Listing 7.3 - add early exit to .pop()

[ITHelpDec]

It seems odd to perform work on a node that could potentially be a nullptr from the moment the function is called.

I hope I'm correct in saying that .compare_exchange_weak(...) will return true if head still refers to our original old_head (i.e. no other thread has had a chance to modify it), but if that old_head was nullptr to begin with, then would old_head->next not throw after a successful CAS check?

ccia_code_samples/listings/listing_7.3.cpp

Lines 24 to 30 in 6134dee

	std::shared_ptr<T> pop()
	{
	if (!head_) { return std::shared_ptr<T>(); }
	node* old_head=head.load();
	while(!head.compare_exchange_weak(old_head,old_head->next));
	return old_head->data;
	}

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The same thing applies to void pop(T &val) a few pages prior - an early exit allows the code the run without throwing for bad access to old_head->next.

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Arguably, maybe changing old_head to original_head would be more conducive to helping readers grasp the concept of .compare_exchange_weak(...).