Resolved merge conflicts with master

13 files changed, 685 insertions, 128 deletions

diff --git a/tools/distrib/python/grpcio_tools/grpc_version.py b/tools/distrib/python/grpcio_tools/grpc_version.py
index 1267d0e45d..4b1e7fcd58 100644
--- a/tools/distrib/python/grpcio_tools/grpc_version.py
+++ b/tools/distrib/python/grpcio_tools/grpc_version.py
@@ -29,4 +29,4 @@
 
 # AUTO-GENERATED FROM `$REPO_ROOT/templates/tools/distrib/python/grpcio_tools/grpc_version.py.template`!!!
 
-VERSION='0.15.0.dev0'
+VERSION='0.16.0.dev0'
diff --git a/tools/doxygen/Doxyfile.c++ b/tools/doxygen/Doxyfile.c++
index 7f9d2df6f6..de7acd7777 100644
--- a/tools/doxygen/Doxyfile.c++
+++ b/tools/doxygen/Doxyfile.c++
@@ -40,7 +40,7 @@ PROJECT_NAME           = "GRPC C++"
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 0.15.0-dev
+PROJECT_NUMBER         = 0.16.0-dev
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a
diff --git a/tools/doxygen/Doxyfile.c++.internal b/tools/doxygen/Doxyfile.c++.internal
index dcf1a4c8c4..76bb3b6c59 100644
--- a/tools/doxygen/Doxyfile.c++.internal
+++ b/tools/doxygen/Doxyfile.c++.internal
@@ -40,7 +40,7 @@ PROJECT_NAME           = "GRPC C++"
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 0.15.0-dev
+PROJECT_NUMBER         = 0.16.0-dev
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a
diff --git a/tools/doxygen/Doxyfile.core b/tools/doxygen/Doxyfile.core
index 72102b2fc5..53ae4e4cf4 100644
--- a/tools/doxygen/Doxyfile.core
+++ b/tools/doxygen/Doxyfile.core
@@ -40,7 +40,7 @@ PROJECT_NAME           = "GRPC Core"
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 0.15.0-dev
+PROJECT_NUMBER         = 0.16.0-dev
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a
diff --git a/tools/doxygen/Doxyfile.core.internal b/tools/doxygen/Doxyfile.core.internal
index 9a2946a4d9..b846237689 100644
--- a/tools/doxygen/Doxyfile.core.internal
+++ b/tools/doxygen/Doxyfile.core.internal
@@ -40,7 +40,7 @@ PROJECT_NAME           = "GRPC Core"
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 0.15.0-dev
+PROJECT_NUMBER         = 0.16.0-dev
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a
@@ -808,6 +808,7 @@ src/core/lib/iomgr/closure.h \
 src/core/lib/iomgr/endpoint.h \
 src/core/lib/iomgr/endpoint_pair.h \
 src/core/lib/iomgr/error.h \
+src/core/lib/iomgr/ev_epoll_linux.h \
 src/core/lib/iomgr/ev_poll_and_epoll_posix.h \
 src/core/lib/iomgr/ev_poll_posix.h \
 src/core/lib/iomgr/ev_posix.h \
