text: 
  /* Thread and interpreter state structures and their interfaces */
  
  #include "Python.h"
  #include "pycore_ceval.h"
  #include "pycore_initconfig.h"
  #include "pycore_pymem.h"
  #include "pycore_pystate.h"
  #include "pycore_pylifecycle.h"
  
  /* --------------------------------------------------------------------------
  CAUTION
  
  Always use PyMem_RawMalloc() and PyMem_RawFree() directly in this file.  A
  number of these functions are advertised as safe to call when the GIL isn't
  held, and in a debug build Python redirects (e.g.) PyMem_NEW (etc) to Python's
  debugging obmalloc functions.  Those aren't thread-safe (they rely on the GIL
  to avoid the expense of doing their own locking).
  -------------------------------------------------------------------------- */
  
  #ifdef HAVE_DLOPEN
  #ifdef HAVE_DLFCN_H
  #include <dlfcn.h>
  #endif
  #if !HAVE_DECL_RTLD_LAZY
  #define RTLD_LAZY 1
  #endif
  #endif
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  #define _PyRuntimeGILState_GetThreadState(gilstate) \
      ((PyThreadState*)_Py_atomic_load_relaxed(&(gilstate)->tstate_current))
  #define _PyRuntimeGILState_SetThreadState(gilstate, value) \
      _Py_atomic_store_relaxed(&(gilstate)->tstate_current, \
                               (uintptr_t)(value))
  
  /* Forward declarations */
  static PyThreadState *_PyGILState_GetThisThreadState(struct _gilstate_runtime_state *gilstate);
  static void _PyThreadState_Delete(_PyRuntimeState *runtime, PyThreadState *tstate);
  
  
  static PyStatus
  _PyRuntimeState_Init_impl(_PyRuntimeState *runtime)
  {
      /* We preserve the hook across init, because there is
         currently no public API to set it between runtime
         initialization and interpreter initialization. */
      void *open_code_hook = runtime->open_code_hook;
      void *open_code_userdata = runtime->open_code_userdata;
      _Py_AuditHookEntry *audit_hook_head = runtime->audit_hook_head;
  
      memset(runtime, 0, sizeof(*runtime));
  
      runtime->open_code_hook = open_code_hook;
      runtime->open_code_userdata = open_code_userdata;
      runtime->audit_hook_head = audit_hook_head;
  
      _PyGC_Initialize(&runtime->gc);
      _PyEval_Initialize(&runtime->ceval);
  
      runtime->preconfig.struct_size = sizeof(PyPreConfig);
      PyStatus status = PyPreConfig_InitPythonConfig(&runtime->preconfig);
      if (_PyStatus_EXCEPTION(status)) {
          return status;
      }
  
      runtime->gilstate.check_enabled = 1;
  
      /* A TSS key must be initialized with Py_tss_NEEDS_INIT
         in accordance with the specification. */
      Py_tss_t initial = Py_tss_NEEDS_INIT;
      runtime->gilstate.autoTSSkey = initial;
  
      runtime->interpreters.mutex = PyThread_allocate_lock();
      if (runtime->interpreters.mutex == NULL) {
          return _PyStatus_ERR("Can't initialize threads for interpreter");
      }
      runtime->interpreters.next_id = -1;
  
      runtime->xidregistry.mutex = PyThread_allocate_lock();
      if (runtime->xidregistry.mutex == NULL) {
          return _PyStatus_ERR("Can't initialize threads for cross-interpreter data registry");
      }
  
      // Set it to the ID of the main thread of the main interpreter.
      runtime->main_thread = PyThread_get_thread_ident();
  
      return _PyStatus_OK();
  }
  
  PyStatus
  _PyRuntimeState_Init(_PyRuntimeState *runtime)
  {
      /* Force default allocator, since _PyRuntimeState_Fini() must
         use the same allocator than this function. */
      PyMemAllocatorEx old_alloc;
      _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
  
      PyStatus status = _PyRuntimeState_Init_impl(runtime);
  
      PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
      return status;
  }
  
  void
  _PyRuntimeState_Fini(_PyRuntimeState *runtime)
  {
      /* Force the allocator used by _PyRuntimeState_Init(). */
      PyMemAllocatorEx old_alloc;
      _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
  
      if (runtime->interpreters.mutex != NULL) {
          PyThread_free_lock(runtime->interpreters.mutex);
          runtime->interpreters.mutex = NULL;
      }
  
      if (runtime->xidregistry.mutex != NULL) {
          PyThread_free_lock(runtime->xidregistry.mutex);
          runtime->xidregistry.mutex = NULL;
      }
  
      PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
  }
  
  /* This function is called from PyOS_AfterFork_Child to ensure that
   * newly created child processes do not share locks with the parent.
   */
  
  void
  _PyRuntimeState_ReInitThreads(_PyRuntimeState *runtime)
  {
      // This was initially set in _PyRuntimeState_Init().
      runtime->main_thread = PyThread_get_thread_ident();
  
      /* Force default allocator, since _PyRuntimeState_Fini() must
         use the same allocator than this function. */
      PyMemAllocatorEx old_alloc;
      _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
  
      runtime->interpreters.mutex = PyThread_allocate_lock();
      runtime->interpreters.main->id_mutex = PyThread_allocate_lock();
      runtime->xidregistry.mutex = PyThread_allocate_lock();
  
      PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
  
      if (runtime->interpreters.mutex == NULL) {
          Py_FatalError("Can't initialize lock for runtime interpreters");
      }
  
      if (runtime->interpreters.main->id_mutex == NULL) {
          Py_FatalError("Can't initialize ID lock for main interpreter");
      }
  
      if (runtime->xidregistry.mutex == NULL) {
          Py_FatalError("Can't initialize lock for cross-interpreter data registry");
      }
  }
  
  #define HEAD_LOCK(runtime) \
      PyThread_acquire_lock((runtime)->interpreters.mutex, WAIT_LOCK)
  #define HEAD_UNLOCK(runtime) \
      PyThread_release_lock((runtime)->interpreters.mutex)
  
  /* Forward declaration */
  static void _PyGILState_NoteThreadState(
      struct _gilstate_runtime_state *gilstate, PyThreadState* tstate);
  
  PyStatus
  _PyInterpreterState_Enable(_PyRuntimeState *runtime)
  {
      struct pyinterpreters *interpreters = &runtime->interpreters;
      interpreters->next_id = 0;
  
      /* Py_Finalize() calls _PyRuntimeState_Fini() which clears the mutex.
         Create a new mutex if needed. */
      if (interpreters->mutex == NULL) {
          /* Force default allocator, since _PyRuntimeState_Fini() must
             use the same allocator than this function. */
          PyMemAllocatorEx old_alloc;
          _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
  
          interpreters->mutex = PyThread_allocate_lock();
  
          PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
  
          if (interpreters->mutex == NULL) {
              return _PyStatus_ERR("Can't initialize threads for interpreter");
          }
      }
  
      return _PyStatus_OK();
  }
  
  PyInterpreterState *
  PyInterpreterState_New(void)
  {
      if (PySys_Audit("cpython.PyInterpreterState_New", NULL) < 0) {
          return NULL;
      }
  
