Lib/test/test_signal.py

import os
import random
import signal
import socket
import statistics
import subprocess
import sys
import threading
import time
import unittest
from test import support
from test.support.script_helper import assert_python_ok, spawn_python
try:
    import _testcapi
except ImportError:
    _testcapi = None


class GenericTests(unittest.TestCase):

    def test_enums(self):
        for name in dir(signal):
            sig = getattr(signal, name)
            if name in {'SIG_DFL', 'SIG_IGN'}:
                self.assertIsInstance(sig, signal.Handlers)
            elif name in {'SIG_BLOCK', 'SIG_UNBLOCK', 'SIG_SETMASK'}:
                self.assertIsInstance(sig, signal.Sigmasks)
            elif name.startswith('SIG') and not name.startswith('SIG_'):
                self.assertIsInstance(sig, signal.Signals)
            elif name.startswith('CTRL_'):
                self.assertIsInstance(sig, signal.Signals)
                self.assertEqual(sys.platform, "win32")


@unittest.skipIf(sys.platform == "win32", "Not valid on Windows")
class PosixTests(unittest.TestCase):
    def trivial_signal_handler(self, *args):
        pass

    def test_out_of_range_signal_number_raises_error(self):
        self.assertRaises(ValueError, signal.getsignal, 4242)

        self.assertRaises(ValueError, signal.signal, 4242,
                          self.trivial_signal_handler)

    def test_setting_signal_handler_to_none_raises_error(self):
        self.assertRaises(TypeError, signal.signal,
                          signal.SIGUSR1, None)

    def test_getsignal(self):
        hup = signal.signal(signal.SIGHUP, self.trivial_signal_handler)
        self.assertIsInstance(hup, signal.Handlers)
        self.assertEqual(signal.getsignal(signal.SIGHUP),
                         self.trivial_signal_handler)
        signal.signal(signal.SIGHUP, hup)
        self.assertEqual(signal.getsignal(signal.SIGHUP), hup)

    # Issue 3864, unknown if this affects earlier versions of freebsd also
    def test_interprocess_signal(self):
        dirname = os.path.dirname(__file__)
        script = os.path.join(dirname, 'signalinterproctester.py')
        assert_python_ok(script)


@unittest.skipUnless(sys.platform == "win32", "Windows specific")
class WindowsSignalTests(unittest.TestCase):
    def test_issue9324(self):
        # Updated for issue #10003, adding SIGBREAK
        handler = lambda x, y: None
        checked = set()
        for sig in (signal.SIGABRT, signal.SIGBREAK, signal.SIGFPE,
                    signal.SIGILL, signal.SIGINT, signal.SIGSEGV,
                    signal.SIGTERM):
            # Set and then reset a handler for signals that work on windows.
            # Issue #18396, only for signals without a C-level handler.
            if signal.getsignal(sig) is not None:
                signal.signal(sig, signal.signal(sig, handler))
                checked.add(sig)
        # Issue #18396: Ensure the above loop at least tested *something*
        self.assertTrue(checked)

        with self.assertRaises(ValueError):
            signal.signal(-1, handler)

        with self.assertRaises(ValueError):
            signal.signal(7, handler)


class WakeupFDTests(unittest.TestCase):

    def test_invalid_call(self):
        # First parameter is positional-only
        with self.assertRaises(TypeError):
            signal.set_wakeup_fd(signum=signal.SIGINT)

        # warn_on_full_buffer is a keyword-only parameter
        with self.assertRaises(TypeError):
            signal.set_wakeup_fd(signal.SIGINT, False)

    def test_invalid_fd(self):
        fd = support.make_bad_fd()
        self.assertRaises((ValueError, OSError),
                          signal.set_wakeup_fd, fd)

    def test_invalid_socket(self):
        sock = socket.socket()
        fd = sock.fileno()
        sock.close()
        self.assertRaises((ValueError, OSError),
                          signal.set_wakeup_fd, fd)

    def test_set_wakeup_fd_result(self):
        r1, w1 = os.pipe()
        self.addCleanup(os.close, r1)
        self.addCleanup(os.close, w1)
        r2, w2 = os.pipe()
        self.addCleanup(os.close, r2)
        self.addCleanup(os.close, w2)

        if hasattr(os, 'set_blocking'):
            os.set_blocking(w1, False)
            os.set_blocking(w2, False)

        signal.set_wakeup_fd(w1)
        self.assertEqual(signal.set_wakeup_fd(w2), w1)
        self.assertEqual(signal.set_wakeup_fd(-1), w2)
        self.assertEqual(signal.set_wakeup_fd(-1), -1)

    def test_set_wakeup_fd_socket_result(self):
        sock1 = socket.socket()
        self.addCleanup(sock1.close)
        sock1.setblocking(False)
        fd1 = sock1.fileno()

        sock2 = socket.socket()
        self.addCleanup(sock2.close)
        sock2.setblocking(False)
        fd2 = sock2.fileno()

        signal.set_wakeup_fd(fd1)
        self.assertEqual(signal.set_wakeup_fd(fd2), fd1)
        self.assertEqual(signal.set_wakeup_fd(-1), fd2)
        self.assertEqual(signal.set_wakeup_fd(-1), -1)

