(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.
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.
It's actually quite reasonable to complain about the use of the term semaphore here. As you recognize, stopping the train is only one of their uses. Railway signals can convey many different types of information about the state of the track, not just free/blocked.
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.
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:
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.
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).
