Add extra information to the repr of greenlets.issue215

Fixes #215

3 files changed, 128 insertions, 21 deletions

diff --git a/CHANGES.rst b/CHANGES.rst
index 3c80a6e..dd8fc00 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -41,6 +41,9 @@
   alter that at compile time have been removed (no combination other
   than the defaults was ever tested). This helps define a
   stable ABI.
+- The repr of greenlet objects now includes extra information about
+  its state. This is purely informative and the details are subject to
+  change. See `issue 215 <https://github.com/python-greenlet/greenlet/issues/215>`_.
 
 
 0.4.17 (2020-09-22)
diff --git a/src/greenlet/greenlet.c b/src/greenlet/greenlet.c
index 11fd17a..aacfb09 100644
--- a/src/greenlet/greenlet.c
+++ b/src/greenlet/greenlet.c
@@ -1301,10 +1301,17 @@ green_setdict(PyGreenlet* self, PyObject* val, void* c)
     return 0;
 }
 
+static int
+_green_not_dead(PyGreenlet* self)
+{
+    return PyGreenlet_ACTIVE(self) || !PyGreenlet_STARTED(self);
+}
+
+
 static PyObject*
 green_getdead(PyGreenlet* self, void* c)
 {
-    if (PyGreenlet_ACTIVE(self) || !PyGreenlet_STARTED(self)) {
+    if (_green_not_dead(self)) {
         Py_RETURN_FALSE;
     }
     else {
@@ -1512,6 +1519,50 @@ green_getstate(PyGreenlet* self)
     return NULL;
 }
 
+static PyObject*
+green_repr(PyGreenlet* self)
+{
+    /*
+      Return a string like
+      <greenlet.greenlet at 0xdeadbeef [current][active started]|dead main>
+
+      The handling of greenlets across threads is not super good.
+      We mostly use the internal definitions of these terms, but they
+      generally should make sense to users as well.
+     */
+    PyObject* result;
+    int never_started = !PyGreenlet_STARTED(self) && !PyGreenlet_ACTIVE(self);
+
+    if (!STATE_OK) {
+        return NULL;
+    }
+
+    if (_green_not_dead(self)) {
+        result = PyUnicode_FromFormat(
+            "<%s object at %p (otid=%p)%s%s%s%s>",
+            Py_TYPE(self)->tp_name,
+            self,
+            self->run_info,
+            ts_current == self
+                ? " current"
+                : (PyGreenlet_STARTED(self) ? " suspended" : ""),
+            PyGreenlet_ACTIVE(self) ? " active" : "",
+            never_started ? " pending" : " started",
+            PyGreenlet_MAIN(self) ? " main" : ""
+        );
+    }
+    else {
+        /* main greenlets never really appear dead. */
+        result = PyUnicode_FromFormat(
+            "<%s object at %p (otid=%p) dead>",
+            Py_TYPE(self)->tp_name,
+            self,
+            self->run_info
+            );
+    }
+    return result;
+}
+
 /*****************************************************************************
  * C interface
  *
@@ -1662,7 +1713,7 @@ PyTypeObject PyGreenlet_Type = {
     0,                         /* tp_getattr */
     0,                         /* tp_setattr */
     0,                         /* tp_compare */
-    0,                         /* tp_repr */
+    (reprfunc)green_repr,      /* tp_repr */
     &green_as_number,          /* tp_as _number*/
     0,                         /* tp_as _sequence*/
     0,                         /* tp_as _mapping*/
diff --git a/src/greenlet/tests/test_greenlet.py b/src/greenlet/tests/test_greenlet.py
index 5a3fe10..b75e423 100644
--- a/src/greenlet/tests/test_greenlet.py
+++ b/src/greenlet/tests/test_greenlet.py
@@ -3,15 +3,10 @@ import sys
 import time
 import threading
 import unittest
+from abc import ABCMeta, abstractmethod
 
 from greenlet import greenlet
 
-try:
-    from abc import ABCMeta, abstractmethod
-except ImportError:
-    ABCMeta = None
-    abstractmethod = None
-
 
 class SomeError(Exception):
     pass
@@ -469,22 +464,22 @@ class GreenletTests(unittest.TestCase):
             g = greenlet(switchapply)
             self.assertEqual(g.switch(), kwargs)
 
-    if ABCMeta is not None and abstractmethod is not None:
-        def test_abstract_subclasses(self):
-            AbstractSubclass = ABCMeta(
-                'AbstractSubclass',
-                (greenlet,),
-                {'run': abstractmethod(lambda self: None)})
 
-            class BadSubclass(AbstractSubclass):
-                pass
+    def test_abstract_subclasses(self):
+        AbstractSubclass = ABCMeta(
+            'AbstractSubclass',
+            (greenlet,),
+            {'run': abstractmethod(lambda self: None)})
 
-            class GoodSubclass(AbstractSubclass):
-                def run(self):
-                    pass
+        class BadSubclass(AbstractSubclass):
+            pass
 
-            GoodSubclass() # should not raise
-            self.assertRaises(TypeError, BadSubclass)
+        class GoodSubclass(AbstractSubclass):
+            def run(self):
+                pass
+
+        GoodSubclass() # should not raise
+        self.assertRaises(TypeError, BadSubclass)
 
     def test_implicit_parent_with_threads(self):
         if not gc.isenabled():
@@ -540,3 +535,61 @@ class GreenletTests(unittest.TestCase):
         for i in range(5):
             if attempt():
                 break
+
+class TestRepr(unittest.TestCase):
+
+    def assertEndsWith(self, got, suffix):
+        self.assertTrue(got.endswith(suffix), (got, suffix))
+
+    def test_main_while_running(self):
+        r = repr(greenlet.getcurrent())
+        self.assertEndsWith(r, " current active started main>")
+
+    def test_main_in_background(self):
+        main = greenlet.getcurrent()
+        def run():
+            return repr(main)
+
+        g = greenlet(run)
+        r = g.switch()
+        self.assertEndsWith(r, ' suspended active started main>')
+
+    def test_initial(self):
+        r = repr(greenlet())
+        self.assertEndsWith(r, ' pending>')
+
+    def test_main_from_other_thread(self):
+        main = greenlet.getcurrent()
+
+        class T(threading.Thread):
+            original_main = thread_main = None
+            main_glet = None
+            def run(self):
+                self.original_main = repr(main)
+                self.main_glet = greenlet.getcurrent()
+                self.thread_main = repr(self.main_glet)
+
+        t = T()
+        t.start()
+        t.join(10)
+
+        self.assertEndsWith(t.original_main, ' suspended active started main>')
+        self.assertEndsWith(t.thread_main, ' current active started main>')
+
+        r = repr(t.main_glet)
+        # main greenlets, even from dead threads, never really appear dead
+        # TODO: Can we find a better way to differentiate that?
+        assert not t.main_glet.dead
+        self.assertEndsWith(r, ' suspended active started main>')
+
+
+    def test_dead(self):
+        g = greenlet(lambda: None)
+        g.switch()
+        self.assertEndsWith(repr(g), ' dead>')
+        self.assertNotIn('suspended', repr(g))
+        self.assertNotIn('started', repr(g))
+        self.assertNotIn('active', repr(g))
+
+if __name__ == '__main__':
+    unittest.main()