[tfdbg] Load metadata in DebugDataReader

- This resolves a TODO item realted to DebugDataReader not reading the
  .metadata file in the file set.
- This is needed by the debugger_v2/runs route of in the DebuggerV2 work
  in TensorBoard.
- A unit test is added.

Also in this CL:
- Clean up some inadvertently left-over cruft in debug_events_reader.py.

PiperOrigin-RevId: 288046710
Change-Id: I663255f2822ffec9247823ac0099592af48ebac9

tensorflow/python/debug/lib/debug_events_reader.py

@@ -632,6 +632,8 @@ class DebugDataReader(object):
 
   def __init__(self, dump_root):
     self._reader = DebugEventsReader(dump_root)
+    self._load_metadata()
+
     # TODO(cais): Implement pagination for memory constraints.
     self._execution_digests = []
 
@@ -651,15 +653,12 @@ class DebugDataReader(object):
     # TODO(cais): Implement pagination for memory constraints.
     self._graph_execution_trace_digests = []
 
-    # The following timestamps keep track where we've reached in each
-    # file of the DebugEvent source file, so that we don't run into race
-    # conditions with the writer.
-    self._source_files_timestamp = 0
-    # Temporary object used to hold DebugEvent protos with stack_frames
-    # field that has been read beyond max_wall_time.
-    # self._last_successful_stack_frames_offset = -1  # TODO(cais): Fix.
+  def _load_metadata(self):
+    metadata_iter = self._reader.metadata_iterator()
+    debug_event = next(metadata_iter).debug_event
+    self._starting_wall_time = debug_event.wall_time
+    self._tensorflow_version = debug_event.debug_metadata.tensorflow_version
 
-  # TODO(cais): Read metadata.
   def _load_source_files(self):
     """Incrementally read the .source_files DebugEvent file."""
     source_files_iter = self._reader.source_files_iterator()
@@ -667,7 +666,6 @@ class DebugDataReader(object):
       source_file = debug_event.source_file
       self._host_name_file_path_to_offset[
           (source_file.host_name, source_file.file_path)] = offset
-      self._source_file_timestamp = debug_event.wall_time
 
   def _load_stack_frames(self):
     """Incrementally read the .stack_frames file.
@@ -789,6 +787,25 @@ class DebugDataReader(object):
     offset = self._host_name_file_path_to_offset[(host_name, file_path)]
     return list(self._reader.read_source_files_event(offset).source_file.lines)
 
+  def starting_wall_time(self):
+    """Wall timestamp for when the debugged TensorFlow program started.
+
+    Returns:
+      Stating wall time as seconds since the epoch, as a `float`.
+    """
+    return self._starting_wall_time
+
+  def tensorflow_version(self):
+    """TensorFlow version used in the debugged TensorFlow program.
+
+    Note: this is not necessarily the same as the version of TensorFlow used to
+    load the DebugEvent file set.
+
+    Returns:
+      TensorFlow version used by the debugged program, as a `str`.
+    """
+    return self._tensorflow_version
+
   def outermost_graphs(self):
     """Get the number of outer most graphs read so far."""
     return [graph for graph in self._graph_by_id.values()

tensorflow/python/debug/lib/debug_events_writer_test.py

@@ -21,12 +21,14 @@ from __future__ import print_function
 import glob
 import os
 import threading
+import time
 
 from tensorflow.core.protobuf import debug_event_pb2
 from tensorflow.python.debug.lib import debug_events_reader
 from tensorflow.python.debug.lib import debug_events_writer
 from tensorflow.python.debug.lib import dumping_callback_test_lib
 from tensorflow.python.framework import ops
+from tensorflow.python.framework import versions
 from tensorflow.python.platform import googletest
 
 
@@ -192,6 +194,15 @@ class DebugEventsWriterTest(dumping_callback_test_lib.DumpingCallbackTestBase):
     graph_op_names = sorted([actual.op_name for actual in actuals])
     self.assertEqual(graph_op_names, ["Op0", "Op1", "Op2"])
 
+  def testWriteAndReadMetadata(self):
+    t0 = time.time()
+    writer = debug_events_writer.DebugEventsWriter(self.dump_root)
+    writer.Close()
+    with debug_events_reader.DebugDataReader(self.dump_root) as reader:
+      self.assertIsInstance(reader.starting_wall_time(), float)
+      self.assertGreaterEqual(reader.starting_wall_time(), t0)
+      self.assertEqual(reader.tensorflow_version(), versions.__version__)
+
   def testWriteExecutionEventsWithCircularBuffer(self):
     writer = debug_events_writer.DebugEventsWriter(self.dump_root)
     num_execution_events = debug_events_writer.DEFAULT_CIRCULAR_BUFFER_SIZE * 2