Timing a Module Load

geekondemand has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Timing a Module Load by Fletch (Bishop) on Apr 29, 2005 at 19:48 UTC
For one thing, `use` happens at compile time so you're not really timing anything with your code. What you'd really want to do is use `require` instead and clobber the corresponding entry in `%INC` before attempting to reload. Update: Alternately, load the module source into a scalar and use `eval "$source"` instead.	[reply] [d/l] [select]
Re^2: Timing a Module Load by geekondemand (Scribe) on Apr 29, 2005 at 20:00 UTC
Thanks! I actually figured this out and now have `do "my_module.pm";` [download] instead of `use my_module;` [download] I think that does the clobber of %INC and forces the reload. My guess is that this differs from eval "$source" solution you mention only in that I'm actually reading the module from disk each time with the "do" solution.	[reply] [d/l] [select]
Re: Timing a Module Load by mda2 (Hermit) on Apr 29, 2005 at 22:45 UTC
After other monks considers (use is a compile time call and eval), consider two others methods to get this times: 1. Use a Perl Code Profiler : More info: Devel::DProf dprofpp `$ perl -d:DProf <script> $ dprofpp # select args` [download] 2. Consider use require+import: perldoc use use my_module is equal to BEGIN{ require "my_module"; import my_module }; *. Eval is a option -- Marco Antonio Rio-PM	[reply] [d/l]
Re^2: Timing a Module Load by salva (Canon) on Apr 30, 2005 at 15:52 UTC
Profiling in perl has a big overhead. You can use it to find hot spots on the code, but not to time things.	[reply]
Re: Timing a Module Load by saintmike (Vicar) on Apr 29, 2005 at 20:08 UTC
The previous responders hit the nail on the head, just in case if you're interested in timing the `use`: You need to put the starting timer code into a `BEGIN` block before the `use` call: `BEGIN{ $t0 = [gettimeofday]; } use my_module; $elapsed = tv_interval( $t0, [gettimeofday] );` [download]	[reply] [d/l] [select]
Re^2: Timing a Module Load by suaveant (Parson) on Apr 29, 2005 at 20:40 UTC
Not exactly correct... ALL the code has to be in the begin, otherwise other things may happen (uses, other begin blocks) before the tv_interval runs. - Ant - Some of my best work - (1 2 3)	[reply]
Re: Timing a Module Load by halley (Prior) on Apr 30, 2005 at 18:18 UTC
A technique which nobody has mentioned above is simply comparing against a control group. Time a few thousand iterations loading the module, % for e in `seq 1000` ; do perl -Mmymodule -e1 ; done [download] Then time a few thousand iterations of not loading the module. % for e in `seq 1000` ; do perl -e1 ; done [download] Subtract the control group timing from the target group timing. What difference do you find? -- `[ e d @ h a l l e y . c c ]`	[reply] [d/l] [select]
Re: Timing a Module Load by eibwen (Friar) on Apr 30, 2005 at 01:54 UTC
Is there a way to force the module to "unload". I would presume that a `use` statement which falls out of scope would automatically "unload" the module: `#!/usr/bin/perl -w use strict; { use Date::Manip; } print Date::Manip::UnixDate(localtime);` [download] However the above code parses and runs without error, indicating that `use` isn't limited to a particular scope. Can someone explain why modules aren't (or at least do not appear to be) limited by scope?	[reply] [d/l] [select]
Re^2: Timing a Module Load by Tanktalus (Canon) on Apr 30, 2005 at 03:57 UTC
When you "use" a pragma, it gets scoped. But using a module is not scoped. Either way, this is all done during compile time, not run time (even though it may affect the runtime, such as "no warnings qw(uninitialized)"). So, you use Data::Manip. This is done during compilation. Then, at run time, those braces really have nothing in them (the use being completed at run time only).	[reply]