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Date: Tue, 6 Oct 2015 10:54:18 +0300
Message-ID: <CA+9eiLtOzhWdJ5VHL102PchvygqqJ_B8FquvDNPU1Gc6Jytv8w@mail.gmail.com>
To: Eric Stenson <ericsten@microsoft.com>
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" <dmitry@php.net>
Content-Type: multipart/alternative; boundary=001a11415902e453a005216aef14
Subject: Re: [PHP-DEV] Re: Windows OpCache bug fix
From: dmitry@zend.com (Dmitry Stogov)

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Hi Eric,


On Mon, Oct 5, 2015 at 9:49 PM, Eric Stenson <ericsten@microsoft.com> wrote:

> >From: Dmitry Stogov [mailto:dmitry@zend.com]
> >
> >> On Thu, Oct 1, 2015 at 11:54 AM, Matt Ficken <themattficken@gmail.com>
> >> wrote:
> >>
> >>> Pierre Joy wrote:
> >>> And what wincache does. It is slower but the request is served.
> >>
> >> WinCache (file cache) if it can't reattach, creates a new shared mem
> >> file
> >
> > I'm not sure how WinCache works, but opcache already implements most
> > necessary functionality.
>
> Sorry for getting to the party late, but let me clarify what WinCache does:
>
> 1. For the opcode cache, if WinCache can't map to the same address, it
> falls back to using process-local (heap) memory for the opcode arrays.
> This is because the elements in the opcode arrays contain absolute
> pointers, and we don't want to spend cycles (a) converting all pointers to
> offsets when copying opcode arrays into shared memory, and then (b)
> converting all offsets back to absolute addresses when copying the opcode
> array back out of shared memory.  WinCache simply gets the pointer to the
> opcode array in shared memory and returns it, unmodified, to the PHP Core
> for execution.
>

Opcache uses the same strategy,.


> When WinCache falls back to process-local memory, it does NOT create a
> second memory mapped segment, and does not chew additional cross-process
> resources.
>

Opcahce but don't have a fall-back mechanism in case of inability to remap
SHM into the same address space


> 2. WinCache's file cache does not map to an identical address in all
> processes.  We simply map it to *any* address (using NULL for the suggested
> address to MapViewOfFileEx), and then use relative offsets in the cache
> structures for all entries in shared memory.
>

File-cache in opcache is a second level opcode cache. Instead of SHM (or in
addition to SHM) we may store precompiled php scripts on disk.

Thanks. Dmitry.


>
> 3. WinCache's user cache and session cache are similar to the file cache,
> and do not have to map to the same address in all processes. Cache entries
> use relative offsets to locate cache entries, and the values do not contain
> absolute addresses.
>
> Finally, For PHP7, WinCache has removed its opcode cache.  We assume that
> Windows consumers of PHP7 will use Zend Opcache for opcode caching.
>

>
>
> Thx!
>     --E.
>

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