Extension Writing Part I: Introduction to PHP and Zend

March 1, 2005

Tutorials

Introduction
What’s an Extension?
Lifecycles
Memory Allocation
Setting Up a Build Environment
Hello World
Building Your Extension
INI Settings
Global Values
INI Settings as Global Values
Sanity Check
What’s Next?


Introduction

If you’re reading this tutorial, you probably have some interest in writing an
extension for the PHP language. If not… well perhaps when we’re done you’ll have
discovered an interest you didn’t know existed!

This tutorial assumes basic familiarity with both the PHP language and the
language the PHP interpreter is written in: C.

Let’s start by identifying why you might want to write a PHP extension.

  1. There is some library or OS specific call which cannot be made from PHP
    directly because of the degree of abstraction inherent in the language.
  2. You want to make PHP itself behave in some unusual way.
  3. You’ve already got some PHP code written, but you know it could be faster,
    smaller, and consume less memory while running.
  4. You have a particularly clever bit of code you want to sell, and it’s
    important that the party you sell it to be able to execute it, but not view the
    source.

These are all perfectly valid reasons, but in order to create an extension, you
need to understand what an extension is first.


What’s an Extension?

If you’ve used PHP, you’ve used extensions. With only a few exceptions, every
userspace function in the PHP language is grouped into one extension or another. A
great many of these functions are part of the standard extension – over 400
of them in total. The PHP source bundle comes with around 86 extensions, having an
average of about 30 functions each. Do the math, that’s about 2500 functions. As if
this weren’t enough, the PECL
repository
offers over 100 additional extensions, and even more can be found
elsewhere on the Internet.

“With all these functions living in extensions, what’s left?” I hear you ask.
“What are they an extension to? What is the ‘core’ of PHP?”

PHP’s core is made up of two separate pieces. At the lowest levels you find
the Zend Engine (ZE). ZE handles parsing a human-readable script into
machine-readable tokens, and then executing those tokens within a process space. ZE
also handles memory management, variable scope, and dispatching function calls. The
other half of this split personality is the PHP core. PHP handles
communication with, and bindings to, the SAPI layer (Server Application
Programming Interface, also commonly used to refer to the host environment – Apache,
IIS, CLI, CGI, etc). It also provides a unified control layer for
safe_mode and open_basedir checks, as well as the streams
layer which associates file and network I/O with userspace functions like
fopen(), fread(), and fwrite().


Lifecycles

When a given SAPI starts up, for example in response to
/usr/local/apache/bin/apachectl start, PHP begins by initializing its
core subsystems. Towards the end of this startup routine, it loads the code for each
extension and calls their Module Initialization routine (MINIT).
This gives each extension a chance to initialize internal variables, allocate
resources, register resource handlers, and register its functions with ZE, so that
if a script calls one of those functions, ZE knows which code to execute.

Next, PHP waits for the SAPI layer to request a page to be processed. In the case
of the CGI or CLI SAPIs, this happens immediately and only once. In the case of
Apache, IIS, or other fully-fledged web server SAPIs, it occurs as pages are
requested by remote users and repeats any number of times, possibly concurrently. No
matter how the request comes in, PHP begins by asking ZE to setup an environment for
the script to run in, then calls each extension’s Request Initialization
(RINIT) function. RINIT gives the extension a chance to
set up specific environment variables, allocate request specific resources, or
perform other tasks such as auditing. A prime example of the RINIT
function in action is in the sessions extension where, if the
session.auto_start option is enabled, RINIT will
automatically trigger the userspace session_start() function and
pre-populate the $_SESSION variable.

Once the request is initialized, ZE takes over by translating the PHP script into
tokens, and finally to opcodes which it can step through and execute.
Should one of these opcodes require an extension function to be called, ZE will
bundle up the arguments for that function, and temporarily give over control until
it completes.

After a script has finished executing, PHP calls the Request Shutdown
(RSHUTDOWN) function of each extension to perform any last minute
cleanup (such as saving session variables to disk). Next, ZE performs a cleanup
process (known as garbage collection) which effectively performs an
unset() on every variable used during the previous request.

Once completed, PHP waits for the SAPI to either request another document or
signal a shutdown. In the case of the CGI and CLI SAPIs, there is no “next
request”, so the SAPI initiates a shutdown immediately. During shutdown, PHP again
cycles through each extension calling their Module Shutdown
(MSHUTDOWN) functions, and finally shuts down its own core
subsystems.

This process may sound daunting at first, but once you dive into a working
extension it should all gradually start to make sense.


Memory Allocation

In order to avoid losing memory to poorly written extensions, ZE performs its own
internal memory management using an additional flag that indicates persistence. A
persistent allocation is a memory allocation that is meant to last for longer
than a single page request. A non-persistent allocation, by contrast, is
freed at the end of the request in which it was allocated, whether or not the free
function is called. Userspace variables, for example, are allocated non-persistently
because at the end of a request they’re no longer useful.

While an extension may, in theory, rely on ZE to free non-persistent memory
automatically at the end of each page request, this is not recommended. Memory
allocations will remain unreclaimed for longer periods of time, resources associated
with that memory will be less likely to be shutdown properly, and it’s just poor
practice to make a mess without cleaning it up. As you’ll discover later on, it’s
actually quite easy to ensure that all allocated data is cleaned up properly

Let’s briefly compare traditional memory allocation functions (which should only
be used when working with external libraries) with persistent and non-persistent
memory allocation within PHP/ZE.

