I can make your example, using the Zn variants, work with the following change:
StdioStream>>#atEnd ^ peekBuffer isNil or: [ (peekBuffer := self next) isNil ] 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 <[email protected]> wrote: > > On 11 April 2018 at 15:11, Sven Van Caekenberghe <[email protected]> wrote: >> >> >>> On 11 Apr 2018, at 11:12, Sven Van Caekenberghe <[email protected]> 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
