Change timeout from milliseconds to seconds in ray.wait. (#3706)

* Change timeout from milliseconds to seconds in ray.wait.

* Suppress warning.

* Suppress warning.

* Add prominent warning in API documentation.

python/ray/worker.py

@@ -2259,6 +2259,11 @@ def put(value, worker=global_worker):
 def wait(object_ids, num_returns=1, timeout=None, worker=global_worker):
     """Return a list of IDs that are ready and a list of IDs that are not.
 
+    .. warning::
+
+        The **timeout** argument used to be in **milliseconds** (up through
+        ``ray==0.6.1``) and now it is in **seconds**.
+
     If timeout is set, the function returns either when the requested number of
     IDs are ready or when the timeout is reached, whichever occurs first. If it
     is not set, the function simply waits until that number of objects is ready
@@ -2278,8 +2283,8 @@ def wait(object_ids, num_returns=1, timeout=None, worker=global_worker):
         object_ids (List[ObjectID]): List of object IDs for objects that may or
             may not be ready. Note that these IDs must be unique.
         num_returns (int): The number of object IDs that should be returned.
-        timeout (int): The maximum amount of time in milliseconds to wait
-            before returning.
+        timeout (float): The maximum amount of time in seconds to wait before
+            returning.
 
     Returns:
         A list of object IDs that are ready and a list of the remaining object
@@ -2294,6 +2299,15 @@ def wait(object_ids, num_returns=1, timeout=None, worker=global_worker):
         raise TypeError("wait() expected a list of ObjectID, got {}".format(
             type(object_ids)))
 
+    if isinstance(timeout, int) and timeout != 0:
+        logger.warning("The 'timeout' argument now requires seconds instead "
+                       "of milliseconds. This message can be suppressed by "
+                       "passing in a float.")
+
+    if timeout is not None and timeout < 0:
+        raise ValueError("The 'timeout' argument must be nonnegative. "
+                         "Received {}".format(timeout))
+
     if worker.mode != LOCAL_MODE:
         for object_id in object_ids:
             if not isinstance(object_id, ray.ObjectID):
@@ -2328,9 +2342,11 @@ def wait(object_ids, num_returns=1, timeout=None, worker=global_worker):
         with worker.state_lock:
             current_task_id = worker.get_current_thread_task_id()
 
-        timeout = timeout if timeout is not None else 2**30
+        timeout = timeout if timeout is not None else 10**6
+        timeout_milliseconds = int(timeout * 1000)
         ready_ids, remaining_ids = worker.raylet_client.wait(
-            object_ids, num_returns, timeout, False, current_task_id)
+            object_ids, num_returns, timeout_milliseconds, False,
+            current_task_id)
         return ready_ids, remaining_ids