192 lines
6.5 KiB
Python
192 lines
6.5 KiB
Python
# Copyright 2017 Mycroft AI Inc.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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#
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from signal import getsignal, signal, SIGKILL, SIGINT, SIGTERM, \
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SIG_DFL, default_int_handler, SIG_IGN # signals
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import os # Operating System functions
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#
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# Wrapper around chain of handler functions for a specific system level signal.
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# Often used to trap Ctrl-C for specific application purposes.
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from mycroft.util import LOG
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class Signal: # python 3+ class Signal
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"""
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Capture and replace a signal handler with a user supplied function.
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The user supplied function is always called first then the previous
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handler, if it exists, will be called. It is possible to chain several
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signal handlers together by creating multiply instances of objects of
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this class, providing a different user functions for each instance. All
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provided user functions will be called in LIFO order.
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"""
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#
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# Constructor
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# Get the previous handler function then set the passed function
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# as the new handler function for this signal
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def __init__(self, sig_value, func):
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"""
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Create an instance of the signal handler class.
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sig_value: The ID value of the signal to be captured.
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func: User supplied function that will act as the new signal handler.
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"""
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super(Signal, self).__init__() # python 3+ 'super().__init__()
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self.__sig_value = sig_value
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self.__user_func = func # store user passed function
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self.__previous_func = signal(sig_value, self)
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self.__previous_func = { # Convert signal codes to functions
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SIG_DFL: default_int_handler,
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SIG_IGN: lambda a, b: None
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}.get(self.__previous_func, self.__previous_func)
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#
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# Called to handle the passed signal
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def __call__(self, signame, sf):
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"""
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Allows the instance of this class to be called as a function.
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When called it runs the user supplied signal handler than
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checks to see if there is a previously defined handler. If
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there is a previously defined handler call it.
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"""
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self.__user_func()
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self.__previous_func(signame, sf)
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#
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# reset the signal handler
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def __del__(self):
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"""
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Class destructor. Called during garbage collection.
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Resets the signal handler to the previous function.
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"""
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signal(self.__sig_value, self.__previous_func)
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# End class Signal
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# ----------------------------------------------------------------------------
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# ----------------------------------------------------------------------------
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#
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# Create, delete and manipulate a PID file for this service
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# ------------------------------------------------------------------------------
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class Lock: # python 3+ 'class Lock'
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"""
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Create and maintains the PID lock file for this application process.
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The PID lock file is located in /tmp/mycroft/*.pid. If another process
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of the same type is started, this class will 'attempt' to stop the
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previously running process and then change the process ID in the lock file.
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"""
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#
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# Class constants
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DIRECTORY = '/tmp/mycroft'
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FILE = '/{}.pid'
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#
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# Constructor
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def __init__(self, service):
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"""
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Builds the instance of this object. Holds the lock until the
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object is garbage collected.
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service: Text string. The name of the service application
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to be locked (ie: skills, voice)
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"""
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super(Lock, self).__init__() # python 3+ 'super().__init__()'
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self.__pid = os.getpid() # PID of this application
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self.path = Lock.DIRECTORY + Lock.FILE.format(service)
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self.set_handlers() # set signal handlers
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self.create()
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#
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# Reset the signal handlers to the 'delete' function
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def set_handlers(self):
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"""
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Trap both SIGINT and SIGTERM to gracefully clean up PID files
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"""
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self.__handlers = {SIGINT: Signal(SIGINT, self.delete),
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SIGTERM: Signal(SIGTERM, self.delete)}
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#
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# Check to see if the PID already exists
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# If it does exits perform several things:
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# Stop the current process
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# Delete the exiting file
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def exists(self):
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"""
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Check to see if the PID lock file currently exists. If it does
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than send a SIGTERM signal to the process defined by the value
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in the lock file. Catch the keyboard interrupt exception to
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prevent propagation if stopped by use of Ctrl-C.
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"""
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if not os.path.isfile(self.path):
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return
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with open(self.path, 'r') as L:
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try:
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os.kill(int(L.read()), SIGKILL)
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except Exception as E:
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pass
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#
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# Create a lock file for this server process
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def touch(self):
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"""
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If needed, create the '/tmp/mycroft' directory than open the
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lock file for writting and store the current process ID (PID)
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as text.
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"""
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if not os.path.exists(Lock.DIRECTORY):
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os.makedirs(Lock.DIRECTORY)
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with open(self.path, 'w') as L:
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L.write('{}'.format(self.__pid))
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#
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# Create the PID file
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def create(self):
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"""
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Checks to see if a lock file for this service already exists,
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if so have it killed. In either case write the process ID of
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the current service process to to the existing or newly created
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lock file in /tmp/mycroft/
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"""
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self.exists() # check for current running process
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self.touch()
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#
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# Delete the PID file - but only if it has not been overwritten
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# by a duplicate service application
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def delete(self, *args):
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"""
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If the PID lock file contains the PID of this process delete it.
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*args: Ignored. Required as this fuction is called as a signel
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handler.
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"""
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try:
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with open(self.path, 'r') as L:
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pid = int(L.read())
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if self.__pid == pid:
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os.unlink(self.path)
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except IOError:
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pass
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# End class Lock
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