nachos.threads
Class LotteryScheduler

java.lang.Object
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  +--nachos.threads.Scheduler
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        +--nachos.threads.PriorityScheduler
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              +--nachos.threads.LotteryScheduler

public class LotteryScheduler

extends PriorityScheduler

A scheduler that chooses threads using a lottery.

A lottery scheduler associates a number of tickets with each thread. When a thread needs to be dequeued, a random lottery is held, among all the tickets of all the threads waiting to be dequeued. The thread that holds the winning ticket is chosen.

Note that a lottery scheduler must be able to handle a lot of tickets (sometimes billions), so it is not acceptable to maintain state for every ticket.

A lottery scheduler must partially solve the priority inversion problem; in particular, tickets must be transferred through locks, and through joins. Unlike a priority scheduler, these tickets add (as opposed to just taking the maximum).

Inner classes inherited from class nachos.threads.PriorityScheduler

PriorityScheduler.PriorityQueue, PriorityScheduler.ThreadState

Fields inherited from class nachos.threads.PriorityScheduler

priorityDefault, priorityMaximum, priorityMinimum

Constructor Summary

LotteryScheduler()
Allocate a new lottery scheduler.

Method Summary

ThreadQueue

newThreadQueue(boolean transferPriority) Allocate a new lottery thread queue.

Methods inherited from class nachos.threads.PriorityScheduler

decreasePriority, getEffectivePriority, getPriority, getThreadState, increasePriority, setPriority

Methods inherited from class nachos.threads.Scheduler

getEffectivePriority, getPriority, setPriority

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

LotteryScheduler

public LotteryScheduler()

Allocate a new lottery scheduler.

Method Detail

newThreadQueue

public ThreadQueue newThreadQueue(boolean transferPriority)

Allocate a new lottery thread queue.

Overrides:

newThreadQueue in class PriorityScheduler

Parameters:

transferPriority - true if this queue should transfer tickets from waiting threads to the owning thread.

Returns:

a new lottery thread queue.