Chapter 21

What is a critical section?

Critical sections indicate shared resources that are accessed by multiple processes or threads in a concurrent application, which can lead to unexpected, and even erroneous, behaviors.

What is a race condition, and why is it undesirable in a concurrent program?

A race condition occurs when two or more threads/processes access and alter a shared resource simultaneously, resulting in mishandled and corrupted data.

What is the underlying cause of a race condition?

The root cause of a race condition is multiple threads/process reading in and altering a shared resource simultaneously; and, when all of the threads/processes finish their execution, only the result of the last thread/process is registered.

How can locks solve the problem of a race condition?

Since the race conditions arise when multiple threads or processes access and write to a shared resource simultaneously, the solution is to isolate the execution of different threads/processes, especially when interacting with the shared resource. With locks, we can turn a shared resource in a concurrent program into a critical section, whose integrity of data is guaranteed to be protected.

Why are locks sometimes undesirable in a concurrent program?

There are a number of disadvantages to using locks: with enough locks implemented in a concurrent program, the whole program might become entirely sequential; locks don't lock anything.

What are the problems race conditions raise in real-life systems and applications?

The problems race conditions raise in real-life systems and applications are as follows:

• Security: A race condition can be both exploited as a security vulnerability (to give external agents illegal access to a system) and used as random key generation, for security processes.

• Operating systems: A race condition occurring when two agents (users and applications) interact with the same memory space can lead to unpredictable behaviors.
• Networking: In networking, a race condition can lead to giving multiple users powerful privileges in a network.