Open Source Monorail

appengine/monorail/framework/profiler.py

Index: appengine/monorail/framework/profiler.py
diff --git a/appengine/monorail/framework/profiler.py b/appengine/monorail/framework/profiler.py
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+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is govered by a BSD-style
+# license that can be found in the LICENSE file or at
+# https://developers.google.com/open-source/licenses/bsd
+
+"""A simple profiler object to track how time is spent on a request.
+
+The profiler is called from application code at the begining and
+end of each major phase and subphase of processing.  The profiler
+object keeps track of how much time was spent on each phase or subphase.
+
+This class is useful when developers need to understand where
+server-side time is being spent.  It includes durations in
+milliseconds, and a simple bar chart on the HTML page.
+
+On-page debugging and performance info is useful because it makes it easier
+to explore performance interactively.
+"""
+
+import logging
+import time
+
+from contextlib import contextmanager
+
+
+class Profiler(object):
+  """Object to record and help display request processing profiling info.
+
+  The Profiler class holds a list of phase objects, which can hold additional
+  phase objects (which are subphases).  Each phase or subphase represents some
+  meaningful part of this application's HTTP request processing.
+  """
+
+  _COLORS = ['900', '090', '009', '360', '306', '036',
+             '630', '630', '063', '333']
+
+  def __init__(self):
+    """Each request processing profile begins with an empty list of phases."""
+    self.top_phase = _Phase('overall profile', -1, None)
+    self.current_phase = self.top_phase
+    self.next_color = 0
+
+  @contextmanager
+  def Phase(self, name='unspecified phase'):
+    """Context manager to automatically begin and end (sub)phases."""
+    color = self._COLORS[self.next_color % len(self._COLORS)]
+    self.next_color += 1
+    self.current_phase = _Phase(name, color, self.current_phase)
+    try:
+      yield
+    finally:
+      self.current_phase = self.current_phase.End()
+
+  def LogStats(self):
+    """Log sufficiently-long phases and subphases, for debugging purposes."""
+    self.top_phase.LogStats()
+
+
+class _Phase(object):
+  """A _Phase instance represents a period of time during request processing."""
+
+  def __init__(self, name, color, parent):
+    """Initialize a (sub)phase with the given name and current system clock."""
+    self.start = time.time()
+    self.name = name
+    self.color = color
+    self.subphases = []
+    self.elapsed_seconds = None
+    self.ms = 'in_progress'  # shown if the phase never records a finish.
+    self.uncategorized_ms = None
+    self.parent = parent
+    if self.parent is not None:
+      self.parent._RegisterSubphase(self)
+
+  def _RegisterSubphase(self, subphase):
+    """Add a subphase to this phase."""
+    self.subphases.append(subphase)
+
+  def End(self):
+    """Record the time between the start and end of this (sub)phase."""
+    self.elapsed_seconds = time.time() - self.start
+    self.ms = str(int(self.elapsed_seconds * 1000))
+    categorized = sum(sub.elapsed_seconds for sub in self.subphases)
+    self.uncategorized_ms = int((self.elapsed_seconds - categorized) * 1000)
+    return self.parent
+
+  def LogStats(self):
+    # Phases that took longer than 30ms are interesting.
+    if self.elapsed_seconds > 0.03:
+      logging.info('%5s: %s', self.ms, self.name)
+      for subphase in self.subphases:
+        subphase.LogStats()