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package Lock; # This package contains the locking primitives. Once I had 2 things t +hat # needed locking I decided to use these... use strict; use Symbol; use Carp; use Fcntl qw(LOCK_EX LOCK_NB); use vars qw( $lock_dir $text_lock $text_unlock $timeout_limit $verbose ); $verbose ||=0; # The default lockfile $lock_dir = "/set/your/default/here"; # The default text for the lock file when it is in use: $text_lock = <<EOT; This file is for locking access to the production machines. Please +do not delete or rename it as that may mess up flocks. It is currently in use by $0 (process id $$) so it is really importa +nt not to disturb it now. EOT # The default text for the lock file when it is not in use: $text_unlock = <<EOT; This file is for locking access to the production machines. Please +do not delete or rename it as that may mess up flocks. If it was being used it would say which process had it locked. EOT # By default $timeout_limit is undef which means forever. # Truncates a file. (Used for clearing the contents of a lock-file) sub clear_file { local *FOO = shift; my $file = shift; seek (FOO, 0, 0) or confess("Cannot seek to beginning of $file: $!\n +"); truncate (FOO, 0) or confess("Cannot truncate $file: $!\n"); } sub Drop { my $obj = shift; if ($obj->{is_dropped}) { croak("Attempting to drop a lock on $obj->{lockfile} twice!\n"); } else { $obj->{is_dropped} = 1; } my $fh = $obj->{fh}; &clear_file($fh, $obj->{lock_file}); print $fh $obj->{text_unlock}; close $fh; # The right way to drop if ($verbose) { print "Unlocked lock on $obj->{lock_dir}/$obj->{lock_file}\n"; } } sub DESTROY { my $obj = shift; unless ($obj->{is_dropped}) { $obj->Drop; } } # Gets a lock. The constructor passes it a hash of arguments. Here a +re # current possibilities: # # lock_dir - the base directory for the lockfile to go in # lock_file - the file you need to lock. # no_block - return false if you would have to wait for a lock # text_lock - use this text in the lockfile while the file is locked # text_unlock - leave this text in the lockfile when you are done # timeout_limit - Try every second for this many seconds before faili +ng # # Only lock_file is required. sub Get { my $class = shift; my $obj; %$obj = @_; # Validation here unless ($obj->{lock_file}) { croak("No lock_file was requested!\n"); } my %is_allowed = map {($_, 1)} qw/ lock_dir lock_file no_block text_lock text_unlock timeout_limit /; foreach my $arg (keys %$obj) { unless (exists $is_allowed{$arg}) { croak("Unknown argument $arg"); } } $obj->{lock_dir} ||= $lock_dir; $obj->{text_lock} ||= $text_lock; $obj->{text_unlock} ||= $text_unlock; my $lockfile = "$obj->{lock_dir}/$obj->{lock_file}"; my $fh = $obj->{fh} = gensym(); if ($verbose) { print "Getting lock on $lockfile\n"; } my $open_cmd = "+< $lockfile"; unless (-e $lockfile) { print STDERR "$lockfile not found! Creating\n"; local *FH; open (FH, ">> $lockfile") or confess("Cannot create $lockfile! $!" +); close(FH); sleep 1; } open ($fh, "+< $lockfile") or confess("Cannot open $lockfile! $!"); if (-l $fh) { confess("Refusing to use symlink '$lockfile' as a lockfile."); } if ($obj->{no_block}) { # test_only unless( flock ($fh, LOCK_EX | LOCK_NB)) { if ($verbose) { print "Failed to get lock on $lockfile\n"; } return (); } } elsif (defined($timeout_limit)) { # Test every second until we hit the limit. my $limit = time + $timeout_limit; until (flock ($fh, LOCK_EX | LOCK_NB)) { if ($limit < time) { if ($verbose) { print "Failed to get lock on $lockfile within $timeout_limit +\n"; } return (); } sleep 1; } } else { flock ($fh, LOCK_EX) or confess("Cannot get lock! $!"); } &clear_file($fh, $lockfile); # Set autoflush and print lock message my $old_fh = select ($fh); $| = 1; select ($old_fh); print $fh $obj->{text_lock}; bless ($obj, $class); } 1;

In reply to Simple Locking by tilly

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