Prior to working through the rest of this chapter, you should retrieve
clean, unmodified source trees of your favorite Web server. We're working with
Apache (available at
and, of course, with PHP (available at
http://www.php.net/ - does
it need to be said?).
Make sure that you can compile a working PHP environment by
yourself! We won't go into this issue here, however, as you should
already have this most basic ability when studying this chapter.
Before we start discussing code issues, you should familiarize
yourself with the source tree to be able to quickly navigate
through PHP's files. This is a must-have ability to implement and
The following table describes the contents of the major directories.
Main PHP source files and main header files; here you'll find
all of PHP's API definitions, macros, etc. (important).
Everything else is below this directory.
Repository for dynamic and built-in modules; by default, these
are the "official" PHP modules that have been integrated into
the main source tree. From PHP 4.0, it's possible to compile
these standard extensions as dynamic loadable modules (at
least, those that support it).
This directory contains the main php macros and definitions. (important)
Directory for the PHP Extension and Application Repository. This directory contains
core PEAR files.
Contains the code for the different server abstraction layers.
Location of the "Thread Safe Resource Manager" (TSRM) for Zend
Location of the Zend Engine files; here you'll
find all of Zend's API definitions, macros, etc. (important).
Discussing all the files included in the PHP package is beyond the
scope of this chapter. However, you should take a close look at the
php-src/main/php.h, located in the main PHP directory.
This file contains most of PHP's macro and API definitions.
php-src/Zend/zend.h, located in the main Zend directory.
This file contains most of Zend's macros and definitions.
php-src/Zend/zend_API.h, also located in the Zend
directory, which defines Zend's API.
You should also follow some sub-inclusions from
these files; for example, the ones relating to the Zend executor,
the PHP initialization file support, and such. After reading these
files, take the time to navigate around the package a little to see
the interdependencies of all files and modules - how they relate to
each other and especially how they make use of each other. This
also helps you to adapt to the coding style in which PHP is
authored. To extend PHP, you should quickly adapt to this style.
For almost every important task, Zend ships predefined macros that
are extremely handy. The tables and figures in the following
sections describe most of the basic functions, structures, and
macros. The macro definitions can be found mainly in
zend.h and zend_API.h.
We suggest that you take a close look at these files after having
studied this chapter. (Although you can go ahead and read them
now, not everything will make sense to you yet.)
Resource management is a crucial issue, especially in server
software. One of the most valuable resources is memory, and memory
management should be handled with extreme care. Memory management
has been partially abstracted in Zend, and you should stick to
this abstraction for obvious reasons: Due to the abstraction, Zend
gets full control over all memory allocations. Zend is able to
determine whether a block is in use, automatically freeing unused
blocks and blocks with lost references, and thus prevent memory
leaks. The functions to be used are described in the following
Serves as replacement for
strndup(). Faster than
estrdup() and binary-safe. This is the
recommended function to use if you know the string length
prior to duplicating it.
Serves as replacement for
Serves as replacement for
ecalloc(), and erealloc()
allocate internal memory; efree() frees these
previously allocated blocks. Memory handled by the
e*() functions is considered local to the
current process and is discarded as soon as the script executed by
this process is terminated.
To allocate resident memory that survives termination of
the current script, you can use malloc() and
free(). This should only be done with extreme
care, however, and only in conjunction with demands of the Zend
API; otherwise, you risk memory leaks.
Zend also features a thread-safe resource manager to
provide better native support for multithreaded Web servers. This
requires you to allocate local structures for all of your global
variables to allow concurrent threads to be run. Because the
thread-safe mode of Zend was not finished back when this was written,
it is not yet extensively covered here.
Strings are handled a bit differently by the Zend engine
than other values such as integers, Booleans, etc., which don't require
additional memory allocation for storing their values. If you want to
return a string from a function, introduce a new string variable to the symbol
table, or do something similar, you have to make sure that the memory the
string will be occupying has previously been allocated, using the
aforementioned e*() functions for allocation. (This might
not make much sense to you yet; just keep it somewhere in your head for now - we'll get
back to it shortly.)
Complex types such as arrays and objects require
different treatment. Zend features a single API for these types - they're
stored using hash tables.
To reduce complexity in the following source examples, we're only
working with simple types such as integers at first. A discussion about
creating more advanced types follows later in this chapter.