testing_refleaks.py

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"""A subclass of unittest.TestCase which checks for reference leaks.
 
To use:
- Use testing_refleak.BaseTestCase instead of unittest.TestCase
- Configure and compile Python with --with-pydebug
 
If sys.gettotalrefcount() is not available (because Python was built without
the Py_DEBUG option), then this module is a no-op and tests will run normally.
"""
 
import gc
import sys
 
try:
  import copy_reg as copyreg  #PY26
except ImportError:
  import copyreg
 
try:
  import unittest2 as unittest  #PY26
except ImportError:
  import unittest
 
 
class LocalTestResult(unittest.TestResult):
  """A TestResult which forwards events to a parent object, except for Skips."""
 
  def __init__(self, parent_result):
    unittest.TestResult.__init__(self)
    self.parent_result = parent_result
 
  def addError(self, test, error):
    self.parent_result.addError(test, error)
 
  def addFailure(self, test, error):
    self.parent_result.addFailure(test, error)
 
  def addSkip(self, test, reason):
    pass
 
 
class ReferenceLeakCheckerMixin(object):
  """A mixin class for TestCase, which checks reference counts."""
 
  NB_RUNS = 3
 
  def run(self, result=None):
    # python_message.py registers all Message classes to some pickle global
    # registry, which makes the classes immortal.
    # We save a copy of this registry, and reset it before we could references.
    self._saved_pickle_registry = copyreg.dispatch_table.copy()
 
    # Run the test twice, to warm up the instance attributes.
    super(ReferenceLeakCheckerMixin, self).run(result=result)
    super(ReferenceLeakCheckerMixin, self).run(result=result)
 
    oldrefcount = 0
    local_result = LocalTestResult(result)
 
    refcount_deltas = []
    for _ in range(self.NB_RUNS):
      oldrefcount = self._getRefcounts()
      super(ReferenceLeakCheckerMixin, self).run(result=local_result)
      newrefcount = self._getRefcounts()
      refcount_deltas.append(newrefcount - oldrefcount)
    print(refcount_deltas, self)
 
    try:
      self.assertEqual(refcount_deltas, [0] * self.NB_RUNS)
    except Exception:  # pylint: disable=broad-except
      result.addError(self, sys.exc_info())
 
  def _getRefcounts(self):
    copyreg.dispatch_table.clear()
    copyreg.dispatch_table.update(self._saved_pickle_registry)
    # It is sometimes necessary to gc.collect() multiple times, to ensure
    # that all objects can be collected.
    gc.collect()
    gc.collect()
    gc.collect()
    return sys.gettotalrefcount()
 
 
if hasattr(sys, 'gettotalrefcount'):
 
  def TestCase(test_class):
    new_bases = (ReferenceLeakCheckerMixin,) + test_class.__bases__
    new_class = type(test_class)(
        test_class.__name__, new_bases, dict(test_class.__dict__))
    return new_class
  SkipReferenceLeakChecker = unittest.skip
 
else:
  # When PyDEBUG is not enabled, run the tests normally.
 
  def TestCase(test_class):
    return test_class
 
  def SkipReferenceLeakChecker(reason):
    del reason  # Don't skip, so don't need a reason.
    def Same(func):
      return func
    return Same