Bug 17432 (https://bugs.r-project.org/bugzilla3/show_bug.cgi?id=17432) is still
a problem when using pipes for IPC.
The bug is evident when calling R from another process and trying to
communicate via StdIn. R will buffer the input and not read lines until the
buffer is exceeded or StdIn is closed by the sending process. This prevents
interactive communication between a calling process and a child R process.
>From a quick look at the source code, it looks like the bug is caused by only
>disabling buffering when isatty() returns true for a file descriptor
>(connections.c). This fixes the original bug when the script is run in a
>terminal, but doesn't help for pipes, which will return false for isatty().
An example R script and python script are provided to demonstrate the problem:
R script (example.r):
================
f <- file("stdin")
open(f)
while(length(line <- readLines(f,n=1)) > 0) {
write(line, stderr())
}
Python3 script:
============
import sys, os, subprocess
process = subprocess.Popen(['Rscript', 'example.r'], stdin=subprocess.PIPE,
stdout=subprocess.PIPE)
for line in sys.stdin:
process.stdin.write((line + '\n').encode('utf-8'))
process.stdin.flush()
Expected Behaviour:
Run python script, each line entered is echoed back immediately by the R script
- which is what happens on 3.4.4
Observed Behaviiour on >=3.5.0 (include devel):
The R script does not process lines as they are sent, it only receives them
when StdIn is closed.
Best Regards
Chris
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