How to run a per second cron job every two minutes

0
votes

I have to set up a cron job on my hosting provider.

This cron job needs to run every second. It's not intensive, just doing a check.

The hosting provider however only allows cron jobs to be run every two minutes. (can't change hosting btw)

So, I'm clueless on how to go about this?

My thoughts so far: If it can only run every two minutes, I need to make it run every second for two minutes. 1) How do I make my script run for two minutes executing a function every second?

But it's important that there are no interruptions. 2) I have to ensure that it runs smoothly and that it remains constantly active.

Maybe I can also try making it run forever, and run the cron job every two minutes checking whether it is running? 3) Is this possible?

My friend mentioned using multithreading to ensure it's running every second. 4) any comments on this?

Thanks for any advice. I'm using ZF.

2
hostingcron

2 Answers

1
votes

Approach #3 is the standard solution. For instance you can have the cron job touch a file every time it runs. Then on startup you can check whether that file has been touched recently, and if it has then exit immediately. Else start running. (Other approaches include using file locking, or else writing the pid to a file and on startup check whether that pid exists and is the expected program.)

As for the one second timeout, I would suggest calling usleep at the end of your query, supplying the number of milliseconds from now to when you next want to run. If you do a regular sleep then you'll actually run less than once a second because sleeps sometimes last longer than expected, and your check takes time. As long as your check takes under a second to run, this should work fine.

0
votes

I don't think cron allows second level resolution. http://unixhelp.ed.ac.uk/CGI/man-cgi?crontab+5

      field      allowed values
      -----      --------------
      minute         0-59
      hour       0-23
      day of month   1-31
      month      1-12 (or names, see below)
      day of week    0-7 (0 or 7 is Sun, or use names)

So, even if your hosting provider allows you can't run a process that repeats every second. However, you can user command something like watch for repeated execution of your script. see here