Allow Ray API to be used from multiple threads (#2422)

test/runtest.py

@@ -4,6 +4,7 @@ import os
 import re
 import string
 import sys
+import threading
 import time
 import unittest
 from collections import defaultdict, namedtuple, OrderedDict
@@ -1144,6 +1145,37 @@ class APITest(unittest.TestCase):
         with self.assertRaises(Exception):
             ray.get(3)
 
+    def testMultithreading(self):
+        self.init_ray(driver_mode=ray.SILENT_MODE)
+
+        @ray.remote
+        def f():
+            pass
+
+        def g(n):
+            for _ in range(1000 // n):
+                ray.get([f.remote() for _ in range(n)])
+            res = [ray.put(i) for i in range(1000 // n)]
+            ray.wait(res, len(res))
+
+        def test_multi_threading():
+            threads = [
+                threading.Thread(target=g, args=(n, ))
+                for n in [1, 5, 10, 100, 1000]
+            ]
+
+            [thread.start() for thread in threads]
+            [thread.join() for thread in threads]
+
+        @ray.remote
+        def test_multi_threading_in_worker():
+            test_multi_threading()
+
+        # test multi-threading in the driver
+        test_multi_threading()
+        # test multi-threading in the worker
+        ray.get(test_multi_threading_in_worker.remote())
+
 
 @unittest.skipIf(
     os.environ.get('RAY_USE_NEW_GCS', False),