App - Backplane for core App services

App-Context documentation Contained in the App-Context distribution.

Index

Code Index:

NAME

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App - Backplane for core App services

SYNOPSIS

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    use App;

    my ($context, $conf, $object);
    $context = App->context();  # singleton per process
    $conf    = App->conf();   # returns a hashref to conf
    $context = App->new();
    $object  = App->new($class);
    $object  = App->new($class, $method);
    $object  = App->new($class, $method, @args);

DOCUMENT STATUS

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This documentation is out of date and needs review and revision.

Please start with the App::quickstart document.

DESCRIPTION

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The App module is the module from which core services are called.

Distribution: App-Context

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The App-Context distribution is the core set of modules implementing the core of an enterprise application development framework.

    http://www.officevision.com/pub/App-Context

    * Version: 0.01

It provides the following services.

    * Application Configuration (App::Conf::*)
    * Session Management (App::Session::*)
    * Remote Procedure Call (App::Procedure::*)
    * Session Objects and Remote Method Invocation (App::SessionObject::*)
    * Multiprocess-safe Name-Value Storage (App::SharedDatastore::*)
    * Shared Resource Pooling and Locking (App::SharedResourceSet::*)

One of App-Context's extended services (App::Repository::*) adds distributed transaction capabilities and access to data from a variety of sources through a uniform interface.

In the same distribution (App-Repository), is a base class, App::RepositoryObject, which serves as the base class for implementing persistent business objects.

    http://www.officevision.com/pub/App-Repository

Another of App-Context's extended services (App::Widget::*) adds simple and complex active user interface widgets. These widgets can be used to supplement an existing application's user interface technology (template systems, hard-coded HTML, etc.) or the Widget system can be used as the central user interface paradigm.

    http://www.officevision.com/pub/App-Widget

App-Context and its extended service distributions were inspired by work on the Perl 5 Enterprise Environment project, and its goal is to satisfy the all of the requirements embodied in the Attributes of an Enterprise System.

See the following web pages for more information about the P5EE project.

    http://p5ee.perl.org/
    http://www.officevision.com/pub/p5ee/

Distribution Requirements

The following are enumerated requirements for the App-Context distribution. It forms a high-level feature list. The requirements which have been satisfied (or features implemented) have an "x" by them, whereas the requirements which have yet-to-be satisfied have an "o" by them.

    o an Enterprise Software Architecture, supporting all the Attributes
        http://www.officevision.com/pub/p5ee/definitions.html
    o a Software Architecture supporting many Platforms
        http://www.officevision.com/pub/p5ee/platform.html
    o a pluggable interface/implementation service architecture
    o support developers who wish to use portions of the App-Context
        framework without giving up their other styles of programming
        (and support gradual migration)

Distribution Design

The distribution is designed in such a way that most of the functionality is actually provided by modules outside the App namespace.

The goal of the App-Context framework is to bring together many technologies to make a unified whole. In essence, it is collecting and unifying the good work of a multitude of excellent projects which have already been developed. This results in a Pluggable Service design which allows just about everything in App-Context to be customized. These Class Groups are described in detail below.

Where a variety of excellent, overlapping or redundant, low-level modules exist on CPAN (i.e. date and time modules (App::datetime)), a document is written to explain the pros and cons of each.

Where uniquely excellent modules exist on CPAN, they are named outright as the standard for the App-Context framework. They are identified as dependencies in the App-Context CPAN Bundle file.

Class Groups

The major Class Groups in the App-Context distribution fall into three categories: Core, Core Services, and Services.

* Class Group: Core|"Class Group: Core"
* Class Group: Context|App::Context - encapsulates the runtime environment and the event loop
* Class Group: Conf|App::Conf - retrieve and access configuration information
* Class Group: Session|App::Session - represents the state associated with a sequence of multiple events
* Class Group: Serializer|App::Serializer - transforms a perl struct to a scalar and back
* Class Group: Procedure|App::Procedure - a (potentially remote) procedure which may be executed
* Class Group: Messaging|App::Messaging - a message queue with configurable quality of service
* Class Group: Security|App::Security - provides authentication and authorization
* Class Group: LogChannel|App::LogChannel - a logging channel through which messages may be logged
* Class Group: SharedDatastore|App::SharedDatastore - a data storage area which is shared between processes
* Class Group: SharedResourceSet|App::SharedResourceSet - a set of shared resources which may be locked for exclusive access

Class Group: Core

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The Core Class Group contains the following classes.

