信号量应用

#include<linux/sem.h>

#include<stdio.h>

#include<errno.h>

#defineSEM_PATH"/home/my_sem"

#definemax_tries3



intsemid;

main()

{

intflag1,flag2,key,i,init_ok,tmperrno;

structsemid_dssem_info;

structseminfosem_info2;

unionsemunarg;//unionsemun£ºÇë²Î¿ŒžœÂŒ2

structsembufaskfor_res,free_res;

flag1=IPC_CREAT|IPC_EXCL|00666;

flag2=IPC_CREAT|00666;

key=ftok(SEM_PATH,'a');

//errorhandlingforftokhere;

init_ok=0;

semid=semget(key,1,flag1);//createasemaphoresetthatonlyincludesonesemphore.

if(semid<0)

{

tmperrno=errno;

perror("semget");

if(tmperrno==EEXIST)

//errnoisundefinedafterasuccessfullibrarycall(includingperrorcall)soitissaved//intmperrno.

{

semid=semget(key,1,flag2);

//flag2Ö»°üº¬ÁËIPC_CREAT±êÖŸ,²ÎÊýnsems(ÕâÀïΪ1)±ØÐëÓëÔ­ÀŽµÄÐźŵÆÊýÄ¿Ò»ÖÂ

arg.buf=&sem_info;

for(i=0;i<max_tries;i++)

{

if(semctl(semid,0,IPC_STAT,arg)==-1)

{perror("semctlerror");i=max_tries;}

else

{

if(arg.buf->sem_otime!=0){i=max_tries;init_ok=1;}

elsesleep(1);

}

}

if(!init_ok)

//dosomeinitializing,hereweassumethatthefirstprocessthatcreatesthesemwill

//finishinitializethesemandrunsemopinmax_tries*1seconds.elseitwillnotrun

//semopanymore.

{

arg.val=1;

if(semctl(semid,0,SETVAL,arg)==-1)perror("semctlsetvalerror");

}

}

else

{perror("semgeterror,processexit");

exit(1);

}

}

else//semid>=0;dosomeinitializing

{

arg.val=1;

if(semctl(semid,0,SETVAL,arg)==-1)

perror("semctlsetvalerror");

}

//getsomeinformationaboutthesemaphoreandthelimitofsemaphoreinredhat8.0

arg.buf=&sem_info;

if(semctl(semid,0,IPC_STAT,arg)==-1)

perror("semctlIPCSTAT");

printf("owner'suidis%d\n",arg.buf->sem_perm.uid);

printf("owner'sgidis%d\n",arg.buf->sem_perm.gid);

printf("creater'suidis%d\n",arg.buf->sem_perm.cuid);

printf("creater'sgidis%d\n",arg.buf->sem_perm.cgid);



arg.__buf=&sem_info2;

if(semctl(semid,0,IPC_INFO,arg)==-1)

perror("semctlIPC_INFO");

printf("thenumberofentriesinsemaphoremapis%d\n",arg.__buf->semmap);

printf("maxnumberofsemaphoreidentifiersis%d\n",arg.__buf->semmni);

printf("masnumberofsemaphoresinsystemis%d\n",arg.__buf->semmns);

printf("thenumberofundostructuressystemwideis%d\n",arg.__buf->semmnu);

printf("maxnumberofsemaphorespersemidis%d\n",arg.__buf->semmsl);

printf("maxnumberofopspersemopcallis%d\n",arg.__buf->semopm);

printf("maxnumberofundoentriesperprocessis%d\n",arg.__buf->semume);

printf("thesizeofofstructsem_undois%d\n",arg.__buf->semusz);

printf("themaximumsemaphorevalueis%d\n",arg.__buf->semvmx);



//nowaskforavailableresource:

askfor_res.sem_num=0;

askfor_res.sem_op=-1;

askfor_res.sem_flg=SEM_UNDO;



if(semop(semid,&askfor_res,1)==-1)//askforresource

perror("semoperror");



sleep(3);//dosomehandlingonthesharingresourcehere,justsleeponit3seconds

printf("nowfreetheresource\n");



//nowfreeresource

free_res.sem_num=0;

free_res.sem_op=1;

free_res.sem_flg=SEM_UNDO;



if(semop(semid,&free_res,1)==-1)//freetheresource.

if(errno==EIDRM)

printf("thesemaphoresetwasremoved\n");

//youcancommentoutthecodesbelowtocompileadifferentversion:

if(semctl(semid,0,IPC_RMID)==-1)

perror("semctlIPC_RMID");

elseprintf("removesemok\n");

}

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