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When Python is embedded, it should be possible to call the following Python function multiple times:
void func(void)
{
 Py_Initialize();
 /* do something in Python */
 Py_Finalize();
}
Py_Finalize() ends by calling _PyRuntime_Finalize().
Problem: when Py_Initialize() is called the second time, _PyRuntime_Initialize() does nothing:
_PyInitError
_PyRuntime_Initialize(void)
{
 /* XXX We only initialize once in the process, which aligns with
 the static initialization of the former globals now found in
 _PyRuntime. However, _PyRuntime *should* be initialized with
 every Py_Initialize() call, but doing so breaks the runtime.
 This is because the runtime state is not properly finalized
 currently. */
 static int initialized = 0;
 if (initialized) {
 return _Py_INIT_OK();
 }
 initialized = 1;
 return _PyRuntimeState_Init(&_PyRuntime);
}
For example, Py_Finalize() clears runtime->interpreters.mutex and runtime->xidregistry.mutex, whereas mutexes are still needed the second time func() is called.
There is currently a *workaround*:
_PyInitError
_PyInterpreterState_Enable(_PyRuntimeState *runtime)
{
 ...
 if (runtime->interpreters.mutex == NULL) {
 ...
 runtime->interpreters.mutex = PyThread_allocate_lock();
 ...
 }
 ...
}
I would prefer that _PyRuntime_Initialize() calls _PyRuntimeState_Init() each time, and that _PyRuntimeState_Init() does nothing at the following call (except after Py_Finalize?).
Note: _PyRuntimeState_Fini() doesn't free runtime->xidregistry.mutex currently.

PR 12443 fix the issue.

New changeset fd23cfa464ab93273370475900819c1ea37c852f by Victor Stinner in branch 'master':
bpo-35388: Fix _PyRuntime_Finalize() (GH-12443)
https://github.com/python/cpython/commit/fd23cfa464ab93273370475900819c1ea37c852f