* Class: App|"Class: App"
* Class: App::Reference|App::Exceptions
* Class: App::Reference|App::Reference
* Class: App::Service|App::Service
* Document: Perlstyle, Perl Style Guide|App::perlstyle
* Document: Podstyle, POD Documentation Guide|App::podstyle
* Document: Datetime, Dates and Times in App-Context|App::datetime

Class: App

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App is the main class through which all of the features of the Perl 5 Enterprise Environment may be accessed.

 * Throws: Exception::Class::Base
 * Throws: App::Exception
 * Throws: App::Exception::Conf
 * Throws: App::Exception::Context
 * Since:  0.01

Class Design

The class is entirely made up of static (class) methods. There are no constructors for objects of this class itself. Rather, all of the constructors in this package are really factory-style constructors that return objects of different classes. In particular, the new() method is really a synonym for context(), which returns a Context object.

Class Capabilities

This class supports the following capabilities.

* Capability: Service Factory

This package allows you to construct objects (services) that you do not know the classes for at development time. These classes are specified through the configuration and are produced using this package as a class factory.

Attributes, Constants, Global Variables, Class Variables

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Global Variables

 * Global Variable: %App::scope              scope for debug or tracing output
 * Global Variable: $App::scope_exclusive    flag saying that the scope is exclusive (a list of things *not* to debug/trace)
 * Global Variable: %App::trace              trace level
 * Global Variable: $App::DEBUG              debug level
 * Global Variable: $App::DEBUG_FILE         file for debug output

Code Inclusion and Instrumentation

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use()

    * Signature: App->use($class);
    * Param:  $class      string  [in]
    * Return: void
    * Throws: <none>
    * Since:  0.01

    Sample Usage: 

    App->use("App::Widget::Entity");

The use() method loads additional perl code and enables aspect-oriented programming (AOP) features if they are appropriate. If these did not need to be turned on or off, it would be easier to simply use the following.

  eval "use $class;"

The first AOP feature planned is the printing of arguments on entry to a method and the printing of arguments and return values on exit of a a method.

This is useful for debugging and the generation of object-message traces to validate or document the flow of messages through the system.

Detailed Conditions:

  * use(001) class does not exist: throw a App::Exception
  * use(002) class never used before: should succeed
  * use(003) class used before: should succeed
  * use(004) can use class after: should succeed

printargs()

    * Signature: App->printargs($depth, $skipatend, @args);
    * Param:     $depth       integer  [in]
    * Param:     $skipatend   integer  [in]
    * Param:     @args        any      [in]
    * Return:    void
    * Throws:    none
    * Since:     0.01

Constructor Methods:

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new()

The App->new() method is not a constructor for an App class. Rather, it is a Factory-style constructor, returning an object of the class given as the first parameter.

If no parameters are given, it is simply a synonym for "App->context()".

    * Signature: $context = App->new()
    * Signature: $object = App->new($class)
    * Signature: $object = App->new($class,$method)
    * Signature: $object = App->new($class,$method,@args)
    * Param:  $class       class  [in]
    * Param:  $method      string [in]
    * Return: $context     App::Context
    * Return: $object      ref
    * Throws: Exception::Class::Base
    * Since:  0.01

    Sample Usage: 

    $context = App->new();
    $dbh = App->new("DBI", "new", "dbi:mysql:db", "dbuser", "xyzzy");
    $cgi = App->new("CGI", "new");

context()

    * Signature: $context = App->context();      # most common, used in "app"
    * Signature: $context = App->context(%named);                 # also used
    * Signature: $context = App->context($named, %named);         # variation
    * Signature: $context = App->context($name, %named);               # rare
    * Signature: $context = App->context($named, $name, %named);       # rare
    * Param:     context_class   class  [in]
    * Param:     config_file     string [in]
    * Param:     prefix          string [in]
    * Return:    $context        App::Context
    * Throws:    App::Exception::Context
    * Since:     0.01

    Sample Usage: 

    $context = App->context();
    $context = App->context(
        context_class => "App::Context::HTTP",
        config_file => "app.xml",
    );

This static (class) method returns the $context object of the context in which you are running. It tries to use some intelligence in determining which context is the right one to instantiate, although you can override it explicitly.

