"Extending and Embedding PHP" by Sara Golemon, a long-time contributor to the PHP project, remedies the fact that the internals of PHP are far from being as well documented as the rest of PHP. It brings writing extensions for PHP "to the masses", so to speak.

Sebastian covers the contents of the book, one chapter at a time - everything from "Memory Management" out to the "Streams" chapters. His opinion of the book is a good one, too, noting that it brings a topic that could have been rendered unreadable by the wrong author into the realm of "the masses" with plenty of explaination and code throughout.

One of the most jarring differences between a managed language like PHP, and an unmanaged language like C is control over memory pointers.

The chapter looks at:

• Freeing up unneeded resources
• Handling error requests correctly
• An introduction to the Zend Memory Manager
• Counting references to avoid unnecessary copying
• The usefulness of "copy on write"
• Saving resources with "change on write"
• Difficulties with handling seperation of values

Each of the above items is accompanied by a good bit of text and code examples where appropriate (even a diagram or two to make things clearer).

It's always good to get a better idea of what's going on behind the scenes. Too many people just use PHP and think new versions just magically appear. In truth, there are a huge number of developers working on new features and fixing bugs to help make PHP, the language, a better place. And, thanks to Sara, the work those folks do gets a bit more recognition.