Comment by viraptor | Hacker News Reader

Comment by viraptor | Hacker News Reader

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Not sure if it's reasonable to complain really... I mean, it's not covering everything semaphores do, but the basics are there - gives information and stops two trains/threads colliding. References to trains when talking about cs semaphores are all over the place. Universities:

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?

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.

Since when does a name have to provide sufficient 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.

I'm not saying a name has to provide sufficient context. I'm saying a name that provides that context is superior to one that does not.

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).

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