def _start(self):
		in_pr, in_pw = os.pipe()
		out_pr, out_pw = os.pipe()
		self._files = {}
		self._files['pipe_in'] = in_pr
		self._files['pipe_out'] = out_pw

		fcntl.fcntl(in_pr, fcntl.F_SETFL,
			fcntl.fcntl(in_pr, fcntl.F_GETFL) | os.O_NONBLOCK)

		# FD_CLOEXEC is enabled by default in Python >=3.4.
		if sys.hexversion < 0x3040000:
			try:
				fcntl.FD_CLOEXEC
			except AttributeError:
				pass
			else:
				fcntl.fcntl(in_pr, fcntl.F_SETFD,
					fcntl.fcntl(in_pr, fcntl.F_GETFD) | fcntl.FD_CLOEXEC)

		self._reg_id = self.scheduler.io_add_watch(in_pr,
			self.scheduler.IO_IN, self._output_handler)
		self._registered = True
		self._proc = SpawnProcess(
			args=[portage._python_interpreter,
				os.path.join(portage._bin_path, 'lock-helper.py'), self.path],
				env=dict(os.environ, PORTAGE_PYM_PATH=portage._pym_path),
				fd_pipes={0:out_pr, 1:in_pw, 2:sys.__stderr__.fileno()},
				scheduler=self.scheduler)
		self._proc.addExitListener(self._proc_exit)
		self._proc.start()
		os.close(out_pr)
		os.close(in_pw)

def _create_pty_or_pipe(copy_term_size=None):
	"""
	Try to create a pty and if then fails then create a normal
	pipe instead.

	@param copy_term_size: If a tty file descriptor is given
		then the term size will be copied to the pty.
	@type copy_term_size: int
	@rtype: tuple
	@returns: A tuple of (is_pty, master_fd, slave_fd) where
		is_pty is True if a pty was successfully allocated, and
		False if a normal pipe was allocated.
	"""

	got_pty = False

	global _disable_openpty, _fbsd_test_pty

	if _fbsd_test_pty and not _disable_openpty:
		# Test for python openpty breakage after freebsd7 to freebsd8
		# upgrade, which results in a 'Function not implemented' error
		# and the process being killed.
		pid = os.fork()
		if pid == 0:
			pty.openpty()
			os._exit(os.EX_OK)
		pid, status = os.waitpid(pid, 0)
		if (status & 0xff) == 140:
			_disable_openpty = True
		_fbsd_test_pty = False

	if _disable_openpty:
		master_fd, slave_fd = os.pipe()
	else:
		try:
			master_fd, slave_fd = pty.openpty()
			got_pty = True
		except EnvironmentError as e:
			_disable_openpty = True
			writemsg("openpty failed: '%s'\n" % str(e),
				noiselevel=-1)
			del e
			master_fd, slave_fd = os.pipe()

	if got_pty:
		# Disable post-processing of output since otherwise weird
		# things like \n -> \r\n transformations may occur.
		mode = termios.tcgetattr(slave_fd)
		mode[1] &= ~termios.OPOST
		termios.tcsetattr(slave_fd, termios.TCSANOW, mode)

	if got_pty and \
		copy_term_size is not None and \
		os.isatty(copy_term_size):
		rows, columns = get_term_size()
		set_term_size(rows, columns, slave_fd)

	return (got_pty, master_fd, slave_fd)

	def _pipe(self, fd_pipes):
		"""When appropriate, use a pty so that fetcher progress bars,
		like wget has, will work properly."""
		if self.background or not sys.stdout.isatty():
			# When the output only goes to a log file,
			# there's no point in creating a pty.
			return os.pipe()
		stdout_pipe = fd_pipes.get(1)
		got_pty, master_fd, slave_fd = \
			_create_pty_or_pipe(copy_term_size=stdout_pipe)
		return (master_fd, slave_fd)

	def _start(self):
		in_pr, in_pw = os.pipe()
		out_pr, out_pw = os.pipe()
		self._files = {}
		self._files['pipe_in'] = in_pr
		self._files['pipe_out'] = out_pw
		fcntl.fcntl(in_pr, fcntl.F_SETFL,
			fcntl.fcntl(in_pr, fcntl.F_GETFL) | os.O_NONBLOCK)
		self._reg_id = self.scheduler.register(in_pr,
			self.scheduler.IO_IN, self._output_handler)
		self._registered = True
		self._proc = SpawnProcess(
			args=[portage._python_interpreter,
				os.path.join(portage._bin_path, 'lock-helper.py'), self.path],
				env=dict(os.environ, PORTAGE_PYM_PATH=portage._pym_path),
				fd_pipes={0:out_pr, 1:in_pw, 2:sys.stderr.fileno()},
				scheduler=self.scheduler)
		self._proc.addExitListener(self._proc_exit)
		self._proc.start()
		os.close(out_pr)
		os.close(in_pw)