    # On Windows, files are always blocking and Windows does not provide a
    # function to test if a socket is in non-blocking mode.
    @unittest.skipIf(sys.platform == "win32", "tests specific to POSIX")
    def test_set_wakeup_fd_blocking(self):
        rfd, wfd = os.pipe()
        self.addCleanup(os.close, rfd)
        self.addCleanup(os.close, wfd)

        # fd must be non-blocking
        os.set_blocking(wfd, True)
        with self.assertRaises(ValueError) as cm:
            signal.set_wakeup_fd(wfd)
        self.assertEqual(str(cm.exception),
                         "the fd %s must be in non-blocking mode" % wfd)

        # non-blocking is ok
        os.set_blocking(wfd, False)
        signal.set_wakeup_fd(wfd)
        signal.set_wakeup_fd(-1)


@unittest.skipIf(sys.platform == "win32", "Not valid on Windows")
class WakeupSignalTests(unittest.TestCase):
    @unittest.skipIf(_testcapi is None, 'need _testcapi')
    def check_wakeup(self, test_body, *signals, ordered=True):
        # use a subprocess to have only one thread
        code = """if 1:
        import _testcapi
        import os
        import signal
        import struct

        signals = {!r}

        def handler(signum, frame):
            pass

        def check_signum(signals):
            data = os.read(read, len(signals)+1)
            raised = struct.unpack('%uB' % len(data), data)
            if not {!r}:
                raised = set(raised)
                signals = set(signals)
            if raised != signals:
                raise Exception("%r != %r" % (raised, signals))

        {}

        signal.signal(signal.SIGALRM, handler)
        read, write = os.pipe()
        os.set_blocking(write, False)
        signal.set_wakeup_fd(write)

        test()
        check_signum(signals)

        os.close(read)
        os.close(write)
        """.format(tuple(map(int, signals)), ordered, test_body)

        assert_python_ok('-c', code)

    @unittest.skipIf(_testcapi is None, 'need _testcapi')
    def test_wakeup_write_error(self):
        # Issue #16105: write() errors in the C signal handler should not
        # pass silently.
        # Use a subprocess to have only one thread.
        code = """if 1:
        import _testcapi
        import errno
        import os
        import signal
        import sys
        from test.support import captured_stderr

        def handler(signum, frame):
            1/0

        signal.signal(signal.SIGALRM, handler)
        r, w = os.pipe()
        os.set_blocking(r, False)

        # Set wakeup_fd a read-only file descriptor to trigger the error
        signal.set_wakeup_fd(r)
        try:
            with captured_stderr() as err:
                _testcapi.raise_signal(signal.SIGALRM)
        except ZeroDivisionError:
            # An ignored exception should have been printed out on stderr
            err = err.getvalue()
            if ('Exception ignored when trying to write to the signal wakeup fd'
                not in err):
                raise AssertionError(err)
            if ('OSError: [Errno %d]' % errno.EBADF) not in err:
                raise AssertionError(err)
        else:
            raise AssertionError("ZeroDivisionError not raised")

        os.close(r)
        os.close(w)
        """
        r, w = os.pipe()
        try:
            os.write(r, b'x')
        except OSError:
            pass
        else:
            self.skipTest("OS doesn't report write() error on the read end of a pipe")
        finally:
            os.close(r)
            os.close(w)

        assert_python_ok('-c', code)

    def test_wakeup_fd_early(self):
        self.check_wakeup("""def test():
            import select
            import time

            TIMEOUT_FULL = 10
            TIMEOUT_HALF = 5

            class InterruptSelect(Exception):
                pass

            def handler(signum, frame):
                raise InterruptSelect
            signal.signal(signal.SIGALRM, handler)

            signal.alarm(1)

            # We attempt to get a signal during the sleep,
            # before select is called
            try:
                select.select([], [], [], TIMEOUT_FULL)
            except InterruptSelect:
                pass
            else:
                raise Exception("select() was not interrupted")

            before_time = time.monotonic()
            select.select([read], [], [], TIMEOUT_FULL)
            after_time = time.monotonic()
            dt = after_time - before_time
            if dt >= TIMEOUT_HALF:
                raise Exception("%s >= %s" % (dt, TIMEOUT_HALF))
        """, signal.SIGALRM)

    def test_wakeup_fd_during(self):
        self.check_wakeup("""def test():
            import select
            import time

