Agregar un bloqueo de lectura o escritura al archivo

1. Agregue un bloqueo de lectura al archivo

#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <sys/file.h>
#include <fcntl.h>
#include <stdlib.h>
int lock_set(int fd,int type)
{
    
    
	struct flock old_lock,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 already set by %d\n",lock.l_pid);
		}
		else if (lock.l_type ==F_WRLCK)
		{
    
    
			printf("write lock already 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;
	}
	else
	{
    
    
		switch(lock.l_type)
		{
    
    
		case F_RDLCK :
			{
    
    
				printf("read lock set by %d",getpid());
			}
			break;
		case F_WRLCK :
			{
    
    
				printf("write lock set by %d\n",getpid());
			}
			break;
		case F_UNLCK :
			{
    
    
				printf("Release lock set by %d\n",getpid());
			}
			break;
			default :
			break;
		}
		}
			return 0;
}

int main(void)
{
    
    
	int fd;
	fd=open("hello",O_RDWR|O_CREAT,0644);
	if(fd<0)
	{
    
    
		printf("Open file error\n");
		exit(1);
	}
	lock_set(fd,F_RDLCK);
	getchar();
	lock_set(fd,F_UNLCK);
	getchar();
	close(fd);
	exit(0);
}

2. Escribir y bloquear archivos

#include<unistd.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<stdio.h>
#include<stdlib.h>
#include<sys/file.h>
#include<fcntl.h>

int lock_set(int fd,int type)
{
    
    
	struct flock old_lock, 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);//判断是否可以给文件上锁

	if(lock.l_type!= F_UNLCK)
	{
    
    
		/*判断文件不能上锁的原因*/
		if (lock.l_type == F_RDLCK)
			printf("read lock already set by %d\n",lock.l_pid);
		else if(lock.l_type == F_WRLCK)
			printf("write lock already set by %d\n", lock.l_pid);
	}
	

	lock.l_type=type;//l_type可能已经被F_SETLK修改过。
	
	/*根据不同的type值进行阻塞式上锁或解锁*/
	
	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 set by %d\n", getpid());
			break;
		default:
			break;
	}
	return 0;
}	
int main(void)
{
    
    
	int fd;
	fd=open("hello",O_RDWR|O_CREAT,0644);
	if(fd<0)
	{
    
    
		printf("Open file error\n");
		exit(1);
	}
	lock_set(fd,F_WRLCK);//给文件上写入锁
	getchar();
	lock_set(fd,F_UNLCK);//给文件解锁
	getchar();
	close(fd);
	exit(0);
}