bpo-37266: Daemon threads are now denied in subinterpreters (GH-14049)

In a subinterpreter, spawning a daemon thread now raises an
exception. Daemon threads were never supported in subinterpreters.
Previously, the subinterpreter finalization crashed with a Pyton
fatal error if a daemon thread was still running.

* Add _thread._is_main_interpreter()
* threading.Thread.start() now raises RuntimeError if the thread is a
  daemon thread and the method is called from a subinterpreter.
* The _thread module now uses Argument Clinic for the new function.
* Use textwrap.dedent() in test_threading.SubinterpThreadingTests

2 files changed, 46 insertions, 0 deletions

diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
index d5e40ef..9ab8e7a 100644
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -8,6 +8,14 @@
 #include "structmember.h" /* offsetof */
 #include "pythread.h"
 
+#include "clinic/_threadmodule.c.h"
+
+/*[clinic input]
+module _thread
+[clinic start generated code]*/
+/*[clinic end generated code: output=da39a3ee5e6b4b0d input=be8dbe5cc4b16df7]*/
+
+
 static PyObject *ThreadError;
 static PyObject *str_dict;
 
@@ -1442,6 +1450,21 @@ PyDoc_STRVAR(excepthook_doc,
 \n\
 Handle uncaught Thread.run() exception.");
 
+/*[clinic input]
+_thread._is_main_interpreter
+
+Return True if the current interpreter is the main Python interpreter.
+[clinic start generated code]*/
+
+static PyObject *
+_thread__is_main_interpreter_impl(PyObject *module)
+/*[clinic end generated code: output=7dd82e1728339adc input=cc1eb00fd4598915]*/
+{
+    _PyRuntimeState *runtime = &_PyRuntime;
+    PyInterpreterState *interp = _PyRuntimeState_GetThreadState(runtime)->interp;
+    return PyBool_FromLong(interp == runtime->interpreters.main);
+}
+
 static PyMethodDef thread_methods[] = {
     {"start_new_thread",        (PyCFunction)thread_PyThread_start_new_thread,
      METH_VARARGS, start_new_doc},
@@ -1471,6 +1494,7 @@ static PyMethodDef thread_methods[] = {
      METH_NOARGS, _set_sentinel_doc},
     {"_excepthook",              thread_excepthook,
      METH_O, excepthook_doc},
+    _THREAD__IS_MAIN_INTERPRETER_METHODDEF
     {NULL,                      NULL}           /* sentinel */
 };
 
diff --git a/Modules/clinic/_threadmodule.c.h b/Modules/clinic/_threadmodule.c.h
new file mode 100644
index 0000000..07ea08b
--- /dev/null
+++ b/Modules/clinic/_threadmodule.c.h
@@ -0,0 +1,22 @@
+/*[clinic input]
+preserve
+[clinic start generated code]*/
+
+PyDoc_STRVAR(_thread__is_main_interpreter__doc__,
+"_is_main_interpreter($module, /)\n"
+"--\n"
+"\n"
+"Return True if the current interpreter is the main Python interpreter.");
+
+#define _THREAD__IS_MAIN_INTERPRETER_METHODDEF    \
+    {"_is_main_interpreter", (PyCFunction)_thread__is_main_interpreter, METH_NOARGS, _thread__is_main_interpreter__doc__},
+
+static PyObject *
+_thread__is_main_interpreter_impl(PyObject *module);
+
+static PyObject *
+_thread__is_main_interpreter(PyObject *module, PyObject *Py_UNUSED(ignored))
+{
+    return _thread__is_main_interpreter_impl(module);
+}
+/*[clinic end generated code: output=505840d1b9101789 input=a9049054013a1b77]*/