[asterisk-dev] [Code Review] 4108: Weak Proxy Objects

[Corey Farrell]

> On Dec. 9, 2014, 7:36 p.m., rmudgett wrote:
> > /trunk/main/astobj2.c, line 432
> > <https://reviewboard.asterisk.org/r/4108/diff/3/?file=68553#file68553line432>
> >
> >     Use of obj->priv_data.weakptr is not protected from other threads creating a weak object from the object.  This wouldn't be a problem if the object were required to be immediately weakened after creation.
> 
> Corey Farrell wrote:
>     I've transfered the actual creation of weak proxy objects from ao2_weaken to ao2_alloc (with an option).

I've changed my mind.  Creation of ao2_weakproxy objects requires it's own allocation function.  I'm envisioning scenarios where the weakproxy can be a persistant object.  So after the object a weakproxy points to is free'd, we may want to point the weakproxy to a new object.  Previous patches did not allow for this although there is no technical reason against it.

So to your original finding, I've documented the thread safety concerns about ao2_weakproxy_set_object.  Documentation / wording is not my strongest area, I'm open to any suggestions that make it clear when it's safe to associate an object to a weakproxy.


- Corey


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On March 4, 2015, 4:43 p.m., Corey Farrell wrote:
> 
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> https://reviewboard.asterisk.org/r/4108/
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> 
> (Updated March 4, 2015, 4:43 p.m.)
> 
> 
> Review request for Asterisk Developers, George Joseph and rmudgett.
> 
> 
> Repository: Asterisk
> 
> 
> Description
> -------
> 
> This implements "weak" references.  The weakproxy object is a real ao2 with normal reference counting of its own.  When a weakproxy is pointed to a normal object they hold references to each other.  The normal object is automatically freed when a single reference remains (the weakproxy).  The weakproxy also supports subscriptions that will notify callbacks when the normal object is about to be destroyed.
> 
> 
> Diffs
> -----
> 
>   /trunk/tests/test_astobj2_weaken.c PRE-CREATION 
>   /trunk/main/astobj2.c 432445 
>   /trunk/include/asterisk/astobj2.h 432445 
> 
> Diff: https://reviewboard.asterisk.org/r/4108/diff/
> 
> 
> Testing
> -------
> 
> Ran the included test with REF_DEBUG enabled under valgrind.  No reference leaks or improper memory access.  Though this does not test for races, I don't know of an automated way to do that.
> 
> 
> Thanks,
> 
> Corey Farrell
> 
>

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