Dijkstra was a computer scientist in times where being a computer scientist meant you were basically a mathematician with a specialty. Semaphores were first introduced by him in one of his early EWDs (EWD35, http://www.cs.utexas.edu/users/EWD/ewd00xx/EWD35.PDF). At the time of EWD35, his EWDs were non-official musings, written in Dutch, intended to be shared amongst interested colleagues and such. It's not like he was writing a scientific paper.

I don't think Torvalds really meant anything much by it. He's just trying to be funny.

If he was making this point, I find it ironic, considering that the purpose of the post is to explain the distinction between two obscure, poorly-named technical words, which nobody ever intuitively understands.

(ˈsɛməˌfɔː) n 1. (Telecommunications) an apparatus for conveying information by means of visual signals, as with movable arms or railway signals, flags, etc 2. (Telecommunications) a system of signalling by holding a flag in each hand and moving the arms to designated positions to denote each letter of the alphabet vb 3. (Telecommunications) to signal (information) by means of semaphore

which definition fits your understanding that you 'wait'? It's not a good name.

https://en.wikipedia.org/wiki/Railway_semaphore_signal

Edit: Ok, actually that could be within your first meaning. But the practical result for railway semaphores is that one of their uses is to stop trains from entering a blocked segment.

And moreover, a semaphore is just a specific type of railway signal, one with a pivoting arm. It's very hard to see how a pivoting arm is at all related to the CS concept.

http://ro.uow.edu.au/cgi/viewcontent.cgi?article=1027&contex...

http://courses.teresco.org/cs432_f02/lectures/07-synch/07-sy...

https://www.cs.cmu.edu/~410-f03/lectures/L09_Synch.txt

https://www.cs.ucsb.edu/~rich/class/cs170/notes/Semaphores/

Documentations:

https://doc.micrium.com/display/osiiidoc/Semaphores+in+uC-OS...

Articles:

http://realtimepartner.com/articles/semaphores.html

http://lycog.com/distributed-systems/semaphore-mutual-exclus...

If we're going to compare it to any real life object, it may as well be a semaphore. Anything else will have the same issues. Traffic lights: what about yellow / blinking. Stop signs: why do they sometimes stop, sometimes not. etc.

Is there any single word/phrase concept which you'd rather use instead? Is it much more convenient and clear than a semaphore?

My point was simply that the only reason "semaphore" is clear is that you've already heard or read those lectures talking about it. There's nothing about the railroad meaning of the term that would imply the computer science meaning. A counter that can never go below zero is entirely unrelated to a pivoting arm. Once you know the connection it can serve as something of a reminder, but that's different from having an intuitive understanding in the first place.

EDIT: Getting from RR semaphore to CS semaphore requires several leaps of intuition. On the railroad side you need to recognize that it is a signal that's important, and it's irrelevant whether that signal is implemented as a semaphore, an electric signal, or even a flagman. On the computer science side you need to know the difference between a semaphore and the many other types of mutual exclusion mechanisms.

So in that sense "semaphore" is poorly named: it provides insufficient context to distinguish the concept from other similar, yet distinct, ideas.

For example, tree data structures. There are:

2–3 tree, 2–3–4 tree, AA tree, (a,b)-tree, AVL tree, B-tree, B+ tree, B*-tree, Bx-tree, Binary search tree, Optimal binary search tree, Dancing tree, HTree, Interval tree, Order statistic tree, Red–black tree, Scapegoat tree, Splay tree, T-tree, Treap, UB-tree

In many of those the name doesn't provide much context at all to distinguish the concept from another one.

Names of things, at least in CS, are rarely ever named in a way to provide sufficient context of their meaning, without having some level of background context.

That is what the description of the concept is for, not the name. A name is too short to provide this. Usually the name is at the discretion of the original author (aka Dijkstra in this case). If you are trying to determine the complete concept of something, or you are trying to distinguish the concept from other similar ideas, only from the name, you are doing it wrong. Go read the documentation about the concept for that.

A red-black tree is named so because those were the colors their laser printer supplied. This is (much like semaphore) a historical accident. Yet, just by the name red-black, you do indeed have enough context to distinguish it from a plain old binary search tree. The defining feature is that you color every node either red or black, thus red-black in the name.

Likewise with splay tree: the defining function is the splay operation, which the name is a vivid reminder of.

Splay tree and red-black tree are Good Names (TM). B tree, B+ tree, B* tree, Bx tree are Bad Names (TM).

If you use a word too common, it's too easy to confuse the definition of that word with the definition of its use in a different context. You must not understand the pain of reading two mathematical books and trying, with the utmost sincerity, to figure out whether the authors are actually using the words the same (such as set, relation, abstraction, object, even things like function). There's the distinct definition, and there is the contextual use, which can theoretically differ for everyone depending on the origin path of native language. You can never know if someone is altering the definition or discovering / describing something new, and they are using the wrong word. Discovering the perfect word for the concept you construct in code or math is an art.

I personally have made remarks that were WAY more potentially offensive than that, verbally, with friends. But, accusing Dijkstra of being a drug user, on the Linux kernel mailing list, from a @transmeta address?

That's grounds for termination in many companies, even if you don't get lawyers involved. I think he's only able to get away with it because he's Linus.

Or were you talking about Linus?