In a non-preemptive threading environment, a thread must volunteer to give up control of the CPU and move to the RUNNABLE state. Many methods in the Java language classes contain code that volunteers to give up control, and are typically associated with actions that might take a long time. For example, reading from the network generally causes a thread to wait for a packet to arrive. A thread that is waiting on the availability of some event or resource is in the BLOCKED state. When the event occurs or the resource becomes available, the thread becomes RUNNABLE.