Trying to optimize de-referenced hash slice without scope variables...

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

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Re: Trying to optimize de-referenced hash slice without scope variables... by borisz (Canon) on Jun 15, 2004 at 17:15 UTC
write: `@{$_[3]}{'a','b','c','d'};` since perl reads it as `@{$_}[3]{...}` otherwise. Boris	[reply] [d/l] [select]
Re^2: Trying to optimize de-referenced hash slice without scope variables... by monsieur_champs (Curate) on Jun 15, 2004 at 17:26 UTC
Fellow boriz Thank you very much for your suggestion, but I'm not sure if `perl -MData::Dumper -e "print Dumper @{$_[3]}{'a','b','c','d'}, $_[3]; + " $VAR1 = undef; $VAR2 = undef; $VAR3 = undef; $VAR4 = undef; $VAR1 = undef; $VAR2 = undef; $VAR3 = undef; $VAR4 = undef; $VAR1 = undef; $VAR2 = undef; $VAR3 = undef; $VAR4 = undef; $VAR5 = '1';` [download] is the same thing as `perl -MData::Dumper -e 'print Dumper @$data{"a","b","c"}, $data' $VAR1 = undef; $VAR2 = undef; $VAR3 = undef; $VAR4 = { 'c' => undef, 'a' => undef, 'b' => undef };` [download] or I'm doing something really wrong here, or your data structure definition is not the same as my example. :-) Nice try, anyway. -- monsieur_champs	[reply] [d/l] [select]
Re^3: Trying to optimize de-referenced hash slice without scope variables... by Joost (Canon) on Jun 15, 2004 at 17:31 UTC
Your $data and @_ are empty here, so this won't work the same because of autovivication. The number of $VAR variables is different, because you have a .. d in the first and a .. c in the second expample. All of this should work if you actually fill $data and `$_[3]` with a hash reference that uses those keys. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l]
Re^4: Trying to optimize de-referenced hash slice without scope variables... by monsieur_champs (Curate) on Jun 15, 2004 at 17:56 UTC
Re^3: Trying to optimize de-referenced hash slice without scope variables... by borisz (Canon) on Jun 15, 2004 at 17:37 UTC
My perl works this way, Im sure there is another mistake. `#!/usr/bin/perl use Data::Dumper; %xx = ( a => 1, b => 2 ); sub inputBox{ @{$_[3]}{'a','b','c','d'}; } sub inputBox2{ my $data = $_[3]; @$data{'a','b','c','d'}; } print Dumper (inputBox( 1,2,3,\%xx)); print Dumper (inputBox2( 1,2,3,\%xx));` [download] Boris	[reply] [d/l]
Re: Trying to optimize de-referenced hash slice without scope variables... by Joost (Canon) on Jun 15, 2004 at 17:26 UTC
In addition to the post above, I would think that just copying one scalar is not that big a deal. Remember that you're copying only the hash reference, not the complete %data hash. In fact, if you use `$_[3]` a lot in the same function, it might even be slower than copying it to a lexical variable, because of the array indexing that needs to be done. (haven't benchmarked this at all, so I might be wrong) "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l]
Re^2: Trying to optimize de-referenced hash slice without scope variables... by meetraz (Hermit) on Jun 15, 2004 at 17:43 UTC
