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POClean-up code in the C++ exception's destructor
 

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  1. POClean-up code in the C++ exception's destructor
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    <p>Can we use the destructor of an exception as a place to put some clean-up code? </p> <p>In this manner we may allow the client to control the finalization step as opposed to RAII. Is this a good or a bad design? Is this a correct solution in the context of OOP and C++?</p> <p>I'm currently working on an asynchronous procedure which itself starts asynchronously multiple tasks. The pattern looks as follows:</p> <pre><code>struct IAsyncResult { ... virtual void EndCall() const; } typedef std::shared_ptr&lt;IAsyncResult&gt; IAsyncResultPtr; struct IAsyncTask { virtual IAsyncResultPtr BeginTask() = 0; virtual void EndTask(IAsyncResultPtr async) const = 0; } class CompositeTask : public IAsyncTask { … } </code></pre> <p>Unfortunately I’m unable to guarantee that each subtask’s BeginTask method will not fail. So it is possible that N-1 subtasks would start successfully and the Nth fail. </p> <p>In general it is vital to be sure that no background tasks are running before the client’s code finishes. But sometimes the client doesn’t care if some tasks fail.</p> <p>So my current solution involves a custom exception which is thrown from the CompositeTask’s BeginAsync method in case if one task failed to start. This allows a client to control the clean-up stage:</p> <pre><code>class composite_async_exception : public std::exception { std::vector&lt;IAsyncResultPtr&gt; successfully_started_tasks; mutable bool manage_cleanup; public: composite_async_exception(std::vector&lt;IAsyncResultPtr&gt; const&amp; _successfully_started_tasks) : successfully_started_tasks(_successfully_started_tasks) , manage_cleanup(true) { } virtual ~composite_async_exception() throw() { if(!manage_cleanup) return; for( auto task = successfully_started_tasks.begin(); task != successfully_started_tasks.end(); ++task) { task-&gt;CancelTask(); } } void Giveup() const throw() { manage_cleanup = false; } }; </code></pre> <p>And the client uses the code as shown:</p> <pre><code>try { compositeTask.BeginAsync(); } catch(composite_async_exception const&amp; ex) { //prevent the exception to cancel tasks ex.Giveup(); // some handling } </code></pre> <p>Are there some best practices to handle such a situation?</p>
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    1. USIgor Chornous
    1. USIgor Chornous
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    1. COOne possibility is to have an ITaskProgress interface in which you could give the progress of each child task class ITaskProgress{ public : void updateProgress(<some child task identification>, bool aSuccess, bool& aContinue) = 0; }; Clients could implement this interface and register and instance with the composite task. Now, clients would get the notification and clients can decide to continue or not.
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    2. COI see, that my question was incorrectly formulated. So I've changed it.
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      1. USIgor Chornous
 

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