For implementers, the locking model adds a fair amount of non-trivial internal bookkeeping. Every operation must check lock state, readers must be tracked, and the interplay between locks, cancellation, and error states creates a matrix of edge cases that must all be handled correctly.
(and thanks to Matthew Miller for reviewing and providing feedback on this post)
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Step through the Python implementation. Watch the algorithm decide which branches to visit and which to prune:
Georgina RannardScience reporter