gh-126914: Store the Preallocated Thread State's Pointer in a PyInterpreterState Field

Include/internal/pycore_interp.h

@@ -130,6 +130,7 @@ struct _is{
  uint64_t next_unique_id;
  /* The linked list of threads, newest first. */
  PyThreadState *head;
+ _PyThreadStateImpl *preallocated;
  /* The thread currently executing in the __main__ module, if any. */
  PyThreadState *main;
  /* Used in Modules/_threadmodule.c. */
@@ -278,9 +279,10 @@ struct _is{
  struct _Py_interp_cached_objects cached_objects;
  struct _Py_interp_static_objects static_objects;
 
+ Py_ssize_t _interactive_src_count;
+
  /* the initial PyInterpreterState.threads.head */
  _PyThreadStateImpl _initial_thread;
- Py_ssize_t _interactive_src_count;
 };
 
 

Include/internal/pycore_runtime_init.h

@@ -118,6 +118,9 @@ extern PyTypeObject _PyExc_MemoryError;
 {\
  .id_refcount = -1, \
  ._whence = _PyInterpreterState_WHENCE_NOTSET, \
+ .threads ={\
+ .preallocated = &(INTERP)._initial_thread, \
+ }, \
  .imports = IMPORTS_INIT, \
  .ceval ={\
  .recursion_limit = Py_DEFAULT_RECURSION_LIMIT, \

Lib/test/test_interpreters/test_stress.py

@@ -23,6 +23,7 @@ def test_create_many_sequential(self):
  alive.append(interp)
 
  @support.requires_resource('cpu')
+ @threading_helper.requires_working_threading()
  def test_create_many_threaded(self):
  alive = []
  def task():
@@ -32,6 +33,35 @@ def task():
  with threading_helper.start_threads(threads):
  pass
 
+ @support.requires_resource('cpu')
+ @threading_helper.requires_working_threading()
+ def test_many_threads_running_interp_in_other_interp(self):
+ interp = interpreters.create()
+
+ script = f"""if True:
+ import _interpreters
+ _interpreters.run_string({interp.id}, '1')
+ """
+
+ def run():
+ interp = interpreters.create()
+ alreadyrunning = (f'{interpreters.InterpreterError}: '
+ 'interpreter already running')
+ success = False
+ while not success:
+ try:
+ interp.exec(script)
+ except interpreters.ExecutionFailed as exc:
+ if exc.excinfo.msg != 'interpreter already running':
+ raise # re-raise
+ assert exc.excinfo.type.__name__ == 'InterpreterError'
+ else:
+ success = True
+
+ threads = (threading.Thread(target=run) for _ in range(200))
+ with threading_helper.start_threads(threads):
+ pass
+
 
 if __name__ == '__main__':
  # Test needs to be a package, so we can do relative imports.

Python/pystate.c

@@ -629,6 +629,8 @@ init_interpreter(PyInterpreterState *interp,
  assert(next != NULL || (interp == runtime->interpreters.main));
  interp->next = next;
 
+ interp->threads.preallocated = &interp->_initial_thread;
+
  // We would call _PyObject_InitState() at this point
  // if interp->feature_flags were alredy set.
 
@@ -766,7 +768,6 @@ PyInterpreterState_New(void)
  return interp;
 }
 
-
 static void
 interpreter_clear(PyInterpreterState *interp, PyThreadState *tstate)
 {
@@ -910,6 +911,9 @@ interpreter_clear(PyInterpreterState *interp, PyThreadState *tstate)
  // 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.
+
+ // We could clear interp->threads.freelist here
+ // if it held more than just the initial thread state.
 }
 
 
@@ -1386,22 +1390,45 @@ allocate_chunk(int size_in_bytes, _PyStackChunk* previous)
  return res;
 }
 