	def _start(self):
		pr, pw = os.pipe()
		self.fd_pipes = {}
		self.fd_pipes[pw] = pw
		self._digest_pw = pw
		self._digest_pipe_reader = PipeReader(
			input_files={"input":pr},
			scheduler=self.scheduler)
		self._digest_pipe_reader.addExitListener(self._digest_pipe_reader_exit)
		self._digest_pipe_reader.start()
		ForkProcess._start(self)
		os.close(pw)

	def testLazyImportPortageBaseline(self):
		"""
		Check what modules are imported by a baseline module import.
		"""

		env = os.environ.copy()
		pythonpath = env.get('PYTHONPATH')
		if pythonpath is not None and not pythonpath.strip():
			pythonpath = None
		if pythonpath is None:
			pythonpath = ''
		else:
			pythonpath = ':' + pythonpath
		pythonpath = PORTAGE_PYM_PATH + pythonpath
		env['PYTHONPATH'] = pythonpath

		# If python is patched to insert the path of the
		# currently installed portage module into sys.path,
		# then the above PYTHONPATH override doesn't help.
		env['PORTAGE_PYM_PATH'] = PORTAGE_PYM_PATH

		scheduler = PollScheduler().sched_iface
		master_fd, slave_fd = os.pipe()
		master_file = os.fdopen(master_fd, 'rb', 0)
		slave_file = os.fdopen(slave_fd, 'wb')
		producer = SpawnProcess(
			args=self._baseline_import_cmd,
			env=env, fd_pipes={1:slave_fd},
			scheduler=scheduler)
		producer.start()
		slave_file.close()

		consumer = PipeReader(
			input_files={"producer" : master_file},
			scheduler=scheduler)

		consumer.start()
		consumer.wait()
		self.assertEqual(producer.wait(), os.EX_OK)
		self.assertEqual(consumer.wait(), os.EX_OK)

		output = consumer.getvalue().decode('ascii', 'replace').split()

		unexpected_modules = " ".join(sorted(x for x in output \
			if self._module_re.match(x) is not None and \
			x not in self._baseline_imports))

		self.assertEqual("", unexpected_modules)

	def _start(self):
		pr, pw = os.pipe()
		self._files = {}
		self._files['pipe_read'] = os.fdopen(pr, 'rb', 0)
		self._files['pipe_write'] = os.fdopen(pw, 'wb', 0)
		for k, f in self._files.items():
			fcntl.fcntl(f.fileno(), fcntl.F_SETFL,
				fcntl.fcntl(f.fileno(), fcntl.F_GETFL) | os.O_NONBLOCK)
		self._reg_id = self.scheduler.register(self._files['pipe_read'].fileno(),
			PollConstants.POLLIN, self._output_handler)
		self._registered = True
		threading_mod = threading
		if self._force_dummy:
			threading_mod = dummy_threading
		self._thread = threading_mod.Thread(target=self._run_lock)
		self._thread.start()

	def _testPipeReader(self, test_string):
		"""
		Use a poll loop to read data from a pipe and assert that
		the data written to the pipe is identical to the data
		read from the pipe.
		"""

		if self._use_pty:
			got_pty, master_fd, slave_fd = _create_pty_or_pipe()
			if not got_pty:
				os.close(slave_fd)
				os.close(master_fd)
				skip_reason = "pty not acquired"
				self.portage_skip = skip_reason
				self.fail(skip_reason)
				return
		else:
			master_fd, slave_fd = os.pipe()

		# WARNING: It is very important to use unbuffered mode here,
		# in order to avoid issue 5380 with python3.
		master_file = os.fdopen(master_fd, 'rb', 0)
		slave_file = os.fdopen(slave_fd, 'wb', 0)
		task_scheduler = TaskScheduler(max_jobs=2)
		producer = SpawnProcess(
			args=["bash", "-c", self._echo_cmd % test_string],
			env=os.environ, fd_pipes={1:slave_fd},
			scheduler=task_scheduler.sched_iface)
		task_scheduler.add(producer)
		slave_file.close()

		consumer = PipeReader(
			input_files={"producer" : master_file},
			scheduler=task_scheduler.sched_iface, _use_array=self._use_array)

		task_scheduler.add(consumer)