            TIMEOUT_FULL = 10
            TIMEOUT_HALF = 5

            class InterruptSelect(Exception):
                pass

            def handler(signum, frame):
                raise InterruptSelect
            signal.signal(signal.SIGALRM, handler)

            signal.alarm(1)
            before_time = time.monotonic()
            # We attempt to get a signal during the select call
            try:
                select.select([read], [], [], TIMEOUT_FULL)
            except InterruptSelect:
                pass
            else:
                raise Exception("select() was not interrupted")
            after_time = time.monotonic()
            dt = after_time - before_time
            if dt >= TIMEOUT_HALF:
                raise Exception("%s >= %s" % (dt, TIMEOUT_HALF))
        """, signal.SIGALRM)

    def test_signum(self):
        self.check_wakeup("""def test():
            import _testcapi
            signal.signal(signal.SIGUSR1, handler)
            _testcapi.raise_signal(signal.SIGUSR1)
            _testcapi.raise_signal(signal.SIGALRM)
        """, signal.SIGUSR1, signal.SIGALRM)

    @unittest.skipUnless(hasattr(signal, 'pthread_sigmask'),
                         'need signal.pthread_sigmask()')
    def test_pending(self):
        self.check_wakeup("""def test():
            signum1 = signal.SIGUSR1
            signum2 = signal.SIGUSR2

            signal.signal(signum1, handler)
            signal.signal(signum2, handler)

            signal.pthread_sigmask(signal.SIG_BLOCK, (signum1, signum2))
            _testcapi.raise_signal(signum1)
            _testcapi.raise_signal(signum2)
            # Unblocking the 2 signals calls the C signal handler twice
            signal.pthread_sigmask(signal.SIG_UNBLOCK, (signum1, signum2))
        """,  signal.SIGUSR1, signal.SIGUSR2, ordered=False)


@unittest.skipUnless(hasattr(socket, 'socketpair'), 'need socket.socketpair')
class WakeupSocketSignalTests(unittest.TestCase):

    @unittest.skipIf(_testcapi is None, 'need _testcapi')
    def test_socket(self):
        # use a subprocess to have only one thread
        code = """if 1:
        import signal
        import socket
        import struct
        import _testcapi

        signum = signal.SIGINT
        signals = (signum,)

        def handler(signum, frame):
            pass

        signal.signal(signum, handler)

        read, write = socket.socketpair()
        read.setblocking(False)
        write.setblocking(False)
        signal.set_wakeup_fd(write.fileno())

        _testcapi.raise_signal(signum)

        data = read.recv(1)
        if not data:
            raise Exception("no signum written")
        raised = struct.unpack('B', data)
        if raised != signals:
            raise Exception("%r != %r" % (raised, signals))

        read.close()
        write.close()
        """

        assert_python_ok('-c', code)

    @unittest.skipIf(_testcapi is None, 'need _testcapi')
    def test_send_error(self):
        # Use a subprocess to have only one thread.
        if os.name == 'nt':
            action = 'send'
        else:
            action = 'write'
        code = """if 1:
        import errno
        import signal
        import socket
        import sys
        import time
        import _testcapi
        from test.support import captured_stderr

        signum = signal.SIGINT

        def handler(signum, frame):
            pass

        signal.signal(signum, handler)

        read, write = socket.socketpair()
        read.setblocking(False)
        write.setblocking(False)

        signal.set_wakeup_fd(write.fileno())

        # Close sockets: send() will fail
        read.close()
        write.close()

        with captured_stderr() as err:
            _testcapi.raise_signal(signum)

        err = err.getvalue()
        if ('Exception ignored when trying to {action} to the signal wakeup fd'
            not in err):
            raise AssertionError(err)
        """.format(action=action)
        assert_python_ok('-c', code)

    @unittest.skipIf(_testcapi is None, 'need _testcapi')
    def test_warn_on_full_buffer(self):
        # Use a subprocess to have only one thread.
        if os.name == 'nt':
            action = 'send'
        else:
            action = 'write'
        code = """if 1:
        import errno
        import signal
        import socket
        import sys
        import time
        import _testcapi
        from test.support import captured_stderr

        signum = signal.SIGINT

        # This handler will be called, but we intentionally won't read from
        # the wakeup fd.
        def handler(signum, frame):
            pass

        signal.signal(signum, handler)

        read, write = socket.socketpair()
        read.setblocking(False)
        write.setblocking(False)

        # Fill the send buffer
        try:
            while True:
                write.send(b"x")
        except BlockingIOError:
            pass

