Why in Windows might attempting to delete a file twice work? - php

Question

I've been pulling my hair out trying to write a continuous integration script with PHP for the Windows machine I develop on.
Having cloned a Git repository, I was unable to make a script that deleted it all. (The .git folder and everything in them). I was getting "Permission denied" errors.
It seemed intermittent. I tried Phing, but that failed but lead me to this Phing ticket, so I'm not alone - but that solution using attrib didn't work for me.
I finally realised that it was just taking two attempts to delete some folders and/or files within it. So my PHP code that finally worked, was this:
<?php
function delTree($dir, $ignore = array()) {
// no need to continue if $dir doesn't exist
if (!file_exists($dir))
return true;
// must not continue if it's a link. trigger an error.
if (is_link($dir)) {
trigger_error("Cannot delete $dir: it's a link.", E_ERROR);
return false;
}
// if it's a file, delete it and return.
if (is_file($dir)) {
return tryUnlink($dir, 2);
}
// it's a directory. so...
// build an array of files/directories within it to delete
$files = array_diff(
scandir($dir), array('.', '..'), $ignore
);
// delete each directory within $dir
foreach ($files as $file) {
delTree("$dir/$file", $ignore);
}
// delete $dir itself
return tryRmdir($dir, 2);
}
function tryUnlink($file, $attempts = 2){
$result = unlink($file);
if (!$result) {
if ($attempts > 1){
return tryUnlink($file, $attempts--);
} else {
trigger_error("Cannot delete file $file", E_ERROR);
return false;
}
}
return true;
}
function tryRmdir($dir, $attempts = 2){
$result = rmdir($dir);
if (!$result) {
if ($attempts > 1){
return tryRmdir($dir, $attempts--);
} else {
trigger_error("Cannot delete directory $dir", E_ERROR);
return false;
}
}
return true;
}
And calling them with the $attempts argument set to 2 solved everything (12 hours later).
I'd tried things like chmoding the file to 0666, closing the IDE, closing SourceTree, any open explorer windows, wearing a tin foil hat, and even calling exec() with commands like:
rm -r .git -Force
rmdir .git /s /q
and probably 10 others that are buried somewhere in my repo now.
What might the cause have been?

Answer 1

Both you functions tryUnlink() and tryRmdir() will cause an infinite loop (unless it's actually deleted). Look at the following snippet + output.
code:
<?php
function foo ($attempts = 2) {
echo "attempts = $attempts\n";
if ($attempts > 1) {
foo ($attempts--);
} else {
echo "returning with \$attempts <= 1\n";
}
}
foo(2);
output:
attempts = 2
attempts = 2
attempts = 2
[...many many many dupes...]
attempts = 2
attempts = 2
attempts = 2
Segmentation fault (core dumped)
Given that it's not said that deletion kicks in on the second run.

Answer 2

As of Windows 7 (or perhaps Vista?) it is rare, but not abnormal, for the first attempt to remove a directory tree to fail. I think this due to a race condition due to the deletions being processed asynchronously by the file system.
As you've already discovered, you can work around this by retrying the operation; personally, I've never seen it fail twice in a row, though I usually allow it to retry three or four times to be on the safe side.