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How does tricolor garbage collection work?

Golang’s garbage collector uses a “tricolor” algorithm. This means it divides the heap objects into three sets: black, white, and grey. Initially, all objects are white, and as the algorithm proceeds, objects are moved into the grey and then black sets, in such a way that eventually the orphaned (collectible) objects are left in the white set, which is then cleared. An important property of this algorithm is that it can run concurrently with the “mutator” (program).

The meaning of the three sets is this:

The important invariant is the “tricolor” invariant: no pointers go directly from the black set to the white set. It is this invariant which lets us eventually clear the white set.

What can computers do? What are the limits of mathematics? And just how busy can a busy beaver be? This year, I’m writing Busy Beavers, a unique interactive book on computability theory. You and I will take a practical and modern approach to answering these questions — or at least learning why some questions are unanswerable!

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After months of secret toil, I and Andrew Carr released Everyday Data Science, a unique interactive online course! You’ll make the perfect glass of lemonade using Thompson sampling. You’ll lose weight with differential equations. And you might just qualify for the Olympics with a bit of statistics!

It’s $29, but you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

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