文件加锁的例题示范

    　　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..