diff python-daemon-2.0.5/daemon/daemon.py @ 33:7ceb967147c3

start xena with no gui add library files

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/python-daemon-2.0.5/daemon/daemon.py	Wed Jul 22 13:24:44 2015 -0700
@@ -0,0 +1,926 @@
+# -*- coding: utf-8 -*-
+
+# daemon/daemon.py
+# Part of ‘python-daemon’, an implementation of PEP 3143.
+#
+# Copyright © 2008–2015 Ben Finney <[e-mail]>
+# Copyright © 2007–2008 Robert Niederreiter, Jens Klein
+# Copyright © 2004–2005 Chad J. Schroeder
+# Copyright © 2003 Clark Evans
+# Copyright © 2002 Noah Spurrier
+# Copyright © 2001 Jürgen Hermann
+#
+# This is free software: you may copy, modify, and/or distribute this work
+# under the terms of the Apache License, version 2.0 as published by the
+# Apache Software Foundation.
+# No warranty expressed or implied. See the file ‘LICENSE.ASF-2’ for details.
+
+""" Daemon process behaviour.
+    """
+
+from __future__ import (absolute_import, unicode_literals)
+
+import os
+import sys
+import resource
+import errno
+import signal
+import socket
+import atexit
+try:
+    # Python 2 has both ‘str’ (bytes) and ‘unicode’ (text).
+    basestring = basestring
+    unicode = unicode
+except NameError:
+    # Python 3 names the Unicode data type ‘str’.
+    basestring = str
+    unicode = str
+
+
+class DaemonError(Exception):
+    """ Base exception class for errors from this module. """
+
+    def __init__(self, *args, **kwargs):
+        self._chain_from_context()
+
+        super(DaemonError, self).__init__(*args, **kwargs)
+
+    def _chain_from_context(self):
+        _chain_exception_from_existing_exception_context(self, as_cause=True)
+
+
+class DaemonOSEnvironmentError(DaemonError, OSError):
+    """ Exception raised when daemon OS environment setup receives error. """
+
+
+class DaemonProcessDetachError(DaemonError, OSError):
+    """ Exception raised when process detach fails. """
+
+
+class DaemonContext:
+    """ Context for turning the current program into a daemon process.
+
+        A `DaemonContext` instance represents the behaviour settings and
+        process context for the program when it becomes a daemon. The
+        behaviour and environment is customised by setting options on the
+        instance, before calling the `open` method.
+
+        Each option can be passed as a keyword argument to the `DaemonContext`
+        constructor, or subsequently altered by assigning to an attribute on
+        the instance at any time prior to calling `open`. That is, for
+        options named `wibble` and `wubble`, the following invocation::
+
+            foo = daemon.DaemonContext(wibble=bar, wubble=baz)
+            foo.open()
+
+        is equivalent to::
+
+            foo = daemon.DaemonContext()
+            foo.wibble = bar
+            foo.wubble = baz
+            foo.open()
+
+        The following options are defined.
+
+        `files_preserve`
+            :Default: ``None``
+
+            List of files that should *not* be closed when starting the
+            daemon. If ``None``, all open file descriptors will be closed.
+
+            Elements of the list are file descriptors (as returned by a file
+            object's `fileno()` method) or Python `file` objects. Each
+            specifies a file that is not to be closed during daemon start.
+
+        `chroot_directory`
+            :Default: ``None``
+
+            Full path to a directory to set as the effective root directory of
+            the process. If ``None``, specifies that the root directory is not
+            to be changed.
+
+        `working_directory`
+            :Default: ``'/'``
+
+            Full path of the working directory to which the process should
+            change on daemon start.
+
+            Since a filesystem cannot be unmounted if a process has its
+            current working directory on that filesystem, this should either
+            be left at default or set to a directory that is a sensible “home
+            directory” for the daemon while it is running.
