Perl XS








By
John Scoles
The Pythian Group

Black Art?

Your Handy Friend?

Misunderstood Brain Sucking Zombie from Hell?

My XS Story!

The funny thing is the Chinese use the same word for catastrophe as they use for opportunity

In The Beginning

1800+ line Makefile.PL

1000+ lines of XS

800+ lines of Perl

5300+ lines of pure 'C'

My 'C' Background

I can Spell 'c' correctly 87.654% of the time 18 times out of 20.

My XS Background at the time

Well I know of them!

Bart Simpson said it best when asked if he knew long division or multiplication

A Complete

FNG

NEWBIE

RETARD

Whatever

So as Johny Cash would say

I Fell into a Burning Ring of Fire

But?

I Survived

So I went Looking for Answers

What there was, wasn't much

However I did learn 10 different ways to say Hello World

What there was, didn't help much

What there was, and still is, was dated

What there was, usually ended with

Read Perl Guts

Why Is This?

This sums up the nature of XS programming

There are 10 ways to do the same thing!

None of them are 100% wrong

None of them are 100% right

Lets go back to the start

We all know that Perl is written in 'C'

Big Deal most languages are written in 'C'

Most 'C' stuff will be familiar to a 'Perl' programmer

Perl is very cozy with 'C'

A Few Things to know about 'C'

Can't do shit without a 'lib'

I stand on the shoulders of giants!

NANOS GIGANTIUM HUMERIS INSIDENTES

Compiled

Strictly Typed

No Memory Management

Function params are by value only

A Few Things to say about Perl

Interpreted

Loosely Typed

Managed Memory

Function params are by 'Ref' only

Perl is Just 'C' without types

Stop, Look, Listen!

What is it we are trying to do?

Credits to Navy Beans it is already on CPAN

Access an API

Improve performance of Perl

Link into a static Lib

How about DBI and DBD::Oracle

Access an API (OCI) for DBD::Oracle for sure

'C' for DBI to make it speedy for one

26 lines of code to do a fetch

Way back in the dark days there was a

direct link to OCI but it has died

Now with Dynamic Linking no need for static perl

Part the Second

'C' and 'Perl' in Detail

Libs

Memory

Data

Data in 'C'

Those that go down to the 'C' in Structs

Defined Types (U32, oratext)

Arrays of types (int[], char[])

Primitive types (int char etc)

Structs (named collection of types)

Struc

struc say_hi_in {

char* english;

char* french;

int* binary;

}

Must be declared at compile time

It takes up a block of memory

So an unitialized struc takes up the same space as an initialized one

NOT A HASH!!!

Memory in 'C'

If it is the Captain's mess? Let him clean it up!

We have to do it.

malloc

free

'C' is dumb must know what type it is pointing to

Pointers and such *,& and **

* a pointer to something

& the value the Pointer is pointing to

** a pointer to a pointer

char * name;

Libs in 'C'

Points to an Object file .obj, .o, .so, .dll or even an exe

That can be shared

A .h or 'header file' is not necessarily code it is just a promise of code needed at compile time.

Usually just a prototype of the function or struct.

Data in Perl

Metadata

struc sv {

void* sv_any;

U32 sv_refcnt;

U32 sv_flags;

}

or Perl knows about itself.

This is 'undef' in Perl!!!!

Our first look of the Guts of Perl

struc sv {

void* sv_any;

U32 sv_refcnt;

U32 sv_flags;

}

sv_any

Is a pointer to any other of the 'Perl' strucs

sv_refcnt

A count of the number of times this struc has been referenced

sv_flags

Holds the metadata of a 'Perl' variable.

It utilizes bit logic (bitmask)

Memory in 'PERL' II

When an object is referenced it is

Incremented by one

sv_refcnt

When an object goes out of scope it is

decremented by one

(most times)

(most times)

When it reaches 0 it is garbage collected by Perl

And the memory is freed

Libs in 'Perl'

A .pm file is code that can be shared.

How 'C' and 'Perl' Work

'C'

Source ->

Compiler ->

Machine Code

'Perl'

Source ->

Interpreter ->

Syntax Tree ->

Interpreter ->

Machine Code

Syntax Tree->

{opcodes} =

struc{}

struc{} ->xsub pointer

If this just happens to point to a 'C' function

It will run

Finally down to Brass Tacks

Thank you good by:)

X

External

S

Subroutines

eXternal Subroutines or

XS

Now Some Code

Far be it form me to break with tradition

#Include

void print_hi_larry(void) {

printf(Hello Larry!);

}

Int main(int argc,char *argv[]){

print_hi_larry();

exit(0);

}

So to the left is hello Larry in 'C'

How about a Perl File for it

lib/Hi_larry.pm

Hi_larry.xs

Makefile.PL

README

t/test.t

Changes

MANIFEST

Like most things in perl we have a Helper called

h2sx

In our case we do

H2sx -A -n Hi_larry

And it generates all of our perl files thank you very much

So all we do is open the .xs file and add in our includes and function but not the main

#include EXTERN.h

#include perl.h

#include XSUB.h

#Include

void print_hi_larry(void) {

printf(Hello Larry!);

}

MODULE = Hi_larryPACKAGE = Hi_larry

void

print_hi_larry();

Now edit the Hi_larry.pm

package Hi_larry;

use 5.008009;

use strict;

use warnings;

Use base (qw(Exporter DynaLoader))

@EXPORT_OK

our @EXPORT = qw( print_hi_larry());

our $VERSION = '0.01';

1;

__END__

How about the test file as well

use Test::More tests => 2;

BEGIN { use_ok('Hi_larry') };

ok(Hi_larry::print_hi_larry,"Hello Larry")

Now everyones fab

Perl Makefile.PL

c:\>nmake test

And at the very end

t/Hi_larry....ok

Files=1, Tests=2, 0 wallclock secs ( 0.00 cusr + 0.00 csys = 0.00 CPU)

All tests successful