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POC++ memory management patterns for objects used in callback chains
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copied!<p>A couple codebases I use include classes that manually call <code>new</code> and <code>delete</code> in the following pattern:</p> <pre><code>class Worker { public: void DoWork(ArgT arg, std::function<void()> done) { new Worker(std::move(arg), std::move(done)).Start(); } private: Worker(ArgT arg, std::function<void()> done) : arg_(std::move(arg)), done_(std::move(done)), latch_(2) {} // The error-prone Latch interface isn't the point of this question. :) void Start() { Async1(<args>, [=]() { this->Method1(); }); } void Method1() { StartParallel(<args>, [=]() { this->latch_.count_down(); }); StartParallel(<other_args>, [=]() { this->latch_.count_down(); }); latch_.then([=]() { this->Finish(); }); } void Finish() { done_(); // Note manual memory management! delete this; } ArgT arg_ std::function<void()> done_; Latch latch_; }; </code></pre> <p>Now, in modern C++, explicit <code>delete</code> is a code smell, as, to some extent is <code>delete this</code>. However, I think this pattern (creating an object to represent a chunk of work managed by a callback chain) is fundamentally a good, or at least not a bad, idea.</p> <p>So my question is, how should I rewrite instances of this pattern to encapsulate the memory management?</p> <p>One option that I <em>don't</em> think is a good idea is storing the <code>Worker</code> in a <code>shared_ptr</code>: fundamentally, ownership is not shared here, so the overhead of reference counting is unnecessary. Furthermore, in order to keep a copy of the <code>shared_ptr</code> alive across the callbacks, I'd need to inherit from <code>enable_shared_from_this</code>, and remember to call that <em>outside</em> the lambdas and capture the <code>shared_ptr</code> into the callbacks. If I ever wrote the simple code using <code>this</code> directly, or called <code>shared_from_this()</code> inside the callback lambda, the object could be deleted early.</p>

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