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- Added new section ("Basic constructs") detailing stuff you don't have to look at more than once.
- Wrote section on declaring per-module globals git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@259907 c90b9560-bf6c-de11-be94-00142212c4b1
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Gwynne Raskind
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3 changed files with 195 additions and 2 deletions
154
internals2/structure/basics.xml
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154
internals2/structure/basics.xml
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<?xml version="1.0" encoding="ISO-8859-1" ?>
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<!-- $Revision: 1.1 $ -->
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<sect1 xml:id="internals2.structure.basics" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>Basic constructs</title>
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<simpara>
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C is a very low-level language by modern definitions. This means that it has
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no built-in support for many features that PHP takes for granted, such as
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reflection, dynamic module loading, bounds checking, threadsafe data
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management and various useful data structures including linked lists and
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hash tables. At the same time, C is a common denominator of language support
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and functionality. Given enough work, none of these concepts are impossible;
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the Zend Engine uses them all.
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</simpara>
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<simpara>
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A lot of effort has gone into making the Zend API both extensible and
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understandable, but C forces certain necessary declarations upon any
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extension that to an inexperienced eye seem redundant or plain unnecessary.
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All of those constructs, detailed in this section, are "write once and
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forget" in Zend Engine 2 and 3. Here are some excerpts from the pregenerated
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<filename>php_counter.h</filename> and <filename>counter.c</filename> files
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created by PHP 5.3's <command>ext_skel</command>, showing the pregenerated
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declarations:
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</simpara>
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<note>
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<simpara>
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The astute reader will notice that there are several delcarations in the
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real files that aren't shown here. Those declaractions are specific to
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various Zend subsystems and are discussed elsewhere as appropriate.
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</simpara>
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</note>
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<screen>
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<![CDATA[
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extern zend_module_entry counter_module_entry;
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#define phpext_counter_ptr &counter_module_entry
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#ifdef PHP_WIN32
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# define PHP_COUNTER_API __declspec(dllexport)
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#elif defined(__GNUC__) && __GNUC__ >= 4
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# define PHP_COUNTER_API __attribute__ ((visibility("default")))
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#else
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# define PHP_COUNTER_API
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#endif
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#ifdef ZTS
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#include "TSRM.h"
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#endif
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]]></screen>
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<screen>
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<![CDATA[
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include "php.h"
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#include "php_ini.h"
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#include "ext/standard/info.h"
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#include "php_counter.h"
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/* ... */
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#ifdef COMPILE_DL_COUNTER
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ZEND_GET_MODULE(counter)
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#endif
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]]></screen>
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<itemizedlist>
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<listitem>
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<simpara>
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The lines concerning <literal>counter_module_entry</literal> declare a
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global variable, and a macroed pointer to it, which contains the
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<literal>zend_module_entry</literal> for the extension. Despite the later
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discussion regarding the drawbacks of "true" globals, this usage is
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intentional; Zend takes precautions to avoid misusing this variable.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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<constant>PHP_COUNTER_API</constant> is declared for use by non-PHP
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functions the module intends to export for the use of other modules. The
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counter extension doesn't declare any of these, and in the final version of
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the header file, this macro has been removed. The
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<constant>PHPAPI</constant> macro is declared identically elsewhere and is
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used by the standard extension to make the <function>phpinfo</function>
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utility functions available to other extensions.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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The include of <filename>TSRM.h</filename> is skipped if PHP, or the
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extension, isn't being compiled with thread-safety, since in that case TSRM
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isn't used.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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A standard list of includes, especially the extension's own
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<filename>php_counter.h</filename>, is given. <filename>config.h</filename>
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gives the extension access to determinations made by
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<command>configure</command>. <filename>php.h</filename> is the gateway to
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the entire PHP and Zend APIs. <filename>php_ini.h</filename> adds the APIs
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for runtime configuration (INI) entries. Not all extensions will use this.
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Finally, <filename>ext/standard/info.h</filename> imports the
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aforementioned <function>phpinfo</function> utility API.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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<constant>COMPILE_DL_COUNTER</constant> will only be defined by
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<command>configure</command> if the counter extension is both enabled and
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wants to be built as a dynamically loadable module instead of being
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statically linked into PHP. <constant>ZEND_GET_MODULE</constant> defines a
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tiny function which Zend can use to get the extension's
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<literal>zend_module_entry</literal> at runtime.
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</simpara>
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<note>
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<simpara>
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The astute reader who has peeked into
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<filename>main/php_config.h</filename> after trying to build with the
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counter module enabled statically may have noticed that there is also a
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<constant>HAVE_COUNTER</constant> constant defined that the source code
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doesn't check for. There's a simple reason this check isn't done: It's
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unnecessary. If the extension isn't enabled, the source file will never be
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compiled.
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</simpara>
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</note>
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</listitem>
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</itemizedlist>
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</sect1>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"../../../manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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@ -1,5 +1,5 @@
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<?xml version="1.0" encoding="ISO-8859-1" ?>
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<!-- $Revision: 1.2 $ -->
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<!-- $Revision: 1.3 $ -->
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<sect1 xml:id="internals2.structure.globals" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>Extension globals</title>
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@ -69,6 +69,44 @@ PHP_FUNCTION(counter_get)
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</sect2>
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<sect2 xml:id="internals2.structure.globals.declaring">
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<title>Declaring module globals</title>
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<simpara>
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Whether a module uses only a single global or dozens, they must be defined
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in a structure, and that structure must be declared. There are some macros
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that assist with doing so in a way that avoids name conflicts between
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modules: <function>ZEND_BEGIN_MODULE_GLOBALS</function>,
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<function>ZEND_END_MODULE_GLOBALS</function>, and
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<function>ZEND_DECLARE_MODULE_GLOBALS</function>. All three take as a
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parameter the short name of the module, which in the case of the counter
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module is simply <literal>"counter"</literal>. Here is the global structure
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declaration from <filename>php_counter.h</filename>:
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</simpara>
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<example xml:id="internals2.structure.globals.declaring.doth">
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<title>The counter module's globals</title>
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<programlisting role="c">
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<![CDATA[
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ZEND_BEGIN_MODULE_GLOBALS(counter)
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long basic_counter_value;
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ZEND_END_MODULE_GLOBALS(counter)
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]]>
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</programlisting>
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</example>
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<simpara>
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And this is the declaration from <filename>counter.c</filename>:
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</simpara>
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<example xml:id="internals2.structure.globals.declaring.dotc">
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<title>The counter module's global structure declaration</title>
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<programlisting role="c">
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<![CDATA[
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ZEND_DECLARE_MODULE_GLOBALS(counter)
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]]>
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</programlisting>
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</example>
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</sect2>
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</sect1>
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<!-- Keep this comment at the end of the file
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@ -1,5 +1,5 @@
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<?xml version="1.0" encoding="ISO-8859-1" ?>
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<!-- $Revision: 1.3 $ -->
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<!-- $Revision: 1.4 $ -->
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<chapter xml:id="internals2.structure" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>Extension structure</title>
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</para>
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&internals2.structure.files;
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&internals2.structure.basics;
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&internals2.structure.modstruct;
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&internals2.structure.globals;
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&internals2.structure.lifecycle;
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