utils: handle signal errors with threads

We might not be able to rebind signals if we're running in a thread,
so ignore ValueError when setting the handler.

Bug: None
Test: unittests
Change-Id: I81a222bf00ff433c8570bb7058871817f15da003

1 files changed, 13 insertions, 4 deletions

diff --git a/rh/utils.py b/rh/utils.py
index 157e31b..4f1a063 100644
--- a/rh/utils.py
+++ b/rh/utils.py
@@ -369,18 +369,27 @@ def run(cmd, redirect_stdout=False, redirect_stderr=False, cwd=None, input=None,
         old_sigint = signal.getsignal(signal.SIGINT)
         handler = functools.partial(_kill_child_process, proc, int_timeout,
                                     kill_timeout, cmd, old_sigint)
-        signal.signal(signal.SIGINT, handler)
+        # We have to ignore ValueError in case we're run from a thread.
+        try:
+            signal.signal(signal.SIGINT, handler)
+        except ValueError:
+            old_sigint = None
 
         old_sigterm = signal.getsignal(signal.SIGTERM)
         handler = functools.partial(_kill_child_process, proc, int_timeout,
                                     kill_timeout, cmd, old_sigterm)
-        signal.signal(signal.SIGTERM, handler)
+        try:
+            signal.signal(signal.SIGTERM, handler)
+        except ValueError:
+            old_sigterm = None
 
         try:
             (result.stdout, result.stderr) = proc.communicate(input)
         finally:
-            signal.signal(signal.SIGINT, old_sigint)
-            signal.signal(signal.SIGTERM, old_sigterm)
+            if old_sigint is not None:
+                signal.signal(signal.SIGINT, old_sigint)
+            if old_sigterm is not None:
+                signal.signal(signal.SIGTERM, old_sigterm)
 
             if popen_stdout:
                 # The linter is confused by how stdout is a file & an int.