Since the very first version of the C# language, it was thought important to have language-level support for mutual-exclusion execution of code. The central concept here is that of a lock, which is acquired upon entrance of a block of code and released at the end of it. Lock ownership is an exclusive right; no two blocks of code should be allowed to execute simultaneously. When a lock is already held when another piece of code tries to acquire it, the latter piece of code will have to wait until the lock is released again. The idea of threads acquiring and releasing locks is shown in Figure 8.28.