Databases
StackOverflow2013
Postsdbo
POAvoiding indirect cyclic references when using shared_ptr and weak_ptr
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POAvoiding indirect cyclic references when using shared_ptr and weak_ptr
    primarykey
    data
    text
    <p>I'm currently putting together an application that relies heavily on <a href="http://www.boost.org/doc/libs/1_41_0/libs/smart_ptr/smart_ptr.htm" rel="nofollow noreferrer"><code>shared_ptr</code></a> and everything looks good so far - I've done my <a href="https://stackoverflow.com/questions/701456/what-are-potential-dangers-when-using-boostsharedptr">homework</a> and have a pretty good idea of some of the pitfalls of using <code>shared_ptr</code>s.</p> <p>One of the most recognised problems with <code>shared_ptr</code> is cyclic dependencies - these issues can be solved by storing <code>weak_ptr</code>s that don't affect the lifetime of objects up the chain. However, I'm struggling to get my head around times where it's necessary to store a pointer to an external object via a <code>weak_ptr</code> - <strong>I'm not sure whether it's forbidden, discouraged, or whether it's safe</strong>.</p> <p>The following diagram describes what I mean (black arrows indicate <code>shared_ptr</code>; dashed indicate <code>weak_ptr</code>):</p> <p><a href="http://img694.imageshack.us/img694/6628/sharedweakptr.png" rel="nofollow noreferrer">alt text http://img694.imageshack.us/img694/6628/sharedweakptr.png</a></p> <ul> <li>A parent contains <code>shared_ptr</code>s to two children, both of which point back to the parent using a <code>weak_ptr</code>. </li> <li>In the constructor of the <em>first child</em> I retrieve via the parent <code>weak_ptr</code> the pointer to the <em>second child</em> and store it locally.</li> </ul> <p>The code looks like this:</p> <pre><code>#include &lt;boost/shared_ptr.hpp&gt; #include &lt;boost/weak_ptr.hpp&gt; #include &lt;boost/make_shared.hpp&gt; #include &lt;boost/enable_shared_from_this.hpp&gt; class child; class child2; class parent; class parent : public boost::enable_shared_from_this&lt;parent&gt; { public: void createChildren() { _child2 = boost::make_shared&lt;child2&gt;(shared_from_this()); _child = boost::make_shared&lt;child&gt;(shared_from_this()); } boost::shared_ptr&lt;child&gt; _child; boost::shared_ptr&lt;child2&gt; _child2; }; class child { public: child(boost::weak_ptr&lt;parent&gt; p) { _parent = p; _child2 = boost::shared_ptr&lt;parent&gt;(p)-&gt;_child2; // is this safe? } boost::weak_ptr&lt;parent&gt; _parent; boost::shared_ptr&lt;child2&gt; _child2; }; class child2 { public: child2(boost::weak_ptr&lt;parent&gt; p) { this-&gt;_parent = p; } boost::weak_ptr&lt;parent&gt; _parent; }; int main() { boost::shared_ptr&lt;parent&gt; master(boost::make_shared&lt;parent&gt;()); master-&gt;createChildren(); } </code></pre> <p>I've tested this and it <em>seems</em> to work ok (I don't get any reports of memory leaks), however my question is: <strong>Is this safe? And if not, why not?</strong></p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCommunity
    1. USAlan
    plurals
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POAvoiding indirect cyclic references when using shared_ptr and weak_ptr
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POAvoiding indirect cyclic references when using shared_ptr and weak_ptr
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POAvoiding indirect cyclic references when using shared_ptr and weak_ptr
      1. This table or related slice is empty.
      1. VTUpMod
    1. COPossible duplicate: http://stackoverflow.com/questions/1826902/how-to-avoid-memory-leak-with-boostsharedptr
      singulars
      1. POAvoiding indirect cyclic references when using shared_ptr and weak_ptr
      1. USKirill V. Lyadvinsky
    2. CONot a duplicate. I'm using a weak_ptr to break the cyclic reference between parent and child. My question is regarding storing a shared_ptr to a sibling, retrieved via the parent.
      singulars
      1. POAvoiding indirect cyclic references when using shared_ptr and weak_ptr
      1. USAlan
    3. CORelying heavily on shared_ptr is not a good idea IMHO. This is a specialized tool, with certain use-cases in mind. In your example why not make the children scoped_ptrs, and the handle-to-parent a raw pointer?
      singulars
      1. POAvoiding indirect cyclic references when using shared_ptr and weak_ptr
      1. USrpg
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload