Seeing the following stack trace when running with --run-singly on iso-simulator: Traceback (most recent call last): File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 810, in __bootstrap_inner self.run() File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/layout_tests/controllers/layout_test_runner.py", line 369, in run self.result = worker._run_single_test(driver, test_input, stop_when_done) File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/layout_tests/controllers/layout_test_runner.py", line 410, in _run_single_test self._name, driver, test_input, stop_when_done) File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/layout_tests/controllers/single_test_runner.py", line 46, in run_single_test return runner.run() File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/layout_tests/controllers/single_test_runner.py", line 105, in run return self._run_compare_test() File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/layout_tests/controllers/single_test_runner.py", line 108, in _run_compare_test driver_output = self._driver.run_test(self._driver_input(), self._stop_when_done) File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/port/driver.py", line 685, in run_test return self._driver.run_test(driver_input, stop_when_done) File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/port/driver.py", line 185, in run_test self.start(driver_input.should_run_pixel_test, driver_input.args) File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/port/driver.py", line 329, in start self._start(pixel_tests, per_test_args) File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/port/driver.py", line 380, in _start self._server_process.start() File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/port/server_process.py", line 341, in start self._start() File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/port/simulator_process.py", line 96, in _start self._pid = self._target_host.launch_app(self._bundle_id, self._cmd[1:], env=self._env) File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/port/device.py", line 45, in launch_app return self.platform_device.launch_app(bundle_id, args, env) File "/Volumes/Data/slave/trunk-tigris-ios-sim-production-wk2-tests/build/OpenSource/Tools/Scripts/webkitpy/xcode/simulated_device.py", line 178, in launch_app signal.signal(signal.SIGALRM, _install_timeout) ValueError: signal only works in main thread
<rdar://problem/33526305>