== Quote from Andrei Alexandrescu (seewebsiteforem...@erdani.org)'s article > dsimcha wrote: > > == Quote from Andrei Alexandrescu (seewebsiteforem...@erdani.org)'s article > >> Yes, it will be because the book has a few failing unittests. In fact, I > >> was hoping I could talk you or David into doing it :o). > >> Andrei > > > > Unfortunately, I've come to hate the MRU idea because it would fail > > miserably for > > large arrays. I've explained this before, but not particularly thoroughly, > > so > > I'll try to explain it more thoroughly here. Let's say you have an array > > that > > takes up more than half of the total memory you are using. You try to > > append to > > it and: > > > > 1. The GC runs. The MRU cache is therefore cleared. > > > > 2. Your append succeeds, but the array is reallocated. > > > > 3. You try to append again. Now, because you have a huge piece of garbage > > that > > you just created by reallocating on the last append, the GC needs to run > > again. > > The MRU cache is cleared again. > > > > 4. Goto 2. > This is not a matter of principles, but one of implementation. When you > GC, you can adjust the cache instead of clearing it.
Technically true, but what is a matter of principles is whether the implementation of arrays should be very tightly coupled to the implementation of the GC. Fixing this issue would have massive ripple effects throughout the already spaghetti code-like GC, and might affect GC performance. For every single object the GC freed, it would have to look through the MRU cache and remove it from there if present, too. The point is that this **can** be done, but we probably don't **want** to introduce this kind of coupling, especially if we want our GC model to be sane enough that people might actually come along and write us a better GC one day.