		# This will ensure that both tasks have exited, which
		# is necessary to avoid "ResourceWarning: unclosed file"
		# warnings since Python 3.2 (and also ensures that we
		# don't leave any zombie child processes).
		task_scheduler.run()
		self.assertEqual(producer.returncode, os.EX_OK)
		self.assertEqual(consumer.returncode, os.EX_OK)

		return consumer.getvalue().decode('ascii', 'replace')

	def _testPipeReader(self, test_string):
		"""
		Use a poll loop to read data from a pipe and assert that
		the data written to the pipe is identical to the data
		read from the pipe.
		"""

		if self._use_pty:
			got_pty, master_fd, slave_fd = _create_pty_or_pipe()
			if not got_pty:
				os.close(slave_fd)
				os.close(master_fd)
				skip_reason = "pty not acquired"
				self.portage_skip = skip_reason
				self.fail(skip_reason)
				return
		else:
			master_fd, slave_fd = os.pipe()

		# WARNING: It is very important to use unbuffered mode here,
		# in order to avoid issue 5380 with python3.
		master_file = os.fdopen(master_fd, 'rb', 0)
		scheduler = global_event_loop()

		consumer = PipeReader(
			input_files={"producer" : master_file},
			_use_array=self._use_array,
			scheduler=scheduler)

		producer = PopenProcess(
			pipe_reader=consumer,
			proc=subprocess.Popen(["bash", "-c", self._echo_cmd % test_string],
				stdout=slave_fd),
			scheduler=scheduler)

		producer.start()
		os.close(slave_fd)
		producer.wait()

		self.assertEqual(producer.returncode, os.EX_OK)
		self.assertEqual(consumer.returncode, os.EX_OK)

		return consumer.getvalue().decode('ascii', 'replace')

	def testPipeReader(self):
		"""
		Use a poll loop to read data from a pipe and assert that
		the data written to the pipe is identical to the data
		read from the pipe.
		"""

		test_string = 2 * "blah blah blah\n"

		scheduler = PollScheduler().sched_iface
		master_fd, slave_fd = os.pipe()
		master_file = os.fdopen(master_fd, 'rb', 0)
		slave_file = os.fdopen(slave_fd, 'wb')
		producer = SpawnProcess(
			args=["bash", "-c", "echo -n '%s'" % test_string],
			env=os.environ, fd_pipes={1:slave_fd},
			scheduler=scheduler)
		producer.start()
		slave_file.close()

		consumer = PipeReader(
			input_files={"producer" : master_file},
			scheduler=scheduler)

		consumer.start()

		# This will ensure that both tasks have exited, which
		# is necessary to avoid "ResourceWarning: unclosed file"
		# warnings since Python 3.2 (and also ensures that we
		# don't leave any zombie child processes).
		scheduler.schedule()
		self.assertEqual(producer.returncode, os.EX_OK)
		self.assertEqual(consumer.returncode, os.EX_OK)

		output = consumer.getvalue().decode('ascii', 'replace')
		self.assertEqual(test_string, output)

	def testDoebuild(self):
		"""
		Invoke portage.doebuild() with the fd_pipes parameter, and
		check that the expected output appears in the pipe. This
		functionality is not used by portage internally, but it is
		supported for API consumers (see bug #475812).
		"""

		output_fd = 200
		ebuild_body = ['S=${WORKDIR}']
		for phase_func in ('pkg_info', 'pkg_nofetch', 'pkg_pretend',
			'pkg_setup', 'src_unpack', 'src_prepare', 'src_configure',
			'src_compile', 'src_test', 'src_install'):
			ebuild_body.append(('%s() { echo ${EBUILD_PHASE}'
				' 1>&%s; }') % (phase_func, output_fd))

		ebuild_body.append('')
		ebuild_body = '\n'.join(ebuild_body)

		ebuilds = {
			'app-misct/foo-1': {
				'EAPI'      : '5',
				"MISC_CONTENT": ebuild_body,
			}
		}

