utils.py: Don't block on the call's `communicate` call

This ensures that, if we were to receive signals or other things while
we are on this blocking call, we would be able to process them instead
of waiting for the end of the process

1 files changed, 15 insertions, 1 deletions

diff --git a/src/buildstream/utils.py b/src/buildstream/utils.py
index 438543b83..e9f06aad6 100644
--- a/src/buildstream/utils.py
+++ b/src/buildstream/utils.py
@@ -32,6 +32,7 @@ import signal
 import stat
 from stat import S_ISDIR
 import subprocess
+from subprocess import TimeoutExpired
 import tempfile
 import time
 import datetime
@@ -1402,7 +1403,20 @@ def _call(*popenargs, terminate=False, **kwargs):
         process = subprocess.Popen(  # pylint: disable=subprocess-popen-preexec-fn
             *popenargs, preexec_fn=preexec_fn, universal_newlines=True, **kwargs
         )
-        output, _ = process.communicate()
+        # Here, we don't use `process.communicate()` directly without a timeout
+        # This is because, if we were to do that, and the process would never
+        # output anything, the control would never be given back to the python
+        # process, which might thus not be able to check for request to
+        # shutdown, or kill the process.
+        # We therefore loop with a timeout, to ensure the python process
+        # can act if it needs.
+        while True:
+            try:
+                output, _ = process.communicate(timeout=1)
+                break
+            except TimeoutExpired:
+                continue
+
         exit_code = process.poll()
 
     return (exit_code, output)