+
+        `umask`
+            :Default: ``0``
+
+            File access creation mask (“umask”) to set for the process on
+            daemon start.
+
+            A daemon should not rely on the parent process's umask value,
+            which is beyond its control and may prevent creating a file with
+            the required access mode. So when the daemon context opens, the
+            umask is set to an explicit known value.
+
+            If the conventional value of 0 is too open, consider setting a
+            value such as 0o022, 0o027, 0o077, or another specific value.
+            Otherwise, ensure the daemon creates every file with an
+            explicit access mode for the purpose.
+
+        `pidfile`
+            :Default: ``None``
+
+            Context manager for a PID lock file. When the daemon context opens
+            and closes, it enters and exits the `pidfile` context manager.
+
+        `detach_process`
+            :Default: ``None``
+
+            If ``True``, detach the process context when opening the daemon
+            context; if ``False``, do not detach.
+
+            If unspecified (``None``) during initialisation of the instance,
+            this will be set to ``True`` by default, and ``False`` only if
+            detaching the process is determined to be redundant; for example,
+            in the case when the process was started by `init`, by `initd`, or
+            by `inetd`.
+
+        `signal_map`
+            :Default: system-dependent
+
+            Mapping from operating system signals to callback actions.
+
+            The mapping is used when the daemon context opens, and determines
+            the action for each signal's signal handler:
+
+            * A value of ``None`` will ignore the signal (by setting the
+              signal action to ``signal.SIG_IGN``).
+
+            * A string value will be used as the name of an attribute on the
+              ``DaemonContext`` instance. The attribute's value will be used
+              as the action for the signal handler.
+
+            * Any other value will be used as the action for the
+              signal handler. See the ``signal.signal`` documentation
+              for details of the signal handler interface.
+
+            The default value depends on which signals are defined on the
+            running system. Each item from the list below whose signal is
+            actually defined in the ``signal`` module will appear in the
+            default map:
+
+            * ``signal.SIGTTIN``: ``None``
+
+            * ``signal.SIGTTOU``: ``None``
+
+            * ``signal.SIGTSTP``: ``None``
+
+            * ``signal.SIGTERM``: ``'terminate'``
+
+            Depending on how the program will interact with its child
+            processes, it may need to specify a signal map that
+            includes the ``signal.SIGCHLD`` signal (received when a
+            child process exits). See the specific operating system's
+            documentation for more detail on how to determine what
+            circumstances dictate the need for signal handlers.
+
+        `uid`
+            :Default: ``os.getuid()``
+
+        `gid`
+            :Default: ``os.getgid()``
+
+            The user ID (“UID”) value and group ID (“GID”) value to switch
+            the process to on daemon start.
+
+            The default values, the real UID and GID of the process, will
+            relinquish any effective privilege elevation inherited by the
+            process.
+
+        `prevent_core`
+            :Default: ``True``
+
+            If true, prevents the generation of core files, in order to avoid
+            leaking sensitive information from daemons run as `root`.
+
+        `stdin`
+            :Default: ``None``
+
+        `stdout`
+            :Default: ``None``
+
+        `stderr`
+            :Default: ``None``
+
+            Each of `stdin`, `stdout`, and `stderr` is a file-like object
+            which will be used as the new file for the standard I/O stream
+            `sys.stdin`, `sys.stdout`, and `sys.stderr` respectively. The file
+            should therefore be open, with a minimum of mode 'r' in the case
+            of `stdin`, and mimimum of mode 'w+' in the case of `stdout` and
+            `stderr`.
+
+            If the object has a `fileno()` method that returns a file
+            descriptor, the corresponding file will be excluded from being
+            closed during daemon start (that is, it will be treated as though
+            it were listed in `files_preserve`).
+
+            If ``None``, the corresponding system stream is re-bound to the
+            file named by `os.devnull`.
