In this lecture, we will investigate the mechanisms and principles underlying the use of locks in concurrent programming to manage critical sections effectively. Starting with an exploration of the fundamental challenges presented by concurrency—specifically, the need to execute a series of instructions atomically despite interruptions on a single processor or concurrent executions on multiple processors—we introduce locks as a direct solution to this problem. Locks, essentially annotations around critical sections in source code, ensure that these sections execute as if they were a single atomic instruction, thus preventing data corruption or inconsistent states.
As we progress, we'll cover the basic concept of locks by examining how a lock variable, or mutex, signifies the lock's state at any given moment, whether it be available, acquired by a single thread, or contested among multiple threads. Through detailed examples, we'll understand how locks can be implemented using specific programming constructs and explore the semantics of locking and unlocking operations. This includes discussing the conditions under which threads acquire locks, the use of waiting queues to manage thread access to critical sections, and the strategies to prevent deadlock and ensure fairness among competing threads. By the end of this lecture, students will have a solid understanding of how locks provide a minimal amount of control back to programmers over thread scheduling, transforming the chaos of traditional OS scheduling into a more controlled and orderly activity.
FA 24 version:
https://docs.google.com/presentation/d/1B7Zd_sBL52ImXuSd_moX_3_eiFDV0Ik4YlXoNvvFK7A/edit?usp=sharing
Original version:
https://docs.google.com/presentation/d/1RZfk-9dqhoHArJ8Xu9rgxWyjj61zlmSVcYhBs-R8jt8/edit?usp=sharing
No additional references or resources at this time.