bugfix: write to another transport in resume_writing() fails

tests/test_tcp.py

@@ -652,6 +652,59 @@ async def runner():
         self.assertIsNone(
             self.loop.run_until_complete(connection_lost_called))
 
+    def test_resume_writing_write_different_transport(self):
+        loop = self.loop
+
+        class P1(asyncio.Protocol):
+            def __init__(self, t2):
+                self.t2 = t2
+                self.paused = False
+                self.waiter = loop.create_future()
+
+            def data_received(self, data):
+                self.waiter.set_result(data)
+
+            def pause_writing(self):
+                self.paused = True
+
+            def resume_writing(self):
+                self.paused = False
+                self.t2.write(b'hello')
+
+        s1, s2 = socket.socketpair()
+        s1.setsockopt(socket.SOL_SOCKET, socket.SO_SNDBUF, 1024)
+        s2.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, 1024)
+
+        async def _test(t1, p1, t2):
+            t1.set_write_buffer_limits(1024, 1023)
+
+            # fill s1 up first
+            t2.pause_reading()
+            while not p1.paused:
+                t1.write(b' ' * 1024)
+
+            # trigger resume_writing() in _exec_queued_writes() with tight loop
+            t2.resume_reading()
+            while p1.paused:
+                t1.write(b' ')
+                await asyncio.sleep(0)
+
+            # t2.write() in p1.resume_writing() should work fine
+            data = await asyncio.wait_for(p1.waiter, 5)
+            self.assertEqual(data, b'hello')
+
+        async def test():
+            t2, _ = await loop.create_connection(asyncio.Protocol, sock=s2)
+            t1, p1 = await loop.create_connection(lambda: P1(t2), sock=s1)
+            try:
+                await _test(t1, p1, t2)
+            finally:
+                t1.close()
+                t2.close()
+
+        with s1, s2:
+            loop.run_until_complete(test())
+
 
 class Test_UV_TCP(_TestTCP, tb.UVTestCase):
 

uvloop/loop.pxd

@@ -49,7 +49,7 @@ cdef class Loop:
         object _exception_handler
         object _default_executor
         object _ready
-        set _queued_streams
+        set _queued_streams, _executing_streams
         Py_ssize_t _ready_len
 
         set _servers

uvloop/loop.pyx

@@ -177,6 +177,7 @@ cdef class Loop:
         self._default_executor = None
 
         self._queued_streams = set()
+        self._executing_streams = set()
         self._ready = col_deque()
         self._ready_len = 0
 
@@ -645,25 +646,20 @@ cdef class Loop:
 
         cdef:
             UVStream stream
-            int queued_len
 
-        if UVLOOP_DEBUG:
-            queued_len = len(self._queued_streams)
-
-        for pystream in self._queued_streams:
-            stream = <UVStream>pystream
-            stream._exec_write()
-
-        if UVLOOP_DEBUG:
-            if len(self._queued_streams) != queued_len:
-                raise RuntimeError(
-                    'loop._queued_streams are not empty after '
-                    '_exec_queued_writes')
-
-        self._queued_streams.clear()
+        streams = self._queued_streams
+        self._queued_streams = self._executing_streams
+        self._executing_streams = streams
+        try:
+            for pystream in streams:
+                stream = <UVStream>pystream
+                stream._exec_write()
+        finally:
+            streams.clear()
 
         if self.handler_check__exec_writes.running:
-            self.handler_check__exec_writes.stop()
+            if len(self._queued_streams) == 0:
+                self.handler_check__exec_writes.stop()
 
     cdef inline _call_soon(self, object callback, object args, object context):
         cdef Handle handle