Tornado 5 fix (#61)

* Tornado 5 fix

* Dummy commit

* Use PeriodicCallback from distributed.utils

* Require distributed 1.20.0+

Need this version to get a compat function from distributed for
`PeriodicCallback` that smooths over the Tornado 5.0 differences.

* Require distributed 1.20.0+ for testing

Update the `env.yml` file used for testing to require distributed
1.20.0+.

dask_drmaa/core.py

@@ -9,11 +9,10 @@
 import drmaa
 from toolz import merge
 from tornado import gen
-from tornado.ioloop import PeriodicCallback
 
 from distributed import LocalCluster
 from distributed.utils import log_errors, ignoring
-from distributed.protocol.pickle import dumps
+from distributed.utils import PeriodicCallback
 
 logger = logging.getLogger(__name__)
 
@@ -164,8 +163,7 @@ def remove_script():
                               template or {})
 
         self._cleanup_callback = PeriodicCallback(callback=self.cleanup_closed_workers,
-                                                  callback_time=cleanup_interval,
-                                                  io_loop=self.scheduler.loop)
+                                                  callback_time=cleanup_interval)
         self._cleanup_callback.start()
 
         self.workers = {}  # {job-id: WorkerSpec}

env.yml

@@ -1,7 +1,7 @@
 name: drmaa
 dependencies:
   - dask
-  - distributed
+  - distributed>=1.20.0
   - ipython
   - drmaa
   - python=3

requirements.txt

@@ -1,4 +1,4 @@
 dask
-distributed
+distributed >= 1.20.0
 drmaa
 click