# New Ticket Created by Sam S.
# Please include the string: [perl #129882]
# in the subject line of all future correspondence about this issue.
# <URL: https://rt.perl.org/Ticket/Display.html?id=129882 >
The following code attempts to pipe a large Blob (larger than a pipe's
buffer size) through an external command.
However, it hangs on the `.in.close` line and never finishes:
my $proc = run «cat -», :in, :out, :bin;
my $input = ("a" x 1000000).encode;
my $promise = start {
$proc.in.write: $input;
$proc.in.close;
}
say $proc.out.slurp-rest(:close, :bin).bytes;
await $promise;
More verbose version of the code with debug output showing where it blocks:
https://gist.github.com/smls/75518c746ca65b3287482c491971eac0
IRC comments:
<timotimo> moar sometimes gets confused, i think
<timotimo> or maybe it's libuv
<RabidGravy> shouldn't that give an error as other handles across threads do?
<gfldex> you get the same behaviour with
https://rt.perl.org/Public/Bug/Display.html?id=129787
Note that without the `start` (i.e. when writing to `.in` and then
reading from `.out` in the same thread), it already hangs on the
`.in.write`, as geekosaur explains:
<geekosaur> it will block if the process is not reading, yes. pipes have
finite buffer space
<geekosaur> whether this block is happening at OS level or if libuv is
supposed to be using non-blocking operations and return a "would
block, try again" and some higher level is blocking based on
that, I cannot say
