OS X and iOS Kernel Programming

Synchronization Primitives

Synchronization problems occur when code that is executing on two or more threads attempts to access a common resource or structure. A common synchronization problem for I/O Kit drivers arises when a driver needs to access its instance variables, since these are shared between all of the threads that the driver is executing. To give a concrete example, let's consider an actual example from the I/O Kit, namely, the OSObject base class's implementation of reference counting.

The OSObject class is the base class for all objects in the I/O Kit, and one of its roles is to maintain a reference count for each object instance and to release an object when its reference count is decremented to 0. A simplified version of the ...