      PyInterpreterState *interp = PyMem_RawMalloc(sizeof(PyInterpreterState));
      if (interp == NULL) {
          return NULL;
      }
  
      memset(interp, 0, sizeof(*interp));
      interp->id_refcount = -1;
  
      interp->config.struct_size = sizeof(PyConfig);
      PyStatus status = PyConfig_InitPythonConfig(&interp->config);
      if (_PyStatus_EXCEPTION(status)) {
          /* Don't report status to caller: PyConfig_InitPythonConfig()
             can only fail with a memory allocation error. */
          PyConfig_Clear(&interp->config);
          PyMem_RawFree(interp);
          return NULL;
      }
  
      interp->eval_frame = _PyEval_EvalFrameDefault;
  #ifdef HAVE_DLOPEN
  #if HAVE_DECL_RTLD_NOW
      interp->dlopenflags = RTLD_NOW;
  #else
      interp->dlopenflags = RTLD_LAZY;
  #endif
  #endif
  
      _PyRuntimeState *runtime = &_PyRuntime;
      struct pyinterpreters *interpreters = &runtime->interpreters;
  
      HEAD_LOCK(runtime);
      if (interpreters->next_id < 0) {
          /* overflow or Py_Initialize() not called! */
          PyErr_SetString(PyExc_RuntimeError,
                          "failed to get an interpreter ID");
          PyMem_RawFree(interp);
          interp = NULL;
      }
      else {
          interp->id = interpreters->next_id;
          interpreters->next_id += 1;
          interp->next = interpreters->head;
          if (interpreters->main == NULL) {
              interpreters->main = interp;
          }
          interpreters->head = interp;
      }
      HEAD_UNLOCK(runtime);
  
      if (interp == NULL) {
          return NULL;
      }
  
      interp->tstate_next_unique_id = 0;
  
      interp->audit_hooks = NULL;
  
      return interp;
  }
  
  
  static void
  _PyInterpreterState_Clear(_PyRuntimeState *runtime, PyInterpreterState *interp)
  {
      if (PySys_Audit("cpython.PyInterpreterState_Clear", NULL) < 0) {
          PyErr_Clear();
      }
  
      HEAD_LOCK(runtime);
      for (PyThreadState *p = interp->tstate_head; p != NULL; p = p->next) {
          PyThreadState_Clear(p);
      }
      HEAD_UNLOCK(runtime);
  
      Py_CLEAR(interp->audit_hooks);
  
      PyConfig_Clear(&interp->config);
      Py_CLEAR(interp->codec_search_path);
      Py_CLEAR(interp->codec_search_cache);
      Py_CLEAR(interp->codec_error_registry);
      Py_CLEAR(interp->modules);
      Py_CLEAR(interp->modules_by_index);
      Py_CLEAR(interp->sysdict);
      Py_CLEAR(interp->builtins);
      Py_CLEAR(interp->builtins_copy);
      Py_CLEAR(interp->importlib);
      Py_CLEAR(interp->import_func);
      Py_CLEAR(interp->dict);
  #ifdef HAVE_FORK
      Py_CLEAR(interp->before_forkers);
      Py_CLEAR(interp->after_forkers_parent);
      Py_CLEAR(interp->after_forkers_child);
  #endif
      if (runtime->finalizing == NULL) {
          _PyWarnings_Fini(interp);
      }
      // XXX Once we have one allocator per interpreter (i.e.
      // per-interpreter GC) we must ensure that all of the interpreter's
      // objects have been cleaned up at the point.
  }
  
  void
  PyInterpreterState_Clear(PyInterpreterState *interp)
  {
      _PyInterpreterState_Clear(&_PyRuntime, interp);
  }
  
  
  static void
  zapthreads(_PyRuntimeState *runtime, PyInterpreterState *interp)
  {
      PyThreadState *p;
      /* No need to lock the mutex here because this should only happen
         when the threads are all really dead (XXX famous last words). */
      while ((p = interp->tstate_head) != NULL) {
          _PyThreadState_Delete(runtime, p);
      }
  }
  
  
  static void
  _PyInterpreterState_Delete(_PyRuntimeState *runtime,
                             PyInterpreterState *interp)
  {
      struct pyinterpreters *interpreters = &runtime->interpreters;
      zapthreads(runtime, interp);
      HEAD_LOCK(runtime);
      PyInterpreterState **p;
      for (p = &interpreters->head; ; p = &(*p)->next) {
          if (*p == NULL) {
              Py_FatalError("PyInterpreterState_Delete: invalid interp");
          }
          if (*p == interp) {
              break;
          }
      }
      if (interp->tstate_head != NULL) {
          Py_FatalError("PyInterpreterState_Delete: remaining threads");
      }
      *p = interp->next;
      if (interpreters->main == interp) {
          interpreters->main = NULL;
          if (interpreters->head != NULL) {
              Py_FatalError("PyInterpreterState_Delete: remaining subinterpreters");
          }
      }
      HEAD_UNLOCK(runtime);
      if (interp->id_mutex != NULL) {
          PyThread_free_lock(interp->id_mutex);
      }
      PyMem_RawFree(interp);
  }
  
  
  void
  PyInterpreterState_Delete(PyInterpreterState *interp)
  {
      _PyInterpreterState_Delete(&_PyRuntime, interp);
  }
  
  
  /*
   * Delete all interpreter states except the main interpreter.  If there
   * is a current interpreter state, it *must* be the main interpreter.
   */
  void
  _PyInterpreterState_DeleteExceptMain(_PyRuntimeState *runtime)
  {
      struct _gilstate_runtime_state *gilstate = &runtime->gilstate;
      struct pyinterpreters *interpreters = &runtime->interpreters;
  
      PyThreadState *tstate = _PyThreadState_Swap(gilstate, NULL);
      if (tstate != NULL && tstate->interp != interpreters->main) {
          Py_FatalError("PyInterpreterState_DeleteExceptMain: not main interpreter");
      }
  
      HEAD_LOCK(runtime);
      PyInterpreterState *interp = interpreters->head;
      interpreters->head = NULL;
      while (interp != NULL) {
          if (interp == interpreters->main) {
              interpreters->main->next = NULL;
              interpreters->head = interp;
              interp = interp->next;
              continue;
          }
  
          _PyInterpreterState_Clear(runtime, interp);  // XXX must activate?
          zapthreads(runtime, interp);
          if (interp->id_mutex != NULL) {
              PyThread_free_lock(interp->id_mutex);
          }
          PyInterpreterState *prev_interp = interp;
          interp = interp->next;
          PyMem_RawFree(prev_interp);
      }
      HEAD_UNLOCK(runtime);
  
      if (interpreters->head == NULL) {
          Py_FatalError("PyInterpreterState_DeleteExceptMain: missing main");
      }
      _PyThreadState_Swap(gilstate, tstate);
  }
  
