whippet progress update: feature-complete!

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

Does the fediverse have a vibe? I think that yes, there’s a flave, and with reason: we have things in common. We all left Twitter, or refused to join in the first place. Many of us are technologists or tech-adjacent, but generally not startuppy. There is a pervasive do-it-yourself ethos. This last point often expresses itself as a reaction: if you don’t like it, then do it yourself, a different way. Make your...

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...