use strict; use Benchmark qw(:all); my %data = ( Lore =>'mipsumdo', ente =>'squemoll', lors =>'itametco', isod =>'ioetnonu', nsec =>'tetuerad', mmyf =>'acilisis', ipis =>'cingelit', augu =>'eliberoi', Sedr =>'honcusma', acul =>'isodioat', ssai =>'dmollisp', cons =>'ectetuer', hare =>'travelit', nisl =>'nislquis', null =>'amattise', feli =>'sDonecma', nimq =>'uisferme', gnar =>'isusulla', ntum =>'nequenul', mcor =>'peridele', lase =>'dduiDone', ifen =>'dutfeugi', cbla =>'nditmetu', atas =>'emAliqua', svit =>'aecondim', msed =>'magnaado', entu =>'mluctusa', lorn =>'onummysa', ntem =>'assaeuis', gitt =>'isNuncne', moda =>'nteaport', corc =>'iMorbima', amii =>'psumnonl', ttis =>'blandits', eoAl =>'iquamcon', emPh =>'asellusq', dime =>'ntumblan', uiso =>'rciInfer', ditf =>'elisPell', ment =>'umturpis', ); sub WithCopy { my $hashref = $_[0]; my @dummy = @{$hashref}{'Lore','lors','nsec'}; } sub WithoutCopy { my @dummy = @{$_[0]}{'Lore','lors','nsec'}; } cmpthese(5000000, { 'WithCopy' => 'WithCopy(\%data);', 'WithoutCopy' => 'WithoutCopy(\%data);', }); __END__ Rate WithCopy WithoutCopy WithCopy 548908/s -- -6% WithoutCopy 581801/s 6% -- [download]	[reply] [d/l]
Re^3: Trying to optimize de-referenced hash slice without scope variables... by Joost (Canon) on Jun 15, 2004 at 18:04 UTC
On my machine that gives (with 500000 iterations) `Rate WithCopy WithoutCopy WithCopy 450450/s -- -9% WithoutCopy 495050/s 10% --` [download] But if you access the hashref more than once in the functions - say about 10 times: use strict; use Benchmark qw(:all); my %data = ( Lore =>'mipsumdo', ente =>'squemoll', lors =>'itametco', isod =>'ioetnonu', nsec =>'tetuerad', mmyf =>'acilisis', ipis =>'cingelit', augu =>'eliberoi', Sedr =>'honcusma', acul =>'isodioat', ssai =>'dmollisp', cons =>'ectetuer', hare =>'travelit', nisl =>'nislquis', null =>'amattise', feli =>'sDonecma', nimq =>'uisferme', gnar =>'isusulla', ntum =>'nequenul', mcor =>'peridele', lase =>'dduiDone', ifen =>'dutfeugi', cbla =>'nditmetu', atas =>'emAliqua', svit =>'aecondim', msed =>'magnaado', entu =>'mluctusa', lorn =>'onummysa', ntem =>'assaeuis', gitt =>'isNuncne', moda =>'nteaport', corc =>'iMorbima', amii =>'psumnonl', ttis =>'blandits', eoAl =>'iquamcon', emPh =>'asellusq', dime =>'ntumblan', uiso =>'rciInfer', ditf =>'elisPell', ment =>'umturpis', ); sub WithCopy { my $hashref = $_[0]; my @dummy1 = @{$hashref}{'Lore','lors','nsec'}; my @dummy2 = @{$hashref}{'Lore','lors','nsec'}; my @dummy3 = @{$hashref}{'Lore','lors','nsec'}; my @dummy4 = @{$hashref}{'Lore','lors','nsec'}; my @dummy5 = @{$hashref}{'Lore','lors','nsec'}; my @dummy6 = @{$hashref}{'Lore','lors','nsec'}; my @dummy7 = @{$hashref}{'Lore','lors','nsec'}; my @dummy8 = @{$hashref}{'Lore','lors','nsec'}; my @dummy9 = @{$hashref}{'Lore','lors','nsec'}; my @dummy0 = @{$hashref}{'Lore','lors','nsec'}; } sub WithoutCopy { my @dummy1 = @{$_[0]}{'Lore','lors','nsec'}; my @dummy2 = @{$_[0]}{'Lore','lors','nsec'}; my @dummy3 = @{$_[0]}{'Lore','lors','nsec'}; my @dummy4 = @{$_[0]}{'Lore','lors','nsec'}; my @dummy5 = @{$_[0]}{'Lore','lors','nsec'}; my @dummy6 = @{$_[0]}{'Lore','lors','nsec'}; my @dummy7 = @{$_[0]}{'Lore','lors','nsec'}; my @dummy8 = @{$_[0]}{'Lore','lors','nsec'}; my @dummy9 = @{$_[0]}{'Lore','lors','nsec'}; my @dummy0 = @{$_[0]}{'Lore','lors','nsec'}; } cmpthese(500000, { 'WithCopy' => 'WithCopy(\%data);', 'WithoutCopy' => 'WithoutCopy(\%data);', }); __END__ Rate WithoutCopy WithCopy WithoutCopy 82645/s -- -8% WithCopy 89445/s 8% -- [download] Which seems to show that the performance increase is less when you index the @_ array a lot. Of course it doesn't show that - it could also mean that the time needed to copy the keys of the hash reference 10 times overshadows the time needed to index the array and/or copy the hash reference, thereby decreasing the influence of doing either. Benchmarking is hard. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l] [select]
