[owners] Add BatchListOwners

BatchListOwners uses git_common's ScopedPool method to run
ListOwnersForFile in parallel for multiple paths.

Change-Id: I545072e16181407665c8b009f87fccfb7355d7d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2585657Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>

owners_client.py

@@ -7,6 +7,7 @@ import os
 import random
 
 import gerrit_util
+import git_common
 import owners as owners_db
 import scm
 
@@ -66,6 +67,12 @@ class OwnersClient(object):
     """
     raise Exception('Not implemented')
 
+  def BatchListOwners(self, project, branch, paths):
+    """Returns a dictionary {path: [owners]}."""
+    with git_common.ScopedPool(kind='threads') as pool:
+      return dict(pool.imap_unordered(
+          lambda p: (p, self.ListOwnersForFile(project, branch, p)), paths))
+
   def GetChangeApprovalStatus(self, change_id):
     """Check the approval status for the latest revision_id in a change.
 

tests/owners_client_test.py

@@ -256,6 +256,23 @@ class OwnersClientTest(unittest.TestCase):
             ['abc', 'acb', 'bac', 'bca', 'cab', 'cba']),
         (chris, bob))
 
+  def testBatchListOwners(self):
+    self.client.owners_by_path = {
+        'bar/everyone/foo.txt': [alice, bob],
+        'bar/everyone/bar.txt': [bob],
+        'bar/foo/': [bob, chris]
+    }
+
+    self.assertEquals(
+        {
+            'bar/everyone/foo.txt': [alice, bob],
+            'bar/everyone/bar.txt': [bob],
+            'bar/foo/': [bob, chris]
+        },
+        self.client.BatchListOwners(
+            'project', 'branch',
+            ['bar/everyone/foo.txt', 'bar/everyone/bar.txt', 'bar/foo/']))
+
 
 if __name__ == '__main__':
   unittest.main()