#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<string.h>
#include<fcntl.h>
int lock_set(int fd,int type)
{
struct flock lock;
lock.l_whence= SEEK_SET;
lock.l_start = 0;
lock.l_len = 0;
lock.l_type = type;
lock.l_pid = -1;
fcntl(fd,F_GETLK,&lock);
if(lock.l_type != F_UNLCK)
{
if(lock.l_type == F_RDLCK)
{
printf("Read lock alread set by %d\n",lock.l_pid);
}
else if(lock.l_type == F_WRLCK)
{
printf("Write lock alread set by %d\n",lock.l_pid);
}
}
lock.l_type = type;
if((fcntl(fd,F_SETLKW,&lock)) < 0)
{
printf("Lock failed:type = %d\n",lock.l_type);
return -1;
}
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());
}
break;
}
return 0;
}
int custum()
{
int fs,fd;
int count;
char c;
if((fs = open("produce.txt",O_RDWR)) < 0)
{
printf("open error\n");
return -1;
}
// if((fd = open("temp.txt",O_RDWR)) < 0)
// {
// printf("open error2\n");
// return -1;
// }
while(1)
{
lock_set(fs,F_WRLCK);
lseek(fs,0,SEEK_SET);
fd=open("temp.txt",O_RDWR|O_CREAT|O_TRUNC,0777);
count=read(fs,&c,1);
if(count <= 0)
{
printf("no product!\n");
lock_set(fs,F_UNLCK);
sleep(1);
continue;
}
printf("get a character: %c \n",c);
// lseek(fs,0,SEEK_CUR);
// lseek(fd,0,SEEK_SET);
// count = 0;
while(((count = read(fs,&c,1)) == 1) /*&& c!= ‘\n‘*/)
{
printf("read fs: %c\n", c);
write(fd,&c,count);
}
close(fs);
fs = open("produce.txt",O_RDWR|O_TRUNC);
//liuzx_bj@hqyj.com
lseek(fs,0,SEEK_SET);
lseek(fd,0,SEEK_SET);
while(((count = read(fd,&c,1)) == 1) /*&& c!=‘\n‘*/)
{
// printf("read fd: %c\n", c);
write(fs,&c,count);
}
unlink("temp.txt");
close(fd);
lock_set(fs,F_UNLCK);
sleep(2);
}
}
int main(int argc, const char *argv[])
{
custum();
return 0;
}
运行程序时，生产文件里有ABC 3个产品，运行时发现最后一个C产品一直会重复取出，经检查发现：我将produce.txt中的剩余产品复制到temp.txt中，之后再复制回来，我只是将文件读写位置调到了起始，但是以读写方式打开文件produce.txt，其中的产品仍为ABC，将temp.txt中的BC复制回去时，只是覆盖AB为BC最后的C仍存在，所以会一直有C。解决这个问题是：关闭produce.txt的文件符，重新以读写，清除原文件内容的方式打开，就会成功。只是还有一个问题read函数读到最后貌似自动会读一个‘\n‘。不加语句c!=‘\n‘的话，会将\n一直复制下去。
生产者函数如下：
#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<string.h>
#include<fcntl.h>
int lock_set(int fd,int type)
{
struct flock lock;
lock.l_whence = SEEK_SET;
lock.l_start = 0;
lock.l_len = 0;
lock.l_type = type;
lock.l_pid = -1;
fcntl(fd,F_GETLK,&lock);
if(lock.l_type != F_UNLCK)
{
if(lock.l_type == F_RDLCK)
{
printf("Read lock alread set by %d\n",lock.l_pid);
}
else if(lock.l_type == F_WRLCK)
{
printf("Write lock alread set by %d\n",lock.l_pid);
}
}
lock.l_type = type;
if((fcntl(fd,F_SETLKW,&lock)) < 0)
{
printf("Lock failed:type = %d\n",lock.l_type);
return -1;
}
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());
}
break;
}
return 0;
}
int produce()
{
int fd;
char a=‘A‘;
if((fd = open("produce.txt",O_WRONLY|O_APPEND)) < 0)
{
printf("open failed\n");
return -1;
}
while(1)
{
lock_set(fd,F_WRLCK);
write(fd,&a,1);
printf("hava produce one character %c \n",a);
a++;
lock_set(fd,F_UNLCK);
sleep(3);
}
close(fd);
}
int main(int argc, const char *argv[])
{
produce();
return 0;
}
原文：https://www.cnblogs.com/jiaan/p/9351202.html