Traditional Non-Persistent Persistent
malloc(count)
calloc(count, num)
emalloc(count)
ecalloc(count, num)
pemalloc(count, 1)*
pecalloc(count, num, 1)
strdup(str)
strndup(str, len)
estrdup(str)
estrndup(str, len)
pestrdup(str, 1)
pemalloc() & memcpy()
free(ptr) efree(ptr) pefree(ptr, 1)
realloc(ptr, newsize) erealloc(ptr, newsize) perealloc(ptr, newsize, 1)
malloc(count * num + extr)** safe_emalloc(count, num, extr) safe_pemalloc(count, num, extr)
* The pemalloc() family include a ‘persistent’ flag which allows
them to behave like their non-persistent counterparts.
   For example:
emalloc(1234) is the same as pemalloc(1234,
0)

** safe_emalloc() and (in PHP 5) safe_pemalloc()
perform an additional check to avoid integer overflows


Setting Up a Build Environment

Now that you’ve covered some of the theory behind the workings of PHP and the
Zend Engine, I’ll bet you’d like to dive in and start building something. Before you
can do that however, you’ll need to collect some necessary build tools and set up an
environment suited to your purposes.

First you’ll need PHP itself, and the set of build tools required by PHP. If
you’re unfamiliar with building PHP from source, I suggest you take a look at
http://www.php.net/install.unix.
(Developing PHP extensions for Windows
will be covered in a later article). While it might be tempting to use a binary
package of PHP from your distribution of choice, these versions tend to leave out
two important ./configure options that are very handy during the development
process. The first is --enable-debug. This option will compile PHP with
additional symbol information loaded into the executable so that, if a segfault
occurs, you’ll be able to collect a core dump from it and use gdb to track down
where the segfault occurred and why. The other option depends on which version of
PHP you’ll be developing against. In PHP 4.3 this option is named
--enable-experimental-zts, in PHP 5 and later it’s
--enable-maintainer-zts. This option will make PHP think its operating
in a multi-threaded environment and will allow you to catch common programming
mistakes which, while harmless in a non-threaded environment, will cause your
extension to be unusable in a multi-threaded one. Once you’ve compiled PHP using
these extra options and installed it on your development server (or workstation),
you can begin to put together your first extension.


Hello World

What programming introduction would be complete without the requisite Hello
World
application? In this case, you’ll be making an extension that exports a
single function returning a string containing the words: “Hello World”. In PHP code
you’d probably do it something like this:


<?php

function "color: #0000BB">hello_world() {
    return
'Hello
World'
;
}

?>

Now you’re going to turn that into a PHP extension. First let’s create a
directory called hello under the ext/ directory in your PHP source
tree and chdir into that folder. This directory can actually live
anywhere inside or outside the PHP tree, but I’d like you to place it here to
demonstrate an unrelated concept in a later article. Here you need to create three
files: a source file containing your hello_world function, a
header file containing references used by PHP to load your extension, and a
configuration file used by phpize to prepare your extension for
compiling.

config.m4

PHP_ARG_ENABLE(hello, whether to enable Hello
World support,
[ --enable-hello   Enable Hello World support])

if test "$PHP_HELLO" = "yes"; then
  AC_DEFINE(HAVE_HELLO, 1, [Whether you have Hello World])
  PHP_NEW_EXTENSION(hello, hello.c, $ext_shared)
fi

php_hello.h


#ifndef PHP_HELLO_H
#define PHP_HELLO_H 1

#define PHP_HELLO_WORLD_VERSION "1.0"
#define PHP_HELLO_WORLD_EXTNAME "hello"

PHP_FUNCTION(hello_world);

extern zend_module_entry hello_module_entry;
#define phpext_hello_ptr &hello_module_entry

#endif

hello.c


#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "php.h"
#include "php_hello.h"

static function_entry hello_functions[] = {
    PHP_FE(hello_world, NULL)
    {NULL, NULL, NULL}
};

zend_module_entry hello_module_entry = {
#if ZEND_MODULE_API_NO >= 20010901
    STANDARD_MODULE_HEADER,
#endif
    PHP_HELLO_WORLD_EXTNAME,
    hello_functions,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
#if ZEND_MODULE_API_NO >= 20010901
    PHP_HELLO_WORLD_VERSION,
#endif
    STANDARD_MODULE_PROPERTIES
};

#ifdef COMPILE_DL_HELLO
ZEND_GET_MODULE(hello)
#endif

PHP_FUNCTION(hello_world)
{
    RETURN_STRING("Hello World", 1);
}

Most of the code you can see in the example extension above is just glue -
protocol language to introduce the extension to PHP and establish a dialogue for
them to communicate. Only the last four lines are what you might call “real code”
which performs a task on a level that the userspace script might interact with.
Indeed the code at this level looks very similar to the PHP code we looked at
earlier and can be easily parsed on sight:

  1. Declare a function named hello_world
  2. Have that function return a string: “Hello World”
  3. ….um…. 1? What’s that 1 all about?

