Debugging Multithreaded Applications
A thread is a sequence of instructions to which the operating system allocates processor time. Every process that is running in the operating system consists of at least one thread. Processes that have more than one thread are called multithreaded.
Computers with multiple processors, multi-core processors, or hyperthreading processes can run multiple threads at the same time. Parallel processing of multiple threads can greatly improve program performance, but it can also make debugging more difficult because it introduces the need to keep track of multiple threads.
In addition, multithreading introduces some new types of potential bugs. Often, for example, two or more threads have to access the same resource, but only one thread can safely access the resource at a time. Some form of mutual exclusion is necessary to make sure that only one thread is accessing the resource at a time. If mutual exclusion is performed incorrectly, it can create a deadlock condition where no thread can execute. Deadlocks can be a particularly hard problem to debug.
Visual Studio 2008 provides an improved Threads window and other user interface improvements to make multithreaded debugging easier. The best way to learn about the new threading interface features is by doing the walkthrough. See Walkthrough: Debugging a Multithreaded Application.
Visual Studio also provides powerful breakpoints and tracepoints, which can be very useful when you debug multithreaded applications. You can use breakpoint filters to place breakpoints on individual threads. See How to: Specify a Breakpoint Filter
Debugging a multithreaded application that has a user interface can be especially difficult. In that case, you might consider running the application on a second computer and using remote debugging. For information, see Remote Debugging Setup.