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Re: Thread::Use - use a module inside a thread only

Rafael Garcia-Suarez
July 30, 2002 01:10
Re: Thread::Use - use a module inside a thread only
Message ID:
Elizabeth Mattijsen wrote:
>> ... (for modules that don't
>> export lots of symbols into the caller's namespace).
> If you do some memory benchmarks, you'd be surprised to see how much 
> memory is used by exported symbols.  And all of it copied to any thread 
> that is created.  Using significant amounts of CPU and memory.  Which 
> becomes important in many, long running thread situations as mod_perl 
> with the worker MPM of Apache.

As a mod_perl programmer for a living, I did some benchmarks of these.
That's right but I don't really know why it's so memory-consuming.

>> Does the module gets unloaded in some way when the thread
>> ends ?
> When a thread starts, a clone of the _entire_ interpreter is made, 
> including any modules that are loaded.  However, any modules that you 
> load when in the cloned interpreter (thread), are local to that thread 
> only.  The C<useit> merely ensures that the effective C<use> is done at 
> execution time, rather than at compile time.  And if you place a C<useit 
> Module> inside a thread, then the Module will be C<require>d and its 
> import executed inside the thread only.  And when the thread ends, 
> everything that was that thread, including the newly loaded module, will 
> be gone again.

Thanks for the explanation (and to Arthur too)

>> (BTW your module doesn't provide an interface equivalent to
>>         use Foo ();
>>         no Bar ();
>> --that doesn't call import().)
> Indeed.  Is there a way to find out whether a subroutine is called 
> without any parameters or with an empty list?  Cause when I can do that, 
> I can simulate this behaviour as well...

Well, "useit Foo" should call import() just like "use Foo" does -- without
any arguments. The parser does some magic to distinguish between
"use Foo" and "use Foo ()".
I think you may provide a useit_noimport() subroutine.
But in this case a straight require() is probably simpler. Perl Programming lists via nntp and http.
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