Round-Robin Scheduling

Under the RR scheduling policy, a thread will always execute:

• Voluntarily give up control
• Be preemptible by threads with higher priority
• Time slice used up

As shown in, after a uses its own time slice, it grants the CPU execution permission to thread B, so a leaves the read queue and B enters the read queue.

Once the time slice of the thread is used up, the thread will be preemptible by the thread with the same priority as the next read. A time slice is usually four times of a clock cycle.