Deque leaks memory

[vustef]

Deque uses data::Vector{T} in DequeBlock{T}, but it only empties this vector in rear blocks, never touching this vector in the head block, instead it only invokes reset! on it. But reset! doesn't unset index on data elements that are no longer valid in this head block, causing these objects not to be garbage collected.

I verified this by taking heap snapshot after inserting and dequeuing all elements and running GC.gc(true) - the elements were still in the heap.

Not sure if other data structures have this behaviour, I only checked for Deque (and by proxy Queue)

[vustef]

Thanks for the fix. Does the fix free elements only when a block becomes empty though? I think it should free elements even when an element is dequeued but the block is non-empty. This is needed so that the popped elements can be garbage collected in situations where some other elements remain in queue. This seems to be the case only when block size is 1.

Possible solution is to use Base._unsetindex! when element is dequeued.