  
  PyInterpreterState *
  _PyInterpreterState_Get(void)
  {
      PyThreadState *tstate = _PyThreadState_GET();
      if (tstate == NULL) {
          Py_FatalError("_PyInterpreterState_Get(): no current thread state");
      }
      PyInterpreterState *interp = tstate->interp;
      if (interp == NULL) {
          Py_FatalError("_PyInterpreterState_Get(): no current interpreter");
      }
      return interp;
  }
  
  
  int64_t
  PyInterpreterState_GetID(PyInterpreterState *interp)
  {
      if (interp == NULL) {
          PyErr_SetString(PyExc_RuntimeError, "no interpreter provided");
          return -1;
      }
      return interp->id;
  }
  
  
  static PyInterpreterState *
  interp_look_up_id(_PyRuntimeState *runtime, PY_INT64_T requested_id)
  {
      PyInterpreterState *interp = runtime->interpreters.head;
      while (interp != NULL) {
          PY_INT64_T id = PyInterpreterState_GetID(interp);
          if (id < 0) {
              return NULL;
          }
          if (requested_id == id) {
              return interp;
          }
          interp = PyInterpreterState_Next(interp);
      }
      return NULL;
  }
  
  PyInterpreterState *
  _PyInterpreterState_LookUpID(PY_INT64_T requested_id)
  {
      PyInterpreterState *interp = NULL;
      if (requested_id >= 0) {
          _PyRuntimeState *runtime = &_PyRuntime;
          HEAD_LOCK(runtime);
          interp = interp_look_up_id(runtime, requested_id);
          HEAD_UNLOCK(runtime);
      }
      if (interp == NULL && !PyErr_Occurred()) {
          PyErr_Format(PyExc_RuntimeError,
                       "unrecognized interpreter ID %lld", requested_id);
      }
      return interp;
  }
  
  
  int
  _PyInterpreterState_IDInitref(PyInterpreterState *interp)
  {
      if (interp->id_mutex != NULL) {
          return 0;
      }
      interp->id_mutex = PyThread_allocate_lock();
      if (interp->id_mutex == NULL) {
          PyErr_SetString(PyExc_RuntimeError,
                          "failed to create init interpreter ID mutex");
          return -1;
      }
      interp->id_refcount = 0;
      return 0;
  }
  
  
  void
  _PyInterpreterState_IDIncref(PyInterpreterState *interp)
  {
      if (interp->id_mutex == NULL) {
          return;
      }
      PyThread_acquire_lock(interp->id_mutex, WAIT_LOCK);
      interp->id_refcount += 1;
      PyThread_release_lock(interp->id_mutex);
  }
  
  
  void
  _PyInterpreterState_IDDecref(PyInterpreterState *interp)
  {
      if (interp->id_mutex == NULL) {
          return;
      }
      struct _gilstate_runtime_state *gilstate = &_PyRuntime.gilstate;
      PyThread_acquire_lock(interp->id_mutex, WAIT_LOCK);
      assert(interp->id_refcount != 0);
      interp->id_refcount -= 1;
      int64_t refcount = interp->id_refcount;
      PyThread_release_lock(interp->id_mutex);
  
      if (refcount == 0 && interp->requires_idref) {
          // XXX Using the "head" thread isn't strictly correct.
          PyThreadState *tstate = PyInterpreterState_ThreadHead(interp);
          // XXX Possible GILState issues?
          PyThreadState *save_tstate = _PyThreadState_Swap(gilstate, tstate);
          Py_EndInterpreter(tstate);
          _PyThreadState_Swap(gilstate, save_tstate);
      }
  }
  
  int
  _PyInterpreterState_RequiresIDRef(PyInterpreterState *interp)
  {
      return interp->requires_idref;
  }
  
  void
  _PyInterpreterState_RequireIDRef(PyInterpreterState *interp, int required)
  {
      interp->requires_idref = required ? 1 : 0;
  }
  
  PyObject *
  _PyInterpreterState_GetMainModule(PyInterpreterState *interp)
  {
      if (interp->modules == NULL) {
          PyErr_SetString(PyExc_RuntimeError, "interpreter not initialized");
          return NULL;
      }
      return PyMapping_GetItemString(interp->modules, "__main__");
  }
  
  PyObject *
  PyInterpreterState_GetDict(PyInterpreterState *interp)
  {
      if (interp->dict == NULL) {
          interp->dict = PyDict_New();
          if (interp->dict == NULL) {
              PyErr_Clear();
          }
      }
      /* Returning NULL means no per-interpreter dict is available. */
      return interp->dict;
  }
  
  /* Default implementation for _PyThreadState_GetFrame */
  static struct _frame *
  threadstate_getframe(PyThreadState *self)
  {
      return self->frame;
  }
  
  static PyThreadState *
  new_threadstate(PyInterpreterState *interp, int init)
  {
      _PyRuntimeState *runtime = &_PyRuntime;
      PyThreadState *tstate = (PyThreadState *)PyMem_RawMalloc(sizeof(PyThreadState));
      if (tstate == NULL) {
          return NULL;
      }
  
      if (_PyThreadState_GetFrame == NULL) {
          _PyThreadState_GetFrame = threadstate_getframe;
      }
  
      tstate->interp = interp;
  
      tstate->frame = NULL;
      tstate->recursion_depth = 0;
      tstate->overflowed = 0;
      tstate->recursion_critical = 0;
      tstate->stackcheck_counter = 0;
      tstate->tracing = 0;
      tstate->use_tracing = 0;
      tstate->gilstate_counter = 0;
      tstate->async_exc = NULL;
      tstate->thread_id = PyThread_get_thread_ident();
  
      tstate->dict = NULL;
  
      tstate->curexc_type = NULL;
      tstate->curexc_value = NULL;
      tstate->curexc_traceback = NULL;
  
      tstate->exc_state.exc_type = NULL;
      tstate->exc_state.exc_value = NULL;
      tstate->exc_state.exc_traceback = NULL;
      tstate->exc_state.previous_item = NULL;
      tstate->exc_info = &tstate->exc_state;
  
      tstate->c_profilefunc = NULL;
      tstate->c_tracefunc = NULL;
      tstate->c_profileobj = NULL;
      tstate->c_traceobj = NULL;
  
      tstate->trash_delete_nesting = 0;
      tstate->trash_delete_later = NULL;
      tstate->on_delete = NULL;
      tstate->on_delete_data = NULL;
  
      tstate->coroutine_origin_tracking_depth = 0;
  
      tstate->async_gen_firstiter = NULL;
      tstate->async_gen_finalizer = NULL;
  
      tstate->context = NULL;
      tstate->context_ver = 1;
  
      tstate->id = ++interp->tstate_next_unique_id;
  
      if (init) {
          _PyThreadState_Init(runtime, tstate);
      }
  
      HEAD_LOCK(runtime);
      tstate->prev = NULL;
      tstate->next = interp->tstate_head;
      if (tstate->next)
          tstate->next->prev = tstate;
      interp->tstate_head = tstate;
      HEAD_UNLOCK(runtime);
  
      return tstate;
  }
  
  PyThreadState *
  PyThreadState_New(PyInterpreterState *interp)
  {
      return new_threadstate(interp, 1);
  }
  
  PyThreadState *
  _PyThreadState_Prealloc(PyInterpreterState *interp)
  {
      return new_threadstate(interp, 0);
  }
  
  void
  _PyThreadState_Init(_PyRuntimeState *runtime, PyThreadState *tstate)
  {
      _PyGILState_NoteThreadState(&runtime->gilstate, tstate);
  }
  