@@ -818,6 +819,7 @@ src/core/lib/iomgr/iomgr.h \
 src/core/lib/iomgr/iomgr_internal.h \
 src/core/lib/iomgr/iomgr_posix.h \
 src/core/lib/iomgr/load_file.h \
+src/core/lib/iomgr/network_status_tracker.h \
 src/core/lib/iomgr/polling_entity.h \
 src/core/lib/iomgr/pollset.h \
 src/core/lib/iomgr/pollset_set.h \
@@ -962,6 +964,7 @@ src/core/lib/iomgr/endpoint.c \
 src/core/lib/iomgr/endpoint_pair_posix.c \
 src/core/lib/iomgr/endpoint_pair_windows.c \
 src/core/lib/iomgr/error.c \
+src/core/lib/iomgr/ev_epoll_linux.c \
 src/core/lib/iomgr/ev_poll_and_epoll_posix.c \
 src/core/lib/iomgr/ev_poll_posix.c \
 src/core/lib/iomgr/ev_posix.c \
@@ -972,6 +975,7 @@ src/core/lib/iomgr/iomgr.c \
 src/core/lib/iomgr/iomgr_posix.c \
 src/core/lib/iomgr/iomgr_windows.c \
 src/core/lib/iomgr/load_file.c \
+src/core/lib/iomgr/network_status_tracker.c \
 src/core/lib/iomgr/polling_entity.c \
 src/core/lib/iomgr/pollset_set_windows.c \
 src/core/lib/iomgr/pollset_windows.c \
diff --git a/tools/run_tests/build_package_node.sh b/tools/run_tests/build_package_node.sh
index 6f7211b53f..ff4cfdb8bf 100755
--- a/tools/run_tests/build_package_node.sh
+++ b/tools/run_tests/build_package_node.sh
@@ -86,6 +86,7 @@ for arch in {x86,x64}; do
     cp $input_dir/protoc* bin/
     cp $input_dir/grpc_node_plugin* bin/
     mkdir -p bin/google/protobuf
+    mkdir -p bin/google/protobuf/compiler  # needed for plugin.proto
     for proto in "${well_known_protos[@]}"; do
       cp $base/third_party/protobuf/src/google/protobuf/$proto.proto bin/google/protobuf/$proto.proto
     done
diff --git a/tools/run_tests/build_package_ruby.sh b/tools/run_tests/build_package_ruby.sh
index 4116e29deb..0a755bddb0 100755
--- a/tools/run_tests/build_package_ruby.sh
+++ b/tools/run_tests/build_package_ruby.sh
@@ -59,6 +59,7 @@ for arch in {x86,x64}; do
     input_dir="$EXTERNAL_GIT_ROOT/architecture=$arch,language=protoc,platform=$plat/artifacts"
     output_dir="$base/src/ruby/tools/bin/${ruby_arch}-${plat}"
     mkdir -p $output_dir/google/protobuf
+    mkdir -p $output_dir/google/protobuf/compiler  # needed for plugin.proto
     cp $input_dir/protoc* $output_dir/
     cp $input_dir/grpc_ruby_plugin* $output_dir/
     for proto in "${well_known_protos[@]}"; do
diff --git a/tools/run_tests/dockerjob.py b/tools/run_tests/dockerjob.py
index 326c4faed9..e4ca3b7faa 100755
--- a/tools/run_tests/dockerjob.py
+++ b/tools/run_tests/dockerjob.py
@@ -104,7 +104,7 @@ class DockerJob:
 
