> Re 2. (threading): What happens when the list becomes empty? How do you keep track of the size to determine whether the list is empty? How do you know the size is still up-to-date when you go on to make a modification? I don't think this is as easy (even "in theory") as you make it sound.

No, it isn't easy. I used a single lock to lock both head and tail pointers, and did the pointer-swapping and pointer-comparisons for the pathological cases in that lock[1]. However, that being said, locking for the comparison and head/tail reassignment is *still* preferable to locking while reallocating your array.

For counting items in the list, I post to a semaphore when an item is inserted, wait on the semaphore when an item is removed and simply return the semaphore count when a count of items is required. Because it is a linked list, there is no problem with having the count change in between retrieving it and adding/removing items - that'd only be a problem in array-like structures.

If you want to code-review my implementation then be my guest (it's on github, under my name, a repo called libcmq). I welcome criticism :-)

In any case, I've been considering reimplementing that library as a resizable array precisely because of the downsides of lists. I'm keeping it as it is (for now) because there are other things I want to do that aren't boring.

[1] Empty list and list of exactly one element are problematic.