It implements a "Factory" design pattern. Instead of using the constructor of a class itself to get an instance of that class, the context() method of App is used. The former technique would require us to know at development time which class was to be instantiated. Using the factory style constructor, the developer need not ever know what physical class is implementing the "Context" interface. Rather, it is configured at deployment-time, and the proper physical class is instantiated at run-time.

The new() method of the configured Context class is called to instantiate the proper Context object. The $named args are combined with the %named args and passed as a single hash reference to the new() method.

Environment variables:

    PREFIX - set the $conf->{prefix} variable if not set to set app root dir
    APP_CONTEXT_CLASS - set the Perl module to instantiate for the Context
    GATEWAY_INTERFACE - assume mod_perl, use App::Context::ModPerl
    HTTP_USER_AGENT - assume CGI, use App::Context::HTTP
      (otherwise, use App::Context::Cmd, assuming it is from command line)

conf()

    * Signature: $conf = App->conf(%named);
    * Param:     conf_class  class  [in]
    * Param:     config_file string [in]
    * Return:    $conf      App::Conf
    * Throws:    App::Exception::Conf
    * Since:     0.01

This gets the Conf object from the Context.

If args are passed in, they are only effective in affecting the Context if the Context has not been instantiated before.

After the Context is instantiated by either the App->context() call or the App->conf() call, then subsequent calls to either method may or may not include arguments. It will not have any further effect because the Context object instantiated earlier will be used.

info()

    * Signature: $ident = App->info();
    * Param:     void
    * Return:    $ident     string
    * Throws:    App::Exception
    * Since:     0.01

Gets version info about the framework.

sub_entry()

    * Signature: &App::sub_entry;
    * Signature: &App::sub_entry(@args);
    * Param:     @args        any
    * Return:    void
    * Throws:    none
    * Since:     0.01

This is called at the beginning of a subroutine or method (even before $self may be shifted off).

sub_exit()

    * Signature: &App::sub_exit(@return);
    * Param:     @return      any
    * Return:    void
    * Throws:    none
    * Since:     0.01

This subroutine is called just before you return from a subroutine or method. =cut

in_debug_scope()

    * Signature: &App::in_debug_scope
    * Signature: App->in_debug_scope
    * Param:     <no arg list supplied>
    * Return:    void
    * Throws:    none
    * Since:     0.01

This is called within a subroutine or method in order to see if debug output should be produced.

  if ($App::debug && &App::in_debug_scope) {
      print "This is debug output\n";
  }

Note: The App::in_debug_scope subroutine also checks $App::debug, but checking it in your code allows you to skip the subroutine call if you are not debugging.

  if (&App::in_debug_scope) {
      print "This is debug output\n";
  }

debug_indent()

    * Signature: &App::debug_indent()
    * Signature: App->debug_indent()
    * Param:     void
    * Return:    $indent_str     string
    * Throws:    none
    * Since:     0.01

This subroutine returns the $indent_str string which should be printed before all debug lines if you wish to line the debug output up with the nested/indented trace output.

ACKNOWLEDGEMENTS

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 * Author:  Stephen Adkins <spadkins@gmail.com>
 * License: This is free software. It is licensed under the same terms as Perl itself.

SEE ALSO

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App-Context documentation Contained in the App-Context distribution. 
#############################################################################
## $Id: App.pm 13887 2010-04-06 13:36:42Z spadkins $
#############################################################################

package App;
$VERSION = (q$Revision: 13887 $ =~ /(\d[\d\.]*)/)[0];  # VERSION numbers generated by svn

use strict;

# eliminate warnings about uninitialized values
$SIG{__WARN__} = sub { warn @_ unless $_[0] =~ /Use of uninitialized value/};

use Exception::Class;   # enable Exception inheritance
use App::Exceptions;
use IO::Handle;


#############################################################################
# DISTRIBUTION
#############################################################################


#############################################################################
# CLASS GROUP
#############################################################################


#############################################################################
# CLASS
#############################################################################


#############################################################################
# ATTRIBUTES/CONSTANTS/CLASS VARIABLES/GLOBAL VARIABLES
#############################################################################


if (!defined $App::DEBUG) {
    %App::scope = ();
    $App::scope_exclusive = 0;
    $App::trace = 0;
    $App::DEBUG = 0;
}