   def __init__(self, spec):
     self._spec = spec
-    self._job = jobset.Job(spec, bin_hash=None, newline_on_success=True, travis=True, add_env={})
+    self._job = jobset.Job(spec, newline_on_success=True, travis=True, add_env={})
     self._container_name = spec.container_name
 
   def mapped_port(self, port):
@@ -118,4 +118,4 @@ class DockerJob:
 
   def is_running(self):
     """Polls a job and returns True if given job is still running."""
-    return self._job.state(jobset.NoCache()) == jobset._RUNNING
+    return self._job.state() == jobset._RUNNING
diff --git a/tools/run_tests/jobset.py b/tools/run_tests/jobset.py
index d3259e724d..4fe77487f9 100755
--- a/tools/run_tests/jobset.py
+++ b/tools/run_tests/jobset.py
@@ -29,7 +29,6 @@
 
 """Run a group of subprocesses and then finish."""
 
-import hashlib
 import multiprocessing
 import os
 import platform
@@ -149,7 +148,7 @@ def which(filename):
 class JobSpec(object):
   """Specifies what to run for a job."""
 
-  def __init__(self, cmdline, shortname=None, environ=None, hash_targets=None,
+  def __init__(self, cmdline, shortname=None, environ=None,
                cwd=None, shell=False, timeout_seconds=5*60, flake_retries=0,
                timeout_retries=0, kill_handler=None, cpu_cost=1.0,
                verbose_success=False):
@@ -157,19 +156,14 @@ class JobSpec(object):
     Arguments:
       cmdline: a list of arguments to pass as the command line
       environ: a dictionary of environment variables to set in the child process
-      hash_targets: which files to include in the hash representing the jobs version
-                    (or empty, indicating the job should not be hashed)
       kill_handler: a handler that will be called whenever job.kill() is invoked
       cpu_cost: number of cores per second this job needs
     """
     if environ is None:
       environ = {}
-    if hash_targets is None:
-      hash_targets = []
     self.cmdline = cmdline
     self.environ = environ
     self.shortname = cmdline[0] if shortname is None else shortname
-    self.hash_targets = hash_targets or []
     self.cwd = cwd
     self.shell = shell
     self.timeout_seconds = timeout_seconds
@@ -180,7 +174,7 @@ class JobSpec(object):
     self.verbose_success = verbose_success
 
   def identity(self):
-    return '%r %r %r' % (self.cmdline, self.environ, self.hash_targets)
+    return '%r %r' % (self.cmdline, self.environ)
 
   def __hash__(self):
     return hash(self.identity())
@@ -205,9 +199,8 @@ class JobResult(object):
 class Job(object):
   """Manages one job."""
 
-  def __init__(self, spec, bin_hash, newline_on_success, travis, add_env):
+  def __init__(self, spec, newline_on_success, travis, add_env):
     self._spec = spec
-    self._bin_hash = bin_hash
     self._newline_on_success = newline_on_success
     self._travis = travis
     self._add_env = add_env.copy()
@@ -249,7 +242,7 @@ class Job(object):
       self._process = try_start()
     self._state = _RUNNING
 
-  def state(self, update_cache):
+  def state(self):
     """Poll current state of the job. Prints messages at completion."""
     def stdout(self=self):
       self._tempfile.seek(0)
@@ -293,8 +286,6 @@ class Job(object):
             stdout() if self._spec.verbose_success else None,
             do_newline=self._newline_on_success or self._travis)
         self.result.state = 'PASSED'
-        if self._bin_hash:
-          update_cache.finished(self._spec.identity(), self._bin_hash)
     elif (self._state == _RUNNING and
           self._spec.timeout_seconds is not None and
           time.time() - self._start > self._spec.timeout_seconds):
@@ -329,7 +320,7 @@ class Jobset(object):
   """Manages one run of jobs."""
 
   def __init__(self, check_cancelled, maxjobs, newline_on_success, travis,
-               stop_on_failure, add_env, cache):
+               stop_on_failure, add_env):
     self._running = set()
     self._check_cancelled = check_cancelled
     self._cancelled = False
@@ -338,9 +329,7 @@ class Jobset(object):
     self._maxjobs = maxjobs
     self._newline_on_success = newline_on_success
     self._travis = travis
-    self._cache = cache
     self._stop_on_failure = stop_on_failure
-    self._hashes = {}
     self._add_env = add_env
     self.resultset = {}
     self._remaining = None
@@ -367,29 +356,13 @@ class Jobset(object):
       if current_cpu_cost + spec.cpu_cost <= self._maxjobs: break
       self.reap()
     if self.cancelled(): return False
-    if spec.hash_targets:
-      if spec.identity() in self._hashes:
-        bin_hash = self._hashes[spec.identity()]
-      else:
-        bin_hash = hashlib.sha1()
-        for fn in spec.hash_targets:
-          with open(which(fn)) as f:
-            bin_hash.update(f.read())
-        bin_hash = bin_hash.hexdigest()
-        self._hashes[spec.identity()] = bin_hash
-      should_run = self._cache.should_run(spec.identity(), bin_hash)
-    else:
-      bin_hash = None
-      should_run = True
-    if should_run:
-      job = Job(spec,
-                bin_hash,
-                self._newline_on_success,
-                self._travis,
-                self._add_env)
-      self._running.add(job)
-      if not self.resultset.has_key(job.GetSpec().shortname):
-        self.resultset[job.GetSpec().shortname] = []
+    job = Job(spec,
+              self._newline_on_success,
+              self._travis,
+              self._add_env)
+    self._running.add(job)
+    if not self.resultset.has_key(job.GetSpec().shortname):
+      self.resultset[job.GetSpec().shortname] = []
     return True
 
   def reap(self):
@@ -397,7 +370,7 @@ class Jobset(object):
     while self._running:
       dead = set()
       for job in self._running:
-        st = job.state(self._cache)
+        st = job.state()
         if st == _RUNNING: continue
         if st == _FAILURE or st == _KILLED:
           self._failures += 1
@@ -450,15 +423,6 @@ def _never_cancelled():
   return False
 
