logging: added QueueListener and documentation.
diff --git a/Doc/library/logging.rst b/Doc/library/logging.rst
index 04a1e5b..9aa4dbb 100644
--- a/Doc/library/logging.rst
+++ b/Doc/library/logging.rst
@@ -2651,12 +2651,18 @@
supports sending logging messages to a queue, such as those implemented in the
:mod:`queue` or :mod:`multiprocessing` modules.
+Along with the :class:`QueueListener` class, :class:`QueueHandler` can be used
+to let handlers do their work on a separate thread from the one which does the
+logging. This is important in Web applications and also other service
+applications where threads servicing clients need to respond as quickly as
+possible, while any potentially slow operations (such as sending an email via
+:class:`SMTPHandler`) are done on a separate thread.
.. class:: QueueHandler(queue)
Returns a new instance of the :class:`QueueHandler` class. The instance is
initialized with the queue to send messages to. The queue can be any queue-
- like object; it's passed as-is to the :meth:`enqueue` method, which needs
+ like object; it's used as-is by the :meth:`enqueue` method, which needs
to know how to send messages to it.
@@ -2688,8 +2694,80 @@
The :class:`QueueHandler` class was not present in previous versions.
+.. queue-listener:
+
+QueueListener
+^^^^^^^^^^^^^
+
+The :class:`QueueListener` class, located in the :mod:`logging.handlers`
+module, supports receiving logging messages from a queue, such as those
+implemented in the :mod:`queue` or :mod:`multiprocessing` modules. The
+messages are received from a queue in an internal thread and passed, on
+the same thread, to one or more handlers for processing.
+
+Along with the :class:`QueueHandler` class, :class:`QueueListener` can be used
+to let handlers do their work on a separate thread from the one which does the
+logging. This is important in Web applications and also other service
+applications where threads servicing clients need to respond as quickly as
+possible, while any potentially slow operations (such as sending an email via
+:class:`SMTPHandler`) are done on a separate thread.
+
+.. class:: QueueListener(queue, *handlers)
+
+ Returns a new instance of the :class:`QueueListener` class. The instance is
+ initialized with the queue to send messages to and a list of handlers which
+ will handle entries placed on the queue. The queue can be any queue-
+ like object; it's passed as-is to the :meth:`dequeue` method, which needs
+ to know how to get messages from it.
+
+ .. method:: dequeue(block)
+
+ Dequeues a record and return it, optionally blocking.
+
+ The base implementation uses ``get()``. You may want to override this
+ method if you want to use timeouts or work with custom queue
+ implementations.
+
+ .. method:: prepare(record)
+
+ Prepare a record for handling.
+
+ This implementation just returns the passed-in record. You may want to
+ override this method if you need to do any custom marshalling or
+ manipulation of the record before passing it to the handlers.
+
+ .. method:: handle(record)
+
+ Handle a record.
+
+ This just loops through the handlers offering them the record
+ to handle. The actual object passed to the handlers is that which
+ is returned from :meth:`prepare`.
+
+ .. method:: start()
+
+ Starts the listener.
+
+ This starts up a background thread to monitor the queue for
+ LogRecords to process.
+
+ .. method:: stop()
+
+ Stops the listener.
+
+ This asks the thread to terminate, and then waits for it to do so.
+ Note that if you don't call this before your application exits, there
+ may be some records still left on the queue, which won't be processed.
+
+.. versionadded:: 3.2
+
+The :class:`QueueListener` class was not present in previous versions.
+
.. _zeromq-handlers:
+Subclassing QueueHandler
+^^^^^^^^^^^^^^^^^^^^^^^^
+
You can use a :class:`QueueHandler` subclass to send messages to other kinds
of queues, for example a ZeroMQ "publish" socket. In the example below,the
socket is created separately and passed to the handler (as its 'queue')::
@@ -2716,6 +2794,7 @@
def __init__(self, uri, socktype=zmq.PUB, ctx=None):
self.ctx = ctx or zmq.Context()
socket = zmq.Socket(self.ctx, socktype)
+ socket.bind(uri)
QueueHandler.__init__(self, socket)
def enqueue(self, record):
@@ -2725,6 +2804,23 @@
def close(self):
self.queue.close()
+Subclassing QueueListener
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+You can also subclass :class:`QueueListener` to get messages from other kinds
+of queues, for example a ZeroMQ "subscribe" socket. Here's an example::
+
+ class ZeroMQSocketListener(QueueListener):
+ def __init__(self, uri, *handlers, **kwargs):
+ self.ctx = kwargs.get('ctx') or zmq.Context()
+ socket = zmq.Socket(self.ctx, zmq.SUB)
+ socket.setsockopt(zmq.SUBSCRIBE, '') # subscribe to everything
+ socket.connect(uri)
+
+ def dequeue(self):
+ msg = self.queue.recv()
+ return logging.makeLogRecord(json.loads(msg))
+
.. _formatter-objects:
Formatter Objects