+
+        """
+
+    __metaclass__ = type
+
+    def __init__(
+            self,
+            chroot_directory=None,
+            working_directory="/",
+            umask=0,
+            uid=None,
+            gid=None,
+            prevent_core=True,
+            detach_process=None,
+            files_preserve=None,
+            pidfile=None,
+            stdin=None,
+            stdout=None,
+            stderr=None,
+            signal_map=None,
+            ):
+        """ Set up a new instance. """
+        self.chroot_directory = chroot_directory
+        self.working_directory = working_directory
+        self.umask = umask
+        self.prevent_core = prevent_core
+        self.files_preserve = files_preserve
+        self.pidfile = pidfile
+        self.stdin = stdin
+        self.stdout = stdout
+        self.stderr = stderr
+
+        if uid is None:
+            uid = os.getuid()
+        self.uid = uid
+        if gid is None:
+            gid = os.getgid()
+        self.gid = gid
+
+        if detach_process is None:
+            detach_process = is_detach_process_context_required()
+        self.detach_process = detach_process
+
+        if signal_map is None:
+            signal_map = make_default_signal_map()
+        self.signal_map = signal_map
+
+        self._is_open = False
+
+    @property
+    def is_open(self):
+        """ ``True`` if the instance is currently open. """
+        return self._is_open
+
+    def open(self):
+        """ Become a daemon process.
+
+            :return: ``None``.
+
+            Open the daemon context, turning the current program into a daemon
+            process. This performs the following steps:
+
+            * If this instance's `is_open` property is true, return
+              immediately. This makes it safe to call `open` multiple times on
+              an instance.
+
+            * If the `prevent_core` attribute is true, set the resource limits
+              for the process to prevent any core dump from the process.
+
+            * If the `chroot_directory` attribute is not ``None``, set the
+              effective root directory of the process to that directory (via
+              `os.chroot`).
+
+              This allows running the daemon process inside a “chroot gaol”
+              as a means of limiting the system's exposure to rogue behaviour
+              by the process. Note that the specified directory needs to
+              already be set up for this purpose.
+
+            * Set the process UID and GID to the `uid` and `gid` attribute
+              values.
+
+            * Close all open file descriptors. This excludes those listed in
+              the `files_preserve` attribute, and those that correspond to the
+              `stdin`, `stdout`, or `stderr` attributes.
+
+            * Change current working directory to the path specified by the
+              `working_directory` attribute.
+
+            * Reset the file access creation mask to the value specified by
+              the `umask` attribute.
+
+            * If the `detach_process` option is true, detach the current
+              process into its own process group, and disassociate from any
+              controlling terminal.
+
+            * Set signal handlers as specified by the `signal_map` attribute.
+
+            * If any of the attributes `stdin`, `stdout`, `stderr` are not
+              ``None``, bind the system streams `sys.stdin`, `sys.stdout`,
+              and/or `sys.stderr` to the files represented by the
+              corresponding attributes. Where the attribute has a file
+              descriptor, the descriptor is duplicated (instead of re-binding
+              the name).
+
+            * If the `pidfile` attribute is not ``None``, enter its context
+              manager.
+
+            * Mark this instance as open (for the purpose of future `open` and
+              `close` calls).
+
+            * Register the `close` method to be called during Python's exit
+              processing.
+
+            When the function returns, the running program is a daemon
+            process.
+
+            """
+        if self.is_open:
+            return
+
+        if self.chroot_directory is not None:
+            change_root_directory(self.chroot_directory)
+
+        if self.prevent_core:
+            prevent_core_dump()
+
+        change_file_creation_mask(self.umask)
+        change_working_directory(self.working_directory)
+        change_process_owner(self.uid, self.gid)
+
+        if self.detach_process:
+            detach_process_context()
+
+        signal_handler_map = self._make_signal_handler_map()
+        set_signal_handlers(signal_handler_map)
+
+        exclude_fds = self._get_exclude_file_descriptors()
+        close_all_open_files(exclude=exclude_fds)
+
+        redirect_stream(sys.stdin, self.stdin)
+        redirect_stream(sys.stdout, self.stdout)
+        redirect_stream(sys.stderr, self.stderr)
+
+        if self.pidfile is not None:
+            self.pidfile.__enter__()
+
+        self._is_open = True
+
+        register_atexit_function(self.close)
+
+    def __enter__(self):
+        """ Context manager entry point. """
+        self.open()
+        return self
+
+    def close(self):
+        """ Exit the daemon process context.
