n. An opportunity for the scheduler to execute and select a new task to run. Operating systems are just collections of system calls—invoked by application programs to perform work on their behalf—and interrupt service routines. Depending on the type of scheduler employed in the operating system, there will be one or more system calls that result in scheduler invocation. Every operating system has a scheduling point at the time a task completes its work and exits. At that time, there would be no running task, so the scheduler must select a new task to run. Run-tocompletion and shortest-job-first schedulers might have only this one scheduling point. Most modern operating systems also have a scheduling point at the time that the running task blocks to wait for some event, and preemptiveoperating systems can additionally stop the running task and select a new one whenever a new task is created (always by the running task, by definition) or a previously blocked task unblocks.
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