magicbus / magicbus / plugins /

"""Signal handling for the Process Bus."""

import os
import signal as _signal
import sys

from magicbus._compat import basestring

class SignalHandler(object):
    """Register bus channels (and listeners) for system signals.
    You can modify what signals your application listens for, and what it does
    when it receives signals, by modifying :attr:`SignalHandler.handlers`,
    a dict of {signal name: callback} pairs. The default set is::
        handlers = {'SIGTERM': self.bus.exit,
                    'SIGHUP': self.handle_SIGHUP,
                    'SIGUSR1': self.bus.graceful,
    The :func:`SignalHandler.handle_SIGHUP`` method calls
    if the process is daemonized, but
    if the process is attached to a TTY. This is because Unix window
    managers tend to send SIGHUP to terminal windows when the user closes them.
    Feel free to add signals which are not available on every platform. The
    :class:`SignalHandler` will ignore errors raised from attempting to register
    handlers for unknown signals.
    handlers = {}
    """A map from signal names (e.g. 'SIGTERM') to handlers (e.g. bus.exit)."""
    signals = {}
    """A map from signal numbers to names."""
    for k, v in vars(_signal).items():
        if k.startswith('SIG') and not k.startswith('SIG_'):
            signals[v] = k
    del k, v
    def __init__(self, bus):
        self.bus = bus
        # Set default handlers
        self.handlers = {'SIGTERM': self.bus.exit,
                         'SIGHUP': self.handle_SIGHUP,
                         'SIGUSR1': self.bus.graceful,

        if sys.platform[:4] == 'java':
            del self.handlers['SIGUSR1']
            self.handlers['SIGUSR2'] = self.bus.graceful
            self.bus.log("SIGUSR1 cannot be set on the JVM platform. "
                         "Using SIGUSR2 instead.")
            self.handlers['SIGINT'] = self._jython_SIGINT_handler

        self._previous_handlers = {}
    def _jython_SIGINT_handler(self, signum=None, frame=None):
        # See
        self.bus.log('Keyboard Interrupt: shutting down bus')
    def subscribe(self):
        """Subscribe self.handlers to signals."""
        for sig, func in self.handlers.items():
                self.set_handler(sig, func)
            except ValueError:
    def unsubscribe(self):
        """Unsubscribe self.handlers from signals."""
        for signum, handler in self._previous_handlers.items():
            signame = self.signals[signum]
            if handler is None:
                self.bus.log("Restoring %s handler to SIG_DFL." % signame)
                handler = _signal.SIG_DFL
                self.bus.log("Restoring %s handler %r." % (signame, handler))
                our_handler = _signal.signal(signum, handler)
                if our_handler is None:
                    self.bus.log("Restored old %s handler %r, but our "
                                 "handler was not registered." %
                                 (signame, handler), level=30)
            except ValueError:
                self.bus.log("Unable to restore %s handler %r." %
                             (signame, handler), level=40, traceback=True)
    def set_handler(self, signal, listener=None):
        """Subscribe a handler for the given signal (number or name).
        If the optional 'listener' argument is provided, it will be
        subscribed as a listener for the given signal's channel.
        If the given signal name or number is not available on the current
        platform, ValueError is raised.
        if isinstance(signal, basestring):
            signum = getattr(_signal, signal, None)
            if signum is None:
                raise ValueError("No such signal: %r" % signal)
            signame = signal
                signame = self.signals[signal]
            except KeyError:
                raise ValueError("No such signal: %r" % signal)
            signum = signal
        prev = _signal.signal(signum, self._handle_signal)
        self._previous_handlers[signum] = prev
        if listener is not None:
            self.bus.log("Listening for %s." % signame)
            self.bus.subscribe(signame, listener)
    def _handle_signal(self, signum=None, frame=None):
        """Python signal handler (self.set_handler subscribes it for you)."""
        signame = self.signals[signum]
        self.bus.log("Caught signal %s." % signame)
    def handle_SIGHUP(self):
        """Restart if daemonized, else exit."""
        if os.isatty(sys.stdin.fileno()):
            # not daemonized (may be foreground or background)
            self.bus.log("SIGHUP caught but not daemonized. Exiting.")
            self.bus.log("SIGHUP caught while daemonized. Restarting.")