  PyObject*
  PyState_FindModule(struct PyModuleDef* module)
  {
      Py_ssize_t index = module->m_base.m_index;
      PyInterpreterState *state = _PyInterpreterState_GET_UNSAFE();
      PyObject *res;
      if (module->m_slots) {
          return NULL;
      }
      if (index == 0)
          return NULL;
      if (state->modules_by_index == NULL)
          return NULL;
      if (index >= PyList_GET_SIZE(state->modules_by_index))
          return NULL;
      res = PyList_GET_ITEM(state->modules_by_index, index);
      return res==Py_None ? NULL : res;
  }
  
  int
  _PyState_AddModule(PyObject* module, struct PyModuleDef* def)
  {
      PyInterpreterState *state;
      if (!def) {
          assert(PyErr_Occurred());
          return -1;
      }
      if (def->m_slots) {
          PyErr_SetString(PyExc_SystemError,
                          "PyState_AddModule called on module with slots");
          return -1;
      }
      state = _PyInterpreterState_GET_UNSAFE();
      if (!state->modules_by_index) {
          state->modules_by_index = PyList_New(0);
          if (!state->modules_by_index)
              return -1;
      }
      while (PyList_GET_SIZE(state->modules_by_index) <= def->m_base.m_index)
          if (PyList_Append(state->modules_by_index, Py_None) < 0)
              return -1;
      Py_INCREF(module);
      return PyList_SetItem(state->modules_by_index,
                            def->m_base.m_index, module);
  }
  
  int
  PyState_AddModule(PyObject* module, struct PyModuleDef* def)
  {
      Py_ssize_t index;
      PyInterpreterState *state = _PyInterpreterState_GET_UNSAFE();
      if (!def) {
          Py_FatalError("PyState_AddModule: Module Definition is NULL");
          return -1;
      }
      index = def->m_base.m_index;
      if (state->modules_by_index &&
          index < PyList_GET_SIZE(state->modules_by_index) &&
          module == PyList_GET_ITEM(state->modules_by_index, index)) {
          Py_FatalError("PyState_AddModule: Module already added!");
          return -1;
      }
      return _PyState_AddModule(module, def);
  }
  
  int
  PyState_RemoveModule(struct PyModuleDef* def)
  {
      PyInterpreterState *state;
      Py_ssize_t index = def->m_base.m_index;
      if (def->m_slots) {
          PyErr_SetString(PyExc_SystemError,
                          "PyState_RemoveModule called on module with slots");
          return -1;
      }
      state = _PyInterpreterState_GET_UNSAFE();
      if (index == 0) {
          Py_FatalError("PyState_RemoveModule: Module index invalid.");
          return -1;
      }
      if (state->modules_by_index == NULL) {
          Py_FatalError("PyState_RemoveModule: Interpreters module-list not accessible.");
          return -1;
      }
      if (index > PyList_GET_SIZE(state->modules_by_index)) {
          Py_FatalError("PyState_RemoveModule: Module index out of bounds.");
          return -1;
      }
      Py_INCREF(Py_None);
      return PyList_SetItem(state->modules_by_index, index, Py_None);
  }
  
  /* Used by PyImport_Cleanup() */
  void
  _PyInterpreterState_ClearModules(PyInterpreterState *interp)
  {
      if (!interp->modules_by_index) {
          return;
      }
  
      Py_ssize_t i;
      for (i = 0; i < PyList_GET_SIZE(interp->modules_by_index); i++) {
          PyObject *m = PyList_GET_ITEM(interp->modules_by_index, i);
          if (PyModule_Check(m)) {
              /* cleanup the saved copy of module dicts */
              PyModuleDef *md = PyModule_GetDef(m);
              if (md) {
                  Py_CLEAR(md->m_base.m_copy);
              }
          }
      }
  
      /* Setting modules_by_index to NULL could be dangerous, so we
         clear the list instead. */
      if (PyList_SetSlice(interp->modules_by_index,
                          0, PyList_GET_SIZE(interp->modules_by_index),
                          NULL)) {
          PyErr_WriteUnraisable(interp->modules_by_index);
      }
  }
  
  void
  PyThreadState_Clear(PyThreadState *tstate)
  {
      int verbose = tstate->interp->config.verbose;
  
      if (verbose && tstate->frame != NULL)
          fprintf(stderr,
            "PyThreadState_Clear: warning: thread still has a frame\n");
  
      Py_CLEAR(tstate->frame);
  
      Py_CLEAR(tstate->dict);
      Py_CLEAR(tstate->async_exc);
  
      Py_CLEAR(tstate->curexc_type);
      Py_CLEAR(tstate->curexc_value);
      Py_CLEAR(tstate->curexc_traceback);
  
      Py_CLEAR(tstate->exc_state.exc_type);
      Py_CLEAR(tstate->exc_state.exc_value);
      Py_CLEAR(tstate->exc_state.exc_traceback);
  
      /* The stack of exception states should contain just this thread. */
      if (verbose && tstate->exc_info != &tstate->exc_state) {
          fprintf(stderr,
            "PyThreadState_Clear: warning: thread still has a generator\n");
      }
  
      tstate->c_profilefunc = NULL;
      tstate->c_tracefunc = NULL;
      Py_CLEAR(tstate->c_profileobj);
      Py_CLEAR(tstate->c_traceobj);
  
      Py_CLEAR(tstate->async_gen_firstiter);
      Py_CLEAR(tstate->async_gen_finalizer);
  
      Py_CLEAR(tstate->context);
  }
  
  
  /* Common code for PyThreadState_Delete() and _PyThreadState_DeleteCurrent() */
  static void
  tstate_delete_common(_PyRuntimeState *runtime, PyThreadState *tstate)
  {
      if (tstate == NULL) {
          Py_FatalError("PyThreadState_Delete: NULL tstate");
      }
      PyInterpreterState *interp = tstate->interp;
      if (interp == NULL) {
          Py_FatalError("PyThreadState_Delete: NULL interp");
      }
      HEAD_LOCK(runtime);
      if (tstate->prev)
          tstate->prev->next = tstate->next;
      else
          interp->tstate_head = tstate->next;
      if (tstate->next)
          tstate->next->prev = tstate->prev;
      HEAD_UNLOCK(runtime);
      if (tstate->on_delete != NULL) {
          tstate->on_delete(tstate->on_delete_data);
      }
      PyMem_RawFree(tstate);
  }
  
  
  static void
  _PyThreadState_Delete(_PyRuntimeState *runtime, PyThreadState *tstate)
  {
      struct _gilstate_runtime_state *gilstate = &runtime->gilstate;
      if (tstate == _PyRuntimeGILState_GetThreadState(gilstate)) {
          Py_FatalError("PyThreadState_Delete: tstate is still current");
      }
      if (gilstate->autoInterpreterState &&
          PyThread_tss_get(&gilstate->autoTSSkey) == tstate)
      {
          PyThread_tss_set(&gilstate->autoTSSkey, NULL);
      }
      tstate_delete_common(runtime, tstate);
  }
  
  
  void
  PyThreadState_Delete(PyThreadState *tstate)
  {
      _PyThreadState_Delete(&_PyRuntime, tstate);
  }
  
  
  void
  _PyThreadState_DeleteCurrent(_PyRuntimeState *runtime)
  {
      struct _gilstate_runtime_state *gilstate = &runtime->gilstate;
      PyThreadState *tstate = _PyRuntimeGILState_GetThreadState(gilstate);
      if (tstate == NULL)
          Py_FatalError(
              "_PyThreadState_DeleteCurrent: no current tstate");
      tstate_delete_common(runtime, tstate);
      if (gilstate->autoInterpreterState &&
          PyThread_tss_get(&gilstate->autoTSSkey) == tstate)
      {
          PyThread_tss_set(&gilstate->autoTSSkey, NULL);
      }
      _PyRuntimeGILState_SetThreadState(gilstate, NULL);
      PyEval_ReleaseLock();
  }
  
