I think it was a common term in use by April 1986 when I joined Inmos. I think some terms in common use were used a bit loosely. A channel that was waiting for the other end of the communication to become ready âblockedâ the process
from proceeding. Thus my recollection is that âblocking on a channelâ was commonly used to describe a process that couldnât proceed until the communication could proceed.
I think you have to remember that at the time the transputer came out, lots of people got their hands on it and started parallel programming. Many of these were engineers, without computer science backgrounds, and so made up the
terminology as they went along.
In my own case, I had been programming real time systems (engine controllers, antilock braking etc) in assembler and having graduated in 1975 with a degree in electronic engineering and physical oceanography, the only formal computer
education I had was a 3 day course from the Maths department at university where they had the foresight to teach the engineers Algol instead of Fortran, and some timeshare Basic I had picked up as I went along in order to do a few assignments.
So when I got to Inmos, I came across terms like âcritical sectionsâ and realised that I had been implementing these things in assembler but without knowing the terms or the formal principles behind them. For me, suddenly in Occam
I had a language that described pretty much what I wanted to do. It was my observation that engineers found Occam easier than computer scientists because the CSP model was so similar to engineering â black boxes and wires, glitches, race conditions etc.
When I moved to Inmos France, I had to find out what people used commonly to describe transputer and Occam related terms in French because they had yet to reach any (computing) dictionary.
So I think that in answer to your question, there are a raft of âformalâ terms that were described in the books, but there is also a second group of âinformalâ terms that people used to describe things â some are synonyms (equivalent
words) to the âformalâ terms, but others had slightly different meanings.
This is actually common practice in English â one of the reasons the English language has such a large vocabulary is that English frequently adopts words from other languages (maybe Anglifying them in the process) to express a slightly
different meaning to a word we already have. Over time, that meaning may well change. This is why, when the English are learning French, there are so many words we class as âfaux amisâ â false friends â because they sound/look like a French word so we think
that it has the same meaning in French. (see
http://www.oxfordlanguagedictionaries.com/Public/PublicResources.html?direction=b-fr-en&sp=S/oldo/resources/fr/Difficulties-in-French-fr.html for some examples)
So I cannot give a direct answer to your question, but hope that this information might point you or others into pinning down the origin or original meaning.
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When was the phrase âblocking on a channelâ introduced and by whom? Hoare does not use it in his 1985 book. Roscoe almost does not use it, or I would say, he does not use it at all in this context in his version of the
book thatâs PDFed. If this group does not know this, none will.
I am suggesting using âto yield on a channelâ rather than âto block on a channelâ. I have a blog note about it  and there is a discussion thread on golang-nuts . I include the figure here (and the intro text in golang-nuts):
Readers of golang-nuts know that âblocking is fine in Goâ. But often, when I talk with other programmers I would hear that âblocking
is evilâ. I suggest that we go over to saying that âyielding on a channel is fineâ. Iâll explain:
The literate meaning of blocking is about something we donât want. It means I want to go somewhere but am stopped or delayed
so I arrive too late. Or a door is blocked, in which case we must unblock it, hopefully without a bulldozer. Since this semantics outnumbers the people who understand CSP-based channel semantics we have an explanation problem.
With an explanation problem follows a mission problem.
Tell a basically single-thread programmer in C++ that blocking is good and you ask for much. His attention to try to understand
something rather new, even if heâs used to linux select. Because often the code that does this linux select also does other rather independent matters. And itâs in his spec that these other matters also need to complete. And when you block on one matter itâs
easy to see blocking as something evil. Because he or she is right in their own mind.
So which âblockingâ do you mean?
âBlocking on a channelâ or some shared resource controlled by a non-blocking algorithm. I believe these may be in the
same group, ref. the Wikipedia page about Non-blocking algorithm
âBlockingâ away other required functionality
âBlockingâ as in deadlock, where the system cannot proceed, where there is a cycle in the dependency tree
We already have good words for 2. = blocking as is, and 3 = deadlock. But we reuse blocking for 1.) which is not optimal. As
said, I suggest 1. = yielding. This is an implicit yield that the application doesnât have control of. Not the explicit yield that some operating systems would supply in the API. The channel semantics as implemented in the scheduler does it for us.
What do you think of this? If we start to write âto yield on a channelâ or âyielding on a channelâ it could slowly creep into
our language. And the C/C++ (and even Scala or Erlang) people would give us an ear. Especially if we agree with them that blocking is evil.
(I alse dare take comments on the idea.. Here, there or there)
Med vennlig hilsen / Best regards
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