bpo-20891: Py_Initialize() now creates the GIL (#4700)

The GIL is no longer created "on demand" to fix a race condition when
PyGILState_Ensure() is called in a non-Python thread.

2 files changed, 17 insertions, 12 deletions

diff --git a/Python/ceval.c b/Python/ceval.c
index 128ec2c..52a42b0 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -254,8 +254,8 @@ PyEval_SaveThread(void)
     PyThreadState *tstate = PyThreadState_Swap(NULL);
     if (tstate == NULL)
         Py_FatalError("PyEval_SaveThread: NULL tstate");
-    if (gil_created())
-        drop_gil(tstate);
+    assert(gil_created());
+    drop_gil(tstate);
     return tstate;
 }
 
@@ -264,17 +264,18 @@ PyEval_RestoreThread(PyThreadState *tstate)
 {
     if (tstate == NULL)
         Py_FatalError("PyEval_RestoreThread: NULL tstate");
-    if (gil_created()) {
-        int err = errno;
-        take_gil(tstate);
-        /* _Py_Finalizing is protected by the GIL */
-        if (_Py_IsFinalizing() && !_Py_CURRENTLY_FINALIZING(tstate)) {
-            drop_gil(tstate);
-            PyThread_exit_thread();
-            Py_UNREACHABLE();
-        }
-        errno = err;
+    assert(gil_created());
+
+    int err = errno;
+    take_gil(tstate);
+    /* _Py_Finalizing is protected by the GIL */
+    if (_Py_IsFinalizing() && !_Py_CURRENTLY_FINALIZING(tstate)) {
+        drop_gil(tstate);
+        PyThread_exit_thread();
+        Py_UNREACHABLE();
     }
+    errno = err;
+
     PyThreadState_Swap(tstate);
 }
 
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index d46784a..82ab915 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -681,9 +681,13 @@ _Py_InitializeCore(const _PyCoreConfig *core_config)
        Instead we destroy the previously created GIL here, which ensures
        that we can call Py_Initialize / Py_FinalizeEx multiple times. */
     _PyEval_FiniThreads();
+
     /* Auto-thread-state API */
     _PyGILState_Init(interp, tstate);
 
+    /* Create the GIL */
+    PyEval_InitThreads();
+
     _Py_ReadyTypes();
 
     if (!_PyFrame_Init())