Fix scheduler hang when pending limit is reached

CHANGES/97.bugfix

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

aiojobs/_scheduler.py

@@ -62,12 +62,16 @@ async def spawn(self, coro):
             raise RuntimeError("Scheduling a new job after closing")
         job = Job(coro, self)
         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

@@ -263,19 +263,54 @@ 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
         async with timeout(1):
             await scheduler.spawn(coro(fut3))
 
+    assert scheduler.active_count == 1
     assert scheduler.pending_count == 1
 
 
+async def test_scheduler_concurrency_pending_limit(make_scheduler):
+    scheduler = await make_scheduler(limit=1, pending_limit=1)
+
+    async def coro(fut):
+        await fut
+
+    futures = [asyncio.Future() for _ in range(3)]
+    jobs = []
+
+    async def spawn():
+        for fut in futures:
+            jobs.append(await scheduler.spawn(coro(fut)))
+
+    asyncio.create_task(spawn())
+    await asyncio.sleep(0.05)
+
+    assert len(scheduler) == 2
+    assert scheduler.active_count == 1
+    assert scheduler.pending_count == 1
+
+    for fut in futures:
+        fut.set_result(None)
+
+    for job in jobs:
+        await job.wait()
+
+    assert not len(scheduler)
+    assert scheduler.active_count == 0
+    assert scheduler.pending_count == 0
+    assert all(job.closed for job in jobs)
+
+
 async def test_scheduler_concurrency_limit(make_scheduler):
     scheduler = await make_scheduler(limit=1)