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This is an automatically generated e-mail. To reply, visit:
<a href="https://reviewboard.asterisk.org/r/4108/">https://reviewboard.asterisk.org/r/4108/</a>
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<p style="margin-top: 0;">On March 31st, 2015, 5:52 p.m. EDT, <b>rmudgett</b> wrote:</p>
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<a href="https://reviewboard.asterisk.org/r/4108/diff/5/?file=71780#file71780line450" style="color: black; font-weight: bold; text-decoration: underline;">/trunk/main/astobj2.c</a>
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(Diff revision 5)
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<td colspan="4"><pre style="font-size: 8pt; line-height: 140%; margin: 0; ">static int internal_ao2_ref(void *user_data, int delta, const char *file, int line, const char *func)</pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="tb"> </span><span class="tb"> </span><span class="tb"> </span><span class="n">obj</span><span class="o">-></span><span class="n">priv_data</span><span class="p">.</span><span class="n">ref_counter</span><span class="o">++</span><span class="p">;</span></pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="tb"> </span><span class="tb"> </span><span class="tb"> </span><span class="n">internal_weakproxy</span><span class="o">-></span><span class="n">priv_data</span><span class="p">.</span><span class="n">weakptr</span> <span class="o">=</span> <span class="n">obj</span><span class="o">-></span><span class="n">priv_data</span><span class="p">.</span><span class="n">weakptr</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span></pre></td>
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<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">Isn't the shell game you are playing with the real object's ref count going to mess up the DEBUG_REF output?
How about this code:
Code assumes that weakproxy ref wasn't bumped when set above.
if weakproxy
if current_value == 1
unlink real and weak
unlock weakproxy
if current_value == 1
run weakproxy callbacks (locking between each callback or locking to run all)
unref weakproxy
unref real</pre>
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<pre style="margin-left: 1em; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">Lets use realobj to represent the variable in the callers scope (non-ao2 code), user_data is the variable in internal_ao2_ref. This shell game results in REF_DEBUG logs showing the 2nd to last reference being released by ao2_ref(user_data, -1) a couple lines below your finding, just prior to the user releasing the last reference. REF_DEBUG is produced after internal_ao2_ref completes, so it's impossible for the unref's in this block to be logged after ao2_ref(realobj, -1). So without this REF_DEBUG would say that the object was destroyed due to ao2_ref(user_data, -1) before the 2nd to last reference was released.
This REF_DEBUG output was verified using the provided test.</pre>
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<p style="margin-top: 0;">On March 31st, 2015, 5:52 p.m. EDT, <b>rmudgett</b> wrote:</p>
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<a href="https://reviewboard.asterisk.org/r/4108/diff/5/?file=71780#file71780line798" style="color: black; font-weight: bold; text-decoration: underline;">/trunk/main/astobj2.c</a>
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(Diff revision 5)
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="tb"> </span><span class="n">weakproxy</span> <span class="o">=</span> <span class="n">ao2_alloc</span><span class="p">(</span><span class="n">data_size</span><span class="p">,</span> <span class="n">destructor_fn</span><span class="p">);</span></pre></td>
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<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">I think you need to have a weakproxy destructor callback that performs a sanity check on the proxy object to ensure that it is not still linked with a real object.
Or even better, make the ao2_ref code do this check when it is about to destroy a weakproxy object. This check can also destroy anything in the notify list for the case if the real object was not set but subscribers were.</pre>
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<pre style="margin-left: 1em; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">Once linked to a real object the weakproxy cannot be destroyed until after no references to the real object exist. Remember that until the real object is destroyed it holds a reference to the weakproxy.
As for subscriptions I will have to look into this more, but my intention for subscriptions is a way to request notification as soon as the weakproxy points to NULL. So in the case of adding a subscription when no real object is linked, I think we should run the callback immediately and not add it to the subscription list.</pre>
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<p>- Corey</p>
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<p>On March 4th, 2015, 4:43 p.m. EST, Corey Farrell wrote:</p>
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<div>Review request for Asterisk Developers, George Joseph and rmudgett.</div>
<div>By Corey Farrell.</div>
<p style="color: grey;"><i>Updated March 4, 2015, 4:43 p.m.</i></p>
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<b style="color: #575012; font-size: 10pt;">Repository: </b>
Asterisk
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<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
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<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">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.</pre>
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<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Testing </h1>
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<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">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.</pre>
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<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
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<li>/trunk/tests/test_astobj2_weaken.c <span style="color: grey">(PRE-CREATION)</span></li>
<li>/trunk/main/astobj2.c <span style="color: grey">(432445)</span></li>
<li>/trunk/include/asterisk/astobj2.h <span style="color: grey">(432445)</span></li>
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<p><a href="https://reviewboard.asterisk.org/r/4108/diff/" style="margin-left: 3em;">View Diff</a></p>
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