Lottery Scheduling is a probabilistic

Probability

Probability is ordinarily used to describe an attitude of mind towards some proposition of whose truth we arenot certain. The proposition of interest is usually of the form "Will a specific event occur?" The attitude of mind is of the form "How certain are we that the event will occur?" The...

 scheduling algorithm

Scheduling (computing)

In computer science, a scheduling is the method by which threads, processes or data flows are given access to system resources . This is usually done to load balance a system effectively or achieve a target quality of service...

 for processes in an operating system

Operating system

An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

. Processes are each assigned some number of lottery tickets, and the scheduler draws a random ticket to select the next process. The distribution of tickets need not be uniform; granting a process more tickets provides it a relative higher chance of selection. This technique can be used to approximate other scheduling algorithms, such as
Shortest job next

Shortest job next

Shortest job next , also known as Shortest Job First or Shortest Process Next , is a scheduling policy that selects the waiting process with the smallest execution time to execute next. SJN is a non-preemptive algorithm...

 and Fair-share scheduling

Fair-share scheduling

Fair-share scheduling is a scheduling strategy for computer operating systems in which the CPU usage is equally distributed among system users or groups, as opposed to equal distribution among processes....

.

Lottery scheduling solves the problem of starvation

Resource starvation

In computer science, starvation is a multitasking-related problem, where a process is perpetually denied necessary resources. Without those resources, the program can never finish its task....

. Giving each process at least one lottery ticket guarantees that it has non-zero probability of being selected at each scheduling operation.

Implementation

Implementations of lottery scheduling should take into consideration that there could be billions of tickets distributed among a large pool of threads. To have an array where each index represents a ticket, and each location contains the thread corresponding to that ticket, may be highly inefficient. Lottery scheduling can be preemptive or non-preemptive.

External links

• Operating systems and systems programming - UC Berkeley OS Class
• Implementing Lottery Scheduling - Matching the Specialization in Traditional Schedulers - Paper by David Petrou et al.