Hi all -- I am trying to design a perl script that triggers data collection and logging every X seconds. The problem is that the collection process (reading data from an external instrument via a GPIB port) takes an imprecise amount of time; on a 60-second cycle, I can estimate the time the instrument will take to within two or three seconds, but not more closely than that.

So something as simple as: 

while (1) {
     get_data_taking_exactly_55_seconds;
     sleep(5);
     write_log_file;
     }

[download]

doesn't cut it; my log entries won't be properly aligned because the data collection function may take a bit more or less than 55 seconds.

What I want to do, I think, is along the lines of: 

while (1) {
     set timer;
     get_data_taking_55_seconds_give_or_take_a_few;
     sleep_until_timer_says_60_seconds;
     write_log_file;
     }

[download]

It seems like using the alarm function to trigger the reading process on receipt of SIGALRM should let me do this but I haven't figured out how to make it work reliably; in particular, I can't figure out what kind of loop structure I need to keep the program alive.

I'd sure appreciate any help on how to implement a "sleep until alarm" capability in my program.

Thanks!

In reply to cron-like timing within perl script? by n8ur

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