_frontend/cli.py: Clear stdout/stderr fd flags at startuptristan/spurious-blockingio-error

This fixes #929

1 files changed, 8 insertions, 0 deletions

diff --git a/buildstream/_frontend/cli.py b/buildstream/_frontend/cli.py
index 02ca52e85..f500f8996 100644
--- a/buildstream/_frontend/cli.py
+++ b/buildstream/_frontend/cli.py
@@ -9,6 +9,7 @@ from .. import _yaml
 from .._exceptions import BstError, LoadError, AppError
 from .._versions import BST_FORMAT_VERSION
 from .complete import main_bashcomplete, complete_path, CompleteUnhandled
+import fcntl
 
 
 ##################################################################
@@ -170,6 +171,13 @@ def override_completions(orig_args, cmd, cmd_param, args, incomplete):
 def override_main(self, args=None, prog_name=None, complete_var=None,
                   standalone_mode=True, **extra):
 
+    # Clear file status flags, if stdout/stderr is open in non-blocking
+    # mode for some reason then this can cause BlockingIOError errors
+    # when trying to write to the file.
+    #
+    fcntl.fcntl(sys.stdout.fileno(), fcntl.F_SETFL, 0)
+    fcntl.fcntl(sys.stderr.fileno(), fcntl.F_SETFL, 0)
+
     # Hook for the Bash completion.  This only activates if the Bash
     # completion is actually enabled, otherwise this is quite a fast
     # noop.