Merge with 3.3 for #16661

1 files changed, 5 insertions, 2 deletions

diff --git a/Python/import.c b/Python/import.c
index 2f71b97bc8..6882b57060 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -202,8 +202,11 @@ _PyImport_ReInitLock(void)
     if (import_lock_level > 1) {
         /* Forked as a side effect of import */
         long me = PyThread_get_thread_ident();
-        PyThread_acquire_lock(import_lock, 0);
-        /* XXX: can the previous line fail? */
+        /* The following could fail if the lock is already held, but forking as
+           a side-effect of an import is a) rare, b) nuts, and c) difficult to
+           do thanks to the lock only being held when doing individual module
+           locks per import. */
+        PyThread_acquire_lock(import_lock, NOWAIT_LOCK);
         import_lock_thread = me;
         import_lock_level--;
     } else {