Baby's First Garbage Collector
journal.stuffwithstuff.com
Baby's First Garbage Collector
1–10 of 90 posts
Re: Baby's First Garbage Collector
#2That was actually very easy to understand!.
Thanks for that. I'm thinking in build a toy language and this make on magic thing die..
Re: Baby's First Garbage Collector
#3Not having studied the topic in depth, my first thought is whether true pointers and a garbage collector can coexist (without artificially removing parts of the language). The big condition for knowing if something is still in use is whether any references exist to it. But in a language like C , you could cast a pointer to something else (like a void pointer for some quasi generic linked list), store it somewhere, and then cast it back later after garbage collection has run. That seems like a problematic situation. So is completely giving up on pointers (or just never doing tricky things like casting or pointer arithmetic) a requirement to having a garbage collector?
Re: Baby's First Garbage Collector
#4Not having studied the topic in depth, my first thought is whether true pointers and a garbage collector can coexist (without artificially removing parts of the language). The big condition for knowing if something is still in use is whether any references exist to it. But in a language like C , you could cast a pointer to something else (like a void pointer for some quasi generic linked list), store it somewhere, an…
I don't know of any language that has pointers and a GC. Are there any? C# lets you use pointers but only if you tell the GC to not move your object and promise to behave.
Re: Baby's First Garbage Collector
#5Not having studied the topic in depth, my first thought is whether true pointers and a garbage collector can coexist (without artificially removing parts of the language). The big condition for knowing if something is still in use is whether any references exist to it. But in a language like C , you could cast a pointer to something else (like a void pointer for some quasi generic linked list), store it somewhere, an…
I don't know of any language that has pointers and a GC. Are there any? C# lets you use pointers but only if you tell the GC to not move your object and promise to behave.
Optional GC[1] in a language like C++, and Rust has pointers with task-local GC
Re: Baby's First Garbage Collector
#6Not having studied the topic in depth, my first thought is whether true pointers and a garbage collector can coexist (without artificially removing parts of the language). The big condition for knowing if something is still in use is whether any references exist to it. But in a language like C , you could cast a pointer to something else (like a void pointer for some quasi generic linked list), store it somewhere, an…
When you hear talk of "conservative" Garbage Collectors, what the "conservative" refers to is that anything on the stack that looks like a pointer is treated as if it is a pointer. After all, it doesn't matter what you cast a pointer to, it's all just 1s and 0s on the stack...
Re: Baby's First Garbage Collector
#7Not having studied the topic in depth, my first thought is whether true pointers and a garbage collector can coexist (without artificially removing parts of the language). The big condition for knowing if something is still in use is whether any references exist to it. But in a language like C , you could cast a pointer to something else (like a void pointer for some quasi generic linked list), store it somewhere, an…
I don't know of any language that has pointers and a GC. Are there any? C# lets you use pointers but only if you tell the GC to not move your object and promise to behave.
The Boehm–Demers–Weiser garbage collector is a fairly famous implementation of a GC for vanilla C, pointers and all: http://en.wikipedia.org/wiki/Boehm_garbage_collector
Re: Baby's First Garbage Collector
#8Not having studied the topic in depth, my first thought is whether true pointers and a garbage collector can coexist (without artificially removing parts of the language). The big condition for knowing if something is still in use is whether any references exist to it. But in a language like C , you could cast a pointer to something else (like a void pointer for some quasi generic linked list), store it somewhere, an…
You don't need to give up pointers, or pointer arithmetic, just the ability to obscure what a pointer points to. Casting to void does not do this (and indeed, has no run time effect at all). Metadata is associated with the pointed-to block of memory, so as long as the address is recognizable as a pointer at runtime, you can do GC.
Some of the things that break GC aren't even technically valid C code. For example, say I allocate three memory areas with malloc() then hold on only to the area with the lowest address, and reference the other two areas with offsets relative to the first area. This is illegal in C, though it will work on most existing implementations, because it's illegal to dereference a pointer past the end of an allocation.
Specific GC algorithms might not be able to handle say pointers into the interiors of objects, but that's not a general limitation for GC.
Re: Baby's First Garbage Collector
#9Earlier quoted context omitted.
I don't know of any language that has pointers and a GC. Are there any? C# lets you use pointers but only if you tell the GC to not move your object and promise to behave.
The Boehm–Demers–Weiser garbage collector is a fairly famous implementation of a GC for vanilla C, pointers and all: http://en.wikipedia.org/wiki/Boehm_garbage_collector
Yeah I'm aware of optional GCs. What I meant was languages that ship with a GC as standard and also have pointers. In the case of Boehm, since you choose to bring it in yourself, it's up to you to make sure you don't abuse it.
Re: Baby's First Garbage Collector
#10Not having studied the topic in depth, my first thought is whether true pointers and a garbage collector can coexist (without artificially removing parts of the language). The big condition for knowing if something is still in use is whether any references exist to it. But in a language like C , you could cast a pointer to something else (like a void pointer for some quasi generic linked list), store it somewhere, an…
You don't need to give up pointers, or pointer arithmetic, just the ability to obscure what a pointer points to. Casting to void does not do this (and indeed, has no run time effect at all). Metadata is associated with the pointed-to block of memory, so as long as the address is recognizable as a pointer at runtime, you can do GC. Some of the things that break GC aren't even technically valid C code. For example, say…
Does this still work if the GC compacts memory? I don't know much about GCs, but it seems like once your GC is advanced enough with generational collecting, compacting, etc, then allowing raw pointers seems at odds with what the GC is trying todo. I'm sure it's possible, but it's probably a heck of a lot easier just to not allow pointers.