#################################################################
# DEBUGGING
#################################################################

# Supports the following command-line usage:
#    --debug=1                                     (global debug)
#    --debug=9                                     (detail debug)
#    --scope=App::Context                      (debug class only)
#    --scope=!App::Context             (debug all but this class)
#    --scope=App::Context,App::Session         (multiple classes)
#    --scope=App::Repository::DBI.select_rows    (indiv. methods)
#    --trace=App::Context                      (trace class only)
#    --trace=!App::Context             (trace all but this class)
#    --trace=App::Context,App::Session         (multiple classes)
#    --trace=App::Repository::DBI.select_rows    (indiv. methods)
{
    my $scope = $App::options{scope} || "";

    my $trace = $App::options{trace};
    if ($trace) {
        if ($trace =~ s/^([0-9]+),?//) {
            $App::trace = $1;
        }
        else {
            $App::trace = 9;
        }
    }
    if ($trace) {
        $scope .= "," if ($scope);
        $scope .= $trace;
    }
    $App::trace_width = (defined $App::options{trace_width}) ? $App::options{trace_width} : 1024;
    $App::trace_justify = (defined $App::options{trace_justify}) ? $App::options{trace_justify} : 0;

    my $debug = $App::options{debug};
    if ($debug) {
        if ($debug =~ s/^([0-9]+),?//) {
            $App::DEBUG = $1;
        }
        else {
            $App::DEBUG = 9;
        }
    }
    if ($debug) {
        $scope .= "," if ($scope);
        $scope .= $debug;
    }

    if ($scope =~ s/^!//) {
        $App::scope_exclusive = 1;
    }

    if (defined $scope && $scope ne "") {
        foreach my $pkg (split(/,/,$scope)) {
            $App::scope{$pkg} = 1;
        }
    }

    my $debug_file = $App::options{debug_file};
    if ($debug_file) {
        if ($debug_file eq "STDOUT") {
            $App::DEBUG_FILE = \*STDOUT;
        }
        elsif ($debug_file eq "STDERR") {
            $App::DEBUG_FILE = \*STDERR;
        }
        else {
            if ($debug_file !~ /^[>|]/) {
                $debug_file = "> $debug_file";
            }
            if (open(App::DEBUG_FILE_HANDLE, $debug_file)) {
                $App::DEBUG_FILE = \*App::DEBUG_FILE_HANDLE;
            }
            else {
                warn "WARNING: Couldn't open $debug_file: $!\n";
            }
        }
    }
    else {
        $App::DEBUG_FILE = \*STDOUT;
    }
    $App::DEBUG_FILE->autoflush(1);
}

#############################################################################
# SUPPORT FOR ASPECT-ORIENTED-PROGRAMMING (AOP)
#############################################################################


#############################################################################
# use()
#############################################################################


my (%used);

sub use {
    &App::sub_entry if ($App::trace);
    my ($self, $class) = @_;
    no strict;  # allow fiddling with the symbol table
    if (! defined $used{$class}) {
        # if we try to use() it again, we won't get an exception
        $used{$class} = 1;

        # I could look for a particular variable like $VERSION,
        # local (*VERSION) = ${*{"$class\::"}}{VERSION};
        # print "$class VERSION: ", ${*VERSION{SCALAR}}, "\n";

        # but I decided to look for *any* symbol table entry instead.
        if (%{*{"$class\::"}}) {  # if any symbols exist in the symbol table
            # do nothing
        }
        elsif ($class =~ /^([A-Za-z0-9_:]+)$/) {
            eval "use $1;";
            if ($@) {
                App::Exception->throw(
                    error => "class $class failed to load: $@\n",
                );
            }
        }
        else {
            App::Exception->throw(
                error => "Tried to load class [$class] with illegal characters\n",
            );
        }
    }
    &App::sub_exit() if ($App::trace);
}

# $dir = App->mkdir($prefix, "data", "app", "Context");
sub mkdir {
    &App::sub_entry if ($App::trace);
    my ($self, @dirs) = @_;

    my $dir = shift(@dirs);
    if ($dir) {
        mkdir($dir) if (! -d $dir);
        foreach my $d (@dirs) {
            $dir = File::Spec->catdir($dir, $d);
            mkdir($dir) if (! -d $dir);
        }
    }
    &App::sub_exit($dir) if ($App::trace);
    return($dir);
}