        # By default, we get a warning when a signal arrives
        signal.set_wakeup_fd(write.fileno())

        with captured_stderr() as err:
            _testcapi.raise_signal(signum)

        err = err.getvalue()
        if ('Exception ignored when trying to {action} to the signal wakeup fd'
            not in err):
            raise AssertionError(err)

        # And also if warn_on_full_buffer=True
        signal.set_wakeup_fd(write.fileno(), warn_on_full_buffer=True)

        with captured_stderr() as err:
            _testcapi.raise_signal(signum)

        err = err.getvalue()
        if ('Exception ignored when trying to {action} to the signal wakeup fd'
            not in err):
            raise AssertionError(err)

        # But not if warn_on_full_buffer=False
        signal.set_wakeup_fd(write.fileno(), warn_on_full_buffer=False)

        with captured_stderr() as err:
            _testcapi.raise_signal(signum)

        err = err.getvalue()
        if err != "":
            raise AssertionError("got unexpected output %r" % (err,))

        # And then check the default again, to make sure warn_on_full_buffer
        # settings don't leak across calls.
        signal.set_wakeup_fd(write.fileno())

        with captured_stderr() as err:
            _testcapi.raise_signal(signum)

        err = err.getvalue()
        if ('Exception ignored when trying to {action} to the signal wakeup fd'
            not in err):
            raise AssertionError(err)

        """.format(action=action)
        assert_python_ok('-c', code)


@unittest.skipIf(sys.platform == "win32", "Not valid on Windows")
class SiginterruptTest(unittest.TestCase):

    def readpipe_interrupted(self, interrupt):
        """Perform a read during which a signal will arrive.  Return True if the
        read is interrupted by the signal and raises an exception.  Return False
        if it returns normally.
        """
        # use a subprocess to have only one thread, to have a timeout on the
        # blocking read and to not touch signal handling in this process
        code = """if 1:
            import errno
            import os
            import signal
            import sys

            interrupt = %r
            r, w = os.pipe()

            def handler(signum, frame):
                1 / 0

            signal.signal(signal.SIGALRM, handler)
            if interrupt is not None:
                signal.siginterrupt(signal.SIGALRM, interrupt)

            print("ready")
            sys.stdout.flush()

            # run the test twice
            try:
                for loop in range(2):
                    # send a SIGALRM in a second (during the read)
                    signal.alarm(1)
                    try:
                        # blocking call: read from a pipe without data
                        os.read(r, 1)
                    except ZeroDivisionError:
                        pass
                    else:
                        sys.exit(2)
                sys.exit(3)
            finally:
                os.close(r)
                os.close(w)
        """ % (interrupt,)
        with spawn_python('-c', code) as process:
            try:
                # wait until the child process is loaded and has started
                first_line = process.stdout.readline()

                stdout, stderr = process.communicate(timeout=5.0)
            except subprocess.TimeoutExpired:
                process.kill()
                return False
            else:
                stdout = first_line + stdout
                exitcode = process.wait()
                if exitcode not in (2, 3):
                    raise Exception("Child error (exit code %s): %r"
                                    % (exitcode, stdout))
                return (exitcode == 3)

    def test_without_siginterrupt(self):
        # If a signal handler is installed and siginterrupt is not called
        # at all, when that signal arrives, it interrupts a syscall that's in
        # progress.
        interrupted = self.readpipe_interrupted(None)
        self.assertTrue(interrupted)

    def test_siginterrupt_on(self):
        # If a signal handler is installed and siginterrupt is called with
        # a true value for the second argument, when that signal arrives, it
        # interrupts a syscall that's in progress.
        interrupted = self.readpipe_interrupted(True)
        self.assertTrue(interrupted)

    def test_siginterrupt_off(self):
        # If a signal handler is installed and siginterrupt is called with
        # a false value for the second argument, when that signal arrives, it
        # does not interrupt a syscall that's in progress.
        interrupted = self.readpipe_interrupted(False)
        self.assertFalse(interrupted)