 
-# cache class that caches nothing
-class NoCache(object):
-  def should_run(self, cmdline, bin_hash):
-    return True
-
-  def finished(self, cmdline, bin_hash):
-    pass
-
-
 def tag_remaining(xs):
   staging = []
   for x in xs:
@@ -477,12 +441,10 @@ def run(cmdlines,
         travis=False,
         infinite_runs=False,
         stop_on_failure=False,
-        cache=None,
         add_env={}):
   js = Jobset(check_cancelled,
               maxjobs if maxjobs is not None else _DEFAULT_MAX_JOBS,
-              newline_on_success, travis, stop_on_failure, add_env,
-              cache if cache is not None else NoCache())
+              newline_on_success, travis, stop_on_failure, add_env)
   for cmdline, remaining in tag_remaining(cmdlines):
     if not js.start(cmdline):
       break
diff --git a/tools/run_tests/run_performance_tests.py b/tools/run_tests/run_performance_tests.py
index f037d0d17d..14901caf07 100755
--- a/tools/run_tests/run_performance_tests.py
+++ b/tools/run_tests/run_performance_tests.py
@@ -61,11 +61,11 @@ class QpsWorkerJob:
     self._spec = spec
     self.language = language
     self.host_and_port = host_and_port
-    self._job = jobset.Job(spec, bin_hash=None, newline_on_success=True, travis=True, add_env={})
+    self._job = jobset.Job(spec, newline_on_success=True, travis=True, add_env={})
 
   def is_running(self):
     """Polls a job and returns True if given job is still running."""
-    return self._job.state(jobset.NoCache()) == jobset._RUNNING
+    return self._job.state() == jobset._RUNNING
 
   def kill(self):
     return self._job.kill()
diff --git a/tools/run_tests/run_tests.py b/tools/run_tests/run_tests.py
index e4779e3a4e..3798bf4e65 100755
--- a/tools/run_tests/run_tests.py
+++ b/tools/run_tests/run_tests.py
@@ -33,7 +33,6 @@
 import argparse
 import ast
 import glob
-import hashlib
 import itertools
 import json
 import multiprocessing
@@ -63,7 +62,7 @@ _FORCE_ENVIRON_FOR_WRAPPERS = {}
 
 
 _POLLING_STRATEGIES = {
-  'linux': ['poll', 'legacy']
+  'linux': ['epoll', 'poll', 'legacy']
 }
 
 
@@ -78,24 +77,18 @@ class Config(object):
     if environ is None:
       environ = {}
     self.build_config = config
-    self.allow_hashing = (config != 'gcov')
     self.environ = environ
     self.environ['CONFIG'] = config
     self.tool_prefix = tool_prefix
     self.timeout_multiplier = timeout_multiplier
 
-  def job_spec(self, cmdline, hash_targets, timeout_seconds=5*60,
+  def job_spec(self, cmdline, timeout_seconds=5*60,
                shortname=None, environ={}, cpu_cost=1.0, flaky=False):
     """Construct a jobset.JobSpec for a test under this config
 
        Args:
          cmdline:      a list of strings specifying the command line the test
                        would like to run
-         hash_targets: either None (don't do caching of test results), or
-                       a list of strings specifying files to include in a
-                       binary hash to check if a test has changed
-                       -- if used, all artifacts needed to run the test must
-                          be listed
     """
     actual_environ = self.environ.copy()
     for k, v in environ.iteritems():
@@ -105,8 +98,6 @@ class Config(object):
                           environ=actual_environ,
                           cpu_cost=cpu_cost,
                           timeout_seconds=(self.timeout_multiplier * timeout_seconds if timeout_seconds else None),
-                          hash_targets=hash_targets
-                              if self.allow_hashing else None,
                           flake_retries=5 if flaky or args.allow_flakes else 0,
                           timeout_retries=3 if args.allow_flakes else 0)
 
