PHP file Lock Read and write note

It is said that the text mode is prone to file lock failure, such as messy problems.

In fact, it is not ineffective, but the wording is somewhat wrong.

After the lock_ex file is fopen in read mode, the empty content is read!!!

If you do not have the judgment to do it after the operation and then write a mistake ....

A lot of the problems are here.

Just to add

If a file is fopen in write mode and flock (... LOCK_EX).

There is another program at this time to fopen it, and also to Flock (LOCK_EX), this must be a mistake.

Because the size of the file may have been truncate to 0 by the second fopen.

Do a test-------------below---------------

Test program 1. :::: 1.php
<?php
$FD = fopen ("./test.txt", "w");
Flock ($FD, LOCK_EX);
Sleep (10);
Fwrite ($FD, "Hightman");
Flock ($FD, lock_un);
Fclose ($FD);
?>

Test program 2. :::: 2.php
<?php
$FD = fopen ("./test.txt", "R");
Echo fread ($FD, 512);
Fclose ($FD);
?>
Test Procedure 3::::: 3.php
<?php
if ($FD = @fopen ("./test.txt", "r+")) {
Flock ($FD, LOCK_EX);
Fseek ($FD, 0, seek_end);
Fwrite ($FD, "shit");
Flock ($FD, lock_un);
Fclose ($FD);
}
?>

Program test Method 1: Run 1.php and then go to run 2.php, 2.php output result is empty.
2: Run 1.php then go to run 3.php, 3.php will end after 1.php run
But the result file content is: "Shit" instead of "Hightmanshit"

So pay special attention to what happens when you write.
"W", "r+", "a", "A +" should pay attention to the file length of 0! The file may be empty, or it may be flock