clearByTags in Filesystem adapter crashes when .tag file deleted during GlobIterator loop

[skors]

Hi,

we see the following error when using Filesystem storage adapter and deleting a large set of object from cache with clearByTags() method.

// when file_locking is off in File Zend/Cache/Storage/Adapter/Filesystem.php in line 1363
file_get_contents(my_cache_dir/my_cached_object_4711.tag): failed to open stream: No such file or directory
// when file_locking is on in File Zend/Cache/Storage/Adapter/Filesystem.php in line 1327
fopen(my_cache_dir/my_cached_object_4711.tag): failed to open stream: No such file or directory

It is not that easy to reproduce but occurs as follows:

• the GlobIterator in clearByTags() looks for all .tag files which holds the cached item tags information
• while looping through these items, another process deletes one item (and its .tag file) which is also prior found by the GlobIterator
• clearByTags triggers an error at $this->getFileContent($pathname) because fopen() or file_get_contents try to open a non existing file (not existing anymore)

Should be simple be avoided by adding

if (!file_exists($file)) { // or !$glob->valid()?
    continue;
}

to the foreach loop in clearByTags(), but is this right?

I also can submit a PR, but until now i do not have found a way to reproduce for a unit test

cheers

[skors]

This issue probably also occurs in the other clearBy* methods where the GlobIterator is used as well.

[marc-mabe]

hi @skors - thanks for your bug report!

This one is really hard to solve and test and it can happen on every function looping over different items.

A simple file_exists doesn't fully solve the issue as first the result of file_exists will be cached by PHP itself and calling clear_stat_cache would totally degree performance and secondly there is still a possible race condition between file_exists and reading the file.

A better solution would be to catch the error on reading the file and afterwords check if the reason of the error is a missing file. Than ignore the error in this case. For removing files there is already a the method Filesystem::unlink that works this way.

[skors]

@marc-mabe okay. I'll try to work on it and maybe you can take a review if i have understood you correctly

[marc-mabe]

Nice thanks

[marc-mabe]

@skors any news ?

[skors]

@marc-mabe yes, just give me a few days

[skors]

@marc-mabe please see bugfix/clear-by-tag_on_filesystem-storage branch at skors/zend-cache
https://github.com/skors/zend-cache/tree/bugfix/clear-by-tag_on_filesystem-storage

I've added tests which can reproduce the error now