使用陷阱USR1时Bash随机函数的行为

Question

I have a bash code that gives me random results. I have stripped down my code to some pseudo code that looks like:

#!/usr/bin/bash

function TrapQuit {
    echo "Quitting"
}

function SubFunction {
    echo "Full function call tree ${FUNCNAME[@]}"
}

function DisPatch {
    echo "Running function ${FUNCNAME[0]}"
    SubFunction "1"
}

function test {
    kill -USR1 $$

}

trap DisPatch USR1
trap TrapQuit EXIT HUP

test &
test &
test &
test &
test &

while true; do
    sleep 1
done

Basically, ${FUNCNAME[@]} should list all function calls from current function up to main. When I run this code, I get randomly different results.

The good result is:

Running function DisPatch Full function call tree SubFunction DisPatch main Running function DisPatch Full function call tree SubFunction DisPatch main Running function DisPatch Full function call tree SubFunction DisPatch main Running function DisPatch Full function call tree SubFunction DisPatch test main ^CRunning function DisPatch Full function call tree SubFunction DisPatch main Quitting

The strange result is:

Running function DisPatch Full function call tree SubFunction DisPatch main Running function DisPatch Full function call tree SubFunction DisPatch main Running function DisPatch Full function call tree SubFunction DisPatch DisPatch main Running function DisPatch Full function call tree SubFunction DisPatch SubFunction DisPatch DisPatch main Running function DisPatch Full function call tree SubFunction DisPatch main ^CQuitting

Once every three or five runs, I get the weird result where DisPatch function is three times in ${FUNCNAME[@]}.

How can the DisPatch function end up multiple times in ${FUNCNAME[@]} from SubFunction where it seems that DisPatch has executed itself recursively ?

Thanks for any insight.

Tested with

GNU bash, version 4.2.46(1)-release (x86_64-redhat-linux-gnu) under CentOS 7

GNU bash, version 4.3.42(1)-release (x86_64-redhat-linux-gnu) under Fedora 24

Answer 1

There are two problems. First, $$ is always the process ID of the top-most shell; subshells do not reset its value. Use kill -USR1 $BASHPID instead. Second, subprocesses do not inherit traps. You need to move trap DisPath USR1 into the definition of test .

In the end, your test should look like

function test {
    trap DisPatch USR1
    kill -USR1 $BASHPID
}