Issue #18762: Print debug info on failure to create new forkserver process.

Also modify test code to hopefully avoid deadlock on failure.

1 files changed, 15 insertions, 0 deletions

diff --git a/Lib/multiprocessing/forkserver.py b/Lib/multiprocessing/forkserver.py
index 628808e53f..26bf0c3a11 100644
--- a/Lib/multiprocessing/forkserver.py
+++ b/Lib/multiprocessing/forkserver.py
@@ -66,6 +66,21 @@ def connect_to_new_process(fds):
         try:
             reduction.sendfds(client, allfds)
             return parent_r, parent_w
+        except OSError:
+            # XXX This is debugging info for Issue #18762
+            import fcntl
+            L = []
+            for fd in allfds:
+                try:
+                    flags = fcntl.fcntl(fd, fcntl.F_GETFL)
+                except OSError as e:
+                    L.append((fd, e))
+                else:
+                    L.append((fd, flags))
+            print('*** connect_to_new_process: %r' % L, file=sys.stderr)
+            os.close(parent_r)
+            os.close(parent_w)
+            raise
         except:
             os.close(parent_r)
             os.close(parent_w)