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Re: [Pharo-dev] Changed #atEnd primitive - #atEnd vs #next returning nil

by Alistair Grant

Hi Sven, On 11 April 2018 at 18:53, Sven Van Caekenberghe <sven(a)stfx.eu> wrote: > Something is off (and/or I am getting crazy, probably both). > > $ ./pharo --headless Pharo.image eval '(FileStream stdin binary; next: 3)' > 123 > #[49] > > ?? > > This should return #[49 50 51] AFAIK. I haven't checked properly, but I can take a guess at this... The file read primitive in FilePlugin tries to read from stdin 1 character at a time (presumably to get around the line buffering that is done, but I haven't gone through the history. At one time I think it modified the terminal settings, but that code is #if'd out). For all other streams it attempts to read the requested number of characters. StandardFileStream>>readInto:startingAt:count: assumes that primitiveFileRead will always attempt to read count bytes, but it actually only attempts to read 1. Cheers, Alistair

April 11, 2018

Re: [Pharo-dev] Changed #atEnd primitive - #atEnd vs #next returning nil

by Sven Van Caekenberghe

Something is off (and/or I am getting crazy, probably both). $ ./pharo --headless Pharo.image eval '(FileStream stdin binary; next: 3)' 123 #[49] ?? This should return #[49 50 51] AFAIK. > On 11 Apr 2018, at 18:26, Alistair Grant <akgrant0710(a)gmail.com> wrote: > > Hi Sven, > > On 11 April 2018 at 17:33, Sven Van Caekenberghe <sven(a)stfx.eu> wrote: >> I think we have to reset this whole discussion. >> >> FileStream stdin >> >> and >> >> Stdio stdin >> >> are completely different ! >> >> We'll have to check that first, before talking about the issues raised in this thread. > > Are you sure you're comparing (roughly) equal things? > > I would compare: > > FileStream stdin > > (very roughly) to: > > ZnCharacterReadStream on: > (ZnBufferedReadStream on: > Stdio stdin). > > Actually it is still not a fair comparison because MultiByteFileStream > attempts to be writable as well. If you could notionally do: > > FileStream stdin > readOnly; > binary; > unbuffered; > yourself. > > you could compare FileStream and Stdio :-) > > One important similarity: At the bottom they both use the same set of > primitives to communicate with the OS stdio streams (FilePlugin). > > HTH, > Alistair > > > >> And BTW these terminal streams are a real pain to test ;-)

April 11, 2018

Re: [Pharo-dev] Changed #atEnd primitive - #atEnd vs #next returning nil

by Alistair Grant

Hi Sven, On 11 April 2018 at 17:33, Sven Van Caekenberghe <sven(a)stfx.eu> wrote: > I think we have to reset this whole discussion. > > FileStream stdin > > and > > Stdio stdin > > are completely different ! > > We'll have to check that first, before talking about the issues raised in this thread. Are you sure you're comparing (roughly) equal things? I would compare: FileStream stdin (very roughly) to: ZnCharacterReadStream on: (ZnBufferedReadStream on: Stdio stdin). Actually it is still not a fair comparison because MultiByteFileStream attempts to be writable as well. If you could notionally do: FileStream stdin readOnly; binary; unbuffered; yourself. you could compare FileStream and Stdio :-) One important similarity: At the bottom they both use the same set of primitives to communicate with the OS stdio streams (FilePlugin). HTH, Alistair > And BTW these terminal streams are a real pain to test ;-)

April 11, 2018

Re: [Pharo-dev] Changed #atEnd primitive - #atEnd vs #next returning nil

by Alistair Grant

Hi Denis, On 11 April 2018 at 17:16, Denis Kudriashov <dionisiydk(a)gmail.com> wrote: > > 2018-04-11 17:02 GMT+02:00 Sven Van Caekenberghe <sven(a)stfx.eu>: >> >> >> >> > On 11 Apr 2018, at 16:36, Sven Van Caekenberghe <sven(a)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 ] >> >> Argh, make that >> >> atEnd >> ^ peekBuffer isNil and: [ (peekBuffer := self next) isNil ] > > > But discussion exactly about "self next isNil": how to avoid it. Apologies in advance for being pedantic, but... Do you really mean this (that the discussion is about how to avoid testing "self next isNil")? My argument has been that without making #atEnd blocking it is not possible to avoid the test (and we don't want to make #atEnd blocking). All the existing stream code that deals with character / byte streams does this test (see my "unwritten rules" from a previous reply). We don't want to make #atEnd blocking, so we need to keep the test (and my personal opinion is that changing the Zinc streams to adopt this approach does not add any significant architectural complexity). Assuming we reach agreement on the above, we do need to make the "unwritten rules" written. If we reach a different agreement we should document that. Cheers, Alistair