#############################################################################
# printargs()
#############################################################################


sub printargs {
    my $depth = shift;
    my $skipatend = shift;
    my ($narg);
    for ($narg = 0; $narg <= $#_ - $skipatend; $narg++) {
        print "," if ($narg);
        if (ref($_[$narg]) eq "") {
            print $_[$narg];
        }
        elsif (ref($_[$narg]) eq "ARRAY") {
            print "[";
            if ($depth <= 1) {
                print join(",", @{$_[$narg]});
            }
            else {
                &printdepth($depth-1, 0, @{$_[$narg]});
            }
            print "]";
        }
        elsif (ref($_[$narg]) eq "HASH") {
            print "{";
            if ($depth <= 1) {
                print join(",", %{$_[$narg]});
            }
            else {
                &printdepth($depth-1, 0, %{$_[$narg]});
            }
            print "}";
        }
        else {
            print $_[$narg];
        }
    }
}

#############################################################################
# CONSTRUCTOR METHODS
#############################################################################


#############################################################################
# new()
#############################################################################


sub new {
    &App::sub_entry if ($App::trace);
    my $self = shift;
    if ($#_ == -1) {
        my $context = $self->context();
        &App::sub_exit($context) if ($App::trace);
        return($context);
    }
    my $class = shift;
    if ($class =~ /^([A-Za-z0-9:_]+)$/) {
        $class = $1;  # untaint the $class
        if (! $used{$class}) {
            $self->use($class);
        }
        my $method = ($#_ > -1) ? shift : "new";
        if (wantarray) {
            my @values = $class->$method(@_);
            &App::sub_exit(@values) if ($App::trace);
            return(@values);
        }
        else {
            my $value = $class->$method(@_);
            &App::sub_exit($value) if ($App::trace);
            return($value);
        }
    }
    print STDERR "Illegal Class Name: [$class]\n";
    &App::sub_exit(undef) if ($App::trace);
    return undef;
}

#############################################################################
# context()
#############################################################################


my (%context);  # usually a singleton per process (under "default" name)
                # multiple named contexts are allowed for debugging purposes

sub context {
    &App::sub_entry if ($App::trace);
    my $self = shift;

    my ($name, $options, $i);
    if ($#_ == -1) {               # if no options supplied (the normal case)
        $options = (%App::options) ? \%App::options : {};      # options hash
        $name = "default";                 # name of the singleton is default
    }
    else {                                     # named args were supplied ...
        if (ref($_[0]) eq "HASH") {                 # ... as a hash reference
            $options = shift;                # note that a copy is *not* made
            for ($i = 0; $i < $#_; $i++) {            # copy other named args
                $options->{$_[$i]} = $_[$i+1];        # into the options hash
            }
        }
        else {                                  # ... as a list of var/values
            $name = shift if ($#_ % 2 == 0);    # if odd #, first is the name
            $options = ($#_ > -1) ? { @_ } : {};    # the rest are named args
        }
        $name = $options->{name} if (!$name); # if not given, look in options
        $name = "default" if (!$name);                # use "default" as name
    }

    if (!defined $context{$name}) {
    
        if (! $options->{context_class}) {
            if (defined $ENV{APP_CONTEXT_CLASS}) {        # env variable set?
                $options->{context_class} = $ENV{APP_CONTEXT_CLASS};
            }
            else {   # try autodetection ...
                if ($ENV{MOD_PERL}) {
                    $options->{context_class} = "App::Context::ModPerl";
                }
                elsif ($ENV{HTTP_USER_AGENT}) {  # running as CGI script?
                    $options->{context_class} = "App::Context::HTTP";
                }
                else {   # assume it is from the command line
                    $options->{context_class} = "App::Context::Cmd";
                }
            }
        }
        if (!$options->{prefix}) {                # if this isn't already set
            if ($ENV{PREFIX}) {             # but it's set in the environment
                $options->{prefix} = $ENV{PREFIX};              # then set it
            }
        }

        # instantiate Context and cache it (it's reference) for future use
        $context{$name} = $self->new($options->{context_class}, "new", $options);
    }

