semtool.c

操作系统Interprocess Communication（IPC）实验源码。 在Unix的内核环境中

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

#define SEM_RESOURCE_MAX 1

#if defined(__GNU_LIBRARY__) && !defined(__SEM_SEMUN_UNDEFINED)
/* union semun is defined by includeing <sys/sem.h>
#else
/* according to X/OPEN we have to define it ourselves */
union semun {
  int val;
  struct semid_ds *buf;
  unsigned short int *array;
  struct seminfo *__buf;
};
#endif

void opensem(int *sid,key_t key);
void createsem(int *sid,key_t key,int members);
void locksem(int sid,int member);
void unlocksem(int sid,int member);
void removesem(int sid);
unsigned short get_member_count(int sid);
int getval(int sid,int member);
void dispval(int sid,int member);
void changemode(int sid,char *mode);
void usage();

int main(int argc,char *argv[])
{
  key_t key;
  int semset_id;
  if (argc==1)
    usage();

  key=ftok(".",'s');
  switch (tolower(argv[1][0])) {
  case 'c':
    if (argc!=3)
      usage();
    createsem(&semset_id,key,atoi(argv[2]));
    break;
  case 'l':
    if (argc!=3)
      usage();
    opensem(&semset_id,key);
    locksem(semset_id,atoi(argv[2]));
    break;
  case 'u':
    if (argc!=3)
      usage();
    opensem(&semset_id,key);
    unlocksem(semset_id,atoi(argv[2]));
    break;
  case 'd':
    opensem(&semset_id,key);
    removesem(semset_id);
    break;
  case 'm':
    opensem(&semset_id,key);
    changemode(semset_id,argv[2]);
    break;
  default:
    usage();
  }
  return 0;
}

void opensem(int *sid,key_t key)
{
  if ((*sid=semget(key,0,0666))==-1) {
    printf("Semaphore set does not exist\n");
    exit(1);
  }
}

void createsem(int *sid,key_t key,int members)
{
  int cntr;
  union semun semopts;

  printf("Attempting to create new semaphore set with %d members\n",members);
  if ((*sid=semget(key,members,IPC_CREAT|IPC_EXCL|0666))==-1) {
    fprintf(stderr,"Semaphore set already exists!\n");
    exit(1);
  }

  semopts.val=SEM_RESOURCE_MAX;
  for (cntr=0;cntr<members;cntr++)
    semctl(*sid,cntr,SETVAL,semopts);
}

void locksem(int sid,int member)
{
  struct sembuf sem_lock={0,-1,IPC_NOWAIT};
  
  printf("get member count %d\n",get_member_count(sid));
  if (member<0 || member>(get_member_count(sid)-1)) {
    fprintf(stderr,"semaphore member %d out of range\n",member);
    return;
  }

  if (!getval(sid,member)) {
    fprintf(stderr,"Semaphore resources exhausted (no lock)!\n");
    exit(1);
  }

  sem_lock.sem_num=member;
  if ((semop(sid,&sem_lock,1))==-1) {
    fprintf(stderr,"Lock failed\n");
    exit(1);
  } else
    printf("Semaphore resources decremented by one (locked)\n");
  dispval(sid,member);
}

void unlocksem(int sid,int member)
{
  struct sembuf sem_unlock={member,1,IPC_NOWAIT};
  int semval;

  if (member<0 || member>(get_member_count(sid)-1)) {
    fprintf(stderr,"semaphore member %d out of range\n",member);
    return;
  }

  semval=getval(sid,member);
  if (semval==SEM_RESOURCE_MAX) {
    fprintf(stderr,"Semaphore not locked!\n");
    exit(1);
  }

  sem_unlock.sem_num=member;
  
  if ((semop(sid,&sem_unlock,1))==-1) {
    fprintf(stderr,"Unlock failed\n");
    exit(1);
  } else
    printf("Semaphore resources incremented by one (unlocked)\n");
  dispval(sid,member);
}

void removesem(int sid)
{
  semctl(sid,0,IPC_RMID,0);
  printf("Semaphore removed\n");
}

unsigned short get_member_count(int sid)
{
  union semun semopts;
  struct semid_ds mysem_ds;

  semopts.buf=&mysem_ds;
  semctl(sid,0,IPC_STAT,semopts);
  return (semopts.buf->sem_nsems);
}

int getval(int sid,int member)
{
  int semval;

  semval=semctl(sid,member,GETVAL,0);
  return semval;
}

void changemode(int sid,char *mode)
{
  int rc;
  union semun semopts;
  struct semid_ds mysem_ds;

  semopts.buf=&mysem_ds;
  rc=semctl(sid,0,IPC_STAT,semopts);
  if (rc==-1) {
    perror("semctl");
    exit(1);
  }

  printf("Old permissions were %o\n",semopts.buf->sem_perm.mode);
  sscanf(mode,"%ho",&semopts.buf->sem_perm.mode);
  semctl(sid,0,IPC_SET,semopts);
  printf("Updated...\n");
}

void dispval(int sid,int member)
{
  int semval;
  
  semval=semctl(sid,member,GETVAL,0);
  printf("semval for member %d is %d\n",member,semval);
}

void usage()
{
  fprintf(stderr,"semtool-A utility for tinkering with semaphores\n");
  fprintf(stderr,"Usage: semtool   (c)reate <semcount>\n");
  fprintf(stderr,"                 (l)ock <sem #>\n");
  fprintf(stderr,"                 (u)nlock <sem #>\n");
  fprintf(stderr,"                 (d)elete\n");
  fprintf(stderr,"                 (m)ode <mode>\n");
  exit(1);
}