> On 11 Apr 2018, at 16:36, Sven Van Caekenberghe <s...@stfx.eu> wrote: > > I can make your example, using the Zn variants, work with the following > change: > > StdioStream>>#atEnd > ^ peekBuffer isNil or: [ (peekBuffer := self next) isNil ]
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Argh, make that atEnd ^ peekBuffer isNil and: [ (peekBuffer := self next) isNil ] but I am still testing, this is probably not the final answer/solution. > Which is a literal implementation of your statement that you can only know > that you are atEnd by reading (and thus waiting/blocking) and checking for > nil, which seems logical to me, given the fact that you *are* waiting for > user input. > > BTW, at least on macOS you have to enter ctrl-D (^D) on a separate line, I am > not sure how relevant that is, but that is probably another argument that > stdin is special (being line-buffered by the OS, EOF needing to be on a > separate line). > > And FWIW, I have been writing networking code in Pharo for years, and I have > never had issues with unclear semantics of these primitives (#atEnd, #next, > #peek) on network streams, either the classic SocketStream or the Zdc* > streams (TLS or not). That is why I think we have to be careful. > > That being said, it is important to continue this discussion, I find it very > interesting. I am trying to write some test code using stdin myself, to > better understand the topic. > >> On 11 Apr 2018, at 16:06, Alistair Grant <akgrant0...@gmail.com> wrote: >> >> On 11 April 2018 at 15:11, Sven Van Caekenberghe <s...@stfx.eu> wrote: >>> >>> >>>> On 11 Apr 2018, at 11:12, Sven Van Caekenberghe <s...@stfx.eu> wrote: >>>> >>>> How does one modify #atEnd to block ? I suppose you are talking about >>>> StdioStream>>#atEnd ? >>>> >>>> ^ self peek isNil >>>> >>>> ? >>> >>> Still the same question, how do you implement a blocking #atEnd for stdin ? >>> >>> I have seen your stdio.cs which is indeed needed as the current >>> StdioStream>>#atEnd is bogus for sure. >>> >>> But that is still a non-blocking one, right ? >>> >>> Since there is a peekBuffer in StdioStream, why can't that be used ? >> >> I think you've created a chicken-and-egg problem with this question, >> but ignoring that for now: >> >> >> StdioStream>>peek >> "Answer what would be returned if the message next were sent to the >> receiver. If the receiver is at the end, answer nil. " >> >> self atEnd ifTrue: [^ nil ]. >> >> peekBuffer ifNotNil: [ ^ peekBuffer ]. >> >> ^ peekBuffer := self next. >> >> >> >> So when we first start the program, i.e. the user hasn't entered any >> input yet, and #peek is called: >> >> 1. #atEnd returns false because Ctrl-D (or similar) hasn't been >> entered (assuming it is non-blocking). >> 2. peekBuffer is nil because we haven't previously called #peek. >> 3. The system now blocks on "self next". >> >> >> Just a reminder: for terminal input the end-of-file isn't reached >> until the user explicitly enters the end of file key (Ctrl-D). >> >> So, if there is no buffered input (either none has been entered yet, >> or all input has been consumed) >> >> #atEnd (after the patch) calls #primAtEnd:. >> >> At the moment, #primAtEnd: ends up calling the libc function feof(), >> which is non-blocking and answers the end-of-file flag for the FILE*. >> Since the user hasn't entered Ctrl-D, that's false. >> >> If we want to control iteration over the stream and ensure that we >> don't need to do a "stream next == nil" check, then #primAtEnd: is >> going to have to peek for the next character, and that means waiting >> for the user to enter that character. >> >> In c that is typically done using: >> >> atEnd = ungetc(fgetc(fp), fp); >> >> and fgetc() will block until the user enters something. >> >>> I have run your example testAtEnd.st now, and it works/fails as advertised. >> >> :-) >> >> >> Cheers, >> Alistair >
