Book Image

Hands-On Design Patterns with Delphi

By : Primož Gabrijelčič
Book Image

Hands-On Design Patterns with Delphi

By: Primož Gabrijelčič

Overview of this book

Design patterns have proven to be the go-to solution for many common programming scenarios. This book focuses on design patterns applied to the Delphi language. The book will provide you with insights into the language and its capabilities of a runtime library. You'll start by exploring a variety of design patterns and understanding them through real-world examples. This will entail a short explanation of the concept of design patterns and the original set of the 'Gang of Four' patterns, which will help you in structuring your designs efficiently. Next, you'll cover the most important 'anti-patterns' (essentially bad software development practices) to aid you in steering clear of problems during programming. You'll then learn about the eight most important patterns for each creational, structural, and behavioral type. After this, you'll be introduced to the concept of 'concurrency' patterns, which are design patterns specifically related to multithreading and parallel computation. These will enable you to develop and improve an interface between items and harmonize shared memories within threads. Toward the concluding chapters, you'll explore design patterns specific to program design and other categories of patterns that do not fall under the 'design' umbrella. By the end of this book, you'll be able to address common design problems encountered while developing applications and feel confident while building scalable projects.
Table of Contents (18 chapters)
Title Page
Copyright and Credits
About Packt

Optimistic locking

We saw before that locks can sometimes be replaced with interlocked operations and we also used such operations to implement custom-made locking. Interlocked operations are also the basis for the optimistic locking pattern, which can be used to implement changes in shared data without using a classical locking mechanism.

Optimistic locking works when a chance of conflict between threads is very low. Like a database transaction mechanism, optimistic locking assumes that there will be no problem and applies required modifications on its own copy of the data (creates a new object, for example). In the second step, optimistic locking tries to commit the change. With one atomic step (usually implemented with an interlocked instruction), the current state is replaced with a new value.

This atomic replacement can, however, fail (if the state was modified by another thread in the meantime). In such a case, optimistic locking must revert the change (roll back a transaction). As such...