summaryrefslogtreecommitdiffstats
path: root/src/lib/OpenSLX/ScopedResource.pm
diff options
context:
space:
mode:
Diffstat (limited to 'src/lib/OpenSLX/ScopedResource.pm')
-rw-r--r--src/lib/OpenSLX/ScopedResource.pm174
1 files changed, 174 insertions, 0 deletions
diff --git a/src/lib/OpenSLX/ScopedResource.pm b/src/lib/OpenSLX/ScopedResource.pm
new file mode 100644
index 00000000..af912691
--- /dev/null
+++ b/src/lib/OpenSLX/ScopedResource.pm
@@ -0,0 +1,174 @@
+# Copyright (c) 2008 - OpenSLX GmbH
+#
+# This program is free software distributed under the GPL version 2.
+# See http://openslx.org/COPYING
+#
+# If you have any feedback please consult http://openslx.org/feedback and
+# send your suggestions, praise, or complaints to feedback@openslx.org
+#
+# General information about OpenSLX can be found at http://openslx.org/
+# -----------------------------------------------------------------------------
+package OpenSLX::ScopedResource;
+
+use strict;
+use warnings;
+
+our $VERSION = 1.01; # API-version . implementation-version
+
+=head1 NAME
+
+OpenSLX::ScopedResource - provides a helper class that implements the
+'resource-acquisition-by-definition' pattern.
+
+=head1 SYNOPSIS
+
+{ # some scope
+
+ my $distroSession = OpenSLX::ScopedResource->new({
+ name => 'distro::session',
+ acquire => sub { $distro->startSession(); 1 },
+ release => sub { $distro->finishSession(); 1 },
+ });
+
+ die $@ if ! eval {
+ # do something dangerous and unpredictable here:
+ doRandomStuff();
+ 1;
+ };
+
+}
+# the distro-session will be cleanly finished, no matter if we died or not
+
+=head1 DESCRIPTION
+
+The class C<ScopedResource> wraps any resource such that the resource will be
+acquired when an object of this class is created. Whenever the ScopedResource
+object is being destroyed (e.g. by leaving scope) the wrapped resource will
+automatically be released.
+
+The main purpose of this class is to make it simple to implement reliable
+resource acquisition and release management even if the structure of the code
+that refers to that resource is rather complex.
+
+Furthermore, this class handles cases where the script handling those resources
+is spread across different process and/or makes us of signal handlers.
+
+=cut
+
+# make sure that we catch any signals in order to properly release scoped
+# resources
+use sigtrap qw( die normal-signals error-signals );
+
+use OpenSLX::Basics;
+
+=head1 PUBLIC METHODS
+
+=over
+
+=item B<new($params)>
+
+Creates a ScopedResource object for the resource specified by the given
+I<$params>.
+
+As part of creation of the object, the resource will be acquired.
+
+The I<$params>-hashref requires the following entries:
+
+=over
+
+=item C<name>
+
+Gives a name for the wrapped resource. This is just used in log messages
+concerning the acquisition and release of that resource.
+
+=item C<acuire>
+
+Gives the code that is going to be executed in order to acquire the resource.
+
+=item C<release>
+
+Gives the code that is going to be executed in order to release the resource.
+
+=back
+
+=cut
+
+sub new
+{
+ my $class = shift;
+ my $params = shift;
+
+ checkParams($params, {
+ name => '!',
+ acquire => '!',
+ release => '!',
+ });
+
+ my $self = {
+ name => $params->{name},
+ owner => 0,
+ acquire => $params->{acquire},
+ release => $params->{release},
+ };
+
+ bless $self, $class;
+
+ $self->_acquire();
+
+ return $self;
+}
+
+=item B<DESTROY()>
+
+Releases the resource (if it had been acquired by this process) and cleans up.
+
+=cut
+
+sub DESTROY
+{
+ my $self = shift;
+
+ $self->_release();
+
+ # remove references to functions, in order to release any closures
+ $self->{acquire} = undef;
+ $self->{release} = undef;
+
+ return;
+}
+
+sub _acquire
+{
+ my $self = shift;
+
+ # acquire the resource and set ourselves as owner
+ if ($self->{acquire}->()) {
+ vlog(1, "process $$ acquired resource $self->{name}");
+ $self->{owner} = $$;
+ }
+}
+
+sub _release
+{
+ my $self = shift;
+
+ # only release the resource if invoked by the owning process
+ vlog(3, "process $$ tries to release resource $self->{name}");
+ return if $self->{owner} != $$;
+
+ # ignore ctrl-c while we are trying to release the resource, as otherwise
+ # the resource would be leaked
+ local $SIG{INT} = 'IGNORE';
+
+ # release the resource and unset owner
+ if ($self->{release}->()) {
+ vlog(1, "process $$ released resource $self->{name}");
+ $self->{owner} = 0;
+ }
+}
+
+=back
+
+=cut
+
+1;