  
  /*
   * Delete all thread states except the one passed as argument.
   * Note that, if there is a current thread state, it *must* be the one
   * passed as argument.  Also, this won't touch any other interpreters
   * than the current one, since we don't know which thread state should
   * be kept in those other interpreters.
   */
  void
  _PyThreadState_DeleteExcept(_PyRuntimeState *runtime, PyThreadState *tstate)
  {
      PyInterpreterState *interp = tstate->interp;
      PyThreadState *p, *next, *garbage;
      HEAD_LOCK(runtime);
      /* Remove all thread states, except tstate, from the linked list of
         thread states.  This will allow calling PyThreadState_Clear()
         without holding the lock. */
      garbage = interp->tstate_head;
      if (garbage == tstate)
          garbage = tstate->next;
      if (tstate->prev)
          tstate->prev->next = tstate->next;
      if (tstate->next)
          tstate->next->prev = tstate->prev;
      tstate->prev = tstate->next = NULL;
      interp->tstate_head = tstate;
      HEAD_UNLOCK(runtime);
      /* Clear and deallocate all stale thread states.  Even if this
         executes Python code, we should be safe since it executes
         in the current thread, not one of the stale threads. */
      for (p = garbage; p; p = next) {
          next = p->next;
          PyThreadState_Clear(p);
          PyMem_RawFree(p);
      }
  }
  
  
  PyThreadState *
  _PyThreadState_UncheckedGet(void)
  {
      return _PyThreadState_GET();
  }
  
  
  PyThreadState *
  PyThreadState_Get(void)
  {
      PyThreadState *tstate = _PyThreadState_GET();
      if (tstate == NULL)
          Py_FatalError("PyThreadState_Get: no current thread");
  
      return tstate;
  }
  
  
  PyThreadState *
  _PyThreadState_Swap(struct _gilstate_runtime_state *gilstate, PyThreadState *newts)
  {
      PyThreadState *oldts = _PyRuntimeGILState_GetThreadState(gilstate);
  
      _PyRuntimeGILState_SetThreadState(gilstate, newts);
      /* It should not be possible for more than one thread state
         to be used for a thread.  Check this the best we can in debug
         builds.
      */
  #if defined(Py_DEBUG)
      if (newts) {
          /* This can be called from PyEval_RestoreThread(). Similar
             to it, we need to ensure errno doesn't change.
          */
          int err = errno;
          PyThreadState *check = _PyGILState_GetThisThreadState(gilstate);
          if (check && check->interp == newts->interp && check != newts)
              Py_FatalError("Invalid thread state for this thread");
          errno = err;
      }
  #endif
      return oldts;
  }
  
  PyThreadState *
  PyThreadState_Swap(PyThreadState *newts)
  {
      return _PyThreadState_Swap(&_PyRuntime.gilstate, newts);
  }
  
  /* An extension mechanism to store arbitrary additional per-thread state.
     PyThreadState_GetDict() returns a dictionary that can be used to hold such
     state; the caller should pick a unique key and store its state there.  If
     PyThreadState_GetDict() returns NULL, an exception has *not* been raised
     and the caller should assume no per-thread state is available. */
  
  PyObject *
  PyThreadState_GetDict(void)
  {
      PyThreadState *tstate = _PyThreadState_GET();
      if (tstate == NULL)
          return NULL;
  
      if (tstate->dict == NULL) {
          PyObject *d;
          tstate->dict = d = PyDict_New();
          if (d == NULL)
              PyErr_Clear();
      }
      return tstate->dict;
  }
  
  
  /* Asynchronously raise an exception in a thread.
     Requested by Just van Rossum and Alex Martelli.
     To prevent naive misuse, you must write your own extension
     to call this, or use ctypes.  Must be called with the GIL held.
     Returns the number of tstates modified (normally 1, but 0 if `id` didn't
     match any known thread id).  Can be called with exc=NULL to clear an
     existing async exception.  This raises no exceptions. */
  
  int
  PyThreadState_SetAsyncExc(unsigned long id, PyObject *exc)
  {
      _PyRuntimeState *runtime = &_PyRuntime;
      PyInterpreterState *interp = _PyRuntimeState_GetThreadState(runtime)->interp;
  
      /* Although the GIL is held, a few C API functions can be called
       * without the GIL held, and in particular some that create and
       * destroy thread and interpreter states.  Those can mutate the
       * list of thread states we're traversing, so to prevent that we lock
       * head_mutex for the duration.
       */
      HEAD_LOCK(runtime);
      for (PyThreadState *p = interp->tstate_head; p != NULL; p = p->next) {
          if (p->thread_id == id) {
              /* Tricky:  we need to decref the current value
               * (if any) in p->async_exc, but that can in turn
               * allow arbitrary Python code to run, including
               * perhaps calls to this function.  To prevent
               * deadlock, we need to release head_mutex before
               * the decref.
               */
              PyObject *old_exc = p->async_exc;
              Py_XINCREF(exc);
              p->async_exc = exc;
              HEAD_UNLOCK(runtime);
              Py_XDECREF(old_exc);
              _PyEval_SignalAsyncExc(&runtime->ceval);
              return 1;
          }
      }
      HEAD_UNLOCK(runtime);
      return 0;
  }
  
  
  /* Routines for advanced debuggers, requested by David Beazley.
     Don't use unless you know what you are doing! */
  
  PyInterpreterState *
  PyInterpreterState_Head(void)
  {
      return _PyRuntime.interpreters.head;
  }
  
  PyInterpreterState *
  PyInterpreterState_Main(void)
  {
      return _PyRuntime.interpreters.main;
  }
  
  PyInterpreterState *
  PyInterpreterState_Next(PyInterpreterState *interp) {
      return interp->next;
  }
  
  PyThreadState *
  PyInterpreterState_ThreadHead(PyInterpreterState *interp) {
      return interp->tstate_head;
  }
  
  PyThreadState *
  PyThreadState_Next(PyThreadState *tstate) {
      return tstate->next;
  }
  
  /* The implementation of sys._current_frames().  This is intended to be
     called with the GIL held, as it will be when called via
     sys._current_frames().  It's possible it would work fine even without
     the GIL held, but haven't thought enough about that.
  */
  PyObject *
  _PyThread_CurrentFrames(void)
  {
      PyObject *result;
      PyInterpreterState *i;
  
      if (PySys_Audit("sys._current_frames", NULL) < 0) {
          return NULL;
      }
  
      result = PyDict_New();
      if (result == NULL)
          return NULL;
  
