RE: [PHP-DEV] Re: Windows OpCache bug fix

Hi Dmitry, > -----Original Message----- > From: Dmitry Stogov [mailto:dmitry@zend.com] > Sent: Friday, October 2, 2015 9:34 AM > To: Anatol Belski <anatol.php@belski.net> > Cc: Matt Ficken <themattficken@gmail.com>; Pierre Joye > <pierre.php@gmail.com>; Anatoliy Belsky <ab@php.net>; Laruence > <laruence@php.net>; PHP Internals <internals@lists.php.net>; dmitry@php.net > Subject: Re: [PHP-DEV] Re: Windows OpCache bug fix > > > Dmitry, I'd have a question to this > > > Also. if we can't map SHM into desired address space, we may map it > > > in > > any > > > other address and copy data into the process memory similar to > > file-cache. > > In randomized memory layout, even the base were available and > > OpenFileMapping were worky, some parts of that memory were already > taken. > > How exactly it could be done, could you please give a couple of > > pointers to this? > > > If MapViewOfFileEx(..., wanted_mapping_base) fails, we do > MapViewOfFileEx(..., NULL). > > > > Would the file cache be always required then? > > > > This is not necessary, but depends on implementation of course. > Thanks for the advice. I was playing with this over these days. There are two usual cases where it possibly fails when reattaching ATM - https://github.com/php/php-src/blob/PHP-7.0/ext/opcache/shared_alloc_win32.c#L151 - the saved address is available but is not suitable - https://github.com/php/php-src/blob/PHP-7.0/ext/opcache/shared_alloc_win32.c#L159 - the actual MapViewOfFileEx case An unrelated plain C test shows, that MapViewOfFileEx can possibly fail when called second time, too. Even with NULL or with another address as base. But even if it could map at a different base - the internal structures will probably have invalid addresses. So it looks like there's indeed no profit to do any retry once the actualy base address needed was failed to reattach to. IMHO the scenario that were usable - in case it fails to reattach to the exact address, it has to switch to heap. Just for one request, it should get a heap allocated segment and then invalidate all the cache. That way we fulfill the following - the request is served for sure - the scripts are not cached indeed, so no divergence with the actual real cache A heap fallback memory handler would be probably quite easy to implement. What do you think? Apropos with the heap - it also looks like when PHP is used as module under mpm_winnt, all the cache could use heap instead of SHM. In that case, there is only one Apache process serving with many threads. Except one would want to share that cache outside Apache, using heap there could be a much simpler solution. Regards Anatol