Flock () parameters

Flock () parameter question what is the difference between the three flock parameters ?? & Nbsp; 1. LOCK_SH & nbsp; 2. LOCK_EX & nbsp; 3. LOCK_UN, check the problem of http://www.w3school.com.cn/php/func_filesystem flock () parameter.
What is the difference between the three parameters of flock ??
1. LOCK_SH
2. LOCK_EX
3. LOCK_UN

------ Solution --------------------
Here: http://www.w3school.com.cn/php/func_filesystem_flock.asp
------ Solution --------------------
Locking is for other programs and does not affect the operation of the current program.

1. LOCK_SH readable and not writable
2. LOCK_EX cannot be read or written
3. LOCK_UN readable and writable (that is, the lock is canceled)