      /* for i in all interpreters:
       *     for t in all of i's thread states:
       *          if t's frame isn't NULL, map t's id to its frame
       * Because these lists can mutate even when the GIL is held, we
       * need to grab head_mutex for the duration.
       */
      _PyRuntimeState *runtime = &_PyRuntime;
      HEAD_LOCK(runtime);
      for (i = runtime->interpreters.head; i != NULL; i = i->next) {
          PyThreadState *t;
          for (t = i->tstate_head; t != NULL; t = t->next) {
              PyObject *id;
              int stat;
              struct _frame *frame = t->frame;
              if (frame == NULL)
                  continue;
              id = PyLong_FromUnsignedLong(t->thread_id);
              if (id == NULL)
                  goto Fail;
              stat = PyDict_SetItem(result, id, (PyObject *)frame);
              Py_DECREF(id);
              if (stat < 0)
                  goto Fail;
          }
      }
      HEAD_UNLOCK(runtime);
      return result;
  
   Fail:
      HEAD_UNLOCK(runtime);
      Py_DECREF(result);
      return NULL;
  }
  
  /* Python "auto thread state" API. */
  
  /* Keep this as a static, as it is not reliable!  It can only
     ever be compared to the state for the *current* thread.
     * If not equal, then it doesn't matter that the actual
       value may change immediately after comparison, as it can't
       possibly change to the current thread's state.
     * If equal, then the current thread holds the lock, so the value can't
       change until we yield the lock.
  */
  static int
  PyThreadState_IsCurrent(PyThreadState *tstate)
  {
      /* Must be the tstate for this thread */
      struct _gilstate_runtime_state *gilstate = &_PyRuntime.gilstate;
      assert(_PyGILState_GetThisThreadState(gilstate) == tstate);
      return tstate == _PyRuntimeGILState_GetThreadState(gilstate);
  }
  
  /* Internal initialization/finalization functions called by
     Py_Initialize/Py_FinalizeEx
  */
  void
  _PyGILState_Init(_PyRuntimeState *runtime, PyThreadState *tstate)
  {
      /* must init with valid states */
      assert(tstate != NULL);
      assert(tstate->interp != NULL);
  
      struct _gilstate_runtime_state *gilstate = &runtime->gilstate;
  
      if (PyThread_tss_create(&gilstate->autoTSSkey) != 0) {
          Py_FatalError("Could not allocate TSS entry");
      }
      gilstate->autoInterpreterState = tstate->interp;
      assert(PyThread_tss_get(&gilstate->autoTSSkey) == NULL);
      assert(tstate->gilstate_counter == 0);
  
      _PyGILState_NoteThreadState(gilstate, tstate);
  }
  
  PyInterpreterState *
  _PyGILState_GetInterpreterStateUnsafe(void)
  {
      return _PyRuntime.gilstate.autoInterpreterState;
  }
  
  void
  _PyGILState_Fini(_PyRuntimeState *runtime)
  {
      struct _gilstate_runtime_state *gilstate = &runtime->gilstate;
      PyThread_tss_delete(&gilstate->autoTSSkey);
      gilstate->autoInterpreterState = NULL;
  }
  
  /* Reset the TSS key - called by PyOS_AfterFork_Child().
   * This should not be necessary, but some - buggy - pthread implementations
   * don't reset TSS upon fork(), see issue #10517.
   */
  void
  _PyGILState_Reinit(_PyRuntimeState *runtime)
  {
      struct _gilstate_runtime_state *gilstate = &runtime->gilstate;
      PyThreadState *tstate = _PyGILState_GetThisThreadState(gilstate);
  
      PyThread_tss_delete(&gilstate->autoTSSkey);
      if (PyThread_tss_create(&gilstate->autoTSSkey) != 0) {
          Py_FatalError("Could not allocate TSS entry");
      }
  
      /* If the thread had an associated auto thread state, reassociate it with
       * the new key. */
      if (tstate &&
          PyThread_tss_set(&gilstate->autoTSSkey, (void *)tstate) != 0)
      {
          Py_FatalError("Couldn't create autoTSSkey mapping");
      }
  }
  
  /* When a thread state is created for a thread by some mechanism other than
     PyGILState_Ensure, it's important that the GILState machinery knows about
     it so it doesn't try to create another thread state for the thread (this is
     a better fix for SF bug #1010677 than the first one attempted).
  */
  static void
  _PyGILState_NoteThreadState(struct _gilstate_runtime_state *gilstate, PyThreadState* tstate)
  {
      /* If autoTSSkey isn't initialized, this must be the very first
         threadstate created in Py_Initialize().  Don't do anything for now
         (we'll be back here when _PyGILState_Init is called). */
      if (!gilstate->autoInterpreterState) {
          return;
      }
  
      /* Stick the thread state for this thread in thread specific storage.
  
         The only situation where you can legitimately have more than one
         thread state for an OS level thread is when there are multiple
         interpreters.
  
         You shouldn't really be using the PyGILState_ APIs anyway (see issues
         #10915 and #15751).
  
         The first thread state created for that given OS level thread will
         "win", which seems reasonable behaviour.
      */
      if (PyThread_tss_get(&gilstate->autoTSSkey) == NULL) {
          if ((PyThread_tss_set(&gilstate->autoTSSkey, (void *)tstate)) != 0) {
              Py_FatalError("Couldn't create autoTSSkey mapping");
          }
      }
  
      /* PyGILState_Release must not try to delete this thread state. */
      tstate->gilstate_counter = 1;
  }
  
  /* The public functions */
  static PyThreadState *
  _PyGILState_GetThisThreadState(struct _gilstate_runtime_state *gilstate)
  {
      if (gilstate->autoInterpreterState == NULL)
          return NULL;
      return (PyThreadState *)PyThread_tss_get(&gilstate->autoTSSkey);
  }
  
  PyThreadState *
  PyGILState_GetThisThreadState(void)
  {
      return _PyGILState_GetThisThreadState(&_PyRuntime.gilstate);
  }
  
  int
  PyGILState_Check(void)
  {
  
      if (!_PyGILState_check_enabled) {
          return 1;
      }
  
      struct _gilstate_runtime_state *gilstate = &_PyRuntime.gilstate;
      if (!PyThread_tss_is_created(&gilstate->autoTSSkey)) {
          return 1;
      }
  
      PyThreadState *tstate = _PyRuntimeGILState_GetThreadState(gilstate);
      if (tstate == NULL) {
          return 0;
      }
  
      return (tstate == _PyGILState_GetThisThreadState(gilstate));
  }
  
  PyGILState_STATE
  PyGILState_Ensure(void)
  {
      struct _gilstate_runtime_state *gilstate = &_PyRuntime.gilstate;
      int current;
      PyThreadState *tcur;
      int need_init_threads = 0;
  
      /* Note that we do not auto-init Python here - apart from
         potential races with 2 threads auto-initializing, pep-311
         spells out other issues.  Embedders are expected to have
         called Py_Initialize() and usually PyEval_InitThreads().
      */
      /* Py_Initialize() hasn't been called! */
      assert(gilstate->autoInterpreterState);
  
      tcur = (PyThreadState *)PyThread_tss_get(&gilstate->autoTSSkey);
      if (tcur == NULL) {
          need_init_threads = 1;
  