Recall that ZE includes a sophisticated memory management layer which ensures
that allocated resources are freed when the script exits. In the land of memory
management however, it’s a big no-no to free the same block of memory twice. This
action, called double freeing, is a common cause of segmentation faults, as
it involves the calling program trying to access a block of memory which it no
longer owns. Similarly, you don’t want to allow ZE to free a static string buffer
(such as “Hello World” in our example extension) as it lives in program space and
thus isn’t a data block to be owned by any one process. RETURN_STRING()
could assume that any strings passed to it need to be copied so that they can be
safely freed later; but since it’s not uncommon for an internal function to allocate
memory for a string, fill it dynamically, then return it,
RETURN_STRING() allows us to specify whether it’s necessary to make a
copy of the string value or not. To further illustrate this concept, the following
code snippet is identical to its counterpart above:


PHP_FUNCTION(hello_world)
{
    char *str;

    str = estrdup("Hello World");
    RETURN_STRING(str, 0);
}

In this version, you manually allocated the memory for the “Hello World” string
that will ultimately be passed back to the calling script, then “gave” that memory
to RETURN_STRING(), using a value of 0 in the second
parameter to indicate that it didn’t need to make its own copy, it could have
ours.


Building Your Extension

The final step in this exercise will be building your extension as a dynamically
loadable module. If you’ve copied the example above correctly, this should only take
three commands run from ext/hello/:

$ phpize
$ ./configure --enable-hello
$ make

After running each of these commands, you should have a hello.so
file in ext/hello/modules/ . Now, as with any other PHP extension, you can
just copy this to your extensions directory (/usr/local/lib/php/extensions/
is the default, check your php.ini to be sure) and add the line
extension=hello.so to your php.ini to trigger it to load on
startup. For CGI/CLI SAPIs, this simply means the next time PHP is run; for web
server SAPIs like Apache, this will be the next time the web server is restarted.
Let’s give it a try from the command line for now:

$ php -r 'echo hello_world();'

If everything’s gone as it should, you should see Hello
World
output by this script, since the hello_world() function in
your loaded extension returns that string, and the echo command
displays whatever is passed to it (the result of the function in this case).

Other scalars may be returned in a similar fashion, using
RETURN_LONG() for integer values, RETURN_DOUBLE() for
floating point values, RETURN_BOOL() for true/false values, and
RETURN_NULL() for, you guessed it, NULL values. Let’s take
a look at each of those in action by adding PHP_FE() lines to the
function_entry struct in hello.c and adding some
PHP_FUNCTION()s to the end of the file.


static function_entry hello_functions[] =
{
    PHP_FE(hello_world, NULL)
    PHP_FE(hello_long, NULL)
    PHP_FE(hello_double, NULL)
    PHP_FE(hello_bool, NULL)
    PHP_FE(hello_null, NULL)
    {NULL, NULL, NULL}
};

PHP_FUNCTION(hello_long)
{
    RETURN_LONG(42);
}

PHP_FUNCTION(hello_double)
{
    RETURN_DOUBLE(3.1415926535);
}

PHP_FUNCTION(hello_bool)
{
    RETURN_BOOL(1);
}

PHP_FUNCTION(hello_null)
{
    RETURN_NULL();
}

You’ll also need to add prototypes for these functions alongside the prototype
for hello_world() in the header file, php_hello.h, so that the
build process takes place properly:


PHP_FUNCTION(hello_world);
PHP_FUNCTION(hello_long);
PHP_FUNCTION(hello_double);
PHP_FUNCTION(hello_bool);
PHP_FUNCTION(hello_null);

Since you made no changes to the config.m4 file, it’s technically safe to
skip the phpize and ./configure steps this time and jump straight to
make. However, at this stage of the game I’m going to ask you to go through
all three build steps again just to make sure you have a nice build. In additional,
you should call make clean all rather than simply make in the last
step, to ensure that all source files are rebuilt. Again, this isn’t necessary
because of the types of changes you’ve made so far, but better safe than confused.
Once the module is built, you’ll again copy it to your extension directory,
replacing the old version.

At this point you could call the PHP interpreter again, passing it simple scripts
to test out the functions you just added. In fact, why don’t you do that now? I’ll
wait here…

Done? Good. If you used var_dump() rather than echo to
view the output of each function then you probably noticed that
hello_bool() returned true. That’s what the 1 value in
RETURN_BOOL() represents. Just like in PHP scripts, an integer value of
0 equates to FALSE, while any other integer value equates
to TRUE. Extension authors often use 1 as a matter of
convention, and you’re encouraged to do the same, but don’t feel locked into it. For
added readability, the RETURN_TRUE and RETURN_FALSE macros
are also available; here’s hello_bool() again, this time using
RETURN_TRUE:


PHP_FUNCTION(hello_bool)
{
    RETURN_TRUE;
}

Note that no parentheses were used here. RETURN_TRUE and
RETURN_FALSE are aberrations from the rest of the
RETURN_*() macros in that way, so be sure not to get caught by this
one!

You probably noticed in each of the code samples above that we didn’t pass a zero
or one value indicating whether or not the value should be copied. This is because
no additional memory (beyond the variable container itself – we’ll delve into this
deeper in Part 2) needs to be allocated – or freed
- for simple small scalars such as these.

