gcc/lock-and-run.sh

   1 #! /bin/sh
   2 # Shell-based mutex using mkdir.  This script is used in make to prefer
   3 # serialized execution to avoid consuming too much RAM.  If reusing it,
   4 # bear in mind that the lock-breaking logic is not race-free, so disable
   5 # it in err() if concurrent execution could cause more serious problems.
   6
   7 self=`basename $0`
   8 lockdir="$1" prog="$2"; shift 2 || exit 1
   9
  10 # Remember when we started trying to acquire the lock.
  11 count=0
  12
  13 err () {
  14     if test -f $lockdir/lock-$1.$$; then
  15         rm -rf $lockdir
  16         echo "$self: *** (PID $$) removed stale $lockdir" >&2
  17
  18         # Possible variant for uses where races are more problematic:
  19         #echo "$self: *** (PID $$) giving up, maybe rm -r $lockdir" >&2
  20         #exit 42
  21     else
  22         touch $lockdir/lock-$1.$$
  23     fi
  24 }
  25
  26 until mkdir "$lockdir" 2>/dev/null; do
  27     # Say something periodically so the user knows what's up.
  28     if [ `expr $count % 30` = 0 ]; then
  29         # Check for valid lock.
  30         if pid=`cat $lockdir/pid 2>/dev/null` && kill -0 $pid 2>/dev/null; then
  31             echo "$self: (PID $$) waiting $count sec to acquire $lockdir from PID $pid" >&2
  32         elif test -z "$pid"; then
  33             echo "$self: (PID $$) cannot read $lockdir/pid" >&2
  34             err nopid
  35         else
  36             echo "$self: (PID $$) cannot signal $lockdir owner PID $pid" >&2
  37             err dead
  38         fi
  39     fi
  40     sleep 1
  41     count=`expr $count + 1`
  42 done
  43
  44 trap 'rm -rf "$lockdir"' 0
  45 echo $$ > $lockdir/pidT && mv $lockdir/pidT $lockdir/pid
  46 echo "$self: (PID $$) acquired $lockdir after $count seconds" >&2
  47
  48 echo $prog "$@"
  49 $prog "$@"
  50
  51 # The trap runs on exit.