fedi is for losers

When you have a generational collector, you aim to trace only the part of the object graph that has been allocated recently. To do so, you need to keep a remembered set: a set of old-to-new edges, used as roots when performing a minor collection. A language run-time maintains this set by adding write barriers: little bits of collector code that run when a mutator writes to a field.Whippet’s

Hey all, I had a fun bug this week and want to share it with you.numbers and representationsFirst, though, some background. Guile’s numeric operations are defined over the complex numbers, not over e.g. a finite field of integers. This is generally great when writing an algorithm, because you don’t have to think about how the computer will actually represent the numbers you are working on.In practice, Guile will represent a small exact integer as a

Greetings, gentle readers. Today, an update on recent progress in the Whippet embeddable garbage collection library.feature-completenessWhen I started working on Whippet, two and a half years ago already, I was aiming to make a new garbage collector for Guile. In the beginning I was just focussing on proving that it would be advantageous to switch,...

Should your garbage collector be precise or conservative? The prevailing wisdom is that precise is always better. Conservative GC can retain more objects than strictly necessary, making GC slow: GC has to more frequently, and it has to trace a larger heap on each collection. However the calculus is not as straightforward as most people think, and indeed there are some reasons to expect that conservative root-finding can result in faster systems.(I have made / relayed some of...

Many years ago I read one of those Cliff Click “here’s what I learned” articles in which he was giving advice about garbage collector design, and one of the recommendations was that at a GC pause, running mutator threads should cooperate with the collector by identifying roots from their own stacks. You can read a similar assertion in their VEE2005 paper, The Pauseless...