    &App::sub_exit($context{$name}) if ($App::trace);
    return($context{$name});
}

sub shutdown {
    &App::sub_entry if ($App::trace);
    my ($self, $name) = @_;
    $name = "default" if (!defined $name);
    $context{$name}->shutdown() if (defined $context{$name});
    delete $context{$name};
    &App::sub_exit() if ($App::trace);
}

#############################################################################
# conf()
#############################################################################


sub conf {
    &App::sub_entry if ($App::trace);
    my $self = shift;
    my $retval = $self->context(@_)->conf();
    &App::sub_exit($retval) if ($App::trace);
    $retval;
}

#############################################################################
# info()
#############################################################################


sub info {
    &App::sub_entry if ($App::trace);
    my $self = shift;
    my $retval = "App-Context ($App::VERSION)";
    &App::sub_exit($retval) if ($App::trace);
    return($retval);
}

#############################################################################
# Aspect-oriented programming support
#############################################################################
# NOTE: This can be done much more elegantly at the Perl language level,
# but it requires version-specific code.  I created these subroutines so that
# any method that is instrumented with them will enable aspect-oriented
# programming in Perl versions from 5.5.3 to the present.
#############################################################################

my $calldepth = 0;

#############################################################################
# sub_entry()
#############################################################################


sub sub_entry {
    if ($App::trace) {
        my ($stacklevel, $calling_package, $file, $line, $subroutine, $hasargs, $wantarray, $text);
        $stacklevel = 1;
        ($calling_package, $file, $line, $subroutine, $hasargs, $wantarray) = caller($stacklevel);
        while (defined $subroutine && $subroutine eq "(eval)") {
            $stacklevel++;
            ($calling_package, $file, $line, $subroutine, $hasargs, $wantarray) = caller($stacklevel);
        }
        my ($name, $obj, $class, $package, $sub, $method, $firstarg, $trailer);

        # split subroutine into its "package" and the "sub" within the package
        if ($subroutine =~ /^(.*)::([^:]+)$/) {
            $package = $1;
            $sub = $2;
        }

        # check if it might be a method call rather than a normal subroutine call
        if ($#_ >= 0) {
            $class = ref($_[0]);
            if ($class) {
                $obj = $_[0];
                $method = $sub if ($class ne "ARRAY" && $class ne "HASH");
            }
            else {
                $class = $_[0];
                if ($class =~ /^[A-Z][A-Za-z0-9_:]*$/ && $class->isa($package)) {
                    $method = $sub;  # the sub is a method call on the class
                }
                else {
                    $class = "";     # it wasn't really a class/method
                }
            }
        }

        if (%App::scope) {
            if ($App::scope_exclusive) {
                return if ($App::scope{$package} || $App::scope{"$package.$sub"});
            }
            else {
                return if (!$App::scope{$package} && !$App::scope{"$package.$sub"});
            }
        }

        if ($method) {
            if (ref($obj)) {  # dynamic method, called on an object
                if ($obj->isa("App::Service")) {
                    $text = ("| " x $calldepth) . "+-" . $obj->{name} . "->${method}(";
                }
                else {
                    $text = ("| " x $calldepth) . "+-" . $obj . "->${method}(";
                }
                $trailer = " [$package]";
            }
            else {   # static method, called on a class
                $text = ("| " x $calldepth) . "+-" . "${class}->${method}(";
                $trailer = ($class eq $package) ? "" : " [$package]";
            }
            $firstarg = 1;
        }
        else {
            $text = ("| " x $calldepth) . "+-" . $subroutine . "(";
            $firstarg = 0;
            $trailer = "";
        }
        my ($narg);
        for ($narg = $firstarg; $narg <= $#_; $narg++) {
            $text .= "," if ($narg > $firstarg);
            if (!defined $_[$narg]) {
                $text .= "undef";
            }
            elsif (ref($_[$narg]) eq "") {
                $text .= $_[$narg];
            }
            elsif (ref($_[$narg]) eq "ARRAY") {
                $text .= ("[" . join(",", map { defined $_ ? $_ : "undef" } @{$_[$narg]}) . "]");
            }
            elsif (ref($_[$narg]) eq "HASH") {
                $text .= ("{" . join(",", map { defined $_ ? $_ : "undef" } %{$_[$narg]}) . "}");
            }
            else {
                $text .= $_[$narg];
            }
        }
        #$trailer .= " [package=$package sub=$sub subroutine=$subroutine class=$class method=$method]";
        $text .= ")";
        my $trailer_len = length($trailer);
        $text =~ s/\n/\\n/g;
        my $text_len = length($text);
        if ($App::trace_width) {
            if ($text_len + $trailer_len > $App::trace_width) {
                my $len = $App::trace_width - $trailer_len;
                $len = 1 if ($len < 1);
                print $App::DEBUG_FILE substr($text, 0, $len), $trailer, "\n";
            }
            elsif ($App::trace_justify) {
                my $len = $App::trace_width - $trailer_len - $text_len;
                $len = 0 if ($len < 0);  # should never happen
                print $App::DEBUG_FILE $text, ("." x $len), $trailer, "\n";
            }
            else {
                print $App::DEBUG_FILE $text, $trailer, "\n";
            }
        }
        else {
            print $App::DEBUG_FILE $text, $trailer, "\n";
        }
        $calldepth++;
    }
}

