[Rd] readLines() for non-blocking pipeline behaves differently in R 3.5

[Michael Lawrence]

Probably related to the switch to buffered connections. I will look
into this soon.

On Wed, Apr 25, 2018 at 2:34 PM, Randy Lai <randy.cs.lai at gmail.com> wrote:
> It seems that the behavior of readLines() in R 3.5 has changed for non-blocking pipeline.
>
>
> Consider the following R script, which reads from STDIN line by line.
> ```
> con <- file("stdin")
> open(con, blocking = FALSE)
>
> while (TRUE) {
>     txt <- readLines(con, 1)
>     if (length(txt) > 0) {
>         cat(txt, "\n", file = stdout())
>     }
>     Sys.sleep(0.1)
> }
> close(con)
>
> ```
>
> In R 3.4.4, it works as expected.
>
> ```
> (randymbpro)-Desktop$ echo "abc\nfoo" | R --slave -f test.R
> abc
> foo
> ```
>
> In R 3.5, only the first line is printed
> ```
> (randymbpro)-Desktop$ echo "abc\nfoo" | R --slave -f test.R
> abc
> ```
>
> Is this change expected?  If I change `blocking` to `TRUE` above, the above code would
> work. But I need non-blocking connection in my use case of piping buffer from
> another program.
>
> Best,
>
> R 3.5 @ macOS 10.13
>
>
> Randy
>
>
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>
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