C# 5.0 Programmer's Reference

486 ❘ CHAPTER 22 Parallel Programming
Multithreading Advantages
Multithreading has other advantages in addition to executing code in parallel. For
example, many programs perform tasks that take a long time to finish. Perhaps the
program needs to check a dozen websites to get pricing information for a particular
product. If the program does everything in a single thread, then the main program
is blocked until the web search finishes. That means the user interface is stuck and
the user can’t do anything except watch the screen refuse to refresh. If you run the
user interface and the web search on separate threads, the program can remain
responsive even while the search is still running.
Multithreading can also sometimes simplify your code. Suppose a program needs
to monitor several processes. Perhaps it needs to periodically check a collection
of websites for news and stock prices. You could write a program that repeatedly
loops through each of the websites to check them one after another. That might be
somewhat complicated because the code to deal with each website would be intermingled
with the code needed to loop through the sites, handle timeouts, and deal
with other potential problems on each site.
Another approach would be to assign a separate thread to each website and let each
thread run independently. Now each thread’s code can focus on a single website.
Also if one thread’s website is having problems, it won’t affect the performance of
the other threads.
The .NET Framework provides several methods for multithreading including the following.
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PLINQ—You saw this in Chapter 8, “LINQ.”
BackgroundWorker—This component executes code on a separate thread. It uses events to
communicate with the main user interface thread (the UI thread).
Task Parallel Library (TPL)—These tools let you easily run multiple methods in different
threads or run multiple instances of the same method with different parameters.
Tasks—The Task class lets you create and run threads. The Task class defines some methods
to make certain typical operations easier such as creating and starting a task in a single step,
waiting for a group of tasks to finish, or waiting until any one of a group of tasks finishes.
Threads—The Thread class gives you lower level access to threads. These are more
complicated that using other methods but they provide greater control.
This chapter explains how you can use BackgroundWorker, TPL, threads, and tasks to execute code on
multiple threads simultaneously. (See the section “PLINQ” in Chapter 8 for information about PLINQ.)
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