@@ -399,7 +390,6 @@ class PythonLanguage(object):
     if self.config.build_config != 'gcov':
       return [self.config.job_spec(
           ['tools/run_tests/run_python.sh', tox_env],
-          None,
           environ=dict(environment.items() +
                        [('GRPC_PYTHON_TESTRUNNER_FILTER', suite_name)]),
           shortname='%s.test.%s' % (tox_env, suite_name),
@@ -408,7 +398,6 @@ class PythonLanguage(object):
           for tox_env in self._tox_envs]
     else:
       return [self.config.job_spec(['tools/run_tests/run_python.sh', tox_env],
-                                   None,
                                    environ=environment,
                                    shortname='%s.test.coverage' % tox_env,
                                    timeout_seconds=15*60)
@@ -425,7 +414,7 @@ class PythonLanguage(object):
     return []
 
   def build_steps(self):
-    return [['tools/run_tests/build_python.sh', tox_env] 
+    return [['tools/run_tests/build_python.sh', tox_env]
             for tox_env in self._tox_envs]
 
   def post_tests_steps(self):
@@ -460,7 +449,7 @@ class RubyLanguage(object):
     _check_compiler(self.args.compiler, ['default'])
 
   def test_specs(self):
-    return [self.config.job_spec(['tools/run_tests/run_ruby.sh'], None,
+    return [self.config.job_spec(['tools/run_tests/run_ruby.sh'],
                                  timeout_seconds=10*60,
                                  environ=_FORCE_ENVIRON_FOR_WRAPPERS)]
 
@@ -670,7 +659,7 @@ class Sanity(object):
   def test_specs(self):
     import yaml
     with open('tools/run_tests/sanity/sanity_tests.yaml', 'r') as f:
-      return [self.config.job_spec(cmd['script'].split(), None,
+      return [self.config.job_spec(cmd['script'].split(),
                                    timeout_seconds=None, environ={'TEST': 'true'},
                                    cpu_cost=cmd.get('cpu_cost', 1))
               for cmd in yaml.load(f)]
@@ -1058,46 +1047,6 @@ runs_per_test = args.runs_per_test
 forever = args.forever
 
 
-class TestCache(object):
-  """Cache for running tests."""
-
-  def __init__(self, use_cache_results):
-    self._last_successful_run = {}
-    self._use_cache_results = use_cache_results
-    self._last_save = time.time()
-
-  def should_run(self, cmdline, bin_hash):
-    if cmdline not in self._last_successful_run:
-      return True
-    if self._last_successful_run[cmdline] != bin_hash:
-      return True
-    if not self._use_cache_results:
-      return True
-    return False
-
-  def finished(self, cmdline, bin_hash):
-    self._last_successful_run[cmdline] = bin_hash
-    if time.time() - self._last_save > 1:
-      self.save()
-
-  def dump(self):
-    return [{'cmdline': k, 'hash': v}
-            for k, v in self._last_successful_run.iteritems()]
-
-  def parse(self, exdump):
-    self._last_successful_run = dict((o['cmdline'], o['hash']) for o in exdump)
-
-  def save(self):
-    with open('.run_tests_cache', 'w') as f:
-      f.write(json.dumps(self.dump()))
-    self._last_save = time.time()
-
-  def maybe_load(self):
-    if os.path.exists('.run_tests_cache'):
-      with open('.run_tests_cache') as f:
-        self.parse(json.loads(f.read()))
-
-
 def _start_port_server(port_server_port):
   # check if a compatible port server is running
   # if incompatible (version mismatch) ==> start a new one
@@ -1217,7 +1166,7 @@ class BuildAndRunError(object):
 
 # returns a list of things that failed (or an empty list on success)
 def _build_and_run(
-    check_cancelled, newline_on_success, cache, xml_report=None, build_only=False):
+    check_cancelled, newline_on_success, xml_report=None, build_only=False):
   """Do one pass of building & running tests."""
   # build latest sequentially
   num_failures, resultset = jobset.run(
@@ -1266,7 +1215,6 @@ def _build_and_run(
         all_runs, check_cancelled, newline_on_success=newline_on_success,
         travis=args.travis, infinite_runs=infinite_runs, maxjobs=args.jobs,
         stop_on_failure=args.stop_on_failure,
-        cache=cache if not xml_report else None,
         add_env={'GRPC_TEST_PORT_SERVER': 'localhost:%d' % port_server_port})
     if resultset:
       for k, v in sorted(resultset.items()):
@@ -1295,14 +1243,9 @@ def _build_and_run(
   if num_test_failures:
     out.append(BuildAndRunError.TEST)
 
