bpo-32356: idempotent pause_/resume_reading; new is_reading method. (#4914)

Lib/asyncio/proactor_events.py

@@ -152,21 +152,20 @@ class _ProactorReadPipeTransport(_ProactorBasePipeTransport,
         self._paused = False
         self._loop.call_soon(self._loop_reading)
 
+    def is_reading(self):
+        return not self._paused and not self._closing
+
     def pause_reading(self):
-        if self._closing:
-            raise RuntimeError('Cannot pause_reading() when closing')
-        if self._paused:
-            raise RuntimeError('Already paused')
+        if self._closing or self._paused:
+            return
         self._paused = True
         if self._loop.get_debug():
             logger.debug("%r pauses reading", self)
 
     def resume_reading(self):
-        if not self._paused:
-            raise RuntimeError('Not paused')
-        self._paused = False
-        if self._closing:
+        if self._closing or not self._paused:
             return
+        self._paused = False
         self._loop.call_soon(self._loop_reading, self._read_fut)
         if self._loop.get_debug():
             logger.debug("%r resumes reading", self)

Lib/asyncio/selector_events.py

@@ -702,22 +702,21 @@ class _SelectorSocketTransport(_SelectorTransport):
             self._loop.call_soon(futures._set_result_unless_cancelled,
                                  waiter, None)
 
+    def is_reading(self):
+        return not self._paused and not self._closing
+
     def pause_reading(self):
-        if self._closing:
-            raise RuntimeError('Cannot pause_reading() when closing')
-        if self._paused:
-            raise RuntimeError('Already paused')
+        if self._closing or self._paused:
+            return
         self._paused = True
         self._loop._remove_reader(self._sock_fd)
         if self._loop.get_debug():
             logger.debug("%r pauses reading", self)
 
     def resume_reading(self):
-        if not self._paused:
-            raise RuntimeError('Not paused')
-        self._paused = False
-        if self._closing:
+        if self._closing or not self._paused:
             return
+        self._paused = False
         self._loop._add_reader(self._sock_fd, self._read_ready)
         if self._loop.get_debug():
             logger.debug("%r resumes reading", self)

Lib/asyncio/sslproto.py

@@ -317,6 +317,12 @@ class _SSLProtocolTransport(transports._FlowControlMixin,
                           source=self)
             self.close()
 
+    def is_reading(self):
+        tr = self._ssl_protocol._transport
+        if tr is None:
+            raise RuntimeError('SSL transport has not been initialized yet')
+        return tr.is_reading()
+
     def pause_reading(self):
         """Pause the receiving end.
 

Lib/asyncio/transports.py

@@ -44,6 +44,10 @@ class BaseTransport:
 class ReadTransport(BaseTransport):
     """Interface for read-only transports."""
 
+    def is_reading(self):
+        """Return True if the transport is receiving."""
+        raise NotImplementedError
+
     def pause_reading(self):
         """Pause the receiving end.