		# Override things that may be unavailable, or may have portability
		# issues when running tests in exotic environments.
		#   prepstrip - bug #447810 (bash read builtin EINTR problem)
		true_symlinks = ("find", "prepstrip", "sed", "scanelf")
		true_binary = portage.process.find_binary("true")
		self.assertEqual(true_binary is None, False,
			"true command not found")

		dev_null = open(os.devnull, 'wb')
		playground = ResolverPlayground(ebuilds=ebuilds)
		try:
			QueryCommand._db = playground.trees
			root_config = playground.trees[playground.eroot]['root_config']
			portdb = root_config.trees["porttree"].dbapi
			settings = portage.config(clone=playground.settings)
			if "__PORTAGE_TEST_HARDLINK_LOCKS" in os.environ:
				settings["__PORTAGE_TEST_HARDLINK_LOCKS"] = \
					os.environ["__PORTAGE_TEST_HARDLINK_LOCKS"]
				settings.backup_changes("__PORTAGE_TEST_HARDLINK_LOCKS")

			settings.features.add("noauto")
			settings.features.add("test")
			settings['PORTAGE_PYTHON'] = portage._python_interpreter
			settings['PORTAGE_QUIET'] = "1"
			settings['PYTHONDONTWRITEBYTECODE'] = os.environ.get("PYTHONDONTWRITEBYTECODE", "")

			fake_bin = os.path.join(settings["EPREFIX"], "bin")
			portage.util.ensure_dirs(fake_bin)
			for x in true_symlinks:
				os.symlink(true_binary, os.path.join(fake_bin, x))

			settings["__PORTAGE_TEST_PATH_OVERRIDE"] = fake_bin
			settings.backup_changes("__PORTAGE_TEST_PATH_OVERRIDE")

			cpv = 'app-misct/foo-1'
			metadata = dict(zip(Package.metadata_keys,
				portdb.aux_get(cpv, Package.metadata_keys)))

			pkg = Package(built=False, cpv=cpv, installed=False,
				metadata=metadata, root_config=root_config,
				type_name='ebuild')
			settings.setcpv(pkg)
			ebuildpath = portdb.findname(cpv)
			self.assertNotEqual(ebuildpath, None)

			for phase in ('info', 'nofetch',
				 'pretend', 'setup', 'unpack', 'prepare', 'configure',
				 'compile', 'test', 'install', 'qmerge', 'clean', 'merge'):

				pr, pw = os.pipe()

				producer = DoebuildProcess(doebuild_pargs=(ebuildpath, phase),
					doebuild_kwargs={"settings" : settings,
						"mydbapi": portdb, "tree": "porttree",
						"vartree": root_config.trees["vartree"],
						"fd_pipes": {
							1: dev_null.fileno(),
							2: dev_null.fileno(),
							output_fd: pw,
						},
						"prev_mtimes": {}})

				consumer = PipeReader(
					input_files={"producer" : pr})

				task_scheduler = TaskScheduler(iter([producer, consumer]),
					max_jobs=2)

				try:
					task_scheduler.start()
				finally:
					# PipeReader closes pr
					os.close(pw)

#.........这里部分代码省略.........

def spawn(mycommand, env={}, opt_name=None, fd_pipes=None, returnpid=False,
          uid=None, gid=None, groups=None, umask=None, logfile=None,
          path_lookup=True, pre_exec=None):
	"""
	Spawns a given command.
	
	@param mycommand: the command to execute
	@type mycommand: String or List (Popen style list)
	@param env: A dict of Key=Value pairs for env variables
	@type env: Dictionary
	@param opt_name: an optional name for the spawn'd process (defaults to the binary name)
	@type opt_name: String
	@param fd_pipes: A dict of mapping for pipes, { '0': stdin, '1': stdout } for example
	@type fd_pipes: Dictionary
	@param returnpid: Return the Process IDs for a successful spawn.
	NOTE: This requires the caller clean up all the PIDs, otherwise spawn will clean them.
	@type returnpid: Boolean
	@param uid: User ID to spawn as; useful for dropping privilages
	@type uid: Integer
	@param gid: Group ID to spawn as; useful for dropping privilages
	@type gid: Integer
	@param groups: Group ID's to spawn in: useful for having the process run in multiple group contexts.
	@type groups: List
	@param umask: An integer representing the umask for the process (see man chmod for umask details)
	@type umask: Integer
	@param logfile: name of a file to use for logging purposes
	@type logfile: String
	@param path_lookup: If the binary is not fully specified then look for it in PATH
	@type path_lookup: Boolean
	@param pre_exec: A function to be called with no arguments just prior to the exec call.
	@type pre_exec: callable
	
	logfile requires stdout and stderr to be assigned to this process (ie not pointed
	   somewhere else.)
	
