Linux文件锁无卵用？ - Chinaunix

/*file_lock_set.c*/
int lock_set(int fd,int type)
{
struct flock old_lock,lock;
lock.l_whence=SEEK_SET;
lock.l_start=0;
lock.l_len=25;
lock.l_type=type;
lock.l_pid=-1;
/*judge whether the file has been locked*/
fcntl(fd,F_GETLK,&lock);
if (lock.l_type!=F_UNLCK)/*there is already a lock*/
{
if(lock.l_type==F_RDLCK)
printf("read lock is already setted by %d",lock.l_pid);
else if(lock.l_type==F_WRLCK)
printf("read lock is already setted by %d",lock.l_pid);
}
lock.l_type=type;/*l_type may be changed by F_GETLK*/
if(fcntl(fd,F_SETLKW,&lock)<0)
{
printf("lock failed:type = %d\n",lock.l_type);
}
else if(fcntl(fd,F_SETLKW,&lock)==0)
{
switch(lock.l_type)
{
case F_RDLCK:
printf("read lock set by %d\n",getpid());break;
case F_WRLCK:
printf("write lock set by %d\n",getpid());break;
case F_UNLCK:
printf("release lock by %d\n",getpid());
}
}
}
#include<sys/types.h>
#include<unistd.h>
#include<fcntl.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<signal.h>
#include<pthread.h>
#include<semaphore.h>
#include"file_lock_set.c"
sem_t mywrite,mylock;
pthread_t thread[2];
/*func******************************************************************/
void func(void)
{
int fd;
printf("thread1 is going to open the locked file\n");
fd=open("./datafile",O_RDWR);
if (fd<0)
perror("open datafile fail");
if(fd>0)
{
while(1)
{
if(write(fd,"thread1 has been here \n",22)>0)
printf("thread1 write data sucessfully \n");
else if(write(fd,"thread1 has been here \n",22)<=0)
printf("thread1 failed to write data \n");
sleep(1);
}
}
}
/*locker***************************************************************/
void* locker(void* arg)
{
int fd;
sem_wait(&mylock);
printf("child1 is creating a datafile\n");
fd=open("./datafile",O_RDWR|O_CREAT,0666);/*创建数据文件*/
if(fd<0)
perror("creat datafile fail");
lock_set(fd,F_WRLCK);/*文件上锁*/
if(write(fd,"thread0 has been here \n",22)>0)
printf("thread0 write data sucessfully \n");
else if(write(fd,"thread1 has been here \n",22)<=0)
printf("thread2 failed to write data \n");
sem_post(&mywrite);
sleep(3);
lock_set(fd,F_UNLCK);
sleep(2);
pthread_cancel(thread[1]);
}
/*writer***************************************************************/
void* writer(void* arg)
{
sem_wait(&mywrite);
func();
}
/*main****************************************************************/
int main (int argc,char* argv[])
{
int ret;
/*创建两个线程*/
ret=sem_init(&mylock,0,1);
ret+=sem_init(&mywrite,0,0);
if(ret!=0)
printf("At least one sem init failed");
ret=pthread_create(&thread[0],NULL,locker,NULL);
ret+=pthread_create(&thread[1],NULL,writer,NULL);
if(ret!=0)
printf("At least one thread created failed");
pthread_join(thread[0],NULL);
pthread_join(thread[1],NULL);
return 0;
exit(0);
}

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