There are an additional three return types: RESOURCE (as returned by
mysql_connect(), fsockopen(), and
ftp_connect() to name but a few), ARRAY (also known as a
HASH), and OBJECT (as returned by the keyword
new). We’ll look at these in Part II of this series, when we cover
variables in depth.


INI Settings

The Zend Engine provides two approaches for managing INI values.
We’ll take a look at the simpler approach for now, and explore the fuller, but more
complex, approach later on, when you’ve had a chance to work with global values.

Let’s say you want to define a php.ini value for your extension,
hello.greeting, which will hold the value used to say hello in your
hello_world() function. You’ll need to make a few additions to
hello.c and php_hello.h while making a few key changes to the
hello_module_entry structure. Start off by adding the following
prototypes near the userspace function prototypes in php_hello.h:


PHP_MINIT_FUNCTION(hello);
PHP_MSHUTDOWN_FUNCTION(hello);

PHP_FUNCTION(hello_world);
PHP_FUNCTION(hello_long);
PHP_FUNCTION(hello_double);
PHP_FUNCTION(hello_bool);
PHP_FUNCTION(hello_null);

Now head over to hello.c and take out the current version of
hello_module_entry, replacing it with the following listing:


zend_module_entry hello_module_entry = {
#if ZEND_MODULE_API_NO >= 20010901
    STANDARD_MODULE_HEADER,
#endif
    PHP_HELLO_WORLD_EXTNAME,
    hello_functions,
    PHP_MINIT(hello),
    PHP_MSHUTDOWN(hello),
    NULL,
    NULL,
    NULL,
#if ZEND_MODULE_API_NO >= 20010901
    PHP_HELLO_WORLD_VERSION,
#endif
    STANDARD_MODULE_PROPERTIES
};

PHP_INI_BEGIN()
PHP_INI_ENTRY("hello.greeting", "Hello World", PHP_INI_ALL, NULL)
PHP_INI_END()

PHP_MINIT_FUNCTION(hello)
{
    REGISTER_INI_ENTRIES();

    return SUCCESS;
}

PHP_MSHUTDOWN_FUNCTION(hello)
{
    UNREGISTER_INI_ENTRIES();

    return SUCCESS;
}

Now, you just need to add an #include to the rest of the
#includes at the top of hello.c to get the right headers for
INI file support:


#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "php.h"
#include "php_ini.h"
#include "php_hello.h"

Finally, you can modify your hello_world function to use the
INI value:


PHP_FUNCTION(hello_world)
{
    RETURN_STRING(INI_STR("hello.greeting"), 1);
}

Notice that you’re copying the value returned by INI_STR(). This is
because, as far as the PHP variable stack is concerned, this is a static string. In
fact, if you tried to modify the string returned by this value, the PHP execution
environment would become unstable and might even crash.

The first set of changes in this section introduced two methods you’ll want to
become very familiar with: MINIT, and MSHUTDOWN. As
mentioned earlier, these methods are called during the
initial startup of the SAPI layer and during its final shutdown, respectively. They
are not called between or during requests. In this example you’ve used them to
register the php.ini entries defined in your extension. Later in this series,
you’ll find how to use the MINIT and MSHUTDOWN functions
to register resource, object, and stream handlers as well.

In your hello_world() function you used INI_STR() to
retrieve the current value of the hello.greeting entry as a string. A
host of other functions exist for retrieving values as longs, doubles, and Booleans
as shown in the following table, along with a complementary ORIG
counterpart which provides the value of the referenced INI setting as
it was set in php.ini (before being altered by .htaccess or
ini_set() statements).

Current Value Original Value Type
INI_STR(name) INI_ORIG_STR(name) char * (NULL terminated)
INI_INT(name) INI_ORIG_INT(name) signed long
INI_FLT(name) INI_ORIG_FLT(name) signed double
INI_BOOL(name) INI_ORIG_BOOL(name) zend_bool

The first parameter passed to PHP_INI_ENTRY() is a string containing
the name of the entry to be used in php.ini. In order to avoid
namespace collisions, you should use the same conventions as with your functions;
that is, prefix all values with the name of your extension, as you did with
hello.greeting. As a matter of convention, a period is used to separate
the extension name from the more descriptive part of the ini setting name.

The second parameter is the initial value, and is always given as a
char* string regardless of whether it is a numerical value or not. This
is due primarily to the fact that values in an .ini file are inherently
textual – being a text file and all. Your use of INI_INT(),
INI_FLT(), or INI_BOOL() later in your script will handle
type conversions.

The third value you pass is an access mode modifier. This is a bitmask
field which determines when and where this INI value should be
modifiable. For some, such as register_globals, it simply doesn’t make
sense to allow the value to be changed from within a script using
ini_set() because the setting only has meaning during request startup -
before the script has had a chance to run. Others, such as
allow_url_fopen, are administrative settings which you don’t want to
allow users on a shared hosting environment to change, either via
ini_set() or through the use of .htaccess directives. A typical
value for this parameter might be PHP_INI_ALL, indicating that the
value may be changed anywhere. Then there’s
PHP_INI_SYSTEM|PHP_INI_PERDIR, indicating that the setting may be
changed in the php.ini file, or via an Apache directive in a .htaccess
file, but not through the use of ini_set(). Or there’s
PHP_INI_SYSTEM, meaning that the value may only be changed in the
php.ini file and nowhere else.

