Showing posts from June, 2005


Here's a download of source for all lab sessions. I'll try and keep it up to date as I post new source. I also want to update the distribution from the downloads page to contain the more robust, bug fixed, and useful code (the code I actually use). The labs download is more flakey, experimental code that is not updated with bug fixes and is often left sitting around for a long time.

lab 33 - profile lockfs

NAME lab 33 - profile lockfs NOTES Last lab I talked up the benefits of lockfs. I started using it in my program in place of channel locks and profiled the code using prof (1) to see it's impact on performance. The results were a little disappointing but not really suprising. One of the test programs I'm using while developing btree application is a simple indexer. It reads a set of text files, tokenizes each file into a set of Terms, then in the database creates a document id for each document and a termid for each distinct Term and adds to the database a docid-Hit-termid relation. I then run this on a few megabytes of text data; such as all email messages for a year, % prof -n folkfs/tok -i /n/mbox/2001/*/* I've frequently used prof while developing the btree. Locking always presents a bottleneck. When I had the locks based on channels and a cache that also behaved as a lock, both took up large percentage of samples when profiling lines of code. The te

lab 32 - lockfs

NAME lab 32 - lockfs DESCRIPTION I've struggled for a while trying to get multi-reader-single-writer locks (rwlock) working the way I wanted for a database I've been working on (more in a later lab). I recently realized the answer was in inferno all along. The problem was not in implementing a rwlock, which i had done for tickfs using channels and it worked fine, the problem came when I needed to kill a process that might be holding a lock. A lock based on using channels usually means that a spawned process is waiting for an event on a channel either to obtain or free the lock. However, if the process that holds a lock is killed it doesn't get to send the unlock event to the lock manager process. You might think, just don't kill the processes that might hold locks. But killing processes is sometimes hard to avoid. For example, when a Flush message arrives, or to cancel a query that launched multiple processes. Programs that depend on locking based merely on

lab 31 - accumulator generator in limbo

NAME lab 31 - accumulator generator in limbo DESCRIPTION In lab 25 I tried to tackle the problem of writing an accumulator generator in the languages available on inferno. I blithely assumed it wasn't possible in Inferno. I'm happy to say I was wrong. Roger Peppe emailed me the answers, so I'm just reporting what he gave me. But it was very enlightening, a big Aha!, and made me view limbo in a different way. From rog: "funny thing is, it *is* possible in limbo, if you take a somewhat more liberal definition of the term "function". recall that a limbo channel can act like a function: e.g. c: chan of (int, chan of string); "can represent a function that takes an int and returns a string (through the reply channel). c <-= (99, reply := chan of string); sys->print("result is %s\n", <-reply); "i've attached a Limbo version of the accumulator-generator that uses this kind of thing. i'll leave it