Kevin's Weblog

Chapter 4 of Alexandrescu -- Small Object Allocator

Okay, this chapter didn't make me cringe. Here's a example of where using C is nice, because you can override fairly fundamental parts of the system (i.e. how things are layed out in memory.) This is a lot harder, if not impossible, in most other languages.

I got tripped up for a bit on a little issue of language semantics. The statement:

does totally different things in C++ and Java. I'm used to Java, at this point, where this just creates a null pointer, that you need to assign to later. However, in C++ this actually constructs a Lock object on the stack. Consequently, what looked to me like a bit of dead code can actually do something significant though the implicit invocation of the constructor and destructor (when you exit the block).

A lot of the discussion yesterday revolved around the fact that it seems that this chapter may be largely obsolete. Apparently in the 2 years since publication, compiler writers have learned some of these tricks, so some compilers are as good or better at small object allocation than Loki. Either that, or said compilers are not good at optimizing the Loki allocator.

There was also a bit of talk about the article on templates vs. ML that I posted last week: http://www.kuro5hin.org/story/2003/5/26/22429/7674 but we couldn't seem to remember the details well enough to really discuss the interesting questions.