+
+            :return: ``None``.
+
+            Close the daemon context. This performs the following steps:
+
+            * If this instance's `is_open` property is false, return
+              immediately. This makes it safe to call `close` multiple times
+              on an instance.
+
+            * If the `pidfile` attribute is not ``None``, exit its context
+              manager.
+
+            * Mark this instance as closed (for the purpose of future `open`
+              and `close` calls).
+
+            """
+        if not self.is_open:
+            return
+
+        if self.pidfile is not None:
+            # Follow the interface for telling a context manager to exit,
+            # <URL:http://docs.python.org/library/stdtypes.html#typecontextmanager>.
+            self.pidfile.__exit__(None, None, None)
+
+        self._is_open = False
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        """ Context manager exit point. """
+        self.close()
+
+    def terminate(self, signal_number, stack_frame):
+        """ Signal handler for end-process signals.
+
+            :param signal_number: The OS signal number received.
+            :param stack_frame: The frame object at the point the
+                signal was received.
+            :return: ``None``.
+
+            Signal handler for the ``signal.SIGTERM`` signal. Performs the
+            following step:
+
+            * Raise a ``SystemExit`` exception explaining the signal.
+
+            """
+        exception = SystemExit(
+                "Terminating on signal {signal_number!r}".format(
+                    signal_number=signal_number))
+        raise exception
+
+    def _get_exclude_file_descriptors(self):
+        """ Get the set of file descriptors to exclude closing.
+
+            :return: A set containing the file descriptors for the
+                files to be preserved.
+
+            The file descriptors to be preserved are those from the
+            items in `files_preserve`, and also each of `stdin`,
+            `stdout`, and `stderr`. For each item:
+
+            * If the item is ``None``, it is omitted from the return
+              set.
+
+            * If the item's ``fileno()`` method returns a value, that
+              value is in the return set.
+
+            * Otherwise, the item is in the return set verbatim.
+
+            """
+        files_preserve = self.files_preserve
+        if files_preserve is None:
+            files_preserve = []
+        files_preserve.extend(
+                item for item in [self.stdin, self.stdout, self.stderr]
+                if hasattr(item, 'fileno'))
+
+        exclude_descriptors = set()
+        for item in files_preserve:
+            if item is None:
+                continue
+            file_descriptor = _get_file_descriptor(item)
+            if file_descriptor is not None:
+                exclude_descriptors.add(file_descriptor)
+            else:
+                exclude_descriptors.add(item)
+
+        return exclude_descriptors
+
+    def _make_signal_handler(self, target):
+        """ Make the signal handler for a specified target object.
+
+            :param target: A specification of the target for the
+                handler; see below.
+            :return: The value for use by `signal.signal()`.
+
+            If `target` is ``None``, return ``signal.SIG_IGN``. If `target`
+            is a text string, return the attribute of this instance named
+            by that string. Otherwise, return `target` itself.
+
+            """
+        if target is None:
+            result = signal.SIG_IGN
+        elif isinstance(target, unicode):
+            name = target
+            result = getattr(self, name)
+        else:
+            result = target
+
+        return result
+
+    def _make_signal_handler_map(self):
+        """ Make the map from signals to handlers for this instance.
+
+            :return: The constructed signal map for this instance.
+
+            Construct a map from signal numbers to handlers for this
+            context instance, suitable for passing to
+            `set_signal_handlers`.
