Improvements to file storage.

[colinmollenhour]

• saveFileToFilesystem returns void instead of bool in some cases.
• fileExists loads entire file from database just to return a bool.
• Use of Varien_Io_File seems pointless; deleting file before saving is also pointless.
• fix multi-process concurrency issues in get.php.
• use more efficient readfile() method to send files

[colinmollenhour]

Thanks for the review guys, I have pushed a new commit to address issues you raised. I agree about the return value so reverted it back but also made some new changes. I believe this keeps 100% compatibility but the improvements to get.php should improve stability a lot.

Explanation:
Let's assume we have a cold local cache for a given file (e.g. watermark parameters changing invalidates old resized images or a merged js/css file was updated or you simply launched a new instance with an empty media directory). If a few requests come in at the same time for the same file each one will try to read the file from central storage into the local cache. In many cases disks are so fast that race conditions are not a problem but with high traffic there can be two major issues:

1. Multiple processes try to write at the same time. While EX locking was already used before, this just ensures that they don't write at the same time but it does not prevent multiple writes to the same file. This is a waste of disk utilization and slows the response times. Only the first one really needs to write the file.
2. File reads (mime type, filesize, readfile) are not using locking so the file could be changing while it is being read. I've experienced this before even without get.php where js and css files get partially read and unfortunately one error becomes thousands when the file gets cached in a proxy.

Also just spotted a completely pointless block of code which should have simply been "readfile()". Reading files line by line just to echo each line is frankly retarded; imagine an XML sitemap with 100k lines. Leaving proper buffering up to the php devs is definitely the way to go.

[colinmollenhour]

Before you mention the use of the error suppression operator let me explain. :)

Magento registers an error handler so if an error is raised Magento throws an exception or logs an error. Varien_Io_File also uses this operator so I was trying to remain consistent with it. Also, I did not want to modify the use of translated strings to add details to exception messages. Lastly, sometimes an error is expected or at least inconsequential so there is no need to litter logs with unimportant warnings.

[Flyingmana]

besides the true/false Iam ok with it now

[cieslix]

+1
Code looks much better then previous.
I've tested manipulation on files with storage file/database.
Coping/deleting/syncing works perfect.

[tmotyl]

@colinmollenhour shouldn't it be also merged to 1.9.3.x ?