	"""

	# mycommand is either a str or a list
	if isinstance(mycommand, basestring):
		mycommand = mycommand.split()

	if sys.hexversion < 0x3000000:
		# Avoid a potential UnicodeEncodeError from os.execve().
		env_bytes = {}
		for k, v in env.items():
			env_bytes[_unicode_encode(k, encoding=_encodings['content'])] = \
				_unicode_encode(v, encoding=_encodings['content'])
		env = env_bytes
		del env_bytes

	# If an absolute path to an executable file isn't given
	# search for it unless we've been told not to.
	binary = mycommand[0]
	if binary not in (BASH_BINARY, SANDBOX_BINARY, FAKEROOT_BINARY) and \
		(not os.path.isabs(binary) or not os.path.isfile(binary)
	    or not os.access(binary, os.X_OK)):
		binary = path_lookup and find_binary(binary) or None
		if not binary:
			raise CommandNotFound(mycommand[0])

	# If we haven't been told what file descriptors to use
	# default to propagating our stdin, stdout and stderr.
	if fd_pipes is None:
		fd_pipes = {
			0:sys.__stdin__.fileno(),
			1:sys.__stdout__.fileno(),
			2:sys.__stderr__.fileno(),
		}

	# mypids will hold the pids of all processes created.
	mypids = []

	if logfile:
		# Using a log file requires that stdout and stderr
		# are assigned to the process we're running.
		if 1 not in fd_pipes or 2 not in fd_pipes:
			raise ValueError(fd_pipes)

		# Create a pipe
		(pr, pw) = os.pipe()

		# Create a tee process, giving it our stdout and stderr
		# as well as the read end of the pipe.
		mypids.extend(spawn(('tee', '-i', '-a', logfile),
		              returnpid=True, fd_pipes={0:pr,
		              1:fd_pipes[1], 2:fd_pipes[2]}))

		# We don't need the read end of the pipe, so close it.
		os.close(pr)

		# Assign the write end of the pipe to our stdout and stderr.
		fd_pipes[1] = pw
		fd_pipes[2] = pw

	pid = os.fork()

	if pid == 0:
		try:
			_exec(binary, mycommand, opt_name, fd_pipes,
			      env, gid, groups, uid, umask, pre_exec)
#.........这里部分代码省略.........

	def _start(self):
		settings = self.settings
		settings.setcpv(self.cpv)
		ebuild_path = self.ebuild_path

		eapi = None
		if 'parse-eapi-glep-55' in settings.features:
			pf, eapi = portage._split_ebuild_name_glep55(
				os.path.basename(ebuild_path))
		if eapi is None and \
			'parse-eapi-ebuild-head' in settings.features:
			eapi = portage._parse_eapi_ebuild_head(
				codecs.open(_unicode_encode(ebuild_path,
				encoding=_encodings['fs'], errors='strict'),
				mode='r', encoding=_encodings['repo.content'],
				errors='replace'))

		if eapi is not None:
			if not portage.eapi_is_supported(eapi):
				self.metadata_callback(self.cpv, self.ebuild_path,
					self.repo_path, {'EAPI' : eapi}, self.ebuild_mtime)
				self.returncode = os.EX_OK
				self.wait()
				return

			settings.configdict['pkg']['EAPI'] = eapi

		debug = settings.get("PORTAGE_DEBUG") == "1"
		master_fd = None
		slave_fd = None
		fd_pipes = None
		if self.fd_pipes is not None:
			fd_pipes = self.fd_pipes.copy()
		else:
			fd_pipes = {}

		fd_pipes.setdefault(0, sys.stdin.fileno())
		fd_pipes.setdefault(1, sys.stdout.fileno())
		fd_pipes.setdefault(2, sys.stderr.fileno())

		# flush any pending output
		for fd in fd_pipes.values():
			if fd == sys.stdout.fileno():
				sys.stdout.flush()
			if fd == sys.stderr.fileno():
				sys.stderr.flush()

		fd_pipes_orig = fd_pipes.copy()
		self._files = self._files_dict()
		files = self._files

		master_fd, slave_fd = os.pipe()
		fcntl.fcntl(master_fd, fcntl.F_SETFL,
			fcntl.fcntl(master_fd, fcntl.F_GETFL) | os.O_NONBLOCK)

		fd_pipes[self._metadata_fd] = slave_fd

		self._raw_metadata = []
		files.ebuild = os.fdopen(master_fd, 'rb')
		self._reg_id = self.scheduler.register(files.ebuild.fileno(),
			self._registered_events, self._output_handler)
		self._registered = True

		retval = portage.doebuild(ebuild_path, "depend",
			settings["ROOT"], settings, debug,
			mydbapi=self.portdb, tree="porttree",
			fd_pipes=fd_pipes, returnpid=True)

