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POC++11 rvalue calls destructior twice
 

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  1. POC++11 rvalue calls destructior twice
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    <p>I'm trying to make a class runner (run a class at a fixed time freq), which runs a class in another thread, and can be controlled (like pause, resume, stop) from main thread.</p> <p>So I want to take advantage of C++11's Functor and other features. But I have a strange problem, the Functor's destructor passed into Runner has been called twice.</p> <pre><code>#include &lt;iostream&gt; #include &lt;chrono&gt; #include &lt;thread&gt; using namespace std; class Runner { public: typedef function&lt;bool()&gt; fn_t; Runner(fn_t &amp;&amp;fn) : fn_(move(fn)), thread_(Thread, ref(*this)) { cout &lt;&lt; "Runner" &lt;&lt; endl; } ~Runner() { cout &lt;&lt; "~Runner" &lt;&lt; endl; thread_.join(); } private: fn_t fn_; thread thread_; static void Thread(Runner &amp;runner) { while (runner.fn_()) { cout &lt;&lt; "Running" &lt;&lt; endl; this_thread::sleep_for(chrono::milliumseconds(1)); } } }; class Fn { public: Fn() : count(0) { cout &lt;&lt; "Fn" &lt;&lt; endl; } ~Fn() { cout &lt;&lt; "~Fn" &lt;&lt; endl; } bool operator()() { return (++count &lt; 5); } private: int count; }; int main (int argc, char const* argv[]) { Fn fn; Runner runner(move(fn)); return 0; } </code></pre> <p>outpus:</p> <pre><code>Fn Runner ~Fn ~Runner Running Running Running Running Running ~Fn ~Fn </code></pre> <p>and if I change </p> <pre><code>Fn fn; Runner runner(move(fn)); </code></pre> <p>to </p> <pre><code>Runner runner(Fn()); </code></pre> <p>the program outpus nothing and stalls. I have tried to disable compiling optimization, nothing changes. Any explanation?</p> <p>How can I fix this or do the samething in other method? Should I implement this class like std::async / std::thread?</p> <p><strong>Update to</strong> <code>Runner runner(Fn())</code></p> <p>This statement was interrupted as a function declaration.</p> <p><code>Runner runner((Fn()))</code> solved problem.</p> <p>Thanks for all comments and answers. After look into <a href="http://thbecker.net/articles/rvalue_references/" rel="nofollow">rvalue</a>, seems I have misunderstand the meaning of rvalue reference from ground 0. I will try some other ways.</p> <p><strong>Final Solution for this problem</strong></p> <pre><code>#include &lt;iostream&gt; #include &lt;chrono&gt; #include &lt;thread&gt; #include &lt;vector&gt; using namespace std; template&lt;typename T, typename... Args&gt; class Runner { public: Runner(Args&amp;&amp;... args) : t(forward&lt;Args&gt;(args)...), thread_(Thread, ref(*this)) { cout &lt;&lt; "Runner" &lt;&lt; endl; } ~Runner() { cout &lt;&lt; "~Runner" &lt;&lt; endl; thread_.join(); } private: T t; thread thread_; static void Thread(Runner &amp;runner) { while (runner.t()) { cout &lt;&lt; "Running" &lt;&lt; endl; this_thread::sleep_for(chrono::milliseconds(100)); } } }; class Fn { public: Fn() : count(0) { cout &lt;&lt; "Fn" &lt;&lt; endl; } ~Fn() { cout &lt;&lt; "~Fn" &lt;&lt; endl; } bool operator()() { return (count++ &lt; 5); } private: int count; }; int main (int argc, char const* argv[]) { //vector&lt;Fn&gt; fns; //fns.emplace_back(Fn()); Runner&lt;Fn&gt; runner; return 0; } </code></pre> <p>outpus:</p> <pre><code>Fn Runner ~Runner Running Running Running Running Running ~Fn </code></pre>
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    1. COAdd `Fn(Fn const&) { cout << "Fn" << endl; }` and you'll see.
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    2. COdoesn't it use std::move and rvalue should avoid the copy?
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    3. COThe problem here is, if the Functor holds some resource (char* for example) and will automatically free when destruct, those copy and destruct will leave a invalid memory pointer in copied Functor. How to fix this?
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