Concurrency in C# Cookbook

Chapter 11. Synchronization

When your application makes use of concurrency (as practically all .NET applications do), then you need to watch out for situations where one piece of code needs to update data while other code needs to access the same data. Whenever this happens, you need to synchronize access to the data. The recipes in this chapter cover the most common types used to synchronize access. However, if you use the other recipes in this book appropriately, you’ll find that a lot of the more common synchronization is already done for you by the appropriate libraries. Before diving into the synchronization recipes, let’s take a closer look at some common situations where synchronization may or may not be required.

Tip

The synchronization explanations in this section are slightly simplified, but the conclusions are all correct.

There are two major types of synchronization: communication and data protection. Communication is used when one piece of code needs to notify another piece of code of some condition (e.g., a new message has arrived). We’ll cover communication more thoroughly in the actual recipes; the remainder of this intro will discuss data protection.

We need to use synchronization to protect shared data when all three of these conditions are true:

• Multiple pieces of code are running concurrently.
• These pieces are accessing (reading or writing) the same data.
• At least one piece of code is updating (writing) the data.

The reason for the first condition should be obvious; ...