		os.close(slave_fd)

		if isinstance(retval, int):
			# doebuild failed before spawning
			self._unregister()
			self.returncode = retval
			self.wait()
			return

		self.pid = retval[0]
		portage.process.spawned_pids.remove(self.pid)

	def _create_pipe(self):
		return os.pipe()

		def make_pipes():
			return os.pipe(), None

	def _pipe(self, fd_pipes):
		"""
		@type fd_pipes: dict
		@param fd_pipes: pipes from which to copy terminal size if desired.
		"""
		return os.pipe()

	def _start(self):
		settings = self.settings
		settings.setcpv(self.cpv)
		ebuild_path = self.ebuild_hash.location

		# the caller can pass in eapi in order to avoid
		# redundant _parse_eapi_ebuild_head calls
		eapi = self.eapi
		if eapi is None and \
			'parse-eapi-ebuild-head' in settings.features:
			with io.open(_unicode_encode(ebuild_path,
				encoding=_encodings['fs'], errors='strict'),
				mode='r', encoding=_encodings['repo.content'],
				errors='replace') as f:
				eapi = portage._parse_eapi_ebuild_head(f)

		if eapi is not None:
			if not portage.eapi_is_supported(eapi):
				self.metadata = self.metadata_callback(self.cpv,
					self.repo_path, {'EAPI' : eapi}, self.ebuild_hash)
				self._set_returncode((self.pid, os.EX_OK << 8))
				self.wait()
				return

			settings.configdict['pkg']['EAPI'] = eapi

		debug = settings.get("PORTAGE_DEBUG") == "1"
		master_fd = None
		slave_fd = None
		fd_pipes = None
		if self.fd_pipes is not None:
			fd_pipes = self.fd_pipes.copy()
		else:
			fd_pipes = {}

		null_input = open('/dev/null', 'rb')
		fd_pipes.setdefault(0, null_input.fileno())
		fd_pipes.setdefault(1, sys.stdout.fileno())
		fd_pipes.setdefault(2, sys.stderr.fileno())

		# flush any pending output
		for fd in fd_pipes.values():
			if fd == sys.stdout.fileno():
				sys.stdout.flush()
			if fd == sys.stderr.fileno():
				sys.stderr.flush()

		fd_pipes_orig = fd_pipes.copy()
		self._files = self._files_dict()
		files = self._files

		master_fd, slave_fd = os.pipe()
		fcntl.fcntl(master_fd, fcntl.F_SETFL,
			fcntl.fcntl(master_fd, fcntl.F_GETFL) | os.O_NONBLOCK)

		fd_pipes[self._metadata_fd] = slave_fd

		self._raw_metadata = []
		files.ebuild = os.fdopen(master_fd, 'rb', 0)
		self._reg_id = self.scheduler.register(files.ebuild.fileno(),
			self._registered_events, self._output_handler)
		self._registered = True

		retval = portage.doebuild(ebuild_path, "depend",
			settings=settings, debug=debug,
			mydbapi=self.portdb, tree="porttree",
			fd_pipes=fd_pipes, returnpid=True)

		os.close(slave_fd)
		null_input.close()

		if isinstance(retval, int):
			# doebuild failed before spawning
			self._unregister()
			self._set_returncode((self.pid, retval << 8))
			self.wait()
			return

		self.pid = retval[0]
		portage.process.spawned_pids.remove(self.pid)

	def _start(self):
		ebuild_path = self.ebuild_hash.location

		with io.open(_unicode_encode(ebuild_path,
			encoding=_encodings['fs'], errors='strict'),
			mode='r', encoding=_encodings['repo.content'],
			errors='replace') as f:
			self._eapi, self._eapi_lineno = portage._parse_eapi_ebuild_head(f)

		parsed_eapi = self._eapi
		if parsed_eapi is None:
			parsed_eapi = "0"

		if not parsed_eapi:
			# An empty EAPI setting is invalid.
			self._eapi_invalid(None)
			self.returncode = 1
			self._async_wait()
			return

		self.eapi_supported = portage.eapi_is_supported(parsed_eapi)
		if not self.eapi_supported:
			self.metadata = {"EAPI": parsed_eapi}
			self.returncode = os.EX_OK
			self._async_wait()
			return

		settings = self.settings
		settings.setcpv(self.cpv)
		settings.configdict['pkg']['EAPI'] = parsed_eapi

		debug = settings.get("PORTAGE_DEBUG") == "1"
		master_fd = None
		slave_fd = None
		fd_pipes = None
		if self.fd_pipes is not None:
			fd_pipes = self.fd_pipes.copy()
		else:
			fd_pipes = {}

		null_input = open('/dev/null', 'rb')
		fd_pipes.setdefault(0, null_input.fileno())
		fd_pipes.setdefault(1, sys.__stdout__.fileno())
		fd_pipes.setdefault(2, sys.__stderr__.fileno())

