From: Michal Nazarewicz <>

The command_close_bidi_pipe() function will insist on closing both
input and output pipes returned by command_bidi_pipe().  With this
change it is possible to close one of the pipes in advance and
pass undef as an argument.

Signed-off-by: Michal Nazarewicz <>
 perl/ | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/perl/ b/perl/
index 11f310a..9dded54 100644
--- a/perl/
+++ b/perl/
@@ -426,13 +426,26 @@ Note that you should not rely on whatever actually is in 
 currently it is simply the command name but in future the context might
 have more complicated structure.
+C<PIPE_IN> and C<PIPE_OUT> may be C<undef> if they have been closed prior to
+calling this function.  This may be useful in a query-response type of
+commands where caller first writes a query and later reads response, eg:
+       my ($pid, $in, $out, $ctx) = $r->command_bidi_pipe('cat-file 
+       print $out "000000000\n";
+       close $out;
+       while (<$in>) { ... }
+       $r->command_close_bidi_pipe($pid, $in, undef, $ctx);
+This idiom may prevent potential dead locks caused by data sent to the output
+pipe not being flushed and thus not reaching the executed command.
 sub command_close_bidi_pipe {
        local $?;
        my ($self, $pid, $in, $out, $ctx) = _maybe_self(@_);
        foreach my $fh ($in, $out) {
-               unless (close $fh) {
+               if (defined $fh && !close $fh) {
                        if ($!) {
                                carp "error closing pipe: $!";
                        } elsif ($? >> 8) {

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