Windows Internals, Fifth Edition

Synchronization

The concept of mutual exclusion is a crucial one in operating systems development. It refers to the guarantee that one, and only one, thread can access a particular resource at a time. Mutual exclusion is necessary when a resource doesn’t lend itself to shared access or when sharing would result in an unpredictable outcome. For example, if two threads copy a file to a printer port at the same time, their output could be interspersed. Similarly, if one thread reads a memory location while another one writes to it, the first thread will receive unpredictable data. In general, writable resources can’t be shared without restrictions, whereas resources that aren’t subject to modification can be shared. Figure 3-21 illustrates what happens ...