Difference: CSC458Spring2008 (18 vs. 19)

Revision 192008-02-07 - LukeDalessandro

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META TOPICPARENT name="TongxinBai"
This class wiki serves as both a blackboard for technical discussions and a billboard for information sharing. The organization of this wiki is made as simple as possible but hopefully also effective enough for discussion and Q&A. In general, postings go to one of the four sections below. The Announcements is basically used for reminding students of the class schedule and homework due dates. The on Administration is where you put questions about class administration, for instance, about grading criteria. The other two sections are the places for technical discussions. All the specific questions and issues about the assignments go to on Assignments. The other general questions and comments about the course content go to on Technical Content.
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  -- LukeDalessandro - 06 Feb 2008
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An issue that arises is how to deal with an empty queue. The easiest solution is to just fail the dequeue and go on and do whatever your next coinflip tells you to do. The problem with this approach is that this means that in the long run you're going to be enqueueing slightly more often than you dequeue, which will lead to an overall growth trend in the queue. You could precisely compute the probability of dequeueing from an empty queue for any particular insert and adjust your priority accordingly. You could have one "enqueue only" thread but that's going to change the kind of performance that you see.

As a side note, an alternative to preallocating random bits, which can take up a lot of space and cause strange cache behavior, is to use rand_r which is a reentrant rand call that is thread safe. Also in this case it's possible that a thread can run out of local nodes. It makes sense to allocate another block of local nodes rather than waiting for a dequeue to become available.

 

on Technical Content

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