We’ll skip the fourth parameter for now and only mention that it allows the use
of a callback method to be triggered whenever the ini setting is changed, such as
with ini_set(). This allows an extension to perform more precise
control over when a setting may be changed, or trigger a related action dependant on
the new setting.


Global Values

Frequently, an extension will need to track a value through a particular request,
keeping that value independent from other requests which may be occurring at the
same time. In a non-threaded SAPI that might be simple: just declare a global
variable in the source file and access it as needed. The trouble is, since PHP is
designed to run on threaded web servers (such as Apache 2 and IIS), it needs to keep
the global values used by one thread separate from the global values used by
another. PHP greatly simplifies this by using the TSRM (Thread Safe Resource
Management) abstraction layer, sometimes referred to as ZTS (Zend Thread Safety). In
fact, by this point you’ve already used parts of TSRM and didn’t even know it.
(Don’t search too hard just yet; as this series progresses you’ll come to discover
it’s hiding everywhere.)

The first part of creating a thread safe global is, as with any global,
declaring it. For the sake of this example, you’ll declare one global value which
will start out as a long with a value of 0. Each time the
hello_long() function is called you’ll increment this value and return
it. Add the following block of code to php_hello.h just after the
#define PHP_HELLO_H statement:


#ifdef ZTS
#include "TSRM.h"
#endif

ZEND_BEGIN_MODULE_GLOBALS(hello)
    long counter;
ZEND_END_MODULE_GLOBALS(hello)

#ifdef ZTS
#define HELLO_G(v) TSRMG(hello_globals_id, zend_hello_globals *, v)
#else
#define HELLO_G(v) (hello_globals.v)
#endif

You’re also going to use the RINIT method this time around, so you
need to declare its prototype in the header:


PHP_MINIT_FUNCTION(hello);
PHP_MSHUTDOWN_FUNCTION(hello);
PHP_RINIT_FUNCTION(hello);

Now let’s go over to hello.c and add the following just after your include
block:


#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "php.h"
#include "php_ini.h"
#include "php_hello.h"

ZEND_DECLARE_MODULE_GLOBALS(hello)

Change hello_module_entry by adding
PHP_RINIT(hello):


zend_module_entry hello_module_entry = {
#if ZEND_MODULE_API_NO >= 20010901
    STANDARD_MODULE_HEADER,
#endif
    PHP_HELLO_WORLD_EXTNAME,
    hello_functions,
    PHP_MINIT(hello),
    PHP_MSHUTDOWN(hello),
    PHP_RINIT(hello),
    NULL,
    NULL,
#if ZEND_MODULE_API_NO >= 20010901
    PHP_HELLO_WORLD_VERSION,
#endif
    STANDARD_MODULE_PROPERTIES
};

And modify your MINIT function, along with the addition of another
couple of functions, to handle initialization upon request startup:


static void
php_hello_init_globals(zend_hello_globals *hello_globals)
{
}

PHP_RINIT_FUNCTION(hello)
{
    HELLO_G(counter) = 0;

    return SUCCESS;
}

PHP_MINIT_FUNCTION(hello)
{
    ZEND_INIT_MODULE_GLOBALS(hello, php_hello_init_globals,
NULL);

    REGISTER_INI_ENTRIES();

    return SUCCESS;
}

Finally, you can modify the hello_long() function to use this
value:


PHP_FUNCTION(hello_long)
{
    HELLO_G(counter)++;

    RETURN_LONG(HELLO_G(counter));
}

In your additions to php_hello.h, you used a pair of macros -
ZEND_BEGIN_MODULE_GLOBALS() and ZEND_END_MODULE_GLOBALS()
- to create a struct named zend_hello_globals containing one variable
of type long. You then conditionally defined HELLO_G() to
either fetch this value from a thread pool, or just grab it from a global scope – if
you’re compiling for a non-threaded environment.

In hello.c you used the ZEND_DECLARE_MODULE_GLOBALS() macro
to actually instantiate the zend_hello_globals struct either as a true
global (if this is a non-thread-safe build), or as a member of this thread’s
resource pool. As extension authors, this distinction is one we don’t need to worry
about, as the Zend Engine takes care of the job for us. Finally, in
MINIT, you used ZEND_INIT_MODULE_GLOBALS() to allocate a
thread safe resource id – don’t worry about what that is for now.

You may have noticed that php_hello_init_globals() doesn’t actually
do anything, yet we went to the trouble of declaring RINIT to
initialize the counter to 0. Why?

The key lies in when the two functions are called.
php_hello_init_globals() is only called when a new process or thread is
started; however, each process can serve more than one request, so using this
function to initialize our counter to 0 will only work for the first
page request. Subsequent page requests to the same process will still have the old
counter value stored here, and hence will not start counting from 0. To
initialize the counter to 0 for every single page request, we
implemented the RINIT function, which as you
learned earlier
is called prior to every page request. We included the
php_hello_init_globals() function at this point because you’ll be using
it in a few moments, but also because passing a NULL to
ZEND_INIT_MODULE_GLOBALS() for the init function will
result in a segfault on non-threaded platforms.