		# flush any pending output
		stdout_filenos = (sys.__stdout__.fileno(), sys.__stderr__.fileno())
		for fd in fd_pipes.values():
			if fd in stdout_filenos:
				sys.__stdout__.flush()
				sys.__stderr__.flush()
				break

		self._files = self._files_dict()
		files = self._files

		master_fd, slave_fd = os.pipe()

		fcntl.fcntl(master_fd, fcntl.F_SETFL,
			fcntl.fcntl(master_fd, fcntl.F_GETFL) | os.O_NONBLOCK)

		# FD_CLOEXEC is enabled by default in Python >=3.4.
		if sys.hexversion < 0x3040000:
			try:
				fcntl.FD_CLOEXEC
			except AttributeError:
				pass
			else:
				fcntl.fcntl(master_fd, fcntl.F_SETFD,
					fcntl.fcntl(master_fd, fcntl.F_GETFD) | fcntl.FD_CLOEXEC)

		fd_pipes[slave_fd] = slave_fd
		settings["PORTAGE_PIPE_FD"] = str(slave_fd)

		self._raw_metadata = []
		files.ebuild = master_fd
		self.scheduler.add_reader(files.ebuild, self._output_handler)
		self._registered = True

		retval = portage.doebuild(ebuild_path, "depend",
			settings=settings, debug=debug,
			mydbapi=self.portdb, tree="porttree",
			fd_pipes=fd_pipes, returnpid=True)
		settings.pop("PORTAGE_PIPE_FD", None)

		os.close(slave_fd)
		null_input.close()

		if isinstance(retval, int):
			# doebuild failed before spawning
			self.returncode = retval
			self._async_wait()
			return

		self.pid = retval[0]

	def _start(self):
		ebuild_path = self.ebuild_hash.location

		with io.open(_unicode_encode(ebuild_path,
			encoding=_encodings['fs'], errors='strict'),
			mode='r', encoding=_encodings['repo.content'],
			errors='replace') as f:
			self._eapi, self._eapi_lineno = portage._parse_eapi_ebuild_head(f)

		parsed_eapi = self._eapi
		if parsed_eapi is None:
			parsed_eapi = "0"

		if not parsed_eapi:
			# An empty EAPI setting is invalid.
			self._eapi_invalid(None)
			self._set_returncode((self.pid, 1 << 8))
			self.wait()
			return

		self.eapi_supported = portage.eapi_is_supported(parsed_eapi)
		if not self.eapi_supported:
			self.metadata = {"EAPI": parsed_eapi}
			self._set_returncode((self.pid, os.EX_OK << 8))
			self.wait()
			return

		settings = self.settings
		settings.setcpv(self.cpv)
		settings.configdict['pkg']['EAPI'] = parsed_eapi

		debug = settings.get("PORTAGE_DEBUG") == "1"
		master_fd = None
		slave_fd = None
		fd_pipes = None
		if self.fd_pipes is not None:
			fd_pipes = self.fd_pipes.copy()
		else:
			fd_pipes = {}

		null_input = open('/dev/null', 'rb')
		fd_pipes.setdefault(0, null_input.fileno())
		fd_pipes.setdefault(1, sys.__stdout__.fileno())
		fd_pipes.setdefault(2, sys.__stderr__.fileno())

		# flush any pending output
		stdout_filenos = (sys.__stdout__.fileno(), sys.__stderr__.fileno())
		for fd in fd_pipes.values():
			if fd in stdout_filenos:
				sys.__stdout__.flush()
				sys.__stderr__.flush()
				break

		self._files = self._files_dict()
		files = self._files

		master_fd, slave_fd = os.pipe()
		fcntl.fcntl(master_fd, fcntl.F_SETFL,
			fcntl.fcntl(master_fd, fcntl.F_GETFL) | os.O_NONBLOCK)

		fd_pipes[self._metadata_fd] = slave_fd

		self._raw_metadata = []
		files.ebuild = master_fd
		self._reg_id = self.scheduler.register(files.ebuild,
			self._registered_events, self._output_handler)
		self._registered = True

