Ruby popen3 and timeout behavior experiment

Versions

• Ruby: 3.3.6
• Bash: 5.2.37
• timeout: 9.5 (from GNU coreutils)

Explanation

extern.sh is an example of some heavy command. It receives an argument e.g. 0 1 2 3 and if it's > 2 (means it's == 3 in this experiment), the command runs forever (with while :; do sleep 1; done).

Run ./extern.sh with 4 patterns argument

./extern.sh 0
./extern.sh 1
./extern.sh 2
./extern.sh 3 # doesn't finish

from Ruby script.

I want the Ruby script to finish within finite time.

Ruby scripts are 3 different patterns:

• run1.rb: Use system and Ruby standard Timeout
• run2.rb: Use Open3.popen3 and Ruby standard Timeout
• run3.rb: Use Open3.popen3 but run the command with timeout command

Results

ruby run1.rb

"Loop 0"
Finish this command (0)
true
"Loop 0 finished"
"Loop 1"
Finish this command (1)
true
"Loop 1 finished"
"Loop 2"
Finish this command (2)
true
"Loop 2 finished"
"Loop 3"
"Timeout!"
#<Timeout::Error: execution expired>

ruby run2.rb

"Loop 0"
"Finish this command (0)"
"Loop 0 finished"
"Loop 1"
"Finish this command (1)"
"Loop 1 finished"
"Loop 2"
"Finish this command (2)"
"Loop 2 finished"
"Loop 3"

...
Infinite loop

Press Ctrl+C to kill it.

ruby run3.rb

"Loop 0"
"Finish this command (0)"
"Loop 0 finished"
"Loop 1"
"Finish this command (1)"
"Loop 1 finished"
"Loop 2"
"Finish this command (2)"
"Loop 2 finished"
"Loop 3"
"Timeout!"

Why run2 fails?

popen3 waits the command finishes in its ensure block.

Timeout.timeout doesn't raise an error.

Use timeout command to avoid it. I think it's the most simple.

References

• https://yukithm.blogspot.com/2014/03/kill.html
• https://yukithm.blogspot.com/2014/03/capture3timeout.html
• https://redmine.ruby-lang.org/issues/4681
• https://docs.ruby-lang.org/ja/latest/method/Open3/m/popen3.html
• https://zenn.dev/tkebt/articles/42284661377a27
• https://atmarkit.itmedia.co.jp/ait/articles/1906/27/news008.html
• https://www.man7.org/linux/man-pages/man1/timeout.1.html

License

This work is free of known copyright restrictions.