bash-based mutex sort of thing, for MacOS which doesn't have flock or lockf or BASHPID

mutex.sh

#!/usr/bin/env bash

set +m # No noisy background report
(
 set -m # New process group, please - It should survive teamcity finishing its step
 (
  PIDS=$HOME/lockpids
  state=looking
  while true ; do
    t=$(mktemp -tpid); bash -c "while [[ -f $t ]] ; do sleep 1 ; done" & p=$(ps -p $! -o 'ppid=') ; rm $t
    echo $p >>$PIDS
    for i in $(cat $PIDS) ; do
      if [[ "$i" -eq $p ]] ; then
        echo $p > $PIDS.new ; mv $PIDS.new $PIDS
        state=won
        break
      fi    
      if kill -0 $i 2>/dev/null ; then
        [[ "$state" == "lost" ]] && exit
        state=lost
        break
      fi
    done
    [[ "$state" = "won" ]] && break
    sleep 1 # still looking or lost once
  done
  echo "PID $p is $state"
        sleep 10
  echo "PID $p quits"
 )&
)&