Simplify libev default loop handling and let it regenerate itself.

CHANGES.rst

@@ -64,6 +64,11 @@
   extension implementation only) deallocated (garbage collected). See
   :issue:`1098`.
 
+- Simplify handling of the libev default loop and the ``destroy()``
+  method. The default loop, when destroyed, can again be requested and
+  it will regenerate itself. The default loop is the only one that can
+  receive child events.
+
 
 1.3a1 (2018-01-27)
 ==================

src/gevent/_ffi/loop.py

@@ -487,12 +487,11 @@ class AbstractLoop(object):
         """
         if self._ptr:
             try:
-                if self._default:
-                    if not self._can_destroy_default_loop():
+                if not self._can_destroy_loop(self._ptr):
                     return False
-                    type(self)._default_loop_destroyed = True
-
+                self._destroyed_loop(self._ptr)
                 self._stop_aux_watchers()
+
             finally:
                 # not ffi.NULL, we don't want something that can be
                 # passed to C and crash later. This will create nice friendly
@@ -501,8 +500,11 @@ class AbstractLoop(object):
 
             return True
 
-    def _can_destroy_default_loop(self):
-        return not type(self)._default_loop_destroyed
+    def _can_destroy_loop(self, ptr):
+        raise NotImplementedError()
+
+    def _destroyed_loop(self, ptr):
+        raise NotImplementedError()
 
     @property
     def ptr(self):

src/gevent/libev/corecext.pyx

@@ -259,8 +259,6 @@ cdef bint _check_loop(loop loop) except -1:
     return 1
 
 
-cdef bint _default_loop_destroyed = False
-
 
 cdef public class callback [object PyGeventCallbackObject, type PyGeventCallback_Type]:
     cdef public object callback
@@ -419,8 +417,6 @@ cdef public class loop [object PyGeventLoopObject, type PyGeventLoop_Type]:
             c_flags |= libev.EVFLAG_FORKCHECK
             if default is None:
                 default = True
-                if _default_loop_destroyed:
-                    default = False
             if default:
                 self._default = 1
                 self._ptr = libev.gevent_ev_default_loop(c_flags)
@@ -436,6 +432,8 @@ cdef public class loop [object PyGeventLoopObject, type PyGeventLoop_Type]:
             if default or __SYSERR_CALLBACK is None:
                 set_syserr_cb(self._handle_syserr)
 
+        # Mark as not destroyed
+        libev.ev_set_userdata(self._ptr, self._ptr)
 
         libev.ev_prepare_start(self._ptr, &self._prepare)
         libev.ev_unref(self._ptr)
@@ -489,36 +487,35 @@ cdef public class loop [object PyGeventLoopObject, type PyGeventLoop_Type]:
             libev.ev_timer_stop(ptr, &self._periodic_signal_checker)
 
     def destroy(self):
-        global _default_loop_destroyed
-
         cdef libev.ev_loop* ptr = self._ptr
         self._ptr = NULL
 
         if ptr:
-            if self._default and _default_loop_destroyed:
-                # Whoops! Program error. They destroyed the default loop,
+            if not libev.ev_userdata(ptr):
+                # Whoops! Program error. They destroyed the loop,
                 # using a different loop object. Our _ptr is still
                 # valid, but the libev loop is gone. Doing anything
                 # else with it will likely cause a crash.
                 return
+            # Mark as destroyed
+            libev.ev_set_userdata(ptr, NULL)
             self._stop_watchers(ptr)
             if __SYSERR_CALLBACK == self._handle_syserr:
                 set_syserr_cb(None)
-            if self._default:
-                _default_loop_destroyed = True
             libev.ev_loop_destroy(ptr)
 
     def __dealloc__(self):
         cdef libev.ev_loop* ptr = self._ptr
         self._ptr = NULL
         if ptr != NULL:
-            if self._default and _default_loop_destroyed:
+            if not libev.ev_userdata(ptr):
                 # See destroy(). This is a bug in the caller.
                 return
-
             self._stop_watchers(ptr)
             if not self._default:
                 libev.ev_loop_destroy(ptr)
+                # Mark as destroyed
+                libev.ev_set_userdata(ptr, NULL)
 
     @property
     def ptr(self):

src/gevent/libev/corecffi.py

@@ -223,9 +223,6 @@ class loop(AbstractLoop):
         c_flags |= libev.EVFLAG_FORKCHECK
         if default is None:
             default = True
-            if loop._default_loop_destroyed:
-                default = False
-
         if default:
             ptr = libev.gevent_ev_default_loop(c_flags)
             if not ptr:
@@ -237,6 +234,8 @@ class loop(AbstractLoop):
         if default or globals()["__SYSERR_CALLBACK"] is None:
             set_syserr_cb(self._handle_syserr)
 
+        # Mark this loop as being used.
+        libev.ev_set_userdata(ptr, ptr)
         return ptr
 
     def _init_and_start_check(self):
@@ -282,6 +281,14 @@ class loop(AbstractLoop):
             if should_destroy_loop:
                 libev.ev_loop_destroy(ptr)
 
