Author: darcy
Date: Sat Jan 5 10:19:44 2013
New Revision: 487
Log:
Add pgnotify method.
Modified:
trunk/module/pg.py
Modified: trunk/module/pg.py
==============================================================================
--- trunk/module/pg.py Sat Jan 5 10:19:07 2013 (r486)
+++ trunk/module/pg.py Sat Jan 5 10:19:44 2013 (r487)
@@ -18,6 +18,8 @@
"""
+import select
+
from _pg import *
try:
frozenset
@@ -126,9 +128,79 @@
"""Returns ProgrammingError."""
return _db_error(msg, ProgrammingError)
+class pgnotify(object):
+ """A PostgreSQL client-side asynchronous notification handler."""
-# The PostGreSQL database connection interface:
+ def __init__(self, pgconn, event, callback, arg_dict={}, timeout=None):
+ """
+ pgconn - PostgreSQL connection object.
+ event - Event to LISTEN for.
+ callback - Event callback.
+ arg_dict - A dictionary passed as the argument to the callback.
+ timeout - Timeout in seconds; a floating point number denotes
+ fractions of seconds. If it is absent or None, the
+ callers will never time out."""
+
+ self.pgconn = pgconn
+ self.event = event
+ self.stop = 'stop_%s' % event
+ self.callback = callback
+ self.arg_dict = arg_dict
+ self.timeout = timeout
+ def __del__(self):
+ try:
+ self.pgconn.query('unlisten "%s"' % self.event)
+ self.pgconn.query('unlisten "%s"' % self.stop)
+ except pg.DatabaseError:
+ pass
+
+ def __call__(self):
+ """
+ Invoke the handler.
+ The handler actually LISTENs for two NOTIFY messages:
+
+ <event> and stop_<event>.
+
+ When either of these NOTIFY messages are received, its associated
+ 'pid' and 'event' are inserted into <arg_dict>, and the callback is
+ invoked with <arg_dict>. If the NOTIFY message is stop_<event>, the
+ handler UNLISTENs both <event> and stop_<event> and exits."""
+
+ self.pgconn.query('listen "%s"' % self.event)
+ self.pgconn.query('listen "%s"' % self.stop)
+ _ilist = [self.pgconn.fileno()]
+
+ while 1:
+ ilist, olist, elist = select.select(_ilist, [], [], self.timeout)
+ if ilist == []:
+ # We timed out.
+ self.pgconn.query('unlisten "%s"' % self.event)
+ self.pgconn.query('unlisten "%s"' % self.stop)
+ self.callback(None)
+ return
+ else:
+ notice = self.pgconn.getnotify()
+ if notice is None:
+ continue
+ event, pid, extra = notice
+ if event in (self.event, self.stop):
+ self.arg_dict['pid'] = pid
+ self.arg_dict['event'] = event
+ self.callback(self.arg_dict)
+ if event == self.stop:
+ self.pgconn.query('unlisten "%s"' % self.event)
+ self.pgconn.query('unlisten "%s"' % self.stop)
+ return
+ else:
+ self.pgconn.query('unlisten "%s"' % self.event)
+ self.pgconn.query('unlisten "%s"' % self.stop)
+ raise pgnotifyError, \
+ 'listening for ("%s", "%s") but notified of "%s"' \
+ % (self.event, self.stop, event)
+
+
+# The PostGreSQL database connection interface:
class DB(object):
"""Wrapper class for the _pg connection type."""
@@ -838,6 +910,8 @@
self._do_debug(q + " %% %r" % (params,))
return int(self.db.query(q, params))
+ def pgnotify(self, event, callback, arg_dict={}, timeout=None):
+ return pgnotify(self.db, event, callback, arg_dict, timeout)
# if run as script, print some information
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