re: how does purify work?

David Chase <>
5 Aug 2000 21:39:27 -0400

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how does purify work? (2000-08-04)
re: how does purify work? (David Chase) (2000-08-05)
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From: David Chase <>
Newsgroups: comp.compilers
Date: 5 Aug 2000 21:39:27 -0400
Organization: Compilers Central
References: 00-08-027
Keywords: debug, tools

The short (and perhaps relevant) technology is that they use patented
technology. In the-o-ry, if you are "skilled in the art" then it
should all be obvious once you have read the patents. Reed Hastings
is the inventor on most of them.

> [Doesn't it stick extra code into your program to audit all of the
> allocation, freeing, and pointer references? Dunno if it hacks the
> source or rewrites the object. -John]

It rewrites the object, and keeps a bitmap for large hunks of memory,
and uses a replacement version of malloc/free to keep track of what
has been programmatically allocated, and a conservative garbage
collector to keep track of what is leaked and what is not (that part
isn't patented -- Boehm & Weiser talked about it in the Software
Practice and Experience Paper on conservative garbage collection).

That's the quick and sleazy definition, anyway. I worked on C++Expert
at Centerline Software some years back; we went to a lot of trouble to
NOT infringe on those patents, and instrumented at the source level in
a source-to-source transformation, which was an entirely different can
of worms.

David Chase

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