@unittest.skipIf(sys.platform == "win32", "Not valid on Windows")
class ItimerTest(unittest.TestCase):
    def setUp(self):
        self.hndl_called = False
        self.hndl_count = 0
        self.itimer = None
        self.old_alarm = signal.signal(signal.SIGALRM, self.sig_alrm)

    def tearDown(self):
        signal.signal(signal.SIGALRM, self.old_alarm)
        if self.itimer is not None: # test_itimer_exc doesn't change this attr
            # just ensure that itimer is stopped
            signal.setitimer(self.itimer, 0)

    def sig_alrm(self, *args):
        self.hndl_called = True

    def sig_vtalrm(self, *args):
        self.hndl_called = True

        if self.hndl_count > 3:
            # it shouldn't be here, because it should have been disabled.
            raise signal.ItimerError("setitimer didn't disable ITIMER_VIRTUAL "
                "timer.")
        elif self.hndl_count == 3:
            # disable ITIMER_VIRTUAL, this function shouldn't be called anymore
            signal.setitimer(signal.ITIMER_VIRTUAL, 0)

        self.hndl_count += 1

    def sig_prof(self, *args):
        self.hndl_called = True
        signal.setitimer(signal.ITIMER_PROF, 0)

    def test_itimer_exc(self):
        # XXX I'm assuming -1 is an invalid itimer, but maybe some platform
        # defines it ?
        self.assertRaises(signal.ItimerError, signal.setitimer, -1, 0)
        # Negative times are treated as zero on some platforms.
        if 0:
            self.assertRaises(signal.ItimerError,
                              signal.setitimer, signal.ITIMER_REAL, -1)

    def test_itimer_real(self):
        self.itimer = signal.ITIMER_REAL
        signal.setitimer(self.itimer, 1.0)
        signal.pause()
        self.assertEqual(self.hndl_called, True)

    # Issue 3864, unknown if this affects earlier versions of freebsd also
    @unittest.skipIf(sys.platform in ('netbsd5',),
        'itimer not reliable (does not mix well with threading) on some BSDs.')
    def test_itimer_virtual(self):
        self.itimer = signal.ITIMER_VIRTUAL
        signal.signal(signal.SIGVTALRM, self.sig_vtalrm)
        signal.setitimer(self.itimer, 0.3, 0.2)

        start_time = time.monotonic()
        while time.monotonic() - start_time < 60.0:
            # use up some virtual time by doing real work
            _ = pow(12345, 67890, 10000019)
            if signal.getitimer(self.itimer) == (0.0, 0.0):
                break # sig_vtalrm handler stopped this itimer
        else: # Issue 8424
            self.skipTest("timeout: likely cause: machine too slow or load too "
                          "high")

        # virtual itimer should be (0.0, 0.0) now
        self.assertEqual(signal.getitimer(self.itimer), (0.0, 0.0))
        # and the handler should have been called
        self.assertEqual(self.hndl_called, True)

    def test_itimer_prof(self):
        self.itimer = signal.ITIMER_PROF
        signal.signal(signal.SIGPROF, self.sig_prof)
        signal.setitimer(self.itimer, 0.2, 0.2)

        start_time = time.monotonic()
        while time.monotonic() - start_time < 60.0:
            # do some work
            _ = pow(12345, 67890, 10000019)
            if signal.getitimer(self.itimer) == (0.0, 0.0):
                break # sig_prof handler stopped this itimer
        else: # Issue 8424
            self.skipTest("timeout: likely cause: machine too slow or load too "
                          "high")

        # profiling itimer should be (0.0, 0.0) now
        self.assertEqual(signal.getitimer(self.itimer), (0.0, 0.0))
        # and the handler should have been called
        self.assertEqual(self.hndl_called, True)

    def test_setitimer_tiny(self):
        # bpo-30807: C setitimer() takes a microsecond-resolution interval.
        # Check that float -> timeval conversion doesn't round
        # the interval down to zero, which would disable the timer.
        self.itimer = signal.ITIMER_REAL
        signal.setitimer(self.itimer, 1e-6)
        time.sleep(1)
        self.assertEqual(self.hndl_called, True)


class PendingSignalsTests(unittest.TestCase):
    """
    Test pthread_sigmask(), pthread_kill(), sigpending() and sigwait()
    functions.
    """
    @unittest.skipUnless(hasattr(signal, 'sigpending'),
                         'need signal.sigpending()')
    def test_sigpending_empty(self):
        self.assertEqual(signal.sigpending(), set())

    @unittest.skipUnless(hasattr(signal, 'pthread_sigmask'),
                         'need signal.pthread_sigmask()')
    @unittest.skipUnless(hasattr(signal, 'sigpending'),
                         'need signal.sigpending()')
    def test_sigpending(self):
        code = """if 1:
            import os
            import signal

            def handler(signum, frame):
                1/0

            signum = signal.SIGUSR1
            signal.signal(signum, handler)

            signal.pthread_sigmask(signal.SIG_BLOCK, [signum])
            os.kill(os.getpid(), signum)
            pending = signal.sigpending()
            for sig in pending:
                assert isinstance(sig, signal.Signals), repr(pending)
            if pending != {signum}:
                raise Exception('%s != {%s}' % (pending, signum))
            try:
                signal.pthread_sigmask(signal.SIG_UNBLOCK, [signum])
            except ZeroDivisionError:
                pass
            else:
                raise Exception("ZeroDivisionError not raised")
        """
        assert_python_ok('-c', code)

