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POThread-Safe implementation of an object that deletes itself
 

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  1. POThread-Safe implementation of an object that deletes itself
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    <p>I have an object that is called from two different threads and after it was called by both it destroys itself by "delete this".</p> <p>How do I implement this thread-safe? Thread-safe means that the object never destroys itself exactly one time (it must destroys itself after the second callback).</p> <p>I created some example code:</p> <pre><code>class IThreadCallBack { virtual void CallBack(int) = 0; }; class M: public IThreadCallBack { private: bool t1_finished, t2_finished; public: M(): t1_finished(false), t2_finished(false) { startMyThread(this, 1); startMyThread(this, 2); } void CallBack(int id) { if (id == 1) { t1_finished = true; } else { t2_finished = true; } if (t1_finished &amp;&amp; t2_finished) { delete this; } } }; int main(int argc, char **argv) { M* MObj = new M(); while(true); } </code></pre> <p>Obviously I can't use a Mutex as member of the object and lock the delete, because this would also delete the Mutex. On the other hand, if I set a "toBeDeleted"-flag inside a mutex-protected area, where the finised-flag is set, I feel unsure if there are situations possible where the object isnt deleted at all. Note that the thread-implementation makes sure that the callback method is called exactly one time per thread in any case.</p> <p>Edit / Update: What if I change Callback(..) to:</p> <pre><code>void CallBack(int id) { mMutex.Obtain() if (id == 1) { t1_finished = true; } else { t2_finished = true; } bool both_finished = (t1_finished &amp;&amp; t2_finished); mMutex.Release(); if (both_finished) { delete this; } } </code></pre> <p>Can this considered to be safe? (with mMutex being a member of the m class?)</p> <p>I think it is, if I don't access any member after releasing the mutex?!</p>
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    1. USSimon Hayter
    1. USIanH
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    1. COAuto delete ? Why this object coulnd't be destroyed by the threads which use it ?
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      1. USGuillaume Lebourgeois
    2. COHaving objects delete themselves is A Bad Idea.
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    3. COThere two reasons, why the thread using it cannot delete it: 1. The two threads don't know of each other 2. The threads are belonging to an external library.
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