-  if cache: cache.save()
-
   return out
 
 
-test_cache = TestCache(runs_per_test == 1)
-test_cache.maybe_load()
-
 if forever:
   success = True
   while True:
@@ -1312,7 +1255,6 @@ if forever:
     previous_success = success
     errors = _build_and_run(check_cancelled=have_files_changed,
                             newline_on_success=False,
-                            cache=test_cache,
                             build_only=args.build_only) == 0
     if not previous_success and not errors:
       jobset.message('SUCCESS',
@@ -1324,7 +1266,6 @@ if forever:
 else:
   errors = _build_and_run(check_cancelled=lambda: False,
                           newline_on_success=args.newline_on_success,
-                          cache=test_cache,
                           xml_report=args.xml_report,
                           build_only=args.build_only)
   if not errors:
diff --git a/tools/run_tests/sources_and_headers.json b/tools/run_tests/sources_and_headers.json
index 03d4b81d92..227877d3ce 100644
--- a/tools/run_tests/sources_and_headers.json
+++ b/tools/run_tests/sources_and_headers.json
@@ -324,6 +324,22 @@
     ], 
     "headers": [], 
     "language": "c", 
+    "name": "ev_epoll_linux_test", 
+    "src": [
+      "test/core/iomgr/ev_epoll_linux_test.c"
+    ], 
+    "third_party": false, 
+    "type": "target"
+  }, 
+  {
+    "deps": [
+      "gpr", 
+      "gpr_test_util", 
+      "grpc", 
+      "grpc_test_util"
+    ], 
+    "headers": [], 
+    "language": "c", 
     "name": "fd_conservation_posix_test", 
     "src": [
       "test/core/iomgr/fd_conservation_posix_test.c"
@@ -5387,6 +5403,7 @@
       "test/core/end2end/tests/max_concurrent_streams.c", 
       "test/core/end2end/tests/max_message_length.c", 
       "test/core/end2end/tests/negative_deadline.c", 
+      "test/core/end2end/tests/network_status_change.c", 
       "test/core/end2end/tests/no_op.c", 
       "test/core/end2end/tests/payload.c", 
       "test/core/end2end/tests/ping.c", 
@@ -5446,6 +5463,7 @@
       "test/core/end2end/tests/max_concurrent_streams.c", 
       "test/core/end2end/tests/max_message_length.c", 
       "test/core/end2end/tests/negative_deadline.c", 
+      "test/core/end2end/tests/network_status_change.c", 
       "test/core/end2end/tests/no_op.c", 
       "test/core/end2end/tests/payload.c", 
       "test/core/end2end/tests/ping.c", 
@@ -5724,6 +5742,7 @@
       "src/core/lib/iomgr/endpoint.h", 
       "src/core/lib/iomgr/endpoint_pair.h", 
       "src/core/lib/iomgr/error.h", 
+      "src/core/lib/iomgr/ev_epoll_linux.h", 
       "src/core/lib/iomgr/ev_poll_and_epoll_posix.h", 
       "src/core/lib/iomgr/ev_poll_posix.h", 
       "src/core/lib/iomgr/ev_posix.h", 
@@ -5734,6 +5753,7 @@
       "src/core/lib/iomgr/iomgr_internal.h", 
       "src/core/lib/iomgr/iomgr_posix.h", 
       "src/core/lib/iomgr/load_file.h", 
+      "src/core/lib/iomgr/network_status_tracker.h", 
       "src/core/lib/iomgr/polling_entity.h", 
       "src/core/lib/iomgr/pollset.h", 
       "src/core/lib/iomgr/pollset_set.h", 
@@ -5828,6 +5848,8 @@
       "src/core/lib/iomgr/endpoint_pair_windows.c", 
       "src/core/lib/iomgr/error.c", 
       "src/core/lib/iomgr/error.h", 
+      "src/core/lib/iomgr/ev_epoll_linux.c", 
+      "src/core/lib/iomgr/ev_epoll_linux.h", 
       "src/core/lib/iomgr/ev_poll_and_epoll_posix.c", 
       "src/core/lib/iomgr/ev_poll_and_epoll_posix.h", 
       "src/core/lib/iomgr/ev_poll_posix.c", 
@@ -5848,6 +5870,8 @@
       "src/core/lib/iomgr/iomgr_windows.c", 
       "src/core/lib/iomgr/load_file.c", 
       "src/core/lib/iomgr/load_file.h", 
+      "src/core/lib/iomgr/network_status_tracker.c", 
+      "src/core/lib/iomgr/network_status_tracker.h", 
       "src/core/lib/iomgr/polling_entity.c", 
       "src/core/lib/iomgr/polling_entity.h", 
       "src/core/lib/iomgr/pollset.h", 
diff --git a/tools/run_tests/tests.json b/tools/run_tests/tests.json
index c62058ede4..1c97e9a832 100644
--- a/tools/run_tests/tests.json
+++ b/tools/run_tests/tests.json
@@ -380,6 +380,21 @@
   {
     "args": [], 
     "ci_platforms": [
+      "linux"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "gtest": false, 
+    "language": "c", 
+    "name": "ev_epoll_linux_test", 
+    "platforms": [
+      "linux"
+    ]
+  }, 
+  {
+    "args": [], 
+    "ci_platforms": [
       "linux", 
       "mac", 
       "posix"
@@ -732,7 +747,7 @@
       "posix", 
       "windows"
     ], 
-    "cpu_cost": 3, 
+    "cpu_cost": 10, 
     "exclude_configs": [], 
     "flaky": false, 
     "gtest": false, 
@@ -753,7 +768,7 @@
       "posix", 
       "windows"
     ], 
-    "cpu_cost": 1, 
+    "cpu_cost": 10, 
     "exclude_configs": [], 
