate the critical section, and P to reduce semaphores by 1, the V operation adds 1 to the Semaphore, and the code between PV operations is the key code in the critical section. Only one process can be accessed at a time. The program creates a sub-process and has a critical code in each of the two processes. all the functions are output sequentially ~ 9 characters. Ensure that the process is synchronized to www.2cto.com [plain] # include # Include # Include # Include # Include # Include Static int init_semvalue (int); static void del_semvalue (int); static int P (int); static int V (int ); // the custom semun struct union semun {int val; struct semid_ds * buf; unsigned short * array; struct seminfo * _ buf;}; int main (int argc, char * argv []) {int var_cri = 0; int sem_id; pid_t pid; www.2cto.com // Create a semaphore sem_id = semget (key_t) 2234, 1, 0666 | IPC_CREAT ); // initialize a Semaphore if (! Init_semvalue (sem_id) {fprintf (stderr, "Failed to initialize semaphore! \ N "); exit (EXIT_FAILURE);} // create a sub-process if (pid = fork () = 0) // sub-process {while (1) {// critical section if (! P (sem_id) // Apply for resource exit (EXIT_FAILURE); int I; for (I = 0; I! = 10; ++ I) {printf ("[child]: % d \ n", I); sleep (1);} if (! V (sem_id) // release resource exit (EXIT_FAILURE);} www.2cto.com} else if (pid> 0) // parent process {sleep (2); while (1) {// critical section if (! P (sem_id) exit (EXIT_FAILURE); int I; for (I = 0; I! = 10; ++ I) {printf ("[parent]: % d \ n", I); sleep (1) ;}if (! V (sem_id) exit (EXIT_FAILURE);} sleep (8); // destroy the Semaphore del_semvalue (sem_id);} exit (EXIT_SUCCESS);} static int init_semvalue (int id) {union semun sem_union; sem_union.val = 1; if (semctl (id, 0, SETVAL, sem_union) =-1) // set the value return (0) of the signal value in the semaphore set ); return (1);} static void del_semvalue (int id) {www.2cto.com union semun sem_union; if (semctl (id, 0, IPC_RMID, sem_union) =-1) // The IPC--RMID removes the semaphore set from memory fprintf (stderr, "Failed to delete semaphore \ n");} int P (int id) {struct sembuf op; op. sem_num = 0; // single signal op. sem_op =-1; // P operation op. sem_flg = 0; if (semop (id, & op, 1) <0) // change the key, which indicates a resource to be used by the process. return 0; return 1 ;} www.2cto.com int V (int id) {struct sembuf op; op. sem_num = 0; op. sem_op = 1; // V operation op. sem_flg = 0; if (semop (id, & op, 1) <0) return 0; return 1 ;}