Real-Time Java™ Platform Programming

Preemption

Unless a system has at least one processor per concurrent task, the operating system may occasionally preempt a task to give another task access to the processor. Some operating systems permit preemption only at certain points; others have various sections where preemption is deferred. Real-time operating systems take great pains with preemption latency (the maximum duration preemption is deferred) and preemption service time (the length of time it takes to complete preemption after it is enabled).

Any system with real-time pretensions will preempt a task to start a higher-priority task that has become runnable. For instance, a task that is waiting for a switch to be moved will start executing very soon after the switch moves unless ...