FreeBSD Device Drivers

Preventing Race Conditions

Race conditions are prevented using locks. Locks, also known as synchronization primitives, are used to serialize the execution of two or more threads. For example, the race conditions in Example 4-1, which are caused by concurrent access to race_list, can be prevented by using a lock to serialize access to race_list. Before a thread can access race_list, it must first a cquire the foo lock. Only one thread can hold foo at a time. If a thread cannot acquire foo, it cannot access race_list and must wait for the current owner to relinquish foo. This protocol guarantees that at any moment in time only one thread can access race_list, which eliminates Example 4-1’s race conditions.

There are several different types of locks ...