Question

I have a shell script background process that runs “nohupped”. This process shall receive signals in a trap, but when playing around with some code, I noticed that some signals are ignored if the interval between them is too small. The execution of the trap function takes too much time and therefore the subsequent signal goes
unserved. Unfortunately, the trap command doesn’t have some kind of signal queue, that’s why I am asking: What is the best way to solve this problem?

A simple example:

function  receive_signal()
{
local TIMESTAMP=`date '+%Y%m%d%H%M%S'`
echo "some text" > $TIMESTAMP
}

trap receive_signal USR1

while :
do 
   sleep 5
done

Answer 1

The easiest change, without redesigning your approach, is to use realtime signals, which queue.

This is not portable. Realtime signals themselves are an optional extension, and shell and utility support for them are not required by the extension in any case. However, it so happens that the relevant GNU utilities on Linux — bash(1) and kill(1) — do support realtime signals in a commonsense way. So, you can say:

trap sahandler RTMIN+1

and, elsewhere:

$ kill RTMIN+1 $pid_of_my_process