###########################
# Filename: lock.sub      #
# By: Brent Michalski     #
# Date: 10 Oct 96         #
###########################
# This is the subroutine to lock files when writing.
$LOCK_SH=1;  # Shared
$LOCK_EX=2;  # Exclusive
$LOCK_NB=4;  # Don't block when locking
$LOCK_UN=8;  # Unlock
 
# The below locks a file for writing.  It seeks to the end of the
# file once it is open so DON'T use it for searching.
sub wlock {
  local($file)=@_;
  flock($file, $LOCK_EX);
  # and in case someone appended
  # while we were waiting...
  seek($file,0,2);
}
 
# The below locks a file WITHOUT seeking to the end. This is the
# one you want to use if you are searching through a file.
sub lock {
  local($file)=@_;
  flock($file, $LOCK_EX);
}
 
# The below unlocks the file.
sub unlock {
  local($file)=@_;
  flock($file, $LOCK_UN);
}