+static void
+reset_threadstate(_PyThreadStateImpl *tstate)
+{
+ // Set to _PyThreadState_INIT directly?
+ memcpy(tstate,
+ &initial._main_interpreter._initial_thread,
+ sizeof(*tstate));
+}
+
 static _PyThreadStateImpl *
-alloc_threadstate(void)
+alloc_threadstate(PyInterpreterState *interp)
 {
- return PyMem_RawCalloc(1, sizeof(_PyThreadStateImpl));
+ _PyThreadStateImpl *tstate;
+
+ // Try the preallocated tstate first.
+ tstate = _Py_atomic_exchange_ptr(&interp->threads.preallocated, NULL);
+
+ // Fall back to the allocator.
+ if (tstate == NULL){
+ tstate = PyMem_RawCalloc(1, sizeof(_PyThreadStateImpl));
+ if (tstate == NULL){
+ return NULL;
+ }
+ reset_threadstate(tstate);
+ }
+ return tstate;
 }
 
 static void
 free_threadstate(_PyThreadStateImpl *tstate)
 {
+ PyInterpreterState *interp = tstate->base.interp;
  // The initial thread state of the interpreter is allocated
  // as part of the interpreter state so should not be freed.
- if (tstate == &tstate->base.interp->_initial_thread){
- // Restore to _PyThreadState_INIT.
-memcpy(tstate,
- &initial._main_interpreter._initial_thread,
- sizeof(*tstate));
+ if (tstate == &interp->_initial_thread){
+ // Make it available again.
+reset_threadstate(tstate);
+assert(interp->threads.preallocated == NULL);
+_Py_atomic_store_ptr(&interp->threads.preallocated, tstate);
  }
  else{
  PyMem_RawFree(tstate);
@@ -1492,66 +1519,38 @@ add_threadstate(PyInterpreterState *interp, PyThreadState *tstate,
 static PyThreadState *
 new_threadstate(PyInterpreterState *interp, int whence)
 {
- _PyThreadStateImpl *tstate;
- _PyRuntimeState *runtime = interp->runtime;
- // We don't need to allocate a thread state for the main interpreter
- // (the common case), but doing it later for the other case revealed a
- // reentrancy problem (deadlock). So for now we always allocate before
- // taking the interpreters lock. See GH-96071.
- _PyThreadStateImpl *new_tstate = alloc_threadstate();
- int used_newtstate;
- if (new_tstate == NULL){
+ // Allocate the thread state.
+ _PyThreadStateImpl *tstate = alloc_threadstate(interp);
+ if (tstate == NULL){
  return NULL;
  }
+
 #ifdef Py_GIL_DISABLED
  Py_ssize_t qsbr_idx = _Py_qsbr_reserve(interp);
  if (qsbr_idx < 0){
-PyMem_RawFree(new_tstate);
+free_threadstate(tstate);
  return NULL;
  }
  int32_t tlbc_idx = _Py_ReserveTLBCIndex(interp);
  if (tlbc_idx < 0){
-PyMem_RawFree(new_tstate);
+free_threadstate(tstate);
  return NULL;
  }
 #endif
 
  /* We serialize concurrent creation to protect global state. */
- HEAD_LOCK(runtime);
+ HEAD_LOCK(interp->runtime);
 
+ // Initialize the new thread state.
  interp->threads.next_unique_id += 1;
  uint64_t id = interp->threads.next_unique_id;
+ init_threadstate(tstate, interp, id, whence);
 
- // Allocate the thread state and add it to the interpreter.
+ // Add the new thread state to the interpreter.
  PyThreadState *old_head = interp->threads.head;
- if (old_head == NULL){
- // It's the interpreter's initial thread state.
- used_newtstate = 0;
- tstate = &interp->_initial_thread;
- }
- // XXX Re-use interp->_initial_thread if not in use?
- else{
- // Every valid interpreter must have at least one thread.
- assert(id > 1);
- assert(old_head->prev == NULL);
- used_newtstate = 1;
- tstate = new_tstate;
- // Set to _PyThreadState_INIT.
- memcpy(tstate,
- &initial._main_interpreter._initial_thread,
- sizeof(*tstate));
- }
-
- init_threadstate(tstate, interp, id, whence);
  add_threadstate(interp, (PyThreadState *)tstate, old_head);
 
- HEAD_UNLOCK(runtime);
- if (!used_newtstate){
- // Must be called with lock unlocked to avoid re-entrancy deadlock.
- PyMem_RawFree(new_tstate);
- }
- else{
- }
+ HEAD_UNLOCK(interp->runtime);
 
 #ifdef Py_GIL_DISABLED
  // Must be called with lock unlocked to avoid lock ordering deadlocks.