+
+            """
+        signal_handler_map = dict(
+                (signal_number, self._make_signal_handler(target))
+                for (signal_number, target) in self.signal_map.items())
+        return signal_handler_map
+
+
+def _get_file_descriptor(obj):
+    """ Get the file descriptor, if the object has one.
+
+        :param obj: The object expected to be a file-like object.
+        :return: The file descriptor iff the file supports it; otherwise
+            ``None``.
+
+        The object may be a non-file object. It may also be a
+        file-like object with no support for a file descriptor. In
+        either case, return ``None``.
+
+        """
+    file_descriptor = None
+    if hasattr(obj, 'fileno'):
+        try:
+            file_descriptor = obj.fileno()
+        except ValueError:
+            # The item doesn't support a file descriptor.
+            pass
+
+    return file_descriptor
+
+
+def change_working_directory(directory):
+    """ Change the working directory of this process.
+
+        :param directory: The target directory path.
+        :return: ``None``.
+
+        """
+    try:
+        os.chdir(directory)
+    except Exception as exc:
+        error = DaemonOSEnvironmentError(
+                "Unable to change working directory ({exc})".format(exc=exc))
+        raise error
+
+
+def change_root_directory(directory):
+    """ Change the root directory of this process.
+
+        :param directory: The target directory path.
+        :return: ``None``.
+
+        Set the current working directory, then the process root directory,
+        to the specified `directory`. Requires appropriate OS privileges
+        for this process.
+
+        """
+    try:
+        os.chdir(directory)
+        os.chroot(directory)
+    except Exception as exc:
+        error = DaemonOSEnvironmentError(
+                "Unable to change root directory ({exc})".format(exc=exc))
+        raise error
+
+
+def change_file_creation_mask(mask):
+    """ Change the file creation mask for this process.
+
+        :param mask: The numeric file creation mask to set.
+        :return: ``None``.
+
+        """
+    try:
+        os.umask(mask)
+    except Exception as exc:
+        error = DaemonOSEnvironmentError(
+                "Unable to change file creation mask ({exc})".format(exc=exc))
+        raise error
+
+
+def change_process_owner(uid, gid):
+    """ Change the owning UID and GID of this process.
+
+        :param uid: The target UID for the daemon process.
+        :param gid: The target GID for the daemon process.
+        :return: ``None``.
+
+        Set the GID then the UID of the process (in that order, to avoid
+        permission errors) to the specified `gid` and `uid` values.
+        Requires appropriate OS privileges for this process.
+
+        """
+    try:
+        os.setgid(gid)
+        os.setuid(uid)
+    except Exception as exc:
+        error = DaemonOSEnvironmentError(
+                "Unable to change process owner ({exc})".format(exc=exc))
+        raise error
+
+
+def prevent_core_dump():
+    """ Prevent this process from generating a core dump.
+
+        :return: ``None``.
+
+        Set the soft and hard limits for core dump size to zero. On Unix,
+        this entirely prevents the process from creating core dump.
+
+        """
+    core_resource = resource.RLIMIT_CORE
+
+    try:
+        # Ensure the resource limit exists on this platform, by requesting
+        # its current value.
+        core_limit_prev = resource.getrlimit(core_resource)
+    except ValueError as exc:
+        error = DaemonOSEnvironmentError(
+                "System does not support RLIMIT_CORE resource limit"
+                " ({exc})".format(exc=exc))
+        raise error
+
+    # Set hard and soft limits to zero, i.e. no core dump at all.
+    core_limit = (0, 0)
+    resource.setrlimit(core_resource, core_limit)
+
+
+def detach_process_context():
+    """ Detach the process context from parent and session.
+
+        :return: ``None``.
+
+        Detach from the parent process and session group, allowing the
+        parent to exit while this process continues running.
+
+        Reference: “Advanced Programming in the Unix Environment”,
+        section 13.3, by W. Richard Stevens, published 1993 by
+        Addison-Wesley.
