semtool.c

利用信号量实现对共享,通过不同的命令行参数实现信号量的创建,删除,P操作,V操作和修改信号量的存取权限

/*semtool.c*/
#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)
#else
union semun{
int val;
struct semid_ds *buf;
unsigned short int *array;
struct seminfo *_buf;
};
#endif

void opensem(int *sid,key_t key);                 /*打开信号量集*/
void createsem(int *sid,key_t key,int members);   /*创建信号量集*/
void locksem(int sid,int member);            /*对集合中的某个信号量进行P操作*/
void unlocksem(int sid,int member);          /*对集合中的某个信号量进行V操作*/
void removesem(int sid);                     /*删除信号量集*/
unsigned short get_member_count(int sid);    /*活动信号量集中信号量的数目*/
int getval(int sid,int member);              /*获得一个信号量当前的值*/
void dispval(int sid,int member);            /*打印某一信号量当前的值*/
void changemode(int sid,char *mode);         /*改变信号量集的存取权限*/
void usage();                                /*使用方法提示*/

int main(int argc,char *argv[])
{
key_t key;
int semset_id;
if (argc==1)
usage();
/*创建关键字值*/
key=ftok(".",'s');
/*定义各个参数功能*/
switch (tolower(argv[1][0])) {
case 'c':                            /*创建信号量集*/
if (argc!=3)
usage();
createsem(&semset_id,key,atoi(argv[2]));
break;
case 'l':                            /*P操作*/
if (argc!=3)
usage();
opensem(&semset_id,key);
locksem(semset_id,atoi(argv[2]));
break;
case 'u':                            /*V操作*/
if (argc!=3)
usage();
opensem(&semset_id,key);
unlocksem(semset_id,atoi(argv[2]));
break;
case 'd':                            /*删除信号量集*/
if (argc!=2)
usage();
opensem(&semset_id,key);
removesem(semset_id);
break;
case 'm':                            /*修改权限*/
if (argc!=3)
usage();
opensem(&semset_id,key);
changemode(semset_id,argv[2]);
break;
default:
usage();
}
return 0;
}

/*打开信号量集*/

void opensem(int *sid,key_t key)
{
/*semget函数创建信号量.第一个参数为关键字值,第二个指出在新信号量集中应创建的信号量的个数
 第三个为标志位其值等于 IPC_CREAT|IPC_EXCL|位权位*/
if((*sid=semget(key,0,0666))==-1) {                
printf("semaphore set dose not exist\n");
exit (1);
}
}

/*创建信号量集*/

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);
}

/*对集合中的某个信号量进行P操作*/

void locksem(int sid,int member)
{
struct sembuf sem_lock={0,-1,IPC_NOWAIT};  /*0为要处理的信号量在集合中的索引,-1为信号量操作符
					     IPC_NOWAIT为操作标志*/
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;
/*semop函数表示信号量操作.第一个参数代表要操作的信号量集,第二个指向要操作的sembuf数组指针
  第三个为指向sem_buf结构数组的元素个数*/
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);
}

/*对集合中的某个信号量进行V操作*/

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);
}


/*删除信号量集*/


void removesem(int sid)
{
/*semctl函数表示控制和删除信号量. 第一个参数表示要操作的信号量集,第二个指出集中特定的信号量
  第三个表示控制命令*/
semctl(sid,0,IPC_RMID,0);     /*IPC_RMID表示将信号量从内存中删除*/
printf("Semaphore removed\n");
}


/*活动信号量集中信号量的数目*/


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);    /*IPC_STAT表示读取一个信号量集的semid_ds,并存入semun的buf里*/
return(semopts.buf->sem_nsems);
}


/*获得一个信号量当前的值*/


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

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

/*改变信号量集的存取权限*/

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);      /*表示设置semid_ds中的成员ipc_perm,其值取自semun中的buf*/
printf("Updated...\n");
}

/*打印某一信号量当前的值*/

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,"                                       \n");
fprintf(stderr,"   *********************************   \n");
fprintf(stderr,"   **    进程同步机制---信号量    **   \n");
fprintf(stderr,"   *********************************   \n");
fprintf(stderr,"                                       \n");
fprintf(stderr,"   请输入正确的参数:                   \n");
fprintf(stderr,"   semtool c <信号量个数>  功能:创建信号量集         \n");
fprintf(stderr,"           l <信号量位置>  功能:对一信号量进行P操作  \n");
fprintf(stderr,"           u <信号量位置>  功能:对一信号量进行P操作  \n");  
fprintf(stderr,"           d               功能:删除信号量集合       \n");  
fprintf(stderr,"           m <权限>        功能:修改信号量集合存取权限 \n");
fprintf(stderr,"                                         	      \n");
fprintf(stderr,"   *命令执行成功后可以使用ipcs -s 命令查看信号量集  \n");
fprintf(stderr,"                                                      \n");
exit(1);
}