    @unittest.skipUnless(hasattr(signal, 'pthread_kill'),
                         'need signal.pthread_kill()')
    def test_pthread_kill(self):
        code = """if 1:
            import signal
            import threading
            import sys

            signum = signal.SIGUSR1

            def handler(signum, frame):
                1/0

            signal.signal(signum, handler)

            tid = threading.get_ident()
            try:
                signal.pthread_kill(tid, signum)
            except ZeroDivisionError:
                pass
            else:
                raise Exception("ZeroDivisionError not raised")
        """
        assert_python_ok('-c', code)

    @unittest.skipUnless(hasattr(signal, 'pthread_sigmask'),
                         'need signal.pthread_sigmask()')
    def wait_helper(self, blocked, test):
        """
        test: body of the "def test(signum):" function.
        blocked: number of the blocked signal
        """
        code = '''if 1:
        import signal
        import sys
        from signal import Signals

        def handler(signum, frame):
            1/0

        %s

        blocked = %s
        signum = signal.SIGALRM

        # child: block and wait the signal
        try:
            signal.signal(signum, handler)
            signal.pthread_sigmask(signal.SIG_BLOCK, [blocked])

            # Do the tests
            test(signum)

            # The handler must not be called on unblock
            try:
                signal.pthread_sigmask(signal.SIG_UNBLOCK, [blocked])
            except ZeroDivisionError:
                print("the signal handler has been called",
                      file=sys.stderr)
                sys.exit(1)
        except BaseException as err:
            print("error: {}".format(err), file=sys.stderr)
            sys.stderr.flush()
            sys.exit(1)
        ''' % (test.strip(), blocked)

        # sig*wait* must be called with the signal blocked: since the current
        # process might have several threads running, use a subprocess to have
        # a single thread.
        assert_python_ok('-c', code)

    @unittest.skipUnless(hasattr(signal, 'sigwait'),
                         'need signal.sigwait()')
    def test_sigwait(self):
        self.wait_helper(signal.SIGALRM, '''
        def test(signum):
            signal.alarm(1)
            received = signal.sigwait([signum])
            assert isinstance(received, signal.Signals), received
            if received != signum:
                raise Exception('received %s, not %s' % (received, signum))
        ''')

    @unittest.skipUnless(hasattr(signal, 'sigwaitinfo'),
                         'need signal.sigwaitinfo()')
    def test_sigwaitinfo(self):
        self.wait_helper(signal.SIGALRM, '''
        def test(signum):
            signal.alarm(1)
            info = signal.sigwaitinfo([signum])
            if info.si_signo != signum:
                raise Exception("info.si_signo != %s" % signum)
        ''')

    @unittest.skipUnless(hasattr(signal, 'sigtimedwait'),
                         'need signal.sigtimedwait()')
    def test_sigtimedwait(self):
        self.wait_helper(signal.SIGALRM, '''
        def test(signum):
            signal.alarm(1)
            info = signal.sigtimedwait([signum], 10.1000)
            if info.si_signo != signum:
                raise Exception('info.si_signo != %s' % signum)
        ''')

    @unittest.skipUnless(hasattr(signal, 'sigtimedwait'),
                         'need signal.sigtimedwait()')
    def test_sigtimedwait_poll(self):
        # check that polling with sigtimedwait works
        self.wait_helper(signal.SIGALRM, '''
        def test(signum):
            import os
            os.kill(os.getpid(), signum)
            info = signal.sigtimedwait([signum], 0)
            if info.si_signo != signum:
                raise Exception('info.si_signo != %s' % signum)
        ''')

    @unittest.skipUnless(hasattr(signal, 'sigtimedwait'),
                         'need signal.sigtimedwait()')
    def test_sigtimedwait_timeout(self):
        self.wait_helper(signal.SIGALRM, '''
        def test(signum):
            received = signal.sigtimedwait([signum], 1.0)
            if received is not None:
                raise Exception("received=%r" % (received,))
        ''')

    @unittest.skipUnless(hasattr(signal, 'sigtimedwait'),
                         'need signal.sigtimedwait()')
    def test_sigtimedwait_negative_timeout(self):
        signum = signal.SIGALRM
        self.assertRaises(ValueError, signal.sigtimedwait, [signum], -1.0)

    @unittest.skipUnless(hasattr(signal, 'sigwait'),
                         'need signal.sigwait()')
    @unittest.skipUnless(hasattr(signal, 'pthread_sigmask'),
                         'need signal.pthread_sigmask()')
    def test_sigwait_thread(self):
        # Check that calling sigwait() from a thread doesn't suspend the whole
        # process. A new interpreter is spawned to avoid problems when mixing
        # threads and fork(): only async-safe functions are allowed between
        # fork() and exec().
        assert_python_ok("-c", """if True:
            import os, threading, sys, time, signal

