I've just tested with file cache (no Ramdisk) same result.

Only Cache Disabled works fine.

Also, Page Cache Plugin is disabled.

I'm going to suggest this is something very platform specific. If there were indeed a problem in the cache API, joomla.org itself would've crashed once it was updated.

After disabling and re-enabling all backend (server) services, all seems good.

My problem is exactly described here: http://www.itoctopus.com/yet-another-reason-for-a-blank-page-on-a-joomla-website

It's tricky to deal with this, contrary to what the blog post says.

The unserialize() function emits a notice and returns a boolean false on failure. Yet it's possible for a boolean false value to be cached, so that alone can't be the check. At best, maybe a custom error handler could be set (and reverted) with each use of the function.

If the problem occurs in the write cache, then that probably something wrong with using flock function.
If the problem back a lots of time then I suggest to test PR #10767

It may help to not generate errors,
after error occurs only restart (if RAM) or clear all /cache folder can help.

If error still occurs after you apply #10767 then the error is somewhere else.

IMHO Joomla does not use flock properly and data is written without any locking.

Someone tried to check integrity at https://github.com/joomla/joomla-cms/blob/staging/libraries/joomla/cache/storage/file.php#L135
but this is not the best way (in my opinion).

This PR mentions file cache system, could this be applied to APCu cache system too ?

APC(u) caching uses PHP's native functions so some stuff is covered by that. Using the filesystem as the cache handler, we have to implement some things ourselves that would otherwise be covered by a dedicated caching engine.

I do not know if my PR #12556 can help but it fixes an error which may be related to your issue.

[Updated]
Some time ago I have prepared another PR #12312 for cache controllers that can help too.

Most important part is at:
https://github.com/joomla/joomla-cms/pull/12312/files#diff-9673ad112e83780ff1c42edeb527d7b2R199

which do not allow to store data if resource is still locked.

@csthomas i've tried your PR #12556 and it seems that it solves my problem !

Before apply the PR, one of my pages was always a blank page, after the PR, no more blank page.

Also, no more 500 Internal Server Error at this time.

Thanks!!

EDIT: After a more extensive test, blank pages are back again :(

But no more 500 Internal Server Error at this time...

My only solution, at this moment, is disabling cache.

I have to remember that before v3.6.2 i've never had this problem (no new extensions, only server software updates).

My setup is, for the record:

• Joomla 3.6.4 Multi-language (FR & EN)
• Ubuntu 14.04 (VPS w/ 2 vCores + 4Gb RAM)
• Apache/2.4.18 + nGinx/1.11.5 (reverse proxy)
• PHP-FPM 7.0.12 w/ opCache enabled
• APCU 5.1.7

I am closing this here then

@acs-ferreira please mark a successful test at https://issues.joomla.org/tracker/joomla-cms/12556

@brianteeman i've edited my post, full tests aren't conclusive at this time.
This should be re-opened.

testing #12312 at this time.

Same problem with #12312.

If you want to test #12312 please test it together with #12556 which is current only for APC.

Your problem is currently more wide than one PR.
There are other issues in joomla that can generate the blank pages.

For more details you should set Global Configuration -> Server Settings -> Error Reporting as Maximum and then check php error file, ex. error_log

That's what i've done, one PR, other PR, both PR.

My error_log (Apache and PHP) are empty.

Then it may be related to your environment. I would suggest to check php-fpm server logs.

No doubt, what i can't understand is, why the same environment, BUT with j3.6.3, has no problems at all...
Still investigating on my side.