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# -*- coding: utf-8 -*- |
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"""Defines a class to read from a queue and write to a writer plugin. |
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.. moduleauthor:: Kenny Freeman <[email protected]> |
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""" |
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__author__ = 'Kenny Freeman' |
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__email__ = '[email protected]' |
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__license__ = "ISCL" |
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__docformat__ = 'reStructuredText' |
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import time |
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import Queue |
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import random |
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import threading |
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import traceback |
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import plumd |
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import plumd.util |
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class PluginReader(object): |
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"""Reads from a plugin instance by calling pobj.poll() and writes |
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to a list of PluginWriters by calling <writerobj>.queue.put() - loops |
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on a configured interval. |
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:param log: A logger |
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:type log: logging.get_logger() |
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:param pobj: An instance of a Reader plugin. |
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:type pobj: Reader |
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:param pname: The configured name of the plugin. |
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:type pname: str |
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:param interval: The conigured polling interval for thep plugin. |
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:type interval: int |
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:raises: ConfigError, PluginLoadError |
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""" |
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def __init__(self, log, pobj, pname): |
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"""Reads from a plugin instance by calling pobj.poll() and writes |
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to a list of PluginWriters by calling <writerobj>.queue.put() - loops |
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on a configured interval. |
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:param log: A logger |
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:type log: structlog.get_logger() |
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:param pobj: An instance of a Reader plugin. |
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:type pobj: Reader |
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:param pname: The configured name of the plugin. |
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:type pname: str |
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:raises: ConfigError, PluginLoadError |
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""" |
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self.log = log |
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# poll() interval - get from plugins configuration |
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self.interval = pobj.config.get('poll.interval') |
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self._name = pname |
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self.pobj = pobj |
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# what writers should we write metrics to? |
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self.writers = [] |
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# thread that polls for metrics and writes to writers |
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self.thread = None |
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self.stop_evt = threading.Event() |
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@property |
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def name(self): |
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"""Simply return our configured name. |
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:rtype: str |
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""" |
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return self._name |
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def onstart(self): |
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"""Call the plugins onstart function.""" |
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try: |
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self.pobj.onstart() |
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except Exception as e: |
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tb = traceback.format_exc() |
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msg = "read: disabling reader {0}: exception in onstart: {1}: {2}" |
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self.log.error(msg.format(self._name, e, tb)) |
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return |
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View Code Duplication |
def poll(self): |
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"""Calls the plugins poll() function and either returns a valid |
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:class:`plumd.ResultSet` or None. |
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:rtype: plumd.ResultSet |
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""" |
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rset = None |
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# plugins can raise pretty much any exception, wrap in catch all try |
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try: |
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rset = self.pobj.poll() |
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# ensure the result set is valid, if not set it to an empty one |
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if rset is None or not isinstance(rset, plumd.ResultSet): |
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msg = "read: invalid result set from reader {0}: {1}" |
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self.log.error(msg.format(self._name, rset)) |
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rset = plumd.ResultSet() |
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except Exception as e: |
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# print a traceback and ensure the reader thread exits |
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tb = traceback.format_exc() |
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msg="read: disabling reader {0} due to exception in poll: {1} : {2}" |
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self.log.error(msg.format(self._name, e, tb)) |
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self.stop_evt.set() |
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rset = plumd.ResultSet() |
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return rset |
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def write(self, rset, lint): |
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"""Iterates through each writer plugin and writes the |
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:class:`plumd.ResultSet` to the writers input queue. Uses a |
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:class:`plumd.utils.Interval` to determine if it will block when |
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pushing to a writers queue. If there is time remaining in the current |
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poll interval it will block. Also, if a writers queue is full it will |
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drop the metric for that writer. Future versions may use persistance |
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to queue result sets to disk if the backend metrics services are down. |
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:param rset: a result set from a plugin poll() call. |
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:type rset: plumd.ResultSet |
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:param lint: an interval helper. |
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:type lint: plumd.util.Interval |
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""" |
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# only send result sets that have metrics |
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if rset.nresults < 1: |
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return |
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# enqueue onto each writers queue, wait for any remaining time |
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for wobj in self.writers: |
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try: |
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# allow queue puts to block for a short time |
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# this cannot block for long as it will also block shutdown |
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wobj.queue.put(rset, block=True, timeout=1) |
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except Queue.Full: |
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msg = "read: {0}: dropping metrics: writer plugin queue full: {1}" |
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self.log.warn(msg.format(self._name, wobj.name)) |
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def read(self): |
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"""Calls the plugins onstart() function and then iterates over the |
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plugins poll() function, pushing the result to each writer queue.""" |
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self.onstart() |
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## distribute metrics - don't everyone flood all at once |
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time.sleep(random.randrange(int(self.pobj.config.get('delay.poll')))) |
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# loop on calling the plugin objects poll and sending to writers |
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while not self.stop_evt.is_set(): |
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# loop every self.interval seconds |
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with plumd.util.Interval(self.interval, self.stop_evt) as lint: |
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if self.stop_evt.is_set(): |
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break |
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rset = self.poll() |
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self.write(rset, lint) |
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# warn if loop time exceeded |
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if lint.remaining < 0: |
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msg = "read: {0} reader loop time exceeded" |
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self.log.warn(msg.format(self._name)) |
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self.onstop() |
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def start(self): |
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"""Calls pobj.onstart() and starts a thread to poll() metrics.""" |
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self.thread = threading.Thread(target=self.read, group=None) |
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self.thread.start() |
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def stop(self): |
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"""Stops the poll() thread and calls pobj.onstop().""" |
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# set the stop event and the self.read thread falls through. |
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self.stop_evt.set() |
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def onstop(self): |
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"""Calls the plugins onstop callable.""" |
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# this can raise pretty much any exception |
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try: |
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self.pobj.onstop() |
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except Exception as e: |
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tb = traceback.format_exc() |
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msg = "read: exception during onstop for reader {0}: {1}: {2}" |
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self.log.error(msg.format(self._name, e, tb)) |
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def join(self, timeout): |
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"""Joins our thread.""" |
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if self.thread: |
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self.thread.join() |
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def __del__(self): |
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"""Logs __del__ calls.""" |
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self.log.debug("read: del: {0}".format(self._name)) |
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s4z /
plumd
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