Splot

splot is available from hackage: http://hackage.haskell.org/package/splot

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splot - a tool for visualizing the lifecycle of many concurrent multi-stage processes. See http://www.haskell.org/haskellwiki/Splot 
Usage: splot [-o PNGFILE] [-w WIDTH] [-h HEIGHT] [-bh BARHEIGHT] [-tf TIMEFORMAT]
             [-tickInterval TICKINTERVAL]
  -o PNGFILE    - filename to which the output will be written in PNG format.
                  If omitted, it will be shown in a window.
  -w, -h        - width and height of the resulting picture. Default 640x480.
  -bh           - height of the bar depicting each individual process. Default 5 pixels.
                  Use 1 or so if you have a lot of them.
  -tf           - time format, as in http://linux.die.net/man/3/strptime but with 
                  fractional seconds supported via %OS - will parse 12.4039 or 12,4039
  -tickInterval - ticks on the X axis will be this often (in millis).

Input is read from stdin. Example input (speaks for itself):
2010-10-21 16:45:09,431 >foo green
2010-10-21 16:45:09,541 >bar green
2010-10-21 16:45:10,631 >foo yellow
2010-10-21 16:45:10,725 >foo red
2010-10-21 16:45:10,930 >bar blue
2010-10-21 16:45:11,322 <foo
2010-10-21 16:45:12,508 <bar

'>FOO COLOR' means 'start a bar of color COLOR on track FOO',
'<FOO' means 'end the current bar for FOO'.

> cat <<END |splot -tickInterval 100
2010-10-21 16:45:09,431 >foo green
2010-10-21 16:45:09,541 >bar green
2010-10-21 16:45:10,631 >foo yellow
2010-10-21 16:45:10,725 >foo red
2010-10-21 16:45:10,930 >bar blue
2010-10-21 16:45:11,322 <foo
2010-10-21 16:45:12,508 <bar

And here's what we get:

A couple of real-world examples:

(several thousand processes calling memcached; stages are: green is "connecting", yellow is "reading data", red is "retrying after a network error")

Running 160 approx.equal-length tasks on a 120-core cluster.