            # the default handler terminates the process
            signum = signal.SIGUSR1

            def kill_later():
                # wait until the main thread is waiting in sigwait()
                time.sleep(1)
                os.kill(os.getpid(), signum)

            # the signal must be blocked by all the threads
            signal.pthread_sigmask(signal.SIG_BLOCK, [signum])
            killer = threading.Thread(target=kill_later)
            killer.start()
            received = signal.sigwait([signum])
            if received != signum:
                print("sigwait() received %s, not %s" % (received, signum),
                      file=sys.stderr)
                sys.exit(1)
            killer.join()
            # unblock the signal, which should have been cleared by sigwait()
            signal.pthread_sigmask(signal.SIG_UNBLOCK, [signum])
        """)

    @unittest.skipUnless(hasattr(signal, 'pthread_sigmask'),
                         'need signal.pthread_sigmask()')
    def test_pthread_sigmask_arguments(self):
        self.assertRaises(TypeError, signal.pthread_sigmask)
        self.assertRaises(TypeError, signal.pthread_sigmask, 1)
        self.assertRaises(TypeError, signal.pthread_sigmask, 1, 2, 3)
        self.assertRaises(OSError, signal.pthread_sigmask, 1700, [])

    @unittest.skipUnless(hasattr(signal, 'pthread_sigmask'),
                         'need signal.pthread_sigmask()')
    def test_pthread_sigmask(self):
        code = """if 1:
        import signal
        import os; import threading

        def handler(signum, frame):
            1/0

        def kill(signum):
            os.kill(os.getpid(), signum)

        def check_mask(mask):
            for sig in mask:
                assert isinstance(sig, signal.Signals), repr(sig)

        def read_sigmask():
            sigmask = signal.pthread_sigmask(signal.SIG_BLOCK, [])
            check_mask(sigmask)
            return sigmask

        signum = signal.SIGUSR1

        # Install our signal handler
        old_handler = signal.signal(signum, handler)

        # Unblock SIGUSR1 (and copy the old mask) to test our signal handler
        old_mask = signal.pthread_sigmask(signal.SIG_UNBLOCK, [signum])
        check_mask(old_mask)
        try:
            kill(signum)
        except ZeroDivisionError:
            pass
        else:
            raise Exception("ZeroDivisionError not raised")

        # Block and then raise SIGUSR1. The signal is blocked: the signal
        # handler is not called, and the signal is now pending
        mask = signal.pthread_sigmask(signal.SIG_BLOCK, [signum])
        check_mask(mask)
        kill(signum)

        # Check the new mask
        blocked = read_sigmask()
        check_mask(blocked)
        if signum not in blocked:
            raise Exception("%s not in %s" % (signum, blocked))
        if old_mask ^ blocked != {signum}:
            raise Exception("%s ^ %s != {%s}" % (old_mask, blocked, signum))

        # Unblock SIGUSR1
        try:
            # unblock the pending signal calls immediately the signal handler
            signal.pthread_sigmask(signal.SIG_UNBLOCK, [signum])
        except ZeroDivisionError:
            pass
        else:
            raise Exception("ZeroDivisionError not raised")
        try:
            kill(signum)
        except ZeroDivisionError:
            pass
        else:
            raise Exception("ZeroDivisionError not raised")

        # Check the new mask
        unblocked = read_sigmask()
        if signum in unblocked:
            raise Exception("%s in %s" % (signum, unblocked))
        if blocked ^ unblocked != {signum}:
            raise Exception("%s ^ %s != {%s}" % (blocked, unblocked, signum))
        if old_mask != unblocked:
            raise Exception("%s != %s" % (old_mask, unblocked))
        """
        assert_python_ok('-c', code)

    @unittest.skipUnless(hasattr(signal, 'pthread_kill'),
                         'need signal.pthread_kill()')
    def test_pthread_kill_main_thread(self):
        # Test that a signal can be sent to the main thread with pthread_kill()
        # before any other thread has been created (see issue #12392).
        code = """if True:
            import threading
            import signal
            import sys

            def handler(signum, frame):
                sys.exit(3)

            signal.signal(signal.SIGUSR1, handler)
            signal.pthread_kill(threading.get_ident(), signal.SIGUSR1)
            sys.exit(2)
        """

        with spawn_python('-c', code) as process:
            stdout, stderr = process.communicate()
            exitcode = process.wait()
            if exitcode != 3:
                raise Exception("Child error (exit code %s): %s" %
                                (exitcode, stdout))