          /* Create a new thread state for this thread */
          tcur = PyThreadState_New(gilstate->autoInterpreterState);
          if (tcur == NULL)
              Py_FatalError("Couldn't create thread-state for new thread");
          /* This is our thread state!  We'll need to delete it in the
             matching call to PyGILState_Release(). */
          tcur->gilstate_counter = 0;
          current = 0; /* new thread state is never current */
      }
      else {
          current = PyThreadState_IsCurrent(tcur);
      }
  
      if (current == 0) {
          PyEval_RestoreThread(tcur);
      }
  
      /* Update our counter in the thread-state - no need for locks:
         - tcur will remain valid as we hold the GIL.
         - the counter is safe as we are the only thread "allowed"
           to modify this value
      */
      ++tcur->gilstate_counter;
  
      if (need_init_threads) {
          /* At startup, Python has no concrete GIL. If PyGILState_Ensure() is
             called from a new thread for the first time, we need the create the
             GIL. */
          PyEval_InitThreads();
      }
  
      return current ? PyGILState_LOCKED : PyGILState_UNLOCKED;
  }
  
  void
  PyGILState_Release(PyGILState_STATE oldstate)
  {
      _PyRuntimeState *runtime = &_PyRuntime;
      PyThreadState *tcur = PyThread_tss_get(&runtime->gilstate.autoTSSkey);
      if (tcur == NULL) {
          Py_FatalError("auto-releasing thread-state, "
                        "but no thread-state for this thread");
      }
  
      /* We must hold the GIL and have our thread state current */
      /* XXX - remove the check - the assert should be fine,
         but while this is very new (April 2003), the extra check
         by release-only users can't hurt.
      */
      if (!PyThreadState_IsCurrent(tcur)) {
          Py_FatalError("This thread state must be current when releasing");
      }
      assert(PyThreadState_IsCurrent(tcur));
      --tcur->gilstate_counter;
      assert(tcur->gilstate_counter >= 0); /* illegal counter value */
  
      /* If we're going to destroy this thread-state, we must
       * clear it while the GIL is held, as destructors may run.
       */
      if (tcur->gilstate_counter == 0) {
          /* can't have been locked when we created it */
          assert(oldstate == PyGILState_UNLOCKED);
          PyThreadState_Clear(tcur);
          /* Delete the thread-state.  Note this releases the GIL too!
           * It's vital that the GIL be held here, to avoid shutdown
           * races; see bugs 225673 and 1061968 (that nasty bug has a
           * habit of coming back).
           */
          _PyThreadState_DeleteCurrent(runtime);
      }
      /* Release the lock if necessary */
      else if (oldstate == PyGILState_UNLOCKED)
          PyEval_SaveThread();
  }
  
  
  /**************************/
  /* cross-interpreter data */
  /**************************/
  
  /* cross-interpreter data */
  
  crossinterpdatafunc _PyCrossInterpreterData_Lookup(PyObject *);
  
  /* This is a separate func from _PyCrossInterpreterData_Lookup in order
     to keep the registry code separate. */
  static crossinterpdatafunc
  _lookup_getdata(PyObject *obj)
  {
      crossinterpdatafunc getdata = _PyCrossInterpreterData_Lookup(obj);
      if (getdata == NULL && PyErr_Occurred() == 0)
          PyErr_Format(PyExc_ValueError,
                       "%S does not support cross-interpreter data", obj);
      return getdata;
  }
  
  int
  _PyObject_CheckCrossInterpreterData(PyObject *obj)
  {
      crossinterpdatafunc getdata = _lookup_getdata(obj);
      if (getdata == NULL) {
          return -1;
      }
      return 0;
  }
  
  static int
  _check_xidata(_PyCrossInterpreterData *data)
  {
      // data->data can be anything, including NULL, so we don't check it.
  
      // data->obj may be NULL, so we don't check it.
  
      if (data->interp < 0) {
          PyErr_SetString(PyExc_SystemError, "missing interp");
          return -1;
      }
  
      if (data->new_object == NULL) {
          PyErr_SetString(PyExc_SystemError, "missing new_object func");
          return -1;
      }
  
      // data->free may be NULL, so we don't check it.
  
      return 0;
  }
  
  int
  _PyObject_GetCrossInterpreterData(PyObject *obj, _PyCrossInterpreterData *data)
  {
      // _PyInterpreterState_Get() aborts if lookup fails, so we don't need
      // to check the result for NULL.
      PyInterpreterState *interp = _PyInterpreterState_Get();
  
      // Reset data before re-populating.
      *data = (_PyCrossInterpreterData){0};
      data->free = PyMem_RawFree;  // Set a default that may be overridden.
  
      // Call the "getdata" func for the object.
      Py_INCREF(obj);
      crossinterpdatafunc getdata = _lookup_getdata(obj);
      if (getdata == NULL) {
          Py_DECREF(obj);
          return -1;
      }
      int res = getdata(obj, data);
      Py_DECREF(obj);
      if (res != 0) {
          return -1;
      }
  
      // Fill in the blanks and validate the result.
      data->interp = interp->id;
      if (_check_xidata(data) != 0) {
          _PyCrossInterpreterData_Release(data);
          return -1;
      }
  
      return 0;
  }
  
  static void
  _release_xidata(void *arg)
  {
      _PyCrossInterpreterData *data = (_PyCrossInterpreterData *)arg;
      if (data->free != NULL) {
          data->free(data->data);
      }
      Py_XDECREF(data->obj);
  }
  
  static void
  _call_in_interpreter(struct _gilstate_runtime_state *gilstate,
                       PyInterpreterState *interp,
                       void (*func)(void *), void *arg)
  {
      /* We would use Py_AddPendingCall() if it weren't specific to the
       * main interpreter (see bpo-33608).  In the meantime we take a
       * naive approach.
       */
      PyThreadState *save_tstate = NULL;
      if (interp != _PyRuntimeGILState_GetThreadState(gilstate)->interp) {
          // XXX Using the "head" thread isn't strictly correct.
          PyThreadState *tstate = PyInterpreterState_ThreadHead(interp);
          // XXX Possible GILState issues?
          save_tstate = _PyThreadState_Swap(gilstate, tstate);
      }
  
      func(arg);
  
      // Switch back.
      if (save_tstate != NULL) {
          _PyThreadState_Swap(gilstate, save_tstate);
      }
  }
  
  void
  _PyCrossInterpreterData_Release(_PyCrossInterpreterData *data)
  {
      if (data->data == NULL && data->obj == NULL) {
          // Nothing to release!
          return;
      }
  
      // Switch to the original interpreter.
      PyInterpreterState *interp = _PyInterpreterState_LookUpID(data->interp);
      if (interp == NULL) {
          // The interpreter was already destroyed.
          if (data->free != NULL) {
              // XXX Someone leaked some memory...
          }
          return;
      }
  
      // "Release" the data and/or the object.
      struct _gilstate_runtime_state *gilstate = &_PyRuntime.gilstate;
      _call_in_interpreter(gilstate, interp, _release_xidata, data);
  }
  
