DB(3) Perl Programmers Reference Guide DB(3)NAMEDB - programmatic interface to the Perl debugging API
(draft, subject to change)
SYNOPSIS
package CLIENT;
use DB;
@ISA = qw(DB);
# these (inherited) methods can be called by the client
CLIENT->register() # register a client package name
CLIENT->done() # de-register from the debugging API
CLIENT->skippkg('hide::hide') # ask DB not to stop in this package
CLIENT->cont([WHERE]) # run some more (until BREAK or another breakpt)
CLIENT->step() # single step
CLIENT->next() # step over
CLIENT->ret() # return from current subroutine
CLIENT->backtrace() # return the call stack description
CLIENT->ready() # call when client setup is done
CLIENT->trace_toggle() # toggle subroutine call trace mode
CLIENT->subs([SUBS]) # return subroutine information
CLIENT->files() # return list of all files known to DB
CLIENT->lines() # return lines in currently loaded file
CLIENT->loadfile(FILE,LINE) # load a file and let other clients know
CLIENT->lineevents() # return info on lines with actions
CLIENT->set_break([WHERE],[COND])
CLIENT->set_tbreak([WHERE])
CLIENT->clr_breaks([LIST])
CLIENT->set_action(WHERE,ACTION)
CLIENT->clr_actions([LIST])
CLIENT->evalcode(STRING) # eval STRING in executing code's context
CLIENT->prestop([STRING]) # execute in code context before stopping
CLIENT->poststop([STRING])# execute in code context before resuming
# These methods will be called at the appropriate times.
# Stub versions provided do nothing.
# None of these can block.
CLIENT->init() # called when debug API inits itself
CLIENT->stop(FILE,LINE) # when execution stops
CLIENT->idle() # while stopped (can be a client event loop)
CLIENT->cleanup() # just before exit
CLIENT->output(LIST) # called to print any output that API must show
DESCRIPTION
Perl debug information is frequently required not just by
debuggers, but also by modules that need some "special"
information to do their job properly, like profilers.
This module abstracts and provides all of the hooks into
Perl internal debugging functionality, so that various
implementations of Perl debuggers (or packages that want
to simply get at the "privileged" debugging data) can all
benefit from the development of this common code. Cur
rently used by Swat, the perl/Tk GUI debugger.
Note that multiple "front-ends" can latch into this debug
ging API simultaneously. This is intended to facilitate
things like debugging with a command line and GUI at the
same time, debugging debuggers etc. [Sounds nice, but
this needs some serious support -- GSAR]
In particular, this API does not provide the following
functions:
data display
command processing
command alias management
user interface (tty or graphical)
These are intended to be services performed by the clients
of this API.
This module attempts to be squeaky clean w.r.t "use
strict;" and when warnings are enabled.
Global Variables
The following "public" global names can be read by clients
of this API. Beware that these should be considered
"readonly".
$DB::sub
Name of current executing subroutine.
%DB::sub
The keys of this hash are the names of all the
known subroutines. Each value is an encoded
string that has the sprintf(3) format
"("%s:%d-%d", filename, fromline, toline)".
$DB::single
Single-step flag. Will be true if the API will
stop at the next statement.
$DB::signal
Signal flag. Will be set to a true value if a sig
nal was caught. Clients may check for this flag
to abort time-consuming operations.
$DB::trace
This flag is set to true if the API is tracing
through subroutine calls.
@DB::args
Contains the arguments of current subroutine, or
the "@ARGV" array if in the toplevel context.
@DB::dbline
List of lines in currently loaded file.
%DB::dbline
Actions in current file (keys are line numbers).
The values are strings that have the sprintf(3)
format "("%s\000%s", breakcondition, actioncode)".
$DB::package
Package namespace of currently executing code.
$DB::filename
Currently loaded filename.
$DB::subname
Fully qualified name of currently executing sub
routine.
$DB::lineno
Line number that will be executed next.
API Methods
The following are methods in the DB base class. A client
must access these methods by inheritance (*not* by calling
them directly), since the API keeps track of clients
through the inheritance mechanism.
CLIENT->register()
register a client object/package
CLIENT->evalcode(STRING)
eval STRING in executing code context
CLIENT->skippkg('D::hide')
ask DB not to stop in these packages
CLIENT->run()
run some more (until a breakpt is reached)
CLIENT->step()
single step
CLIENT->next()
step over
CLIENT->done()
de-register from the debugging API
Client Callback Methods
The following "virtual" methods can be defined by the
client. They will be called by the API at appropriate
points. Note that unless specified otherwise, the debug
API only defines empty, non-functional default versions of
these methods.
CLIENT->init()
Called after debug API inits itself.
CLIENT->prestop([STRING])
Usually inherited from DB package. If no argu
ments are passed, returns the prestop action
string.
CLIENT->stop()
Called when execution stops (w/ args file, line).
CLIENT->idle()
Called while stopped (can be a client event loop).
CLIENT->poststop([STRING])
Usually inherited from DB package. If no argu
ments are passed, returns the poststop action
string.
CLIENT->evalcode(STRING)
Usually inherited from DB package. Ask for a
STRING to be "eval"-ed in executing code context.
CLIENT->cleanup()
Called just before exit.
CLIENT->output(LIST)
Called when API must show a message (warnings,
errors etc.).
BUGS
The interface defined by this module is missing some of
the later additions to perl's debugging functionality. As
such, this interface should be considered highly experi
mental and subject to change.
AUTHOR
Gurusamy Sarathy gsar@activestate.com
This code heavily adapted from an early version of
perl5db.pl attributable to Larry Wall and the Perl
Porters.
2001-02-22 perl v5.6.1 DB(3)
