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For those wondering, P comes from 'Passering', roughly translated 'pass' (as a noun), and V from 'Vrijgave' ('release'). Apparently somehow this terminology com
by roel_v 12y ago
For those wondering, P comes from 'Passering', roughly translated 'pass' (as a noun), and V from 'Vrijgave' ('release'). Apparently somehow this terminology comes from train systems but there's not a lot of context on that etymology.
As an aside, this paper (it's actually the transcription of a lecture) has some great metaphors that explain problems with concurrence and issues with synchronisation. At the risk of losing much of the nuances, he essentially illustrates the synchronisation using the example of a teacher who needs to find a pupil in a class. When pupils are free to choose a seat, she needs to scan all seats when she is looking for a particular pupil; but when at the same time pupils are free to change seats as she's scanning, there is no guarantee that she will ever find the pupil she's looking for as he might run from the back of the class to the front as soon as she's done scanning the front.
- sgt 12y agoFrom what I've heard, the P comes from "Probeer" (to "try"), and the V from "verhoog" (increase). This makes more sense to me.
- deleted 12y ago[deleted]
- remon 12y agoThat seems the correct one : https://cs.nyu.edu/~yap/classes/os/resources/origin_of_PV.html https://cs.nyu.edu/~yap/classes/os/resources/origin_of_PV.ht...
- pieter_mj 12y agoYou're referring to https://cs.nyu.edu/~yap/classes/os/resources/EWD74.pdf https://cs.nyu.edu/~yap/classes/os/resources/EWD74.pdf while 'passering' and 'vrijgave' are already mentioned in http://www.cs.utexas.edu/users/EWD/ewd00xx/EWD35.PDF http://www.cs.utexas.edu/users/EWD/ewd00xx/EWD35.PDF
- remon 12y agoAh thank you. Fun read.
- pdw 12y agoThat's Dijkstra's later terminology. In EWD35 he introduced the operations as "passering" and "vrijgave". Then in EWD51 he uses "verhogen" and the neologism "prolagen" ("probeer te verlagen"). In EWD74 he switches to "proberen". These documents are available from the Dijkstra archive: http://www.cs.utexas.edu/users/EWD/welcome.html http://www.cs.utexas.edu/users/EWD/welcome.html
- deleted 12y ago[deleted]
- leoc 12y agoIIRC the analogy is to the positions of a stop/go safety flag (or an actual railway semaphore https://en.wikipedia.org/wiki/Railway_semaphore_signal https://en.wikipedia.org/wiki/Railway_semaphore_signal !) meant to ensure that only one train is in a railway tunnel at a time. A Dutch-speaker with EWD35 http://www.cs.utexas.edu/users/EWD/ewd00xx/EWD35.PDF http://www.cs.utexas.edu/users/EWD/ewd00xx/EWD35.PDF should be able to confirm this.
- theoh 12y agoI think that much is clear, (the railway analogy), but the idea that tunnels are the main use case for semaphore signals is daft. All railways use variations on the principle of block signalling, where only one train is allowed on any section of track, even if successive trains are travelling in the same direction. This ensures safe separation of trains, which take some distance to stop.
- mtts 12y agoAn amusing anecdote I heard about this a few weeks ago: he came up with "P" and "V" when explaining the concept to his students at Eindhoven University. He looked outside the window of the classroom he was teaching in and saw the name of the local soccer club on a nearby stadium which is PSV.
- couchand 12y agoThat anecdote is amusing, but it seems unlikely things worked exactly like that. They are near each other in the center of town, but the stadium and the university are a kilometer apart and separated by an elevated railway. At the time EWD35 was written (prior to 1963) the stadium had just installed 40 meter lights, so while it's possible the initials were written on the back of these, it seems more likely that this is a fanciful urban legend. Do you have any more information?