Memory warning hook

2013/3/5 Lazare Inepologlou linepogl@gmail.com

2013/3/5 Tom Boutell tom@punkave.com

Can't you do this already? memory_limit can be fetched via ini_read,
and together with memory_get_usage you should be able to check for
this sort of thing. Admittedly having to parse memory_limit (which can
be in various units) is not perfect.

This is not the same at all. When are you going to run this code? Memory
allocations happen all the time. What Nathan asked for is an event that is
triggered when the memory consumption reaches a threshold.

You can use ticks :)

http://php.net/control-structures.declare#control-structures.declare.ticks

However, there is a different solution, which is better IMHO in the case of
caches: weak references. A weak reference automatically frees the memory of
the object, when the memory is needed.
http://php.net/manual/en/book.weakref.php.

Having said that, none of these solutions scale up to multiple servers.
This is why shared cache systems like memcached are recommended.

Well, maybe I don't understand, what you are trying to tell, but if you run
out of memory, this of course only affects one server on its own.

As PHP applications are turning into large frameworks one of the issues
arriving is memory management. One of the issues is that many
frameworks
use
sophisticated caching techniques to make accessing the same data
quickly,
this improves speed it is at the cost of memory. Often the developer
knows
these areas that cache and often times already have functions in place
to
clear out the cache, however in the case where PHP is approaching or
exceeds
memory limits PHP runs the GC then dies if it cannot allocate enough
memory.
If we implemented "memory warning" triggers or user function that will
be
called before the GC is executed which allows the user to try and free
up
some memory on their own. This hopefully would give more flexibility to
allowing these advanced caching techniques but at the same time allow
the
cache to be cleared out in case memory is getting low.

Thoughts?

Thanks,

Software Developer

Nathan Bruer

--
Tom Boutell
P'unk Avenue
215 755 1330
punkave.com
window.punkave.com

--

Lazare INEPOLOGLOU
Ingénieur Logiciel

--
github.com/KingCrunch

This is not the same at all. When are you going to run this code? Memory allocations happen all the time. What Nathan asked for is an event that is triggered when the memory consumption reaches a >threshold.

However, there is a different solution, which is better IMHO in the case of
caches: weak references. A weak reference automatically frees the memory of the object, when the memory is needed.
http://php.net/manual/en/book.weakref.php.

Having said that, none of these solutions scale up to multiple servers.
This is why shared cache systems like memcached are recommended.

I agree this probably is a good solution and I personally do use it along with shared memory tools, however there may be cases where the dev may gain more benefit from having a memory-warning installable trigger in place. This would allow things like allowing the dev to release certain cache objects before others or something completely different that I have not thought of yet.

Running the GC is most likely faster than most cleanup routines a user could run, also usually there is not that much stuff cached in PHP scripts. If a PHP script has "tons" of data, which it can easily throw >away, in memory this sounds like a smell of an bad architecture. Cache cache-worthy stuff in memcache or such and fetch only the data you need.

Also: What should happen if the system runs out of memory while doing the cleanup? Anything sane doesn't sound good either.
Yes running the GC is much faster except they are two completely different processes... in my example the dev is keeping references to data for possible future use later on however it's not possible to know when to release these references so php's GC can collect them if the user does not implement something quite juristic like ticks or frequent function calls throughout a code base.

You can use ticks :)

http://php.net/control-structures.declare#control-structures.declare.ticks

Yes Ticks are something useable (like said above) however I have found ticks are clunky, frequently shunned, and you'd be ticking for no reason most of the time.