Scheduler Activations

In §2.2, in the paragraph that begins “In a tradition system, when there are…”, the authors describe an issue that can arise when user-level threads are implemented atop regular kernel-level threads. In particular, they describe a scenario where processor time can be wasted as a result of a user-level thread spin-waiting for a lock held by an unscheduled thread.

With scheduler activations, a user-level threading library can prevent this issue from occuring. How? Briefly describe the root cause of the issue. Then describe how scheduler activations solve this problem. Describe both the events that occur in the kernel and the actions that must be taken by the user-level threading library.


Local Stanford students should write up their response on a sheet of paper that includes their name and SUNetID. The sheet of paper with the response should be submitted immediately before lecture.

SCPD students should write up their response in a text file named response.sched-act.txt and upload it via the submission and grades page. You'll need to sign in with your SUNetID to access the page. Responses will be accepted until one week after the corresponding paper's lecture.

In either case, the response should be short, likely only a pithy paragraph in length.


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David Mazières
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