I'd like to be able to have a function (that takes about one second) to run every minute. It samples low frequency system data and generates a plot. I'd really like one point per minute. Any thoughts would be helpful. Here's what I've tried and the problems I've had:
  1. Used sleep 60 at the end of the function. This gives a roughly 61 second period for executing the function. (Because the function takes about a second to execute.) That means that data for some minutes will be skipped.
  2. Used alarm 60 in a signal handler for $SIG{ALRM}. The clock seems to creep with this, too, but I am not sure why. It looks as though I get an interrupt every 60.5 seconds. I'll still lose data points this way.
  3. Used 
    select undef, undef, undef, 1.0;
run_func if ! (time%60);

    [download]
    This seemed to skip every other minute for reasons I cannot figure out.
In cases 1 and 2 above, I've sat in a wait loop (wait while (1);) as the body of the program.

I'm using perl 5.005_003 on Linux 2.2.16 (mostly Red Hat). If it makes any difference, the function (run_func above) is a read of about 50 lines using XML::Simple, a few additions, and a plot made via GD::Graph.

--traveler

In reply to Reasonably accurate timing by traveler

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