INI Settings as Global Values

If you recall from earlier, a php.ini value
declared with PHP_INI_ENTRY() is parsed as a string value and
converted, as needed, to other formats with INI_INT(),
INI_FLT(), and INI_BOOL(). For some settings, that
represents a fair amount of unnecessary work duplication as the value is read over
and over again during the course of a script’s execution. Fortunately it’s possible
to instruct ZE to store the INI value in a particular data type, and
only perform type conversions when its value is changed. Let’s try that out by
declaring another INI value, a Boolean this time, indicating whether
the counter should increment, or decrement. Begin by changing the
MODULE_GLOBALS block in php_hello.h to the following:


ZEND_BEGIN_MODULE_GLOBALS(hello)
    long counter;
    zend_bool direction;
ZEND_ENG_MODULE_GLOBALS(hello)

Next, declare the INI value itself by changing your
PHP_INI_BEGIN() block thus:


PHP_INI_BEGIN()
    PHP_INI_ENTRY("hello.greeting", "Hello World",
PHP_INI_ALL, NULL)
    STD_PHP_INI_ENTRY("hello.direction", "1", PHP_INI_ALL,
OnUpdateBool, direction, zend_hello_globals, hello_globals)
PHP_INI_END()

Now initialize the setting in the init_globals method with:


static void
php_hello_init_globals(zend_hello_globals *hello_globals)
{
    hello_globals->direction = 1;
}

And lastly, use the value of the ini setting in hello_long() to
determine whether to increment or decrement:


PHP_FUNCTION(hello_long)
{
    if (HELLO_G(direction)) {
        HELLO_G(counter)++;
    } else {
        HELLO_G(counter)--;
    }

    RETURN_LONG(HELLO_G(counter));
}

And that’s it. The OnUpdateBool method you specified in the
INI_ENTRY section will automatically convert any value provided in
php.ini, .htaccess, or within a script via ini_set() to
an appropriate TRUE/FALSE value which you can then access
directly within a script. The last three parameters of
STD_PHP_INI_ENTRY tell PHP which global variable to change, what the
structure of our extension globals looks like, and the name of the global scope
container where they’re contained.


Sanity Check

By now our three files should look similar to the following listings. (A few
items have been moved and grouped together, for the sake of readability.)

config.m4

PHP_ARG_ENABLE(hello, whether to enable Hello
World support,
[ --enable-hello   Enable Hello World support])

if test "$PHP_HELLO" = "yes"; then
  AC_DEFINE(HAVE_HELLO, 1, [Whether you have Hello World])
  PHP_NEW_EXTENSION(hello, hello.c, $ext_shared)
fi

php_hello.h


#ifndef PHP_HELLO_H
#define PHP_HELLO_H 1

#ifdef ZTS
#include "TSRM.h"
#endif

ZEND_BEGIN_MODULE_GLOBALS(hello)
    long counter;
    zend_bool direction;
ZEND_END_MODULE_GLOBALS(hello)

#ifdef ZTS
#define HELLO_G(v) TSRMG(hello_globals_id, zend_hello_globals *, v)
#else
#define HELLO_G(v) (hello_globals.v)
#endif

#define PHP_HELLO_WORLD_VERSION "1.0"
#define PHP_HELLO_WORLD_EXTNAME "hello"

PHP_MINIT_FUNCTION(hello);
PHP_MSHUTDOWN_FUNCTION(hello);
PHP_RINIT_FUNCTION(hello);

PHP_FUNCTION(hello_world);
PHP_FUNCTION(hello_long);
PHP_FUNCTION(hello_double);
PHP_FUNCTION(hello_bool);
PHP_FUNCTION(hello_null);

extern zend_module_entry hello_module_entry;
#define phpext_hello_ptr &hello_module_entry

#endif

hello.c


#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "php.h"
#include "php_ini.h"
#include "php_hello.h"

ZEND_DECLARE_MODULE_GLOBALS(hello)

static function_entry hello_functions[] = {
    PHP_FE(hello_world, NULL)
    PHP_FE(hello_long, NULL)
    PHP_FE(hello_double, NULL)
    PHP_FE(hello_bool, NULL)
    PHP_FE(hello_null, NULL)
    {NULL, NULL, NULL}
};

zend_module_entry hello_module_entry = {
#if ZEND_MODULE_API_NO >= 20010901
    STANDARD_MODULE_HEADER,
#endif
    PHP_HELLO_WORLD_EXTNAME,
    hello_functions,
    PHP_MINIT(hello),
    PHP_MSHUTDOWN(hello),
    PHP_RINIT(hello),
    NULL,
    NULL,
#if ZEND_MODULE_API_NO >= 20010901
    PHP_HELLO_WORLD_VERSION,
#endif
    STANDARD_MODULE_PROPERTIES
};