+    def _can_destroy_loop(self, ptr):
+        # Is it marked as destroyed?
+        return libev.ev_userdata(ptr)
+
+    def _destroyed_loop(self, ptr):
+        # Mark as destroyed.
+        libev.ev_set_userdata(ptr, ffi.NULL)
+
     @property
     def MAXPRI(self):
         return libev.EV_MAXPRI

src/gevent/libev/libev.pxd

@@ -202,6 +202,8 @@ cdef extern from "libev.h" nogil:
 
     ev_loop* ev_default_loop(unsigned int flags)
     ev_loop* ev_loop_new(unsigned int flags)
+    void* ev_userdata(ev_loop*)
+    void ev_set_userdata(ev_loop*, void*)
     void ev_loop_destroy(ev_loop*)
     void ev_loop_fork(ev_loop*)
     int ev_is_default_loop(ev_loop*)

src/gevent/libuv/loop.py

@@ -68,8 +68,6 @@ class loop(AbstractLoop):
     # know this in general on libev
     min_sleep_time = 0.001 # 1ms
 
-    DEFAULT_LOOP_REGENERATES = True
-
     error_handler = None
 
     _CHECK_POINTER = 'uv_check_t *'
@@ -296,14 +294,16 @@ class loop(AbstractLoop):
                 closed_failed = libuv.uv_loop_close(ptr)
                 assert closed_failed == 0, closed_failed
 
-    def _can_destroy_default_loop(self):
+    def _can_destroy_loop(self, ptr):
         # We're being asked to destroy a loop that's,
         # at the time it was constructed, was the default loop.
         # If loop objects were constructed more than once,
         # it may have already been destroyed, though.
         # We track this in the data member.
-        return self._ptr.data
+        return ptr.data
 
+    def _destroyed_loop(self, ptr):
+        ptr.data = ffi.NULL
 
     def debug(self):
         """

src/greentest/test__core.py

@@ -19,6 +19,9 @@ class TestCore(unittest.TestCase):
 
 class TestWatchers(unittest.TestCase):
 
+    def makeOne(self):
+        return core.loop()
+
     def test_io(self):
         if sys.platform == 'win32':
             # libev raises IOError, libuv raises ValueError
@@ -28,17 +31,17 @@ class TestWatchers(unittest.TestCase):
             Error = ValueError
             win32 = False
         with self.assertRaises(Error):
-            core.loop().io(-1, 1)
+            self.makeOne().io(-1, 1)
         if hasattr(core, 'TIMER'):
             # libev
             with self.assertRaises(ValueError):
-                core.loop().io(1, core.TIMER)
+                self.makeOne().io(1, core.TIMER)
 
         # Test we can set events and io before it's started
         if not win32:
             # We can't do this with arbitrary FDs on windows;
             # see libev_vfd.h
-            io = core.loop().io(1, core.READ)
+            io = self.makeOne().io(1, core.READ)
             io.fd = 2
             self.assertEqual(io.fd, 2)
             io.events = core.WRITE
@@ -47,15 +50,29 @@ class TestWatchers(unittest.TestCase):
                 self.assertEqual(core._events_to_str(io.events), 'WRITE|_IOFDSET')
             else:
                 self.assertEqual(core._events_to_str(io.events), 'WRITE')
+            io.start(lambda: None)
             io.close()
 
     def test_timer_constructor(self):
         with self.assertRaises(ValueError):
-            core.loop().timer(1, -1)
+            self.makeOne().timer(1, -1)
 
     def test_signal_constructor(self):
         with self.assertRaises(ValueError):
-            core.loop().signal(1000)
+            self.makeOne().signal(1000)
+
+class TestWatchersDefault(TestWatchers):
+
+    def makeOne(self):
+        return core.loop(default=True)
+
+class TestWatchersDefaultDestroyed(TestWatchers):
+
+    def makeOne(self):
+        l = core.loop(default=True)
+        l.destroy()
+        del l
+        return core.loop(default=True)
 
 @skipOnLibuv("Tests for libev-only functions")
 class TestLibev(unittest.TestCase):

src/greentest/test__destroy.py

@@ -40,12 +40,9 @@ class TestDestroyHub(unittest.TestCase):
         self.assertIsNot(hub.loop.ptr, initloop.ptr)
         self.assertNotEqual(hub.loop.ptr, initloop.ptr)
 
-        # Destroy hub including default loop, create new hub with non-default loop.
+        # Destroy hub including default loop. The default loop regenerates.
         hub.destroy(destroy_loop=True)
         hub = gevent.get_hub()
-        if not getattr(hub.loop, 'DEFAULT_LOOP_REGENERATES', False):
-            self.assertFalse(hub.loop.default)
-        else:
         self.assertTrue(hub.loop.default)
 
         hub.destroy()