文件加锁的例题示范

核心提示：以下例子示范了如何为文件建立独享锁: #include<unistd.h> #include<stdlib.h> #include<stdio.h> #include<fcntl.h> #include<errno.h> const char *lock_fi

　　以下例子示范了如何为文件建立独享锁:

#include<unistd.h>
#include<stdlib.h>
#include<stdio.h>
#include<fcntl.h>
#include<errno.h>

const char *lock_file="lock.test1";

int main()
{
int file_desc;
int tries=10;

while(tries--){
file_desc=open(lock_file,O_RDWRO_CREATO_EXCL,0444);
if(file_desc==-1){
PRintf("%d - Lock already present
",getpid());
sleep(1);
} else {
printf("%d - I have exclusive access
",getpid());
sleep(1);
(void)close(file_desc);
(void)unlink(lock_file);
sleep(1);
}
}
exit(EX99v_SUCCESS);
}

要想看到加锁的效果,得运行:./lock&./lock
我在 linux 下运行的结果:
[1] 18396
18396 - I have exclusive access
18397 - Lock already present
18397 - I have exclusive access
18396 - Lock already present
18396 - I have exclusive access
18397 - Lock already present
18397 - I have exclusive access
18396 - Lock already present
18396 - I have exclusive access
18397 - Lock already present
18397 - I have exclusive access
18396 - Lock already present
18396 - I have exclusive access
18397 - Lock already present
18397 - I have exclusive access
18396 - Lock already present
18396 - I have exclusive access
18397 - Lock already present
18397 - I have exclusive access
18396 - Lock already present
[1]+ Done ./lock

结果解析:第一个lock运行的进程号为18396,加锁成功后输出:I have exclusive access,然后休眠1秒,此时第二个lock开始运行,并试图给文件加锁但失败输出:Lock already present,并开始休眠1秒,之后第一个loxk清醒并解锁,再休眠1秒,第二个lock运行加锁成功,如次反复运行10次..