garbage-collection - 常见 VM 中的垃圾收集器实现的规模有多大，可以从中学到什么？

Question

查看 Java/OpenJDK，似乎每个“新”垃圾收集实现都比前一个大一个数量级。

其他运行时（如 CLR）中垃圾收集器实现的大小是多少？垃圾收集的重大改进能否等同于实现规模/复杂性的急剧增加？

更进一步，是否可以对一般的垃圾收集器实现进行这种观察，或者是否有某些设计决策（在 Java 或其他地方）特别促进或强制这些大小增加？

Answer 1

Really interesting question... really broad but I'll try my best to give decent input.

Going further, can this observation be made about Garbage Collector implementations in general or are there certain design decisions (in Java or elsewhere) which especially foster or mandate these size increases?

Well java's garbage collector initially didn't support generations, so adding this feature made it grow in size. One other thing that adds to the size/complexity of the jvm garbage collector is its configuration. The user can tweak the gc in a number of ways which increases the complexity. See this doc if you really want to know all the tun-able features of the jvm garbage collector http://www.oracle.com/technetwork/java/javase/gc-tuning-6-140523.html

This stackoverflow answer goes into this in a bit more depth https://stackoverflow.com/a/492821/25981

As to comparing size vs features...

Here is a very simple garbage collector for C: https://code.google.com/p/dpgc/

It has very few features and even requires the user to mark blocks as references are shared. It's size is very small weighing in at one C file and one header file.

Compare this to a fully featured gc as used in the .net framework. Below I've included a bunch of talks with the two architects of the .net garbage collector. http://channel9.msdn.com/Tags/garbage+collector

Specifcally this link: http://channel9.msdn.com/Shows/Going+Deep/Patrick-Dussud-Garbage-Collection-Past-Present-and-Future they discuss the evolution of the .net gc both interns of featuers and complexity( which is related to lines of code.)