sys_prog.tar.gz_redhat 9

#include <stdlib.h> #include <unistd.h> #include <stdio.h> #include <limits.h> #include <errno.h> #include <string.h> #include <sys/stat.h> #include <sys/wait.h> #include <sys/ipc.h> #include <sys/sem.h> #define PERMS S_IRUSR | S_IWUSR #define SET_SIZE 2 void set_sembuf_struct(struct sembuf *s, int semnum, int semop, int semflg) { s->sem_num = (short)semnum; s->sem_op = semop; s->sem_flg = semflg; return; } int remove_semaphore(int semid) { return semctl(semid, 0, IPC_RMID); } int main (int argc, char *argv[]) { char buffer[MAX_CANON]; char *c; int i; int n; pid_t childpid; int semid; int semop_ret; struct sembuf semwait[1]; struct sembuf semsignal[1]; int status; if ( (argc != 2) || ((n = atoi (argv[1])) <= 0) ) { fprintf (stderr, "Usage: %s number_of_processes\n", argv[0]); exit(1); } /* Create a semaphore containing a single element */ if ((semid = semget(IPC_PRIVATE, SET_SIZE, PERMS)) == -1) { fprintf(stderr, "[%ld]: Could not access semaphore: %s\n", (long)getpid(), strerror(errno)); exit(1); } /* Initialize the semaphore element to 1 */ set_sembuf_struct(semwait, 0, -1, 0); set_sembuf_struct(semsignal, 0, 1, 0); if (semop(semid, semsignal, 1) == -1) { fprintf(stderr, "[%ld]: semaphore increment failed - %s\n", (long)getpid(), strerror(errno)); if (remove_semaphore(semid) == -1) fprintf(stderr, "[%ld], could not delete semaphore - %s\n", (long)getpid(), strerror(errno)); exit(1); } for (i = 1; i < n; ++i) if (childpid = fork()) break; sprintf(buffer, "i:%d process ID:%ld parent ID:%ld child ID:%ld\n", i, (long)getpid(), (long)getppid(), (long)childpid); c = buffer; /************************entry section *************************/ while(( (semop_ret = semop(semid, semwait, 1)) == -1) && (errno == EINTR)) ; if (semop_ret == -1) fprintf(stderr, "[%ld]: semaphore decrement failed - %s\n", (long)getpid(), strerror(errno)); else { /****************start of critical section *********************/ while (*c != '\0') { fputc(*c, stderr); c++; } fputc('\n', stderr); /******************end of critical section *********************/ /*********************** exit section **************************/ while(((semop_ret = semop(semid, semsignal, 1)) == -1) && (errno == EINTR)) ; if (semop_ret == -1) fprintf(stderr, "[%ld]: semaphore increment failed - %s\n", (long)getpid(), strerror(errno)); } /******************** remainder section ************************/ while((wait(&status) == -1) && (errno == EINTR)) ; if (i == 1) /* the original process removes the semaphore */ if (remove_semaphore(semid) == -1) fprintf(stderr, "[%ld], could not delete semaphore - %s\n", (long)getpid(), strerror(errno)); return 0; }