Timber program reacts to events sent to it from its execution environment. This process is potentially infinite, and the order of external events is not known in advance.To capture this intuition, Timber defines its primary run-time structure to be a set of interconnected reactive objects, that each encapsulate a piece of the global program state. A reactive object is a passive entity defined by a set of methods. Between invocations, a Timber object just maintains its state, ready to react . Timber objects evolve in parallel, although the methods belonging to a particular object are always run under mutually exclusion. Concurrency as well as state protection is thus implicit. Methods are either asynchronous or synchronous, as denoted by the keywords action and request, respectively. The most radical property of Timber is that it is free from any indefinitely blocking constructs; because of this, a Timber object is always fully responsive when not actively executing code.