Lecture

Mutexes: Managing Thread Synchronization

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In course

CS-202: Computer systems

This course will teach operating systems and networks in an integrated fashion,emphasising the fundamental concepts and techniques that make their interaction possible/practical. Core lectures will be coupled with C programming lectures and assignments for ...

Description

This lecture covers the concept of mutexes as locks for threads, addressing the inefficiencies of spin locks and busy waiting. The instructor explains how mutexes allow threads to sleep when they cannot acquire a lock, thus freeing CPU cycles for other processes. The lecture introduces the pthread_mutex API, detailing its implementation and semantics, including how it ensures mutual exclusion in critical sections. The instructor discusses the importance of fairness in waking up threads and the potential for starvation if not managed properly. Additionally, the lecture highlights the integration of mutexes with other synchronization primitives, such as condition variables, and notes the existence of faster alternatives like futex in Linux. The key takeaway is the necessity of using mutexes to avoid race conditions and ensure that only one thread can own an object at a time, ultimately leading to more efficient and responsive multi-threaded applications.

Instructors (2)

Edouard Bugnion

Edouard Bugnion joined EPFL in 2012, where his focus is on datacenter systems. His areas of interest include operating systems, datacenter infrastructure (systems and networking), and computer architecture. Before joining EPFL, Edouard spent 18 years in the US, where he studied at Stanford and co-founded two startups: VMware and Nuova Systems (acquired by Cisco). At VMware from 1998 until 2005, he played many roles including CTO. At Nuova/Cisco from 2005 until 2011, he helped build the core engineering team and became the VP/CTO of Ciscos Server, Access, and Virtualization Technology Group, a group that brought to market Ciscos Unified Computing System (UCS) platform for virtualized datacenters. Prof. Bugnion is a Fellow of the ACM. Together with his colleagues, he received the ACM Software System Award for VMware 1.0 in 2009. His paper Disco: Running Commodity Operating Systems on Scalable Multiprocessors" received a Best Paper Award at SOSP '97 and was entered into the ACM SIGOPS Hall of Fame Award in 2008. At EPFL, he received the OSDI 2014 Best Paper Award for his work on the IX dataplane operating system

Jean-Cédric Chappelier

Jean-Cédric Chappelier is currently senior researcher and lecturer in Computational Linguistics at the Ecole Polytechnique Fédérale de Lausanne (Switzerland). He holds an Ms.Sci. and a Ph.D. in Computer Science from the Ecole Nationale Supérieure des Télécommunications de Paris (France).

Official source

Ontological neighbourhood

Computer engineering

High-performance computing: Parallel computing

Related concepts (32)

Pthreads

In computing, POSIX Threads, commonly known as pthreads, is an execution model that exists independently from a programming language, as well as a parallel execution model. It allows a program to control multiple different flows of work that overlap in time. Each flow of work is referred to as a thread, and creation and control over these flows is achieved by making calls to the POSIX Threads API. POSIX Threads is an API defined by the Institute of Electrical and Electronics Engineers (IEEE) standard POSIX.

Busy waiting

In computer science and software engineering, busy-waiting, busy-looping or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as whether keyboard input or a lock is available. Spinning can also be used to generate an arbitrary time delay, a technique that was necessary on systems that lacked a method of waiting a specific length of time. Processor speeds vary greatly from computer to computer, especially as some processors are designed to dynamically adjust speed based on current workload.

Lock (computer science)

In computer science, a lock or mutex (from mutual exclusion) is a synchronization primitive: a mechanism that enforces limits on access to a resource when there are many threads of execution. A lock is designed to enforce a mutual exclusion concurrency control policy, and with a variety of possible methods there exists multiple unique implementations for different applications. Generally, locks are advisory locks, where each thread cooperates by acquiring the lock before accessing the corresponding data.

Spinlock

In software engineering, a spinlock is a lock that causes a thread trying to acquire it to simply wait in a loop ("spin") while repeatedly checking whether the lock is available. Since the thread remains active but is not performing a useful task, the use of such a lock is a kind of busy waiting. Once acquired, spinlocks will usually be held until they are explicitly released, although in some implementations they may be automatically released if the thread being waited on (the one that holds the lock) blocks or "goes to sleep".

Barrier (computer science)

In parallel computing, a barrier is a type of synchronization method. A barrier for a group of threads or processes in the source code means any thread/process must stop at this point and cannot proceed until all other threads/processes reach this barrier. Many collective routines and directive-based parallel languages impose implicit barriers. For example, a parallel do loop in Fortran with OpenMP will not be allowed to continue on any thread until the last iteration is completed.

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Threads: Concurrency and Parallelism in Computer Systems

Covers the thread abstraction in computer systems, focusing on concurrency, parallelism, and the management of threads using the POSIX API.

Concurrency Primitives and Pitfalls

Explores concurrency primitives, mutual exclusion, and synchronization pitfalls in operating systems, focusing on condition variables and semaphores.

Concurrency and Mutual Exclusion

Covers the importance of concurrency, atomic operations, and mutual exclusion using locks.

Locking Primitives: Avoiding Race Conditions in Threads

Covers locking primitives necessary to prevent race conditions in multithreaded programming, focusing on mutual exclusion and atomic operations.

Parallel Programming I