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Bug #72666 touch(): stat cache clearing inconsistent between file:// paths and plain paths
Submitted: 2016-07-25 07:37 UTC Modified: 2016-07-25 11:10 UTC
From: phofstetter at sensational dot ch Assigned:
Status: Open Package: Streams related
PHP Version: 7.1.0beta1 OS: MacOS X and Linux
Private report: No CVE-ID: None
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 [2016-07-25 07:37 UTC] phofstetter at sensational dot ch
Description:
------------
When calling touch() on a plain path, the stat cache doesn't get cleared. However, when calling touch() on a 'file://' URL, the stat cache gets cleared by virtue of `php_plain_files_metadata` which clears the stat cache after all operations.

This leads to the behaviour as shown in the test script (output available here: https://3v4l.org/0VQIo)

Furthermore: fopen(), fwrite(), fclose() does not clear the stat cache in either case and neither does file_put_contents().

I would create a PR to fix the touch() case, but in general, it's probably worth reconsidering the usefulness of the stat-cache these days. Even over an NFS link, when doing nothing but stat()'ing, you still only lose about 10% performance if you call clearstatcache() after every stat().

Plus, the cache really only helps when you continuously stat() the same file within the same request, which probably isn't correct application behaviour anyways.

So in general, I would propose to actually kill the stat cache which would fix this inconsistency as well :-)

Test script:
---------------
<?php

// doesn't update realpath cache
touch('/tmp/foo');
var_dump(filemtime('/tmp/foo'));
touch('/tmp/foo', 1);
var_dump(filemtime('/tmp/foo'));

// does update the realpath cache
touch('file:///tmp/foo');
var_dump(filemtime('file:///tmp/foo'));
touch('file:///tmp/foo', 1);
var_dump(filemtime('file:///tmp/foo'));

Expected result:
----------------
int(1469202653)
int(1)
int(1469202653)
int(1)

Actual result:
--------------
int(1469202653)
int(1469202653)
int(1469202653)
int(1)

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 [2016-07-25 11:02 UTC] ab@php.net
As mentioned on ML, I'd doubt the removal is justified. The most of usage scenarios only profit from the caching, while in other cases cache can be explicitly reset. I/O is one of the usual bottlenecks, even today. So more like expected behavior.

Thanks.
 [2016-07-25 11:10 UTC] phofstetter at sensational dot ch
ok. Thank you. 

I'll prepare a PR then that clears the cache when touch() is used.

What about clearing the cache when fopen() is used with any of the writable flags?
 
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