#ifdef COMPILE_DL_HELLO
ZEND_GET_MODULE(hello)
#endif

PHP_INI_BEGIN()
    PHP_INI_ENTRY("hello.greeting", "Hello World",
PHP_INI_ALL, NULL)
    STD_PHP_INI_ENTRY("hello.direction", "1", PHP_INI_ALL,
OnUpdateBool, direction, zend_hello_globals, hello_globals)
PHP_INI_END()

static void php_hello_init_globals(zend_hello_globals *hello_globals)
{
    hello_globals->direction = 1;
}

PHP_RINIT_FUNCTION(hello)
{
    HELLO_G(counter) = 0;

    return SUCCESS;
}

PHP_MINIT_FUNCTION(hello)
{
    ZEND_INIT_MODULE_GLOBALS(hello, php_hello_init_globals,
NULL);

    REGISTER_INI_ENTRIES();

    return SUCCESS;
}

PHP_MSHUTDOWN_FUNCTION(hello)
{
    UNREGISTER_INI_ENTRIES();

    return SUCCESS;
}

PHP_FUNCTION(hello_world)
{
    RETURN_STRING("Hello World", 1);
}

PHP_FUNCTION(hello_long)
{
    if (HELLO_G(direction)) {
        HELLO_G(counter)++;
    } else {
        HELLO_G(counter)--;
    }

    RETURN_LONG(HELLO_G(counter));
}

PHP_FUNCTION(hello_double)
{
    RETURN_DOUBLE(3.1415926535);
}

PHP_FUNCTION(hello_bool)
{
    RETURN_BOOL(1);
}

PHP_FUNCTION(hello_null)
{
    RETURN_NULL();
}


What’s Next?

In this tutorial we explored the structure of a simple PHP extension which
exported functions, returned values, declared INI settings, and tracked
its internal state during the course of a request.

In the next session we’ll explore the internal
structure of PHP variables, and
how they’re stored, tracked, and maintained within a script environment. We’ll use
zend_parse_parameters to receive parameters from a program when a
function is called, and explore ways to return more complicated results, including
the array, object, and resource types
mentioned in this tutorial.

Copyright © Sara Golemon, 2005. All rights reserved.

20 Responses to “Extension Writing Part I: Introduction to PHP and Zend”

  1. leinchu Says:

    my_ext.c:
    ———————————————————
    PHP_FUNCTION(say_hello)
    {
    zend_printf("hello world 6\n");
    zval *threaded_func;
    char *func_name;
    if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "z", &threaded_func) != SUCCESS) {
    php_error_docref(NULL TSRMLS_CC, E_WARNING, "We need a parameter which is a function.\n");
    return;
    }
    if (Z_TYPE_P(threaded_func) != IS_NULL) {
    if (!zend_is_callable(threaded_func, 0, &func_name TSRMLS_CC)) {
    php_error_docref(NULL TSRMLS_CC, E_WARNING, "’%s’ is not a valid read callback", func_name);
    efree(func_name);
    RETURN_FALSE;
    }
    efree(func_name);
    }
    if (threaded_func) {
    zval_add_ref(&threaded_func);
    }

    pthread_t free_thread;
    if(
    (free_thread=(pthread_t)malloc(sizeof(pthread_t)))==0
    )
    {
    printf("Out Of Memory!\n\a");
    exit(1);
    }

    if(pthread_create(&free_thread,NULL,threaded_func,NULL)!=0) {
    php_error_docref(NULL TSRMLS_CC, E_WARNING, "Start thread failed.\n");
    }
    zend_printf("OK\n");
    }
    ———————————————————
    test.php
    <?php
    function say()
    {
    print "==\n";
    $i=0;
    while($i<3)
    {
    echo $i."\n";
    $i++;
    sleep($i);
    }
    }
    say_hello(say);
    //sleep(10);
    ?>

    I run test.php by using /usr/local/php/bin/php test.php
    I got the following output:
    hello world 6
    OK
    ————————————————————-
    It seems that the thread didn’t work,
    how to make the thread work?

  2. benqktc Says:

    use ext_skel can save you a lot of trouble.

  3. factorial Says:

    This has been mentioned before, but I feel it’s important enough to reiterate. The tutorial is wrong.

    1. Name your files hello.c and hello.h, not php_hello.c & php_hello.h.
    2. use "hello.c" instead of "php_hello.c" in your config.m4 file, line 6.

    Can someone at devzone please correct this tutorial?

  4. spoonerj30 Says:

    If you have gotten the same error as "rakeshs" you should check for a second php.ini file for the CLI. I am running Ubuntu 9.10; php.ini is located in /etc/php5/cli and /etc/php5/apache2.

  5. jasonglades Says:

    I must admit these materials are very helpful for the students who are majored in Computer science disciplines.
    <a href="http://www.customwritings.com">Writing an essay</a>

  6. sandovaledwin Says:

    Some one can help me?

    I get the error "Symbol not found: __estrndup" at the moment of running the php extension hello world in my Mac Book (OS X – Leopard).

    $ phpize

    $ ./configure –enable-hello –with-php-config=/usr/bin/php-config

    $ make

    $ cd modules/

    $ ls

    hello.la hello.so

    $ php -r ‘hello_world();’

    dyld: lazy symbol binding failed: Symbol not found: __estrndup
    Referenced from: /Users/carlosedwinsandovaldiaz/NetBeansProjects/test/modules/hello.so
    Expected in: flat namespace

    dyld: Symbol not found: __estrndup
    Referenced from: /Users/carlosedwinsandovaldiaz/NetBeansProjects/test/modules/hello.so
    Expected in: flat namespace

    Trace/BPT trap

  7. joaorsilva Says:

    I know it’s a little late but.

