NAME
Devel::TraceCalls - Track calls to subs, classes and object instances
SYNOPSIS
## From the command line
perl -d:TraceCalls=Subs,foo,bar script.pl
## Quick & dirty via use
use Devel::TraceCalls { Package => "Foo" };
## Procedural
use Devel::TraceCalls;
trace_calls qw( foo bar Foo::bar ); ## Explicitly named subs
trace_calls {
Subs => [qw( foo bar Foo::bar )],
...options...
};
trace_calls {
Package => "Foo", ## All subs in this package
...options...
};
trace_calls { ## Just these subs
Package => "Foo", ## Optional
Subs => qw( foo, bar ),
...options...
};
trace_calls $object; ## Just track this instance
trace_calls {
Objects => [ $obj1, $obj2 ]; ## Just track these instances
...options...
};
... time passes, sub calls happen ...
my @calls = $t1->calls; ## retrieve what happned
## Object orented
my $t = Devel::TraceCalls->new( ...parameters... );
undef $t; ## disable tracing
DESCRIPTION
ALPHA CODE ALERT. This module may change before "official" release".
Devel::TraceCalls allows subroutine calls to be tracked on a per-subroutine, per-package, per-class, or per object instance basis. This can be quite useful when trying to figure out how some poor thing is being misused in a program you don't fully understand.
The default action is to log the calls to STDERR. Passing in any of the Calls, PreCall, or PostCall options disables this default behavior (and passing in an TraceOutput option reenables it).
Devel::TraceCalls works on subroutines and classes by installing wrapper subroutines and on objects by temporarily reblessing the objects in to specialized subclasses with "shim" methods. Such objects are reblessed back when the tracker is DESTROYed.
There are 4 ways to specify what to trace.
1 By Explicit Sub Name
trace_calls "foo", "bar"; ## trace to STDOUT.
trace_calls {
Subs => [ "foo", "bar" ],
...options...
};
The first form enables tracking with all Capture options enabled
(other than CaptureSelf which has no effect when capturing plain
subs). The second allows you to control the options.
2 By Package Name
trace_calls {
Package => "My::Module",
...options...
};
# Multiple package names
trace_calls {
Package => [ "My::Module", "Another::Module" ],
...options...
};
trace_calls {
Package => "My::Module",
Subs => [ "foo", "bar" ],
...options...
};
This allows you to provide a package prefix for subroutine names to
be tracked. If no "Subs" option is provided, all subroutines in the
package will be tracked.
This does not examine @ISA like the "Class" and "Objects" (covered
next) techniques do.
3 By Class Name
trace_calls {
Class => "My::Class",
...options...
};
trace_calls {
Class => "My::Class",
...options...
};
trace_calls {
Class => "My::Class",
Subs => [ "foo", "bar" ],
...options...
};
This allows tracking of method calls (or things that look like
method calls) for a class and it's base classes. The $self ($_[0])
will not be captured in "Args" (see the Data Capture Format entry
elsewhere in this document), but may be captured in "Self" if
"CaptureSelf" is enabled.
"Devel::TraceCalls" can't differentiate between "$obj-"foo( ... )>
and "foo( $obj, ... )", which can lead to extra calls being tracked
if the latter form is used. The good news is that this means that
idioms like:
$meth = $obj->can( "foo" );
$meth->( $obj, ... ) if $meth;
are captured.
If a "Subs" parameter is provided, only the named methods will be
tracked. Otherwise all subs in the class and in all parent classes
are tracked.
3 By Object Instance
trace_calls $obj1, $obj2;
trace_calls {
Objects => [ $obj1, $obj2 ],
...options...
};
trace_calls {
Objects => [ $obj1, $obj2 ],
Subs => [ "foo", "bar" ],
...options...
};
This allows tracking of method calls (or things that look like
method calls) for specific instances. The $self ($_[0]) will not be
captured in "Args", but may be captured in Self if CaptureSelf is
enabled.
The first form ("track $obj, ...") enables all capture options,
including CaptureSelf.
OPTIONS
there are several options that may be passed in the HASH ref style parameters in addition to the "Package", "Subs", "Objects" and "Class" settings covered above.
LogTo
LogTo => \*FOO,
LogTo => \@array,
LogTo => undef,
Setting this to a filehandle causes tracing messages to be emitted
to that filehandle. This is set to STDERR by default if no PreCall
or PostCall intercepts are given. It may be set to undef to suppress
tracing if you need to.
Setting this to an ARRAY reference allows call data to be captured,
see below for more details.
LogFormatter
This is not supported yet, the API will be changing.
But, it allows you some small control over how the parameters list
gets traced when LogTo points to a filehandle.
PreCall
PreCall => \&sub_to_call_before_calling_the_target,
A reference to a subroutine to call before calling the target sub.
This will be passed a reference to the data captured before the call
and a reference to the options passed in when defining the trace
point (this does not contain the "Package", "Subs", "Objects" and
"Class" settings.
PostCall
PreCall => \&sub_to_call_after_calling_the_target,
A reference to a subroutine to call after calling the target sub.
