Update Engine

http://code.google.com/p/update-engine/

Just add actions into processor, processor will do PerformAction() of each action. When action finish, call processor::ActionComplete() and perform next action.

The action system is the mechanism by which Update Engine accomplishes and manages all of its tasks, asynchronous or not, in a simple and orderly manner. There are three primary abstractions that make up the action system:

KSAction -- an abstract base class that defines a unit of work (e.g., KSDownloadAction, KSInstallAction)
KSActionProcessor -- a queue of KSAction instances that will be run one at a time in the order they appear in the queue
KSActionPipe -- connects the "output" of one KSAction with the "input" of another; analogous to a typical Unix command-line pipe