Geografic-Information-System/lib/python/pygrass/rpc/base.py

# -*- coding: utf-8 -*-
"""
Fast and exit-safe interface to PyGRASS Raster and Vector layer
using multiprocessing

(C) 2015 by the GRASS Development Team
This program is free software under the GNU General Public
License (>=v2). Read the file COPYING that comes with GRASS
for details.

:authors: Soeren Gebbert
"""

from grass.exceptions import FatalError
import time
import threading
import sys
from multiprocessing import Process, Lock, Pipe
import logging

###############################################################################

def dummy_server(lock, conn):
    """Dummy server process

       :param lock: A multiprocessing.Lock
       :param conn: A multiprocessing.Pipe
    """

    while True:
        # Avoid busy waiting
        conn.poll(None)
        data = conn.recv()
        lock.acquire()
        if data[0] == 0:
            conn.close()
            lock.release()
            sys.exit()
        if data[0] == 1:
            raise Exception("Server process intentionally killed by exception")
        lock.release()

class RPCServerBase(object):
    """This is the base class for send and receive RPC server
       It uses a Pipe for IPC.
    
    
        >>> import grass.script as gscript
        >>> from grass.pygrass.rpc.base import RPCServerBase
        >>> provider = RPCServerBase()
        
        >>> provider.is_server_alive()
        True
        
        >>> provider.is_check_thread_alive()
        True

        >>> provider.stop()
        >>> provider.is_server_alive()
        False
        
        >>> provider.is_check_thread_alive()
        False
        
        >>> provider = RPCServerBase()
        >>> provider.is_server_alive()
        True
        >>> provider.is_check_thread_alive()
        True
        
        Kill the server process with an exception, it should restart
        
        >>> provider.client_conn.send([1])
        >>> provider.is_server_alive()
        True
        
        >>> provider.is_check_thread_alive()
        True

    """
    
    def __init__(self):
        self.client_conn = None
        self.server_conn = None
        self.queue = None
        self.server = None
        self.checkThread = None
        self.threadLock = threading.Lock()
        self.start_server()
        self.start_checker_thread()
        self.stopThread = False
        
    def is_server_alive(self):
        return self.server.is_alive()
    
    def is_check_thread_alive(self):
        return self.checkThread.is_alive()

    def start_checker_thread(self):
        if self.checkThread is not None and self.checkThread.is_alive():
            self.stop_checker_thread()

        self.checkThread = threading.Thread(target=self.thread_checker)
        self.checkThread.daemon = True
        self.stopThread = False
        self.checkThread.start()

    def stop_checker_thread(self):
        self.threadLock.acquire()
        self.stopThread = True
        self.threadLock.release()
        self.checkThread.join(None)

    def thread_checker(self):
        """Check every 200 micro seconds if the server process is alive"""
        while True:
            time.sleep(0.2)
            #sys.stderr.write("Check server process\n")
            self._check_restart_server()
            self.threadLock.acquire()
            if self.stopThread == True:
                #sys.stderr.write("Stop thread\n")
                self.threadLock.release()
                return
            self.threadLock.release()

    def start_server(self):
        """This function must be re-implemented in the subclasses
        """
        self.client_conn, self.server_conn = Pipe(True)
        self.lock = Lock()
        self.server = Process(target=dummy_server, args=(self.lock,
                                                             self.server_conn))
        self.server.daemon = True
        self.server.start()

    def check_server(self):
        self._check_restart_server()

    def _check_restart_server(self):
        """Restart the server if it was terminated
        """
        self.threadLock.acquire()
        if self.server.is_alive() is True:
            self.threadLock.release()
            return
        self.client_conn.close()
        self.server_conn.close()
        self.start_server()

        logging.warning("Needed to restart the libgis server")

        self.threadLock.release()

    def safe_receive(self, message):
        """Receive the data and throw an FatalError exception in case the server
           process was killed and the pipe was closed by the checker thread"""
        try:
            ret = self.client_conn.recv()
            if isinstance(ret,  FatalError):
               raise FatalError()
            return ret
        except (EOFError,  IOError,  FatalError):
            # The pipe was closed by the checker thread because
            # the server process was killed
            raise FatalError(message)

    def stop(self):
        """Stop the check thread, the libgis server and close the pipe

           This method should be called at exit using the package atexit
        """
        #sys.stderr.write("###### Stop was called\n")
        self.stop_checker_thread()
        if self.server is not None and self.server.is_alive():
            self.client_conn.send([0, ])
            self.server.join()
        if self.client_conn is not None:
            self.client_conn.close()


if __name__ == "__main__":
    import doctest
    doctest.testmod()