The scheduler, also called the dispatcher, is a part of µC/OS-III responsible for determining which task runs next. µC/OS-III is a preemptive, priority-based kernel. As we have seen, each task is assigned a priority based on its importance. The priority for each task depends on the application, and µC/OS-III supports multiple tasks at the same priority level.
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The word preemptive means that when an event occurs, and that event makes a more important task ready-to-run, then µC/OS-III will immediately give control of the CPU to that task. Thus, when a task signals or sends a message to a higher-priority task, the current task is suspended and the higher-priority task is given control of the CPU. Similarly, if an Interrupt Service Routine (ISR) signals or sends a message to a higher priority task, when the message has been sent, the interrupted task remains suspended, and the new higher priority task resumes.