Manual Reference Pages - DEVEL::NYTPROF::CORE (3)
Devel::NYTProf::Core - load internals of Devel::NYTProf
This module is not meant to be used directly.
See Devel::NYTProf, Devel::NYTProf::Data, and Devel::NYTProf::Reader.
While its not meant to be used directly, it is a handy place to document some
The subroutine profiler intercepts the entersub opcode which perl uses to
invoke a subroutine, both XS subs (henceforth xsubs) and pure perl subs.
The following sections outline the way the subroutine profiler works:
Before the subroutine call
The profiler records the current time, the current value of
cumulative_subr_secs (as initial_subr_secs), and the current
cumulative_overhead_ticks (as initial_overhead_ticks).
The statement profiler measures time at the start and end of processing for
each statement (so time spent in the profiler, writing to the file for example,
is excluded.) It accumulates the measured overhead into the
In a similar way, the subroutine profiler measures the exclusive time spent
in subroutines and accumulates it into the cumulative_subr_secs global.
Make the subroutine call
The call is made by executing the original perl internal code for the
Calling a perl subroutine
If the sub being called is a perl sub then when the entersub opcode returns,
back into the subroutine profiler, the subroutine has been entered but the
first opcode of the subroutine hasnt been executed yet.
Crucially though, a new scope has been entered by the entersub opcode.
The subroutine profiler then pushes a destructor onto the context stack.
The destructor is effectively just inside the sub, like a local, and so will be
triggered when the subroutine exits by any means. Also, because it was the
first thing push onto the context stack, it will be triggered after any
activity caused by the subroutines scope exiting.
When the destructor is invoked it calls a function which completes the
measurement of the time spent in the sub (see below).
In this way the profiling of perl subroutines is very accurate and robust.
Calling an xsub
If the sub being called is an xsub, then control doesnt return from the
entersub opcode until the xsub has returned. The profiler detects this and
calls the function which completes the measurement of the time spent in the
So far so good, but theres a problem. What if the xsub doesnt return normally
but throws an exception instead?
In that case (currently) the profiler acts as if the xsub was never called.
Time spent inside the xsub will be allocated to the calling sub.
Completing the measurement
The function which completes the timing of a subroutine call does the following:
It calculates the time spent in the statement profiler:
overhead_ticks = cumulative_overhead_ticks - initial_overhead_ticks
and subtracts that from the total time spent inside the subroutine:
incl_subr_sec = (time now - time call was made) - overhead_ticks
That gives us an accurate inclusive time. To get the exclusive time
it calculates the time spent in subroutines called from the subroutine call
called_sub_secs = cumulative_subr_secs - initial_subr_secs
and subtracts that from the incl_subr_sec:
excl_subr_sec = incl_subr_sec - called_sub_secs
To make that easier to follow, consider a call to a sub that calls no others.
In that case cumulative_subr_secs remains unchanged during the call, so
called_sub_secs is zero, and excl_subr_sec is the same as incl_subr_sec.
Finally, it adds the exclusive time to the cumulative exclusive time:
cumulative_subr_secs += excl_subr_sec
Tim Bunce, <http://www.tim.bunce.name> and <http://blog.timbunce.org>
COPYRIGHT AND LICENSE
Copyright (C) 2008, 2009 by Tim Bunce.
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself, either Perl version 5.8.8 or,
at your option, any later version of Perl 5 you may have available.
|perl v5.20.3 ||DEVEL::NYTPROF::CORE (3) ||2015-08-03 |
Visit the GSP FreeBSD Man Page Interface.
Output converted with manServer 1.07.