Issue #427

Fix: it's invalid according the API to call
PyGILState_Release(PyGILState_UNLOCKED) manually at startup to release the GIL.
Instead we must call another function, like PyEval_SaveThread().  The
difference shows up in a rare case on CPython 3.7 only.

1 files changed, 9 insertions, 7 deletions

diff --git a/cffi/_embedding.h b/cffi/_embedding.h
index d11b62a..764820e 100644
--- a/cffi/_embedding.h
+++ b/cffi/_embedding.h
@@ -327,13 +327,15 @@ static int _cffi_carefully_make_gil(void)
 #endif
 
     /* call Py_InitializeEx() */
-    {
-        PyGILState_STATE state = PyGILState_UNLOCKED;
-        if (!Py_IsInitialized())
-            _cffi_py_initialize();
-        else
-            state = PyGILState_Ensure();
-
+    if (!Py_IsInitialized()) {
+        _cffi_py_initialize();
+        PyEval_InitThreads();
+        PyEval_SaveThread();  /* release the GIL */
+        /* the returned tstate must be the one that has been stored into the
+           autoTLSkey by _PyGILState_Init() called from Py_Initialize(). */
+    }
+    else {
+        PyGILState_STATE state = PyGILState_Ensure();
         PyEval_InitThreads();
         PyGILState_Release(state);
     }