Do multiple calls to 'use X' abuse the compiler?

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

I'm working with CGI::Application

If I have a cgiapp MyModule using 10 plugins, and each in turn has a

package Plugin; 
use CGI::Application;
# or
use base 'CGI::Application';
# or 
require CGI::Application;
[download]

In addition of course to MyModule using cgiapp as base.. How much is this a slowdown? I do understand that making a require call, this is a runtime action that simply does a hash lookup- no problem.. but what about 'use' and 'use base' at compile time.. if there are multiple calls (for the same package, from different packages)?

If I have 10 calls to require code at runtime, I understand this is fine. If I have 10 calls to 'use' in various modules (same namespace definition).. how much of a hit is that for the interpreter?

Comment on Do multiple calls to 'use X' abuse the compiler? Download Code

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Re: Do multiple calls to 'use X' abuse the compiler? by friedo (Prior) on Feb 29, 2008 at 17:01 UTC
Like `require`, `use` uses the `%INC` hash to keep track of what modules have been loaded and compiled. So extra calls to `use` for the same module won't have any appreciative slowdown effect. Same with `use base` -- all it does is altar the calling module's `@ISA`, assuming the base class has already been loaded. Update `s/INC/ISA/;`# thanks almut	[reply] [d/l] [select]
Re: Do multiple calls to 'use X' abuse the compiler? by ikegami (Patriarch) on Feb 29, 2008 at 16:59 UTC
`use CGI::Application;` imports the symbols from CGI::Application (if any) everytime it's executed. `use CGI::Application qw( );`, on the other hand, is just a `require` that occurs at compile-time. `use base` doesn't seem to have much overhead. If I have 10 calls to 'use' in various modules (same namespace definition).. how much of a hit is that for the interpreter? Benchmark it. It's the only way to know.	[reply] [d/l] [select]
Re^2: Do multiple calls to 'use X' abuse the compiler? by diotalevi (Canon) on Mar 02, 2008 at 02:18 UTC
Quadruple downvotes for saying "Benchmark it" to this question. The real answer is that every use() past the first is only a hash lookup. There's no abuse of the compiler and you should feel very safe in using the same thing from many places. Caveats are of course, that `$class->VERSION eq '...' or die "..."` and `$class->import(...)` are also possibly implicated but neither of those are compiler tasks and you ought to already know if you care about the overhead of each and whether you're invoking them. I can't imagine someone using CGI::Application is going to care about the additional cost of one cheap method call. ⠤⠤ ⠙⠊⠕⠞⠁⠇⠑⠧⠊	[reply] [d/l] [select]
Re^3: Do multiple calls to 'use X' abuse the compiler? by ikegami (Patriarch) on Mar 02, 2008 at 03:17 UTC
The real answer is that every use() past the first is only a hash lookup I said `use Module qw( );` is just a hash lookup, but `use Module;` isn't. Are you contradicting that? you ought to already know if you care about the overhead of each How? I heard `import` can be fairly costly. But to know for sure, one would been benchmark it. And whether or not he ought to know is not important. He asked so I answered.	[reply] [d/l] [select]
Re^4: Do multiple calls to 'use X' abuse the compiler? by diotalevi (Canon) on May 01, 2008 at 15:42 UTC
Re: Do multiple calls to 'use X' abuse the compiler? by chromatic (Archbishop) on Feb 29, 2008 at 18:39 UTC
I'm working with CGI::Application The cost of network communication dwarfs any performs concerns from using modules, unless you have a pathological `@INC` setup.	[reply] [d/l]
Re: Do multiple calls to 'use X' abuse the compiler? by Herkum (Parson) on Feb 29, 2008 at 17:19 UTC
Have you considered making one module that loads all the modules that you need and then have the plugins inherit from that primary module? This will not improve performance but will improve code clarity and reduce the amount of duplicate work.	[reply]
Re: Do multiple calls to 'use X' abuse the compiler? by locked_user sundialsvc4 (Abbot) on Feb 29, 2008 at 17:13 UTC
I would frankly say that this sort of question is very un-likely to ever be “a legitimate cause of concern.” If you are presented with a known, measurable problem that is actually causing pain to the client's business, then you might consider doing something about it ... and that “something” will probably consist of buying newer, faster hardware. From a software point of view, the key elements should be simplicity and clarity of expression. This really is a case where, “unless it's really hollering, don't give it any medicine.”