patch 7.4.1669
Problem:    When writing buffer lines to a pipe Vim may block.
Solution:   Avoid blocking, write more lines later.
diff --git a/src/misc2.c b/src/misc2.c
index ca340b7..a0cce07 100644
--- a/src/misc2.c
+++ b/src/misc2.c
@@ -6230,6 +6230,9 @@
     netbeans_parse_messages();
 # endif
 # ifdef FEAT_JOB_CHANNEL
+    /* Write any buffer lines still to be written. */
+    channel_write_any_lines();
+
     /* Process the messages queued on channels. */
     channel_parse_messages();
 # endif