John Meacham <john@repetae.net> writes:

I have been playing with the heap profiling graphs from ghc and find them quite useful and was wondering if there was a tool to display them in real-time?

Oddly, I found myself looking at heap profiles in real time in the past week. It turns out to be pretty easy to generate a complete heap profile for a running program using a slightly tricky unix command line: head -`fgrep -n END_SAMPLE FOO.hp | tail -1 | cut -d : -f 1` FOO.hp \ | hp2ps > FOO.ps This takes the FOO.hp file of your running program and turns it into a heap profile FOO.ps which includes all the data from the running program. I create a little script which runs this program every few seconds or so. By running gv in "watch file" mode I can see the heap profile of my entire program to date. It's not hard to cook up similar scripts (for example, to display a sliding window of the last n profiling samples) if you load FOO.hp into your favorite editor and take a look at the format. For example, here's parts of the file phc.hp, generated by running the pH/EH compiler on a problematic program: JOB "phc -hC" DATE "Thu Dec 26 18:17 2002" SAMPLE_UNIT "seconds" VALUE_UNIT "bytes" BEGIN_SAMPLE 0.00 END_SAMPLE 0.00 BEGIN_SAMPLE 15.07 ... sample data ... END_SAMPLE 15.07 BEGIN_SAMPLE 30.23 ... sample data ... END_SAMPLE 30.23 ... etc. BEGIN_SAMPLE 11695.47 END_SAMPLE 11695.47 By gluing the header (JOB, DATE, SAMPLE_UNIT, VALUE_UNIT) onto a bunch of samples extracted from the .hp file, you can run hp2ps on arbitrary sample data. Indeed, I use an editor to select and extract interesting chunks of profile data and look at those chunks in greater detail. By using fgrep -n we find the line numbers of the end of each complete sample: % fgrep -n END_SAMPLE phc.hp ... lots of output ... 1004960:END_SAMPLE 11621.34 1006610:END_SAMPLE 11636.61 1008257:END_SAMPLE 11651.85 1009926:END_SAMPLE 11667.08 1011524:END_SAMPLE 11682.33 1011526:END_SAMPLE 11695.47 We select the line number of the last complete sample (the end of a .hp file will contain partially-written sample data while the program is running, causing hp2ps to choke): % fgrep -n END_SAMPLE phc.hp | tail -1 | cut -d : -f 1 1011526 This tells us that the first 1011526 lines of phc.hp will form a properly-formatted heap profile, which we can feed to hp2ps: head -1011526 phc.hp | hp2ps > phc.ps The "watch file" mode of gv is a godsend for this sort of application. It just wouldn't have been worth the effort to me to cook up a gui for the sole purpose of displaying an up-to-date profile. I suspect, by the way, that if .hp files were xml-formatted I would have had a far less pleasant time of things. There's such a thing as TOO much structure. A lesson for us tool-builders, perhaps? -Jan-Willem Maessen