#############################################################################
# sub_exit()
#############################################################################


sub sub_exit {
    if ($App::trace) {
        my ($stacklevel, $calling_package, $file, $line, $subroutine, $hasargs, $wantarray, $text);
        $stacklevel = 1;
        ($calling_package, $file, $line, $subroutine, $hasargs, $wantarray) = caller($stacklevel);
        while (defined $subroutine && $subroutine eq "(eval)") {
            $stacklevel++;
            ($calling_package, $file, $line, $subroutine, $hasargs, $wantarray) = caller($stacklevel);
        }

        my ($package, $sub);
        # split subroutine into its "package" and the "sub" within the package
        if ($subroutine =~ /^(.*)::([^:]+)$/) {
            $package = $1;
            $sub = $2;
        }

        return if (%App::scope && !$App::scope{$package} && !$App::scope{"$package.$sub"});

        $calldepth--;
        $text = ("| " x $calldepth) . "+-> $sub()";
        my ($narg, $arg);
        for ($narg = 0; $narg <= $#_; $narg++) {
            $text .= $narg ? "," : " : ";
            $arg = $_[$narg];
            if (! defined $arg) {
                $text .= "undef";
            }
            elsif (ref($arg) eq "") {
                $text .= $arg;
            }
            elsif (ref($arg) eq "ARRAY") {
                $text .= ("[" . join(",", map { defined $_ ? $_ : "undef" } @$arg) . "]");
            }
            elsif (ref($arg) eq "HASH") {
                $text .= ("{" . join(",", map { defined $_ ? $_ : "undef" } %$arg) . "}");
            }
            else {
                $text .= defined $arg ? $arg : "undef";
            }
        }
        $text =~ s/\n/\\n/g;
        if ($App::trace_width && length($text) > $App::trace_width) {
            print $App::DEBUG_FILE substr($text, 0, $App::trace_width), "\n";
        }
        else {
            print $App::DEBUG_FILE $text, "\n";
        }
    }
    return(@_);
}

#############################################################################
# in_debug_scope()
#############################################################################


sub in_debug_scope {
    if ($App::debug) {
        my ($stacklevel, $calling_package, $file, $line, $subroutine, $hasargs, $wantarray, $text);
        $stacklevel = 1;
        ($calling_package, $file, $line, $subroutine, $hasargs, $wantarray) = caller($stacklevel);
        while (defined $subroutine && $subroutine eq "(eval)") {
            $stacklevel++;
            ($calling_package, $file, $line, $subroutine, $hasargs, $wantarray) = caller($stacklevel);
        }
        my ($package, $sub);

        # split subroutine into its "package" and the "sub" within the package
        if ($subroutine =~ /^(.*)::([^:]+)$/) {
            $package = $1;
            $sub = $2;
        }

        if (%App::scope) {
            if ($App::scope_exclusive) {
                return(undef) if ($App::scope{$package} || $App::scope{"$package.$sub"});
            }
            else {
                return(undef) if (!$App::scope{$package} && !$App::scope{"$package.$sub"});
            }
        }
        return(1);
    }
    return(undef);
}

#############################################################################
# debug_indent()
#############################################################################


sub debug_indent {
    my $text = ("| " x $calldepth) . "  * ";
    return($text);
}


1;