Add basic future interface to bigquery

Author: Jon Wayne Parrott

bigquery/google/cloud/bigquery/job.py

@@ -14,8 +14,11 @@
 
 """Define API Jobs."""
 
+import threading
+
 import six
 
+from google.cloud import exceptions
 from google.cloud.exceptions import NotFound
 from google.cloud._helpers import _datetime_from_microseconds
 from google.cloud.bigquery.dataset import Dataset
@@ -27,6 +30,7 @@
 from google.cloud.bigquery._helpers import UDFResourcesProperty
 from google.cloud.bigquery._helpers import _EnumProperty
 from google.cloud.bigquery._helpers import _TypedProperty
+import google.cloud.future.base
 
 
 class Compression(_EnumProperty):
@@ -82,14 +86,15 @@ class WriteDisposition(_EnumProperty):
     ALLOWED = (WRITE_APPEND, WRITE_TRUNCATE, WRITE_EMPTY)
 
 
-class _BaseJob(object):
+class _BaseJob(google.cloud.future.base.PollingFuture):
     """Base class for jobs.
 
     :type client: :class:`google.cloud.bigquery.client.Client`
     :param client: A client which holds credentials and project configuration
                    for the dataset (which requires a project).
     """
     def __init__(self, client):
+        super(_BaseJob, self).__init__()
         self._client = client
         self._properties = {}
 
@@ -131,6 +136,8 @@ class _AsyncJob(_BaseJob):
     def __init__(self, name, client):
         super(_AsyncJob, self).__init__(client)
         self.name = name
+        self._result_set = False
+        self._completion_lock = threading.Lock()
 
     @property
     def job_type(self):
@@ -273,6 +280,9 @@ def _set_properties(self, api_response):
         self._properties.clear()
         self._properties.update(cleaned)
 
+        # For Future interface
+        self._set_future_result()
+
     @classmethod
     def _get_resource_config(cls, resource):
         """Helper for :meth:`from_api_repr`
@@ -345,7 +355,7 @@ def exists(self, client=None):
             return True
 
     def reload(self, client=None):
-        """API call:  refresh job properties via a GET request
+        """API call:  refresh job properties via a GET request.
 
         See
         https://cloud.google.com/bigquery/docs/reference/rest/v2/jobs/get
@@ -371,12 +381,56 @@ def cancel(self, client=None):
                       ``NoneType``
         :param client: the client to use.  If not passed, falls back to the
                        ``client`` stored on the current dataset.
+
+        :rtype: bool
+        :returns: Boolean indicating that the cancel request was sent.
         """
         client = self._require_client(client)
 
         api_response = client._connection.api_request(
             method='POST', path='%s/cancel' % (self.path,))
         self._set_properties(api_response['job'])
+        return True
+
+    # The following methods implement the PollingFuture interface. Note that
+    # the methods above are from the pre-Future interface and are left for
+    # compatibility. The only "overloaded" method is :meth:`cancel`, which
+    # satisfies both interfaces.
+
+    def _set_future_result(self):
+        """Set the result or exception from the job if it is complete."""
+        # This must be done in a lock to prevent the polling thread
+        # and main thread from both executing the completion logic
+        # at the same time.
+        with self._completion_lock:
+            # If the operation isn't complete or if the result has already been
+            # set, do not call set_result/set_exception again.
+            # Note: self._result_set is set to True in set_result and
+            # set_exception, in case those methods are invoked directly.
+            if not self.state != 'DONE' or self._result_set:
+                return
+
+            if self.error_result:
+                exception = exceptions.GoogleCloudError(
+                    self.error_result, errors=self.errors)
+                self.set_exception(exception)
+            else:
+                self.set_result(self)
+
+    def done(self):
+        # Do not refresh is the state is already done, as the job will not
+        # change once complete.
+        if self.state != 'DONE':
+            self.reload()
+        return self.state == 'DONE'
+
+    def result(self, timeout=None):
+        if self.state is None:
+            self.begin()
+        return super(self, _AsyncJob).result(timeout=timeout)
+
+    def cancelled(self):
+        return False
 
 
 class _LoadConfiguration(object):