     "flaky": false, 
     "gtest": false, 
@@ -4902,6 +4917,28 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_census_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -5760,6 +5797,28 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_compress_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -6594,6 +6653,27 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_fakesec_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -7329,6 +7409,26 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_fd_test", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -8117,6 +8217,28 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_full_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -8831,6 +8953,22 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "linux"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_full+pipe_test", 
+    "platforms": [
+      "linux"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -9577,6 +9715,28 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_full+trace_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -10435,6 +10595,28 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_loadreporting_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -11269,6 +11451,27 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_oauth2_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -12004,6 +12207,27 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_proxy_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -12718,6 +12942,27 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_sockpair_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -13411,6 +13656,27 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_sockpair+trace_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -14125,6 +14391,27 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_sockpair_1byte_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -14926,6 +15213,28 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_ssl_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -15784,6 +16093,28 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_ssl_cert_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -16534,6 +16865,27 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_ssl_proxy_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -17267,6 +17619,26 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_uds_test", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -18073,6 +18445,28 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_census_nosec_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -18909,6 +19303,28 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_compress_nosec_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -19639,6 +20055,26 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_fd_nosec_test", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -20405,6 +20841,28 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_full_nosec_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -21103,6 +21561,22 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "linux"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_full+pipe_nosec_test", 
+    "platforms": [
+      "linux"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -21827,6 +22301,28 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_full+trace_nosec_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -22663,6 +23159,28 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_loadreporting_nosec_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -23392,6 +23910,27 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_proxy_nosec_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -24085,6 +24624,27 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_sockpair_nosec_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -24757,6 +25317,27 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_sockpair+trace_nosec_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -25490,6 +26071,29 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "windows", 
+      "linux", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [
+      "msan"
+    ], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_sockpair_1byte_nosec_test", 
+    "platforms": [
+      "windows", 
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [
@@ -26229,6 +26833,26 @@
   }, 
   {
     "args": [
+      "network_status_change"
+    ], 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix"
+    ], 
+    "cpu_cost": 1.0, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "h2_uds_nosec_test", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix"
+    ]
+  }, 
+  {
+    "args": [
       "no_op"
     ], 
     "ci_platforms": [