Re^2: Trying to optimize de-referenced hash slice without scope variables... by monsieur_champs (Curate) on Jun 15, 2004 at 17:36 UTC
Interesting point. I use `$data` 8 times. Half as a boolean test (no de-reference) and half as a hash reference (to recover one or more values). I guess (and maybe I'm wrong about this) that it doesn't worth the benchmark... Here is the complete function code: sub inputBox{ # Don't uncomment, use @_ instead # my $action_url = shift; # $_[0] # my $msgid = shift; # $_[1] # my $action = shift; # $_[2] my $data = $_[3]; # oh, I needed this one, I wasn't able to use a ha +sh-slice from a hash-reference in one shot. <readmore> return qq{<form action="$_[0]" method="post">\n}. ($_[1]? qq{ <input type="hidden" name="message_id" value="$_[1]" />\n +}:''). qq{ <input type="hidden" name="action" value="$_[2]" /> <input type="hidden" name="commit" value="1" /> <table align="center" border="1" cellpadding="5" cellspacing="0"> <tr valign="middle" align="center" bgcolor="$color{TABLE_HEAD}"> <td colspan="2"> } .($_[2] eq 'edit'? "Edit Message #$_[1]" : 'Compose New Message' ). qq{ </td> </tr> <tr valign="middle" align="left" > <td> Author: </td> <td> }.( $_[2] eq 'edit'? q{ <input type="text" name="author" size=" +40" }. ( $data? qq{value="$data->{author}"} : &TWiki::Func::getWikiUserName +() ) . qq{ />} : &TWiki::Func::getWikiUserName() ) . q{ </td> </tr> <tr valign="middle" align="left"> <td>Due Date: </td> <td>} . &gen_date_selector( 'due', ( $data? @$data{'day','month' +,'year','hour','minute'} : (localtime)[5]+1900, (localtime)[4]+1, (lo +caltime)[3], 23, 59 ) ) . qq{ </td> </tr> <tr valign="middle" align="left"> <td>Message: </td> <td> <textarea rows="5" name="msg" cols="50">}.($data? $data->{msg} + : '' ).qq{</textarea> </td> </tr> <tr valign="middle" align="left"> <td> <input type="checkbox" name="dropped" value="Y" }.($data && $d +ata->{dropped} eq 'Y'? 'CHECKED':'' ).q{> Dropped. </td> <td align="right"> <input type="submit" name="change" value="Change Message"> </td> </tr> </table> </form> }; } [download] -- monsieur_champs	[reply] [d/l] [select]
Re: Trying to optimize de-referenced hash slice without scope variables... by revdiablo (Prior) on Jun 15, 2004 at 20:55 UTC
Like Joost, I am a bit skeptical about the need for this "optimization." If the performance of your application hinges on the speed of accessing subroutine arguments, then I think Perl might not be the right choice. Have you done any profiling to see if this is the case, or are you simply stabbing in the dark? I suggest you do the former, rather than the latter, when it comes to expending time and effort to optimize your code.	[reply]
Re^2: Trying to optimize de-referenced hash slice without scope variables... by monsieur_champs (Curate) on Jun 17, 2004 at 19:05 UTC
Dear fellow revdiablo In fact, you're right about this: I'm stabbling in the dark. But I'm not alone: this is a standard (?), required (?) optimization for TWiki Plugins like this and this. Maybe I shall alert the main project developers about this "optimization". Thank you for the insight. -- monsieur_champs	[reply]


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