		retval = portage.doebuild(ebuild_path, "depend",
			settings=settings, debug=debug,
			mydbapi=self.portdb, tree="porttree",
			fd_pipes=fd_pipes, returnpid=True)

		os.close(slave_fd)
		null_input.close()

		if isinstance(retval, int):
			# doebuild failed before spawning
			self._unregister()
			self._set_returncode((self.pid, retval << 8))
			self.wait()
			return

		self.pid = retval[0]
		portage.process.spawned_pids.remove(self.pid)

	def _spawn(self, args, fd_pipes, **kwargs):
		"""
		Fork a subprocess, apply local settings, and call
		dblink.merge(). TODO: Share code with ForkProcess.
		"""

		elog_reader_fd, elog_writer_fd = os.pipe()
		fcntl.fcntl(elog_reader_fd, fcntl.F_SETFL,
			fcntl.fcntl(elog_reader_fd, fcntl.F_GETFL) | os.O_NONBLOCK)
		blockers = None
		if self.blockers is not None:
			# Query blockers in the main process, since closing
			# of file descriptors in the subprocess can prevent
			# access to open database connections such as that
			# used by the sqlite metadata cache module.
			blockers = self.blockers()
		mylink = portage.dblink(self.mycat, self.mypkg, settings=self.settings,
			treetype=self.treetype, vartree=self.vartree,
			blockers=blockers, pipe=elog_writer_fd)
		fd_pipes[elog_writer_fd] = elog_writer_fd
		self._elog_reg_id = self.scheduler.io_add_watch(elog_reader_fd,
			self._registered_events, self._elog_output_handler)

		# If a concurrent emerge process tries to install a package
		# in the same SLOT as this one at the same time, there is an
		# extremely unlikely chance that the COUNTER values will not be
		# ordered correctly unless we lock the vdb here.
		# FEATURES=parallel-install skips this lock in order to
		# improve performance, and the risk is practically negligible.
		self._lock_vdb()
		counter = None
		if not self.unmerge:
			counter = self.vartree.dbapi.counter_tick()

		parent_pid = os.getpid()
		pid = None
		try:
			pid = os.fork()

			if pid != 0:
				if not isinstance(pid, int):
					raise AssertionError(
						"fork returned non-integer: %s" % (repr(pid),))

				os.close(elog_writer_fd)
				self._elog_reader_fd = elog_reader_fd
				self._buf = ""
				self._elog_keys = set()

				# invalidate relevant vardbapi caches
				if self.vartree.dbapi._categories is not None:
					self.vartree.dbapi._categories = None
				self.vartree.dbapi._pkgs_changed = True
				self.vartree.dbapi._clear_pkg_cache(mylink)

				portage.process.spawned_pids.append(pid)
				return [pid]

			os.close(elog_reader_fd)

			# Use default signal handlers in order to avoid problems
			# killing subprocesses as reported in bug #353239.
			signal.signal(signal.SIGINT, signal.SIG_DFL)
			signal.signal(signal.SIGTERM, signal.SIG_DFL)

			portage.locks._close_fds()
			# We don't exec, so use close_fds=False
			# (see _setup_pipes docstring).
			portage.process._setup_pipes(fd_pipes, close_fds=False)

			portage.output.havecolor = self.settings.get('NOCOLOR') \
				not in ('yes', 'true')

			# Avoid wastful updates of the vdb cache.
			self.vartree.dbapi._flush_cache_enabled = False

			# In this subprocess we don't want PORTAGE_BACKGROUND to
			# suppress stdout/stderr output since they are pipes. We
			# also don't want to open PORTAGE_LOG_FILE, since it will
			# already be opened by the parent process, so we set the
			# "subprocess" value for use in conditional logging code
			# involving PORTAGE_LOG_FILE.
			if not self.unmerge:
				# unmerge phases have separate logs
				if self.settings.get("PORTAGE_BACKGROUND") == "1":
					self.settings["PORTAGE_BACKGROUND_UNMERGE"] = "1"
				else:
					self.settings["PORTAGE_BACKGROUND_UNMERGE"] = "0"
				self.settings.backup_changes("PORTAGE_BACKGROUND_UNMERGE")
			self.settings["PORTAGE_BACKGROUND"] = "subprocess"
			self.settings.backup_changes("PORTAGE_BACKGROUND")

			rval = 1
			try:
				if self.unmerge:
					if not mylink.exists():
						rval = os.EX_OK
					elif mylink.unmerge(
						ldpath_mtimes=self.prev_mtimes) == os.EX_OK:
						mylink.lockdb()
#.........这里部分代码省略.........