asyncio: Handle end of stream condition properly.

By removing any IO watches for associated file handle. The way it's
implemented tries to preserve OS-like separation between event loop and
tasks. So, stream to finish watching fd for IO also issues syscall,
instead of calling methods on loop instance directly. Calling method on
loop would be more efficient, but will require storing reference to loop
in each stream. And those separation matters...

asyncio/asyncio.py

@@ -7,6 +7,10 @@ import logging
 
 log = logging.getLogger("asyncio")
 
+IO_READ  = 1
+IO_WRITE = 2
+
+
 def coroutine(f):
     return f
 
@@ -78,6 +82,12 @@ class EventLoop:
                         elif isinstance(ret, IOWrite):
                             self.add_writer(ret.obj.fileno(), lambda f: self.call_soon(cb, f), ret.obj)
                             continue
+                        elif isinstance(ret, IODone):
+                            if ret.op == IO_READ:
+                                self.remove_reader(ret.obj.fileno())
+                            elif ret.op == IO_WRITE:
+                                self.remove_writer(ret.obj.fileno())
+                            continue
                 except StopIteration as e:
                     log.debug("Gen finished: %s", cb)
                     continue
@@ -156,6 +166,12 @@ class IOWrite(SysCall):
     def __init__(self, obj):
         self.obj = obj
 
+class IODone(SysCall):
+
+    def __init__(self, op, obj):
+        self.op = op
+        self.obj = obj
+
 
 def get_event_loop():
     return EpollEventLoop()
@@ -189,6 +205,8 @@ class StreamReader:
         s = yield IORead(self.s)
         log.debug("StreamReader.readline(): after IORead: %s", s)
         res = self.s.readline()
+        if not res:
+            yield IODone(IO_READ, self.s)
         log.debug("StreamReader.readline(): res: %s", res)
         return res