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 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.