Fixes for

[ 1166660 ] The readline module can cause python to segfault

It seems to me that the code I'm rewriting here attempted to call any
user-supplied hook functions using the thread state of the thread that
called the hook-setting function, as opposed to that of the thread
that is currently executing.  This doesn't work, in general.

Fix this by using the PyGILState API (It wouldn't be that hard to
define a dummy version of said API when #ifndef WITH_THREAD, would
it?).

Also, check the conversion to integer of the return value of a hook
function for errors (this problem was mentioned in the ipython bug
report linked to in the above bug).

Modules/readline.c

@@ -159,8 +159,7 @@ the history file.");
 /* Generic hook function setter */
 
 static PyObject *
-set_hook(const char *funcname, PyObject **hook_var,
-	 PyThreadState **tstate, PyObject *args)
+set_hook(const char *funcname, PyObject **hook_var, PyObject *args)
 {
 	PyObject *function = Py_None;
 	char buf[80];
@@ -170,14 +169,12 @@ set_hook(const char *funcname, PyObject **hook_var,
 	if (function == Py_None) {
 		Py_XDECREF(*hook_var);
 		*hook_var = NULL;
-		*tstate = NULL;
 	}
 	else if (PyCallable_Check(function)) {
 		PyObject *tmp = *hook_var;
 		Py_INCREF(function);
 		*hook_var = function;
 		Py_XDECREF(tmp);
-		*tstate = PyThreadState_GET();
 	}
 	else {
 		PyOS_snprintf(buf, sizeof(buf),
@@ -194,18 +191,15 @@ set_hook(const char *funcname, PyObject **hook_var,
 /* Exported functions to specify hook functions in Python */
 
 static PyObject *startup_hook = NULL;
-static PyThreadState *startup_hook_tstate = NULL;
 
 #ifdef HAVE_RL_PRE_INPUT_HOOK
 static PyObject *pre_input_hook = NULL;
-static PyThreadState *pre_input_hook_tstate = NULL;
 #endif
 
 static PyObject *
 set_startup_hook(PyObject *self, PyObject *args)
 {
-	return set_hook("startup_hook", &startup_hook,
-			&startup_hook_tstate, args);
+	return set_hook("startup_hook", &startup_hook, args);
 }
 
 PyDoc_STRVAR(doc_set_startup_hook,
@@ -222,8 +216,7 @@ before readline prints the first prompt.");
 static PyObject *
 set_pre_input_hook(PyObject *self, PyObject *args)
 {
-	return set_hook("pre_input_hook", &pre_input_hook,
-			&pre_input_hook_tstate, args);
+	return set_hook("pre_input_hook", &pre_input_hook, args);
 }
 
 PyDoc_STRVAR(doc_set_pre_input_hook,
@@ -239,7 +232,6 @@ characters.");
 /* Exported function to specify a word completer in Python */
 
 static PyObject *completer = NULL;
-static PyThreadState *completer_tstate = NULL;
 
 static PyObject *begidx = NULL;
 static PyObject *endidx = NULL;
@@ -403,7 +395,7 @@ get the readline word delimiters for tab-completion");
 static PyObject *
 set_completer(PyObject *self, PyObject *args)
 {
-	return set_hook("completer", &completer, &completer_tstate, args);
+	return set_hook("completer", &completer, args);
 }
 
 PyDoc_STRVAR(doc_set_completer,
@@ -584,28 +576,33 @@ static struct PyMethodDef readline_methods[] =
 /* C function to call the Python hooks. */
 
 static int
-on_hook(PyObject *func, PyThreadState **tstate)
+on_hook(PyObject *func)
 {
 	int result = 0;
 	if (func != NULL) {
 		PyObject *r;
-		/* Note that readline is called with the interpreter
-		   lock released! */
-		PyEval_RestoreThread(*tstate);
+#ifdef WITH_THREAD	      
+		PyGILState_STATE gilstate = PyGILState_Ensure();
+#endif
 		r = PyObject_CallFunction(func, NULL);
 		if (r == NULL)
 			goto error;
 		if (r == Py_None)
 			result = 0;
-		else
+		else {
 			result = PyInt_AsLong(r);
+			if (result == -1 && PyErr_Occurred()) 
+				goto error;
+		}
 		Py_DECREF(r);
 		goto done;
 	  error:
 		PyErr_Clear();
 		Py_XDECREF(r);
 	  done:
-		*tstate = PyEval_SaveThread();
+#ifdef WITH_THREAD	      
+		PyGILState_Release(gilstate);
+#endif
 	}
 	return result;
 }
@@ -613,14 +610,14 @@ on_hook(PyObject *func, PyThreadState **tstate)
 static int
 on_startup_hook(void)
 {
-	return on_hook(startup_hook, &startup_hook_tstate);
+	return on_hook(startup_hook);
 }
 
 #ifdef HAVE_RL_PRE_INPUT_HOOK
 static int
 on_pre_input_hook(void)
 {
-	return on_hook(pre_input_hook, &pre_input_hook_tstate);
+	return on_hook(pre_input_hook);
 }
 #endif
 
@@ -633,11 +630,9 @@ on_completion(char *text, int state)
 	char *result = NULL;
 	if (completer != NULL) {
 		PyObject *r;
-		/* Note that readline is called with the interpreter
-		   lock released! */
-		PyEval_RestoreThread(completer_tstate);
-		/* Don't use the default filename completion if we
-		 * have a custom completion function... */
+#ifdef WITH_THREAD	      
+		PyGILState_STATE gilstate = PyGILState_Ensure();
+#endif
 		rl_attempted_completion_over = 1;
 		r = PyObject_CallFunction(completer, "si", text, state);
 		if (r == NULL)
@@ -657,7 +652,9 @@ on_completion(char *text, int state)
 		PyErr_Clear();
 		Py_XDECREF(r);
 	  done:
-		completer_tstate = PyEval_SaveThread();
+#ifdef WITH_THREAD	      
+		PyGILState_Release(gilstate);
+#endif
 	}
 	return result;
 }