+
+        """
+
+    def fork_then_exit_parent(error_message):
+        """ Fork a child process, then exit the parent process.
+
+            :param error_message: Message for the exception in case of a
+                detach failure.
+            :return: ``None``.
+            :raise DaemonProcessDetachError: If the fork fails.
+
+            """
+        try:
+            pid = os.fork()
+            if pid > 0:
+                os._exit(0)
+        except OSError as exc:
+            error = DaemonProcessDetachError(
+                    "{message}: [{exc.errno:d}] {exc.strerror}".format(
+                        message=error_message, exc=exc))
+            raise error
+
+    fork_then_exit_parent(error_message="Failed first fork")
+    os.setsid()
+    fork_then_exit_parent(error_message="Failed second fork")
+
+
+def is_process_started_by_init():
+    """ Determine whether the current process is started by `init`.
+
+        :return: ``True`` iff the parent process is `init`; otherwise
+            ``False``.
+
+        The `init` process is the one with process ID of 1.
+
+        """
+    result = False
+
+    init_pid = 1
+    if os.getppid() == init_pid:
+        result = True
+
+    return result
+
+
+def is_socket(fd):
+    """ Determine whether the file descriptor is a socket.
+
+        :param fd: The file descriptor to interrogate.
+        :return: ``True`` iff the file descriptor is a socket; otherwise
+            ``False``.
+
+        Query the socket type of `fd`. If there is no error, the file is a
+        socket.
+
+        """
+    result = False
+
+    file_socket = socket.fromfd(fd, socket.AF_INET, socket.SOCK_RAW)
+
+    try:
+        socket_type = file_socket.getsockopt(
+                socket.SOL_SOCKET, socket.SO_TYPE)
+    except socket.error as exc:
+        exc_errno = exc.args[0]
+        if exc_errno == errno.ENOTSOCK:
+            # Socket operation on non-socket.
+            pass
+        else:
+            # Some other socket error.
+            result = True
+    else:
+        # No error getting socket type.
+        result = True
+
+    return result
+
+
+def is_process_started_by_superserver():
+    """ Determine whether the current process is started by the superserver.
+
+        :return: ``True`` if this process was started by the internet
+            superserver; otherwise ``False``.
+
+        The internet superserver creates a network socket, and
+        attaches it to the standard streams of the child process. If
+        that is the case for this process, return ``True``, otherwise
+        ``False``.
+
+        """
+    result = False
+
+    stdin_fd = sys.__stdin__.fileno()
+    if is_socket(stdin_fd):
+        result = True
+
+    return result
+
+
+def is_detach_process_context_required():
+    """ Determine whether detaching the process context is required.
+
+        :return: ``True`` iff the process is already detached; otherwise
+            ``False``.
+
+        The process environment is interrogated for the following:
+
+        * Process was started by `init`; or
+
+        * Process was started by `inetd`.
+
+        If any of the above are true, the process is deemed to be already
+        detached.
+
+        """
+    result = True
+    if is_process_started_by_init() or is_process_started_by_superserver():
+        result = False
+
+    return result
+
+
+def close_file_descriptor_if_open(fd):
+    """ Close a file descriptor if already open.
+
+        :param fd: The file descriptor to close.
+        :return: ``None``.
+
+        Close the file descriptor `fd`, suppressing an error in the
+        case the file was not open.
+
+        """
+    try:
+        os.close(fd)
+    except EnvironmentError as exc:
+        if exc.errno == errno.EBADF:
+            # File descriptor was not open.
+            pass
+        else:
+            error = DaemonOSEnvironmentError(
+                    "Failed to close file descriptor {fd:d} ({exc})".format(
+                        fd=fd, exc=exc))
+            raise error
+
+
+MAXFD = 2048
+
+def get_maximum_file_descriptors():
+    """ Get the maximum number of open file descriptors for this process.
+
+        :return: The number (integer) to use as the maximum number of open
+            files for this process.