This will be passed a reference to the data captured before and
after the call and a reference to the options passed in when
defining the trace point (this does not contain the "Package",
"Subs", "Objects" and "Class" settings.
Data Capture Options
These options affect the data captured in the "Calls" array (see the
The Calls ARRAY entry elsewhere in this document) and passed to the
"PreCall" and "PostCall" handlers.
Options may be added to the hash refs passed to "trace_calls". Here
are the options and their default values (all defaults chosen to
minimize overhead):
CaptureStack => 0,
CaptureCallTimes => 0,
CaptureReturnTimes => 0,
CaptureSelf => 0,
CaptureArgs => 0,
CaptureResult => 0,
CaptureAll => 0, ## Shorthand for setting all of the others
Is CaptureStack is true, the
StackCaptureDepth => 1_000_000,
option controls the maximum number of stack frames that will be
captured. Set this to "1" to capture just a single stack frame
(equiv. to caller 0).
OO API
The object oriented interface provides for more flexible than the other APIs. A tracer will remove all of it's trace points when it is deleted and you can add (and someday, remove) trace points from a running tracer.
Someday you'll also be able to enable and disable tracers.
new
my $t = Devel::TraceCalls->new(
... any params you might pass to trace_calls...
);
add_trace_points
$t->add_trace_points(
...any params you might pass to trace_calls...
);
Add trace points to an existing tracer. Trace points for subs that
already have trace points will be ignored (we can add an option to
enable this; send me a patch or contact me if need be).
Captured Data Format
The LogTo option can be used to log all data to an array instead of to a filehandle by passing it an array reference:
LogTo => \@data,
When passing in an array to capture call data (by using the "Calls" option), the elements will look like:
{
Name => "SubName",
Self => "$obj",
CallTime => $seconds, ## A float if Time::HiRes installed
ReturnTime => $seconds, ## A float if Time::HiRes installed
TraceDepth => $count, ## How deeply nested the trace is.
WantArray => $wantarray_result,
Result => [ "c" ], ## Dumped with Data::Dumper, if need be
Args => [
"foo", ## A scalar was passed
"{ a => 'b' }", ## A HASH (dumped with Data::Dumper)
...
],
Stack => [
[ ... ], ## Results of caller(0).
.... ## More frames if requested
],
}
NOTE: Many of these fields are optional and off by default. See the the OPTIONS entry elsewhere in this document section for details. Tracing (via the "LogTo" parameter) enables several Capture options regardless of the passed-in settings.
"Result" is an array of 0 or more elements. It will always be empty if the sub was called in void context ( WantArray => undef ).
Note that "Self", "Args" and "Result" are converted to strings to avoid keeping references that might prevent things from being destroyed in a timely manner. Data::Dumper is used for "Args" and Result, plain stringification is used for Self.
Using in other Devel:: modules
The main advantage of the Devel:: namespace is that the "perl -d:Foo ..." syntax is pretty handy. Other modules which use this might want to be in the Devel:: namespace. The only trick is avoiding calling Devel::TraceCalls' import() routine when you do this (unless you want to for some reason).
To do this, you can either carefully avoid placing "Devel::TraceCalls" in your Devel::* module's "@ISA" hierarchy or make sure that your module's "import()" method is called instead of "Devel::TraceCalls"'. If you do this, you'll need to have a "sub DB::DB" defined, because "Devel::TraceCalls"' wont be. See the source and the the Devel::TraceSAX manpage module for details.
LIMITATIONS
There are several minor limitations.
Exports a subroutine by default. Do a "use Devel::TraceCalls ();" to suppress that.
If perl's optimized away constant functions, well, there is no call to trace.
Does not get parameters from the call stack. This will change when I get a chance. It will be optional, on by default, if it changes.
Because a wrapper subroutine gets installed in place of the original subroutine, anything that has cached a reference (with code like $foo = \&foo or $foo = Bar->can( "foo" )) will bypass the tracing.
If a subroutine reference is taken while tracing is enabled, then after tracin,g is disabled it will refer to the wrapper subroutine that no longer has something to wrap. We can't use closures to get around this because closures can't be prototyped.
The import based "use Devel::TraceCalls { ... }" feature relies on a "CHECK" subroutine, which is not present on older perls. See the perlmod manpage for details.
Doesn't warn if you point it at an empty class, or if you pass no subs. This is because you might be passing in a possibly empty list. Check the return value's subs method to count up how many overrides occured.
PRIOR ART
See Devel::TraceMethods and Aspect::Trace for similar functionality.
Merlyn also suggested using Class::Prototyped to implement the instance subclassing, but it seems too simple to do without incurring a prerequisite module.
A miscellany of tricky modules like Sub::Versive, Hook::LexWrap, and Sub::Uplevel.
AUTHOR
Barrie Slaymaker <barries@slaysys.com>
COPYRIGHT
Copyright (c) 2002 Barrie Slaymaker, All Rights Reserved.
You may use this module under the terms of the Artistic License or the GPL, any version.