[bug-gawk] flush in the main process but not coprocess?

[Peng Yu]

Hi,

I have to use fflush() in the coprocess, otherwise the program hangs.
This is documented as the following.

I/O buffering may be a problem. gawk automatically flushes all output
down the pipe to the coprocess. However, if the coprocess does not
flush its output, gawk may hang when doing a getline in order to read
the coprocess's results. This could lead to a situation known as
deadlock, where each process is waiting for the other one to do
something.

But when the coprocess was written by somebody else, and I don't have
control of, it is not an option to call flush. Is there a walk-around
to this problem?

~/linux/test/awk/lang/pipe/|&$ cat.sh main.sh  main.awk
==> main.sh <==
#!/usr/bin/env bash

seq 10 | awk.sh -f main.awk


==> main.awk <==
BEGIN {
  subprogram = "awk -e '{print $1 + 10; fflush()}'"
}
{
  print $1 |& subprogram
  subprogram |& getline result
  print result
}
~/linux/test/awk/lang/pipe/|&$ ./main.sh
11
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-- 
Regards,
Peng