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POMixing boost::asio and boost::signals2 giving problems
 

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  1. POMixing boost::asio and boost::signals2 giving problems
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    <p>{boost 1.54}</p> <p>All asio operations are happening on the same io_service which has it's run() called from several std::threads (thus a thread-pool)</p> <pre><code>struct Async : std::enable_shared_from_this&lt;Async&gt; { boost::signals2::signal&lt;void()&gt; m_sig; void read() { auto self = shared_from_this(); boost::asio::async_read_until( /*socket*/, /*bufferToCollectData*/, /*delimiter*/, [self]{self-&gt;onRead(..);} ); } void onRead(..) { m_sig(); } }; struct Process : std::enable_shared_from_this&lt;Process&gt; { std::shared_ptr&lt;Async&gt; m_shrPtrAsync; boost::signals2::connection m_connection; void start() { m_shrPtrAsync = std::make_shared&lt;Async&gt;(); //m_shrPtrAsync-&gt;startUpThings(); auto self = shared_from_this(); m_connection = m_shrPtrAsync-&gt;m_sig.connect( [self]{self-&gt;slot();} ); } void stop() { //this will not delete the slot and have to wait indefinitely until some operation happens on m_sig. //------------------------------- &lt;2&gt; m_connection.disconnect(); //this should force the original slot deletion. m_connection = m_shrPtrAsync-&gt;m_sig.connect([this]{dummy();}); m_connection.disconnect(); } void dummy() {} void slot() { auto self = shared_from_this(); //-------------------- &lt;1&gt; //to not block the calling thread (Async's m_sig()) m_strand.post( [self]{self-&gt;slotPrivateImpl();} ); } void slotPrivateImpl() { /*Processing*/ } }; //This is from the main thread outside the thread-pool {//local scope begins auto shrPtrProcess = std::make_shared&lt;Process&gt;(); shrPtrProcess-&gt;start(); //after sometime shrPtrProcess-&gt;stop(); }//local scope ends. I want shrPtrProcess to delete the contained pointer here //which should in turn delete the Async's pointer in shrPtrProcess-&gt;m_shrPtrAsync </code></pre> <p>Is this safe? When main thread executes <code>shrPtrProcess-&gt;stop();</code> thus deleting the slot from the Async's <code>m_sig</code> and then comes out of the local scope, the last remaining reference to the shared_ptr to <code>Process</code> will have died thus destroying it, but other thread firing <code>m_sig</code> could have entered <code>Process::slot(</code>) by then and about to execute line marked &lt;1> above. Does signals2 guarantee that slots will not be deleted till they are executed completely?</p> <p>If this is not safe then how do i achieve this behaviour of <code>shrPtrProcess</code> destroying <code>Process</code> ptr which in turn destroys <code>Async</code> raw ptr in <code>shrPtrAsync</code> once the local scope ends? If I don't do the hack in place marked &lt;2> above I'll never be able to release resources if m_sig() does not fire anymore as <code>signals2::connection::disconnect()</code> does not cause immediate deletion of slot.</p>
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    1. COAs far as I see, you always call `slot()` through `shared_ptr<Process >`, so there's at least 1 reference alive at this point.
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    2. COThis works btw - The dtor is invoked. From what i read in other posts, signal makes a copy of list of slots before invoking. So when signal executes slot() and stop() is called, the hack at mark <2> deletes the original slot functor and when slot() returns after posting for sloPrivateImpl() to take up further tasks, the temporary functor copy is destroyed too and now you have only one reference which will expire once sloPrivateImpl() execution is over and dtor will then be called - reference http://stackoverflow.com/a/2265979/1060004 and http://stackoverflow.com/a/4490785/1060004
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