Issue python#106: tasklet.setup() now raises RuntimeError, if the tasklet is alive

If you call tasklet.setup(*args, **kwargs) and the tasklet is already alive, Stackless now raises RuntimeError.
Previously the behaviour was undefined.
Additionally this change updates the documentation of tasklet.setup() and adds a test case.

https://bitbucket.org/stackless-dev/stackless/issues/106
(grafted from f25b5c2a3a90475f649c75333864e28dc8e50800)

Author: Anselm Kruis

Doc/library/stackless/tasklets.rst

@@ -78,7 +78,9 @@ The ``tasklet`` class
    >>> t = stackless.tasklet()
    >>> t.bind(func)
    >>> t.setup(1, 2, 3, name="test")
-   
+
+   and
+
    >>> t = stackless.tasklet()
    >>> t.bind(func, (1, 2, 3), {"name":"test"})
    >>> t.insert()
@@ -147,12 +149,17 @@ The ``tasklet`` class
    provided with arguments to pass to it, they are implicitly
    scheduled and will be run in turn when the scheduler is next run.
 
-   The above code is equivalent to::
-   
-   >>> t = stackless.tasklet()
-   >>> t.bind(func, (1, 2), {"name":"test"})
-   >>> t.insert()
-   
+   The method :meth:`setup` is equivalent to::
+
+   >>> def setup(self, *args, **kwargs):
+   >>>     assert isinstance(self, stackless.tasklet)
+   >>>     with stackless.atomic():
+   >>>         if self.alive:
+   >>>             raise(RuntimeError("tasklet is alive")
+   >>>         self.bind(None, args, kwargs)
+   >>>         self.insert()
+   >>>         return self
+
 .. method:: tasklet.insert()
 
    Insert a tasklet at the end of the scheduler runnables queue, given that it isn't blocked.

Stackless/changelog.txt

@@ -9,6 +9,10 @@ What's New in Stackless 3.X.X?
 
 *Release date: 20XX-XX-XX*
 
+- https://bitbucket.org/stackless-dev/stackless/issues/106
+  Raise RuntimeError, if you call tasklet.setup() on a tasklet, that is
+  already alive.
+
 - https://bitbucket.org/stackless-dev/stackless/issues/105
   Fix an occasional NULL-pointer access during interpreter shutdown.
 

Stackless/module/taskletobject.c

@@ -373,6 +373,7 @@ tasklet_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     if (t == NULL)
         return NULL;
     *(int*)&t->flags = 0;
+    t->recursion_depth = 0;
     t->next = NULL;
     t->prev = NULL;
     t->f.frame = NULL;
@@ -1048,6 +1049,27 @@ tasklet_setup(PyObject *self, PyObject *args, PyObject *kwds)
 {
     PyTaskletObject *task = (PyTaskletObject *) self;
 
+    if (PyTasklet_Alive(task)) {
+        RUNTIME_ERROR("tasklet is alive", NULL);
+    }
+
+    /* The implementation of PyTasklet_Alive does not imply,
+     * that the current tasklet is always alive. But I can't figure out,
+     * how to create a current tasklet, that is dead.
+     */
+    assert(task->cstate->tstate == NULL || task->cstate->tstate->st.current != task);
+
+    /* guaranted by !alive && !current.
+     * Equivalent to the call of tasklet_clear_frames(task) in PyTasklet_BindEx().
+     */
+    assert(task->f.frame == NULL);
+
+    /* the following assertions are equivalent to the remaining argument checks
+     * in PyTasklet_BindEx().
+     */
+    assert(!PyTasklet_Scheduled(task));
+    assert(PyTasklet_GetNestingLevel(task) == 0);
+
     if (impl_tasklet_setup(task, args, kwds, 1))
         return NULL;
     Py_INCREF(task);

Stackless/unittests/test_miscell.py

@@ -1123,6 +1123,20 @@ def other_thread_main():
         self.assertGreater(tlet.nesting_level, 0)
         self.assertRaisesRegex(RuntimeError, "tasklet has C state on its stack", tlet.bind, None)
 
+    def test_setup_fail_alive(self):
+        # make sure, that you can't bind a tasklet, which is alive
+        # https://bitbucket.org/stackless-dev/stackless/issues/106
+
+        def task():
+            t = stackless.current
+            t.tempval = lambda: None
+            self.assertTrue(t.alive)
+            self.assertRaisesRegex(RuntimeError, "tasklet is alive", t.setup)
+
+        t = stackless.tasklet(task, ())
+        t.run()
+        self.assertFalse(t.alive)
+
 
 class TestSwitch(StacklessTestCase):
     """Test the new tasklet.switch() method, which allows