April 11, 2018

Re: [Pharo-dev] Changed #atEnd primitive - #atEnd vs #next returning nil

by Sven Van Caekenberghe

I think we have to reset this whole discussion. FileStream stdin and Stdio stdin are completely different ! We'll have to check that first, before talking about the issues raised in this thread. And BTW these terminal streams are a real pain to test ;-) > On 11 Apr 2018, at 17:20, Sven Van Caekenberghe <sven(a)stfx.eu> wrote: > > > >> On 11 Apr 2018, at 17:16, Denis Kudriashov <dionisiydk(a)gmail.com> wrote: >> >> >> 2018-04-11 17:02 GMT+02:00 Sven Van Caekenberghe <sven(a)stfx.eu>: >> >> >>> On 11 Apr 2018, at 16:36, Sven Van Caekenberghe <sven(a)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 ] >> >> Argh, make that >> >> atEnd >> ^ peekBuffer isNil and: [ (peekBuffer := self next) isNil ] >> >> But discussion exactly about "self next isNil": how to avoid it. > > I know, but like this it could/might become an implementation detail. > > The more things that I try, the more that I feel that stdin is so special that it does not fit in the rest of the stream zoo. > >> 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 <akgrant0710(a)gmail.com> wrote: >>>> >>>> On 11 April 2018 at 15:11, Sven Van Caekenberghe <sven(a)stfx.eu> wrote: >>>>> >>>>> >>>>>> On 11 Apr 2018, at 11:12, Sven Van Caekenberghe <sven(a)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

April 11, 2018

Re: [Pharo-dev] Changed #atEnd primitive - #atEnd vs #next returning nil

by Sven Van Caekenberghe

> On 11 Apr 2018, at 17:16, Denis Kudriashov <dionisiydk(a)gmail.com> wrote: > > > 2018-04-11 17:02 GMT+02:00 Sven Van Caekenberghe <sven(a)stfx.eu>: > > > > On 11 Apr 2018, at 16:36, Sven Van Caekenberghe <sven(a)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 ] > > Argh, make that > > atEnd > ^ peekBuffer isNil and: [ (peekBuffer := self next) isNil ] > > But discussion exactly about "self next isNil": how to avoid it. I know, but like this it could/might become an implementation detail. The more things that I try, the more that I feel that stdin is so special that it does not fit in the rest of the stream zoo. > 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 <akgrant0710(a)gmail.com> wrote: > >> > >> On 11 April 2018 at 15:11, Sven Van Caekenberghe <sven(a)stfx.eu> wrote: > >>> > >>> > >>>> On 11 Apr 2018, at 11:12, Sven Van Caekenberghe <sven(a)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 > >

April 11, 2018

Re: [Pharo-dev] Changed #atEnd primitive - #atEnd vs #next returning nil

by Denis Kudriashov

2018-04-11 17:02 GMT+02:00 Sven Van Caekenberghe <sven(a)stfx.eu>: > > > > On 11 Apr 2018, at 16:36, Sven Van Caekenberghe <sven(a)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 ] > > Argh, make that > > atEnd > ^ peekBuffer isNil and: [ (peekBuffer := self next) isNil ] > But discussion exactly about "self next isNil": how to avoid it. > > 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 <akgrant0710(a)gmail.com> wrote: > >> > >> On 11 April 2018 at 15:11, Sven Van Caekenberghe <sven(a)stfx.eu> wrote: > >>> > >>> > >>>> On 11 Apr 2018, at 11:12, Sven Van Caekenberghe <sven(a)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 > > > > >

