Definition of "synchronization primitive"

Question

What exactly does the term synchronization primitive mean? For example: mutex, critical section, waitable timer, event, monitor, conditional variable, semaphore. Are all of them synchronization primitives? Are there any other synchronization primitives I have not listed? And are these a valid questions?

Errancy

Answer 1

Synchronization primitives are simple software mechanisms provided by a platform (e.g. operating system) to its users for the purposes of supporting thread or process synchronization. They're usually built using lower level mechanisms (e.g. atomic operations, memory barriers, spinlocks, context switches etc).

Mutex, event, conditional variables and semaphores are all synchronization primitives. So are shared and exclusive locks. Monitor is generally considered a high-level synchronization tool. It's an object which guarantees mutual exclusion for its methods using other synchronization primitives (usually exclusive locks with condition variables to support waiting and signaling). In some contexts when monitor is used as a building block it is also considered a synchronization primitive.

Critical section is not a synchronization primitive. It's a part of an execution path that must be protected from concurrent execution in order to maintain some invariants. You need to use some synchronization primitives to protect critical section.

Cobbie

"Critical section is not a synchronization primitive." Except on windows, where there is a synchronization primitive called Critical Section: goo.gl/35zir (And yes, I agree it is a terrible misuse of a well defined term but there is nothing I can do to change MS mistake) – Puccoon

Nice explanation but are there official sources which defines what "synchronization primitives" actually are ? – Bibliolatry

Answer 2

As suggested by @Loom, I'm adding this list, offered by the Colombia University, as an answer to your question.

Also check out this article from Microsoft, dated to 03/2017 (I have a feeling it is older, but so is the article from Colombia University).

From what I gathered, synchronization primitives are not well defined, in the sense that there isn't an official list of them.

Nowhere

This is a link-only answer. Could you please edit it and include a summary of what can be found at those links, in case they become invalid? Thank you! – Bipartite