+
+        The maximum is the process hard resource limit of maximum number of
+        open file descriptors. If the limit is “infinity”, a default value
+        of ``MAXFD`` is returned.
+
+        """
+    limits = resource.getrlimit(resource.RLIMIT_NOFILE)
+    result = limits[1]
+    if result == resource.RLIM_INFINITY:
+        result = MAXFD
+    return result
+
+
+def close_all_open_files(exclude=set()):
+    """ Close all open file descriptors.
+
+        :param exclude: Collection of file descriptors to skip when closing
+            files.
+        :return: ``None``.
+
+        Closes every file descriptor (if open) of this process. If
+        specified, `exclude` is a set of file descriptors to *not*
+        close.
+
+        """
+    maxfd = get_maximum_file_descriptors()
+    for fd in reversed(range(maxfd)):
+        if fd not in exclude:
+            close_file_descriptor_if_open(fd)
+
+
+def redirect_stream(system_stream, target_stream):
+    """ Redirect a system stream to a specified file.
+
+        :param standard_stream: A file object representing a standard I/O
+            stream.
+        :param target_stream: The target file object for the redirected
+            stream, or ``None`` to specify the null device.
+        :return: ``None``.
+
+        `system_stream` is a standard system stream such as
+        ``sys.stdout``. `target_stream` is an open file object that
+        should replace the corresponding system stream object.
+
+        If `target_stream` is ``None``, defaults to opening the
+        operating system's null device and using its file descriptor.
+
+        """
+    if target_stream is None:
+        target_fd = os.open(os.devnull, os.O_RDWR)
+    else:
+        target_fd = target_stream.fileno()
+    os.dup2(target_fd, system_stream.fileno())
+
+
+def make_default_signal_map():
+    """ Make the default signal map for this system.
+
+        :return: A mapping from signal number to handler object.
+
+        The signals available differ by system. The map will not contain
+        any signals not defined on the running system.
+
+        """
+    name_map = {
+            'SIGTSTP': None,
+            'SIGTTIN': None,
+            'SIGTTOU': None,
+            'SIGTERM': 'terminate',
+            }
+    signal_map = dict(
+            (getattr(signal, name), target)
+            for (name, target) in name_map.items()
+            if hasattr(signal, name))
+
+    return signal_map
+
+
+def set_signal_handlers(signal_handler_map):
+    """ Set the signal handlers as specified.
+
+        :param signal_handler_map: A map from signal number to handler
+            object.
+        :return: ``None``.
+
+        See the `signal` module for details on signal numbers and signal
+        handlers.
+
+        """
+    for (signal_number, handler) in signal_handler_map.items():
+        signal.signal(signal_number, handler)
+
+
+def register_atexit_function(func):
+    """ Register a function for processing at program exit.
+
+        :param func: A callable function expecting no arguments.
+        :return: ``None``.
+
+        The function `func` is registered for a call with no arguments
+        at program exit.
+
+        """
+    atexit.register(func)
+
+
+def _chain_exception_from_existing_exception_context(exc, as_cause=False):
+    """ Decorate the specified exception with the existing exception context.
+
+        :param exc: The exception instance to decorate.
+        :param as_cause: If true, the existing context is declared to be
+            the cause of the exception.
+        :return: ``None``.
+
+        :PEP:`344` describes syntax and attributes (`__traceback__`,
+        `__context__`, `__cause__`) for use in exception chaining.
+
+        Python 2 does not have that syntax, so this function decorates
+        the exception with values from the current exception context.
+
+        """
+    (existing_exc_type, existing_exc, existing_traceback) = sys.exc_info()
+    if as_cause:
+        exc.__cause__ = existing_exc
+    else:
+        exc.__context__ = existing_exc
+    exc.__traceback__ = existing_traceback
+
+
+# Local variables:
+# coding: utf-8
+# mode: python
+# End:
+# vim: fileencoding=utf-8 filetype=python :