Add Python binding for rabit ops.

python-package/xgboost/rabit.py

@@ -56,6 +56,12 @@ def get_world_size():
     return ret
 
 
+def is_distributed():
+    '''If rabit is distributed.'''
+    is_dist = _LIB.RabitIsDistributed()
+    return is_dist
+
+
 def tracker_print(msg):
     """Print message to the tracker.
 
@@ -143,6 +149,14 @@ def broadcast(data, root):
 }
 
 
+class Op:                     # pylint: disable=too-few-public-methods
+    '''Supported operations for rabit.'''
+    MAX = 0
+    MIN = 1
+    SUM = 2
+    OR = 3
+
+
 def allreduce(data, op, prepare_fun=None):
     """Perform allreduce, return the result.
 

tests/python/test_tracker.py

@@ -1,7 +1,8 @@
-import time
-
 from xgboost import RabitTracker
 import xgboost as xgb
+import pytest
+import testing as tm
+import numpy as np
 
 
 def test_rabit_tracker():
@@ -15,3 +16,39 @@ def test_rabit_tracker():
     ret = xgb.rabit.broadcast('test1234', 0)
     assert str(ret) == 'test1234'
     xgb.rabit.finalize()
+
+
+def run_rabit_ops(client, n_workers):
+    from xgboost.dask import RabitContext, _get_rabit_args, _get_client_workers
+    from xgboost import rabit
+
+    workers = list(_get_client_workers(client).keys())
+    rabit_args = _get_rabit_args(workers, client)
+    assert not rabit.is_distributed()
+
+    def local_test(worker_id):
+        with RabitContext(rabit_args):
+            a = 1
+            assert rabit.is_distributed()
+            a = np.array([a])
+            reduced = rabit.allreduce(a, rabit.Op.SUM)
+            assert reduced[0] == n_workers
+
+            worker_id = np.array([worker_id])
+            reduced = rabit.allreduce(worker_id, rabit.Op.MAX)
+            assert reduced == n_workers - 1
+
+            return 1
+
+    futures = client.map(local_test, range(len(workers)), workers=workers)
+    results = client.gather(futures)
+    assert sum(results) == n_workers
+
+
+@pytest.mark.skipif(**tm.no_dask())
+def test_rabit_ops():
+    from distributed import Client, LocalCluster
+    n_workers = 3
+    with LocalCluster(n_workers=n_workers) as cluster:
+        with Client(cluster) as client:
+            run_rabit_ops(client, n_workers)