    No you can’t return PHP_FUNCTION(structure).

    PHP_FUNCTION just return zval’s, therefore of types,

    bool
    int
    double
    resource
    array
    object

    I think I didn’t miss any type

    The best thing you can do is creating an associative array and return it.

    Cheers

  8. _____anonymous_____ Says:

    Hi Sara,

    I am currently waiting for my copy of your Extending PHP book to arrive and using this series to get me going in the mean time. I am finding it very helpful but I am stumped by initialising of global variables from within php.ini.

    There are number of references to being able to do this in the article but no explanation of how to actually do it.

    I have trwalled the PHP.net manuals and can find lot’s pertaining to the use of the ini_set() from within scipts and the way to initialise from within .htaccess files but nothing on how to achieve the same thing from within the php.ini file.

    Can anyone shed any light on this with an example of the syntax I would need to use.

    Thanks in avance,

    Alex
    alex[dot]adams[at]uk[dot]thalesgroup[dot]com

  9. _____anonymous_____ Says:

    This content is very much useful.. I want to return a structure from the PHP_FUNCTION(return_struct). Can anybody help me out??

  10. _____anonymous_____ Says:

    When compiling the example extension on OS X, I had to use the following:

    ./configure –enable-hello –with-php-config=/usr/local/bin/php-config

    This was after doing a clean build of the latest PHP sources. If I didn’t add the path to php-config, it would use the php-config that came with the system, and PHP would complain on startup that the extension and the PHP core were compiled using different API versions.

    Also note that in PHP.ini, the default location for extensions was set to "./", which meant that the extension would only load if I was calling PHP from the directory in which the .so file resided. Convenient if you don’t feel like copying your .so file into another directory every time you recompile, but confusing if you expect the extensions directory to be set to /usr/local/lib/extensions!

  11. netcelli Says:

    I have the same problem :S Still trying to figure out why it doesnt work

  12. rakeshs Says:

    When I run the command php -r ‘echo hello_world();’ it show me

    Fatal error: Call to undefined function hello_world() in Command line code on line 1

    what should I do ???

  13. sirtoozee Says:

    I need to ./configure –prefix=/somewhere to get the custom_extension.so –with-apxs2=/usr/sbin/apxs2 –enable-custome_extension, then make

    I have to wait for a while, but is there a simple way to complie custom extension during test case especially just like the ffmpeg-php custom extension provides complex functions.

  14. sirtoozee Says:

    I need to ./configure –prefix=/somewhere to get the custom_extension.so –with-apxs2=/usr/sbin/apxs2 –enable-custome_extension, then make

    I have to wait for a while, but is there a simple way to complie custom extension during test case especially just like the ffmpeg-php custom extension provides complex functions.

  15. jdelmour Says:

    hello

    you take php_hello.h/c as the filename in your example, but in config.m4 you just use "hello.h/c"

    if you would correct this, every user outside can safe this time i used for checking this circumstances :)

    kind regards
    h. huebel

  16. jdelmour Says:

    Hi

    thank you very much for this great introduction to building php extensions. even if its very helpful for theory, i get an error after typing "make" (i use openSuse 10.2 with Kernel 2.6.18.8-0.3-default):

    make: *** No rule to make target `/php-5.2.3/ext/hello/hello.c’, needed by `hello.lo’. Stop.

    I have compiled php and apache successfully like described, i typed in the three example files (config.m4, php_hello.h und php_hello.c). i can run phpize and "./configure –enable-hello" successfully, but after i run "make", i get this error described above.

    what to do now?
    thank you very much for any help!

    kind regards
    jdelmour

  17. _____anonymous_____ Says:

    In the INI section of this article look out for the typo "hell_", which should be "hello_". You might get this error when trying to restart Apache:

    root# apachectl start

    Processing config directory: /private/etc/httpd/users/*.conf

    Processing config file: /private/etc/httpd/users/swain.conf

    Processing config file: /private/etc/httpd/users/user.conf

    /usr/sbin/apachectl: line 193: 24504 Trace/BPT trap $HTTPD

    /usr/sbin/apachectl start: httpd could not be started

  18. _____anonymous_____ Says:

    Very nice tutorial! Because it might help other readers here is the link to
    part 2: <a href="http://devzone.zend.com/node/comment/id/1022">http://devzone.zend.com/node/comment/id/1022</a&gt;, part 2/2 is at id 1023 and part 3 at id 1024.

  19. rrykdotua Says:

    How can I write an extension for PHP on Windows? I would appreciate if you’ll explain how to do it using Visual Studio 2005.

    Maybe I am wrong and just missing an article on this topic – then tell me the URL where I can find it.

  20. _____anonymous_____ Says:

    Hey Sara Goleman,
    thanks for this simple and clear instruction! As I have to rewrite an extension from PHP4 to PHP5 it helped me a lot to get started with that and gain an understanding of the principles of the PHP-Extensions. Part IV of the tutorial would be interesting in special, so I’m very excited about that.