INtime® 3.1 Software - tenAsys

Chapter 4: About RT programming
Preemptive, priority-based scheduling
In a preemptive, priority-based system, some threads are more critical than others.
Critical threads run first and can preempt less critical threads, as shown in this figure:
Figure 4-2. Multithreading and preemptive, priority-based scheduling
Event
Thread A
Thread B
Thread A, a low-priority thread, prints data accumulated from the robotic arm in report form.
Thread B, a high-priority thread, controls the robotic arm. If the arm needs to move while thread A
runs, thread B preempts the print thread, then starts and moves the arm.
After thread B repositions the arm, thread A finishes printing.
Multithreading allows an application to respond to internal events and external
interrupts, such as clock ticks from the system clock or receiver ready from a serial
device, based on how critical they are. You determine the priority of threads in your
application; INtime software provides the thread scheduling algorithms.
When you add interrupt processing to multithreading and preemptive, priority-based
scheduling, your application can respond to interrupts as they occur. Your application
becomes event-driven.
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