文件加锁的例题示范 |
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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_RDWR|O_CREAT|O_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(EXIT_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苏醒并解锁,再休眠1秒,第二个lock运行加锁成功,如次反复运行10次..
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