April 11, 2018

Re: [Pharo-dev] Changed #atEnd primitive - #atEnd vs #next returning nil

by Sven Van Caekenberghe

> On 11 Apr 2018, at 16:36, Sven Van Caekenberghe <sven(a)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 ] 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 <akgrant0710(a)gmail.com> wrote: >> >> On 11 April 2018 at 15:11, Sven Van Caekenberghe <sven(a)stfx.eu> wrote: >>> >>> >>>> On 11 Apr 2018, at 11:12, Sven Van Caekenberghe <sven(a)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 >

April 11, 2018

Re: [Pharo-dev] help wanted: normalising LF on tonel for Pharo project

by Ben Coman

On 11 April 2018 at 05:05, Esteban Lorenzano <estebanlm(a)gmail.com> wrote: > Hi, > > Iâve been wondering how to better fix the problem of having windows and > linux/macOS people contributing and the fact that files are written in > their native system format (crlf windows, lf for the rest of the world). > > > I digged a bit and I found a couple a link that helped me (after trying to > understand the doc): https://stackoverflow.com/questions/170961/whats- > the-best-crlf-carriage-return-line-feed-handling-strategy-with-git > > and it seems adding a .gitattributes file with this content: > > # Auto detect text files and perform LF normalization > * text=auto > I see a few posts around that recommend reading http://adaptivepatchwork.com/2012/03/01/mind-the-end-of-your-line/ which about the above line says... "This is certainly better than requiring everyone to be on the same global setting for core.autocrlf, but it means that you really trust Git to do binary detection properly. In my opinion it is better to explicitly specify your text files that you want normalized." and https://tinyurl.com/ya9xsprx says "We had a repo with * text=auto, and Git guessed wrong for an image file that it was a text file, causing it to corrupt it as it replaced CR + LF bytes with LF bytes in the object database." I'm unsure. Without it the system is subject to different users' different global settings and I'd guess that may be a more frequent problem than Git guessing wrong. The latter can be fixed by a user adding an extra .gitattributes entry explicitly specifying the file was binary, whereas the former seems to introduce a confounding factor. So probably a good line to have. > *.st text merge=union eol=lf > > could fix the problem? > can someone confirm this? > "eol=lf" looks appropriate... https://www.scivision.co/git-line-endings-windows-cygwin-wsl/ Most editors on Windows transparently handle LF line endings. https://en.wikipedia.org/wiki/Comparison_of_text_editors#Newline_support " merge=union" I am not familiar with, but I read at... https://git-scm.com/docs/gitattributes "union = Run 3-way file level merge for text files, but take lines from both versions, instead of leaving conflict markers. This tends to leave the added lines in the resulting file in random** order and the user should verify the result. Do not use this if you do not understand the implications." What are the implications of lines being merged in a random order? btw, has doing a callback from libgit to a custom merge driver in Pharo been considered? https://libgit2.github.com/libgit2/#HEAD/group/callback/git_merge_driver_ap… btw2, I found (https://githubengineering.com/move-fast/) interesting... saying... "Despite being a C library, libgit2 contains many powerful abstractions to accomplish complex tasks that Git simply cannot do. One of these features are indexes that exist solely in memory and allow work-tree related operations to be performed without an actual working directory. [...] With the in-memory index, libgit2 is capable of merging two trees in a repository without having to check out any of their files on disk." On 11 April 2018 at 05:55, Esteban Lorenzano <estebanlm(a)gmail.com> wrote: > or a .iceberg file? > > Esteban > > ps: yep, we need itâ¦ we will have it, why not start now? > Do you mean Iceberg would clone a repo, and from its included .iceberg file a matching .gitattributes file would be created? That seems like double handling. Why not have the user edit the .gitattributes file directly from Iceberg? Iceberg might provide some appropriate templates. cheers -ben

April 11, 2018

Re: [Pharo-dev] Changed #atEnd primitive - #atEnd vs #next returning nil

by Sven Van Caekenberghe

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 <akgrant0710(a)gmail.com> wrote: > > On 11 April 2018 at 15:11, Sven Van Caekenberghe <sven(a)stfx.eu> wrote: >> >> >>> On 11 Apr 2018, at 11:12, Sven Van Caekenberghe <sven(a)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

April 11, 2018