class StressTest(unittest.TestCase):
    """
    Stress signal delivery, especially when a signal arrives in
    the middle of recomputing the signal state or executing
    previously tripped signal handlers.
    """

    def setsig(self, signum, handler):
        old_handler = signal.signal(signum, handler)
        self.addCleanup(signal.signal, signum, old_handler)

    def measure_itimer_resolution(self):
        N = 20
        times = []

        def handler(signum=None, frame=None):
            if len(times) < N:
                times.append(time.perf_counter())
                # 1 µs is the smallest possible timer interval,
                # we want to measure what the concrete duration
                # will be on this platform
                signal.setitimer(signal.ITIMER_REAL, 1e-6)

        self.addCleanup(signal.setitimer, signal.ITIMER_REAL, 0)
        self.setsig(signal.SIGALRM, handler)
        handler()
        while len(times) < N:
            time.sleep(1e-3)

        durations = [times[i+1] - times[i] for i in range(len(times) - 1)]
        med = statistics.median(durations)
        if support.verbose:
            print("detected median itimer() resolution: %.6f s." % (med,))
        return med

    def decide_itimer_count(self):
        # Some systems have poor setitimer() resolution (for example
        # measured around 20 ms. on FreeBSD 9), so decide on a reasonable
        # number of sequential timers based on that.
        reso = self.measure_itimer_resolution()
        if reso <= 1e-4:
            return 10000
        elif reso <= 1e-2:
            return 100
        else:
            self.skipTest("detected itimer resolution (%.3f s.) too high "
                          "(> 10 ms.) on this platform (or system too busy)"
                          % (reso,))

    @unittest.skipUnless(hasattr(signal, "setitimer"),
                         "test needs setitimer()")
    def test_stress_delivery_dependent(self):
        """
        This test uses dependent signal handlers.
        """
        N = self.decide_itimer_count()
        sigs = []

        def first_handler(signum, frame):
            # 1e-6 is the minimum non-zero value for `setitimer()`.
            # Choose a random delay so as to improve chances of
            # triggering a race condition.  Ideally the signal is received
            # when inside critical signal-handling routines such as
            # Py_MakePendingCalls().
            signal.setitimer(signal.ITIMER_REAL, 1e-6 + random.random() * 1e-5)

        def second_handler(signum=None, frame=None):
            sigs.append(signum)

        # Here on Linux, SIGPROF > SIGALRM > SIGUSR1.  By using both
        # ascending and descending sequences (SIGUSR1 then SIGALRM,
        # SIGPROF then SIGALRM), we maximize chances of hitting a bug.
        self.setsig(signal.SIGPROF, first_handler)
        self.setsig(signal.SIGUSR1, first_handler)
        self.setsig(signal.SIGALRM, second_handler)  # for ITIMER_REAL

        expected_sigs = 0
        deadline = time.time() + 15.0

        while expected_sigs < N:
            os.kill(os.getpid(), signal.SIGPROF)
            expected_sigs += 1
            # Wait for handlers to run to avoid signal coalescing
            while len(sigs) < expected_sigs and time.time() < deadline:
                time.sleep(1e-5)

            os.kill(os.getpid(), signal.SIGUSR1)
            expected_sigs += 1
            while len(sigs) < expected_sigs and time.time() < deadline:
                time.sleep(1e-5)

        # All ITIMER_REAL signals should have been delivered to the
        # Python handler
        self.assertEqual(len(sigs), N, "Some signals were lost")

    @unittest.skipUnless(hasattr(signal, "setitimer"),
                         "test needs setitimer()")
    def test_stress_delivery_simultaneous(self):
        """
        This test uses simultaneous signal handlers.
        """
        N = self.decide_itimer_count()
        sigs = []

        def handler(signum, frame):
            sigs.append(signum)

        self.setsig(signal.SIGUSR1, handler)
        self.setsig(signal.SIGALRM, handler)  # for ITIMER_REAL

        expected_sigs = 0
        deadline = time.time() + 15.0

        while expected_sigs < N:
            # Hopefully the SIGALRM will be received somewhere during
            # initial processing of SIGUSR1.
            signal.setitimer(signal.ITIMER_REAL, 1e-6 + random.random() * 1e-5)
            os.kill(os.getpid(), signal.SIGUSR1)

            expected_sigs += 2
            # Wait for handlers to run to avoid signal coalescing
            while len(sigs) < expected_sigs and time.time() < deadline:
                time.sleep(1e-5)

        # All ITIMER_REAL signals should have been delivered to the
        # Python handler
        self.assertEqual(len(sigs), N, "Some signals were lost")


def tearDownModule():
    support.reap_children()

if __name__ == "__main__":
    unittest.main()