Fwd: How to create Persistent zval? View as Markdown

Hello,

I am trying to store a zval object into the persistent list in zend VM.
(Using EG(persistent_list) and zend_rscd_list_entry)

Which works fine if I store/fetch the zval in the same request context.

But it seems that zend engine cleans up the zval object after the
request,
when the next request comes, the fetched list entry points to a freed
zval
address and it makes php segmentationfault. I guess zval is allocated by
emalloc, so I cant keep it cross requests?

For persistent alloc, you should use pemalloc() , which is just a
wrapper leading to libc's malloc.
If you use emalloc() , the Zend Memory Manager will free the storage
at the end of the request, thus leading to use-after-free crash if you
reuse your pointer on a next request.

--- Disclaimer ---
I'm passing this along; Joe is having technical difficulties and asked for
help sending this to the list. I provide no warranties or refunds ;)

All zvals passed into the engine must be allocated by the mm, you cannot
pemalloc anything and pass it into the engine safely.

You don't want to store a persistent zval, you want to store a persistent
resource entry, which should be allocated with pemalloc(size, 1)

The reason for this is when cleaning up, the engine has no means by which
to tell if a zval has been pemalloc or emalloc'd, zval_ptr_dtor works the
same for everything.

Cheers
Joe

Thanks again for the detailed answers and your patience. =]

Just want to make sure the mechanism here:

1. an object can not be persistent even the object is allocated with
   pemalloc?
   I actually have tried using pemalloc then init an object few days ago,
   and it doesn't work.

2. an zend object can not be allocated persistently because its property
   HashTable or handlers is not allocated persistently by default?

3. if so, objects must be serialized to string?

4. what about array? can I make the array persistent with pemalloc
   allocation and without serialization?

Thank you so much
Yo-An Lin
http://github.com/c9s

By the way, Is this the reason of date ext always check the global
HashTable and re-initialize the tzdata in every request?

Lin Yo-An cornelius.howl@gmail.com 於 2014年1月19日星期日寫道：

Daniel Lowrey <rdlowrey@php.net <javascript:_e({}, 'cvml',
'rdlowrey@php.net');>> 於 2014年1月19日星期日寫道：

Hello,

I am trying to store a zval object into the persistent list in zend
VM.
(Using EG(persistent_list) and zend_rscd_list_entry)

Which works fine if I store/fetch the zval in the same request
context.

But it seems that zend engine cleans up the zval object after the
request,
when the next request comes, the fetched list entry points to a freed
zval
address and it makes php segmentationfault. I guess zval is allocated
by
emalloc, so I cant keep it cross requests?

For persistent alloc, you should use pemalloc() , which is just a
wrapper leading to libc's malloc.
If you use emalloc() , the Zend Memory Manager will free the storage
at the end of the request, thus leading to use-after-free crash if you
reuse your pointer on a next request.

--- Disclaimer ---
I'm passing this along; Joe is having technical difficulties and asked
for
help sending this to the list. I provide no warranties or refunds ;)

All zvals passed into the engine must be allocated by the mm, you
cannot
pemalloc anything and pass it into the engine safely.

You don't want to store a persistent zval, you want to store a
persistent
resource entry, which should be allocated with pemalloc(size, 1)

The reason for this is when cleaning up, the engine has no means by
which
to tell if a zval has been pemalloc or emalloc'd, zval_ptr_dtor works
the
same for everything.

Thank you so much! That is what i was guessing.. - ref cnt and pemalloc
does not work for persistent zval.

And zend engine cleans up zvals at the end of request no matter the ref
cnt is?

so zval is not persistent, then is HashTable persistent?

It's because I need to store a zval object which has several properties.
Is there a way to do make the object persistent? Or do i need to
serialize
it just like apc?

Cheers
Joe

--
Best Regards,

Yo-An Lin

A HashTable can be persistent:

define zend_hash_init(ht, nSize, pHashFunction, pDestructor, persistent)

HashTable *ht = pemalloc(sizeof(HashTable), 1);

zend_hash_init(ht, 8, NULL, NULL, 1);

When you write the table with zend_hash_update/add/insert the buckets
it creates are also persistently allocated.

You don't need to serialize the data, or not necessarily anyway, a
hashtable can be copied bitwise - which in actual fact is what APC does
do. APC only serializes objects, normal arrays - HashTables are copied
bitwise, bucket by bucket.

Of course, if the persistent table contains references to objects (as
in PHP objects in object_store or anything else emalloc'd) you will have
difficulties.

Probably best to design the tables in such a way that they only need
ever store persistent data.

Hope you're getting somewhere :)

Cheers
Joe

--
Best Regards,

Yo-An Lin