  PyObject *
  _PyCrossInterpreterData_NewObject(_PyCrossInterpreterData *data)
  {
      return data->new_object(data);
  }
  
  /* registry of {type -> crossinterpdatafunc} */
  
  /* For now we use a global registry of shareable classes.  An
     alternative would be to add a tp_* slot for a class's
     crossinterpdatafunc. It would be simpler and more efficient. */
  
  static int
  _register_xidata(struct _xidregistry *xidregistry, PyTypeObject *cls,
                   crossinterpdatafunc getdata)
  {
      // Note that we effectively replace already registered classes
      // rather than failing.
      struct _xidregitem *newhead = PyMem_RawMalloc(sizeof(struct _xidregitem));
      if (newhead == NULL)
          return -1;
      newhead->cls = cls;
      newhead->getdata = getdata;
      newhead->next = xidregistry->head;
      xidregistry->head = newhead;
      return 0;
  }
  
  static void _register_builtins_for_crossinterpreter_data(struct _xidregistry *xidregistry);
  
  int
  _PyCrossInterpreterData_RegisterClass(PyTypeObject *cls,
                                         crossinterpdatafunc getdata)
  {
      if (!PyType_Check(cls)) {
          PyErr_Format(PyExc_ValueError, "only classes may be registered");
          return -1;
      }
      if (getdata == NULL) {
          PyErr_Format(PyExc_ValueError, "missing 'getdata' func");
          return -1;
      }
  
      // Make sure the class isn't ever deallocated.
      Py_INCREF((PyObject *)cls);
  
      struct _xidregistry *xidregistry = &_PyRuntime.xidregistry ;
      PyThread_acquire_lock(xidregistry->mutex, WAIT_LOCK);
      if (xidregistry->head == NULL) {
          _register_builtins_for_crossinterpreter_data(xidregistry);
      }
      int res = _register_xidata(xidregistry, cls, getdata);
      PyThread_release_lock(xidregistry->mutex);
      return res;
  }
  
  /* Cross-interpreter objects are looked up by exact match on the class.
     We can reassess this policy when we move from a global registry to a
     tp_* slot. */
  
  crossinterpdatafunc
  _PyCrossInterpreterData_Lookup(PyObject *obj)
  {
      struct _xidregistry *xidregistry = &_PyRuntime.xidregistry ;
      PyObject *cls = PyObject_Type(obj);
      crossinterpdatafunc getdata = NULL;
      PyThread_acquire_lock(xidregistry->mutex, WAIT_LOCK);
      struct _xidregitem *cur = xidregistry->head;
      if (cur == NULL) {
          _register_builtins_for_crossinterpreter_data(xidregistry);
          cur = xidregistry->head;
      }
      for(; cur != NULL; cur = cur->next) {
          if (cur->cls == (PyTypeObject *)cls) {
              getdata = cur->getdata;
              break;
          }
      }
      Py_DECREF(cls);
      PyThread_release_lock(xidregistry->mutex);
      return getdata;
  }
  
  /* cross-interpreter data for builtin types */
  
  struct _shared_bytes_data {
      char *bytes;
      Py_ssize_t len;
  };
  
  static PyObject *
  _new_bytes_object(_PyCrossInterpreterData *data)
  {
      struct _shared_bytes_data *shared = (struct _shared_bytes_data *)(data->data);
      return PyBytes_FromStringAndSize(shared->bytes, shared->len);
  }
  
  static int
  _bytes_shared(PyObject *obj, _PyCrossInterpreterData *data)
  {
      struct _shared_bytes_data *shared = PyMem_NEW(struct _shared_bytes_data, 1);
      if (PyBytes_AsStringAndSize(obj, &shared->bytes, &shared->len) < 0) {
          return -1;
      }
      data->data = (void *)shared;
      Py_INCREF(obj);
      data->obj = obj;  // Will be "released" (decref'ed) when data released.
      data->new_object = _new_bytes_object;
      data->free = PyMem_Free;
      return 0;
  }
  
  struct _shared_str_data {
      int kind;
      const void *buffer;
      Py_ssize_t len;
  };
  
  static PyObject *
  _new_str_object(_PyCrossInterpreterData *data)
  {
      struct _shared_str_data *shared = (struct _shared_str_data *)(data->data);
      return PyUnicode_FromKindAndData(shared->kind, shared->buffer, shared->len);
  }
  
  static int
  _str_shared(PyObject *obj, _PyCrossInterpreterData *data)
  {
      struct _shared_str_data *shared = PyMem_NEW(struct _shared_str_data, 1);
      shared->kind = PyUnicode_KIND(obj);
      shared->buffer = PyUnicode_DATA(obj);
      shared->len = PyUnicode_GET_LENGTH(obj) - 1;
      data->data = (void *)shared;
      Py_INCREF(obj);
      data->obj = obj;  // Will be "released" (decref'ed) when data released.
      data->new_object = _new_str_object;
      data->free = PyMem_Free;
      return 0;
  }
  
  static PyObject *
  _new_long_object(_PyCrossInterpreterData *data)
  {
      return PyLong_FromSsize_t((Py_ssize_t)(data->data));
  }
  
  static int
  _long_shared(PyObject *obj, _PyCrossInterpreterData *data)
  {
      /* Note that this means the size of shareable ints is bounded by
       * sys.maxsize.  Hence on 32-bit architectures that is half the
       * size of maximum shareable ints on 64-bit.
       */
      Py_ssize_t value = PyLong_AsSsize_t(obj);
      if (value == -1 && PyErr_Occurred()) {
          if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
              PyErr_SetString(PyExc_OverflowError, "try sending as bytes");
          }
          return -1;
      }
      data->data = (void *)value;
      data->obj = NULL;
      data->new_object = _new_long_object;
      data->free = NULL;
      return 0;
  }
  
  static PyObject *
  _new_none_object(_PyCrossInterpreterData *data)
  {
      // XXX Singleton refcounts are problematic across interpreters...
      Py_INCREF(Py_None);
      return Py_None;
  }
  
  static int
  _none_shared(PyObject *obj, _PyCrossInterpreterData *data)
  {
      data->data = NULL;
      // data->obj remains NULL
      data->new_object = _new_none_object;
      data->free = NULL;  // There is nothing to free.
      return 0;
  }
  
  static void
  _register_builtins_for_crossinterpreter_data(struct _xidregistry *xidregistry)
  {
      // None
      if (_register_xidata(xidregistry, (PyTypeObject *)PyObject_Type(Py_None), _none_shared) != 0) {
          Py_FatalError("could not register None for cross-interpreter sharing");
      }
  
      // int
      if (_register_xidata(xidregistry, &PyLong_Type, _long_shared) != 0) {
          Py_FatalError("could not register int for cross-interpreter sharing");
      }
  
      // bytes
      if (_register_xidata(xidregistry, &PyBytes_Type, _bytes_shared) != 0) {
          Py_FatalError("could not register bytes for cross-interpreter sharing");
      }
  
      // str
      if (_register_xidata(xidregistry, &PyUnicode_Type, _str_shared) != 0) {
          Py_FatalError("could not register str for cross-interpreter sharing");
      }
  }
  
  
  #ifdef __cplusplus
  }
  #endif
  