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Post new topic   Forum Index -> Coding & Scripting Corner View previous topic :: View next topic
Reply to topic   Topic: How to get cgi-bin to stop blocking on long processes?
Author
NoViS1



Joined: 14 Apr 2022
Posts: 2
Location: USA, San Diego

PostPosted: Thu 14 Apr '22 8:34    Post subject: How to get cgi-bin to stop blocking on long processes? Reply with quote

I have a series of scripts to open my garage door, one script I press while I'm in my house and waits 60 seconds before opening the garage door so I have time to lock the door and get to the car. While my bash scripts run instantly on the command line, when executed as cgi-bin scripts they are blocking until the sleep function finishes instead of forking off the child to sleep and returning back to the main control page. The code I'm having trouble long block is this:


<OpenGarageIn60SecondsHTML.sh>
Code:
#!/bin/bash

/root/Garage/Office_60s.py 2> /dev/null &
/root/Garage/patio_60s.py 2> /dev/null &
/root/Garage/keypad_arduino_chirp.py 2> /dev/null &
/root/Garage/bedroom_arduino_buzz.py 2> /dev/null &

echo "Content-type: text/html"
echo ""
echo "<HEAD>"
echo "<META HTTP-EQUIV=\"refresh\" CONTENT=\"1; url=http://192.168.12.224/html/index.php\">"
# echo "<META HTTP-EQUIV=\"refresh\" CONTENT=\"1; url=http://192.168.12.224/cgi-bin/OpenIn60InterstitialHTML.sh\">"
echo "</HEAD>"
echo ""
echo ""

/usr/lib/cgi-bin/OpenGarageIn60Seconds.sh 2> /dev/null &


So I'm looking for help to get my script to stop blocking on the long sleeping child process in the last line...
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tangent



Joined: 16 Aug 2020
Posts: 215
Location: UK

PostPosted: Thu 14 Apr '22 21:51    Post subject: Reply with quote

The various processes you background in your script are still owned by that shell, so the shell won't exit normally until they do.

To get round this you need to detach them with the bash 'disown' builtin command.

Try adding this as the last command in your script.

Code:
disown -ah
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NoViS1



Joined: 14 Apr 2022
Posts: 2
Location: USA, San Diego

PostPosted: Fri 15 Apr '22 2:04    Post subject: disown -ah = no change Reply with quote

Still works fine from the command line, still keeps chrome waiting till the script completes executing Sad

Any other ideas?

Thanks,
Robert
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tangent



Joined: 16 Aug 2020
Posts: 215
Location: UK

PostPosted: Fri 15 Apr '22 20:50    Post subject: Reply with quote

Your solution is interesting to say the least, since you're running various Python / shell scripts as well as calling a PHP script in the HTML response.

If it's not doing what you want, I'd be tempted to try a different strategy and decouple the various Python and shell script tasks from Apache CGI, by using a semaphore file of some sort.

So, consider developing a background script which has a loop with a timed delay (say 1 second), and each loop check for the presence of a specific semaphore file. If said file exists, delete it, and then run your various Python and shell scipts.

In the Apache CGI script, apart from creating your HTML response, simply create the semaphore file.

If this approach works, then you can tighten security (owners / permissions), and launch your background script from cron on a reboot.
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James Blond
Moderator


Joined: 19 Jan 2006
Posts: 7138
Location: Germany, Next to Hamburg

PostPosted: Tue 03 May '22 8:52    Post subject: Reply with quote

It might be an option to simply create a text file with a certain value in it. Then a cronjob every minute looks for the file, does the job, and deletes that file. That way you don't have to wait.
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