Fix scheduler hang when pending limit is reached

CHANGES/97.bugfix

@@ -0,0 +1,2 @@
+Fix scheduler hang when pending limit is reached.
+

aiojobs/_scheduler.py

@@ -73,12 +73,16 @@ async def spawn(self, coro):
         job = Job(coro, self, self._loop)
         should_start = (self._limit is None or
                         self.active_count < self._limit)
-        self._jobs.add(job)
         if should_start:
             job._start()
         else:
-            # wait for free slot in queue
-            await self._pending.put(job)
+            try:
+                # wait for free slot in queue
+                await self._pending.put(job)
+            except asyncio.CancelledError:
+                await job.close()
+                raise
+        self._jobs.add(job)
         return job
 
     async def close(self):

tests/test_scheduler.py

@@ -268,16 +268,19 @@ async def coro(fut):
     fut3 = asyncio.Future()
 
     await scheduler.spawn(coro(fut1))
+    assert scheduler.active_count == 1
     assert scheduler.pending_count == 0
 
     await scheduler.spawn(coro(fut2))
+    assert scheduler.active_count == 1
     assert scheduler.pending_count == 1
 
     with pytest.raises(asyncio.TimeoutError):
         # try to wait for 1 sec to add task to pending queue
         with timeout(1, loop=loop):
             await scheduler.spawn(coro(fut3))
 
+    assert scheduler.active_count == 1
     assert scheduler.pending_count == 1