[Telemetry] Make unhandled exception output more useful.

This should help tremendously in diagnosing flake on the bots.

Default format:
---------------------------
Traceback (most recent call last):
  File "tools/perf/run_benchmark", line 23, in <module>
    sys.exit(test_runner.Main())
  File "tools/perf/../telemetry/telemetry/test_runner.py", line 290, in Main
    return command.Run(options, args)
  File "tools/perf/../telemetry/telemetry/test_runner.py", line 198, in Run
    return min(255, self._test().Run(copy.copy(options)))
  File "tools/perf/../telemetry/telemetry/test.py", line 53, in Run
    results = page_runner.Run(test, ps, expectations, options)
  File "tools/perf/../telemetry/telemetry/page/page_runner.py", line 330, in Run
    possible_browser, results, state)
  File "tools/perf/../telemetry/telemetry/page/page_runner.py", line 213, in _PrepareAndRunPage
    credentials_path, page.archive_path)
  File "tools/perf/../telemetry/telemetry/page/page_runner.py", line 54, in StartBrowser
    test.DidStartBrowser(self.browser)
  File "/work/chromium/src/tools/perf/measurements/page_cycler.py", line 71, in DidStartBrowser
    self._memory_metric = memory.MemoryMetric(browser)
  File "/work/chromium/src/tools/perf/metrics/memory.py", line 32, in __init__
    self._start_commit_charge = self._browser.memory_stats['SystemCommitCharge']
  File "tools/perf/../telemetry/telemetry/core/browser.py", line 166, in memory_stats
    result = self._GetStatsCommon(self._platform_backend.GetMemoryStats)
  File "tools/perf/../telemetry/telemetry/core/browser.py", line 99, in _GetStatsCommon
    for child_pid in self._platform_backend.GetChildPids(browser_pid):
  File "tools/perf/../telemetry/telemetry/core/platform/posix_platform_backend.py", line 44, in GetChildPids
    return proc_util.GetChildPids(processes, pid)
  File "tools/perf/../telemetry/telemetry/core/platform/proc_util.py", line 86, in GetChildPids
    for foo, curr_pid, curr_ppid, state in processes:
ValueError: need more than 3 values to unpack
---------------------------

New format:
---------------------------
Traceback (most recent call last):
  <module> at tools/perf/run_benchmark:23
    sys.exit(test_runner.Main())
  Main at tools/telemetry/telemetry/test_runner.py:303
    return command.Run(options, args)
  Run at tools/telemetry/telemetry/test_runner.py:211
    return min(255, self._test().Run(copy.copy(options)))
  Run at tools/telemetry/telemetry/test.py:53
    results = page_runner.Run(test, ps, expectations, options)
  Run at tools/telemetry/telemetry/page/page_runner.py:330
    possible_browser, results, state)
  _PrepareAndRunPage at tools/telemetry/telemetry/page/page_runner.py:213
    credentials_path, page.archive_path)
  StartBrowser at tools/telemetry/telemetry/page/page_runner.py:54
    test.DidStartBrowser(self.browser)
  DidStartBrowser at tools/perf/measurements/page_cycler.py:71
    self._memory_metric = memory.MemoryMetric(browser)
  __init__ at tools/perf/metrics/memory.py:32
    self._start_commit_charge = self._browser.memory_stats['SystemCommitCharge']
  memory_stats at tools/telemetry/telemetry/core/browser.py:166
    result = self._GetStatsCommon(self._platform_backend.GetMemoryStats)
  _GetStatsCommon at tools/telemetry/telemetry/core/browser.py:99
    for child_pid in self._platform_backend.GetChildPids(browser_pid):
  GetChildPids at tools/telemetry/telemetry/core/platform/posix_platform_backend.py:44
    return proc_util.GetChildPids(processes, pid)
  GetChildPids at tools/telemetry/telemetry/core/platform/proc_util.py:86
    for foo, curr_pid, curr_ppid, state in processes:

Locals:
  child_dict : defaultdict(<type 'list'>, {})
  pid        : 5510
  processes  : [['1', '0', 'Ss'], ['15', '1', 'Ss'], ['16', '1', 'Ss'], ['17 ... 99', 'R+'], ['78347', '78344', 'Ss'], ['78349', '78347', 'S']] (truncated)

ValueError: need more than 3 values to unpack
---------------------------

BUG=

Review URL: https://codereview.chromium.org/64553004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234648 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 67 insertions, 0 deletions

diff --git a/tools/telemetry/telemetry/test_runner.py b/tools/telemetry/telemetry/test_runner.py
index adb95a8..ec62132 100644
--- a/tools/telemetry/telemetry/test_runner.py
+++ b/tools/telemetry/telemetry/test_runner.py
@@ -10,9 +10,11 @@ actually running the test is in Test and PageRunner."""
 import copy
 import inspect
 import json
+import math
 import optparse
 import os
 import sys
+import traceback
 
 from telemetry import test
 from telemetry.core import browser_options
@@ -20,6 +22,71 @@ from telemetry.core import discover
 from telemetry.core import util
 
 
+def PrintFormattedException(exception_class, exception, tb):
+  """Prints an Exception in a more useful format than the default.
+
+  TODO(tonyg): Consider further enhancements. For instance:
+    - Report stacks to maintainers like depot_tools does.
+    - Add a debug flag to automatically start pdb upon exception.
+  """
+  def _GetFinalFrame(frame):
+    final_frame = None
+    while frame is not None:
+      final_frame = frame
+      frame = frame.tb_next
+    return final_frame
+
+  def _AbbreviateMiddle(target, middle, length):
+    assert length >= 0, 'Must provide positive length'
+    assert len(middle) <= length, 'middle must not be greater than length'
+    if len(target) <= length:
+      return target
+    half_length = (length - len(middle)) / 2.
+    return '%s%s%s' % (target[:int(math.floor(half_length))],
+                       middle,
+                       target[-int(math.ceil(half_length)):])
+
+  base_dir = os.path.abspath(util.GetChromiumSrcDir())
+  formatted_exception = traceback.format_exception(
+      exception_class, exception, tb)
+  extracted_tb = traceback.extract_tb(tb)
+  traceback_header = formatted_exception[0].strip()
+  exception = formatted_exception[-1].strip()
+  local_variables = _GetFinalFrame(tb).tb_frame.f_locals
+
+  # Format the traceback.
+  print >> sys.stderr
+  print >> sys.stderr, traceback_header
+  for filename, line, function, text in extracted_tb:
+    filename = os.path.abspath(filename).lstrip(base_dir)
+    print >> sys.stderr, '  %s at %s:%d' % (function, filename, line)
+    print >> sys.stderr, '    %s' % text
+
+  # Format the locals.
+  if local_variables:
+    print >> sys.stderr
+    print >> sys.stderr, 'Locals:'
+    longest_variable = max([len(v) for v in local_variables.keys()])
+    for variable, value in sorted(local_variables.iteritems()):
+      if variable == 'self':
+        continue
+      value = repr(value)
+      possibly_truncated_value = _AbbreviateMiddle(value, ' ... ', 128)
+      truncation_indication = ''
+      if len(possibly_truncated_value) != len(value):
+        truncation_indication = ' (truncated)'
+      print >> sys.stderr, '  %s: %s%s' % (variable.ljust(longest_variable + 1),
+                                           possibly_truncated_value,
+                                           truncation_indication)
+
+  # Format the exception.
+  print >> sys.stderr
+  print >> sys.stderr, exception
+
+
+sys.excepthook = PrintFormattedException
+
+
 class Command(object):
   usage = ''