文件加鎖的例題示范

2019-11-17 05:32:01

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供稿：網(wǎng)友

　　以下例子示范了如何為文件建立獨(dú)享鎖:

#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){
",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);
}

要想看到加鎖的效果,得運(yùn)行:./lock&./lock
我在 linux 下運(yùn)行的結(jié)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

結(jié)果解析:第一個(gè)lock運(yùn)行的進(jìn)程號為18396,加鎖成功后輸出:I have exclusive access,然后休眠1秒,此時(shí)第二個(gè)lock開始運(yùn)行,并試圖給文件加鎖但失敗輸出:Lock already present,并開始休眠1秒,之后第一個(gè)loxk清醒并解鎖,再休眠1秒,第二個(gè)lock運(yùn)行加鎖成功,如次反復(fù)運(yùn)行10次..

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