sysvitals/api/db.py

import contextlib

import gevent.queue
from gevent.socket import wait_read, wait_write
import psycopg2
import psycopg2.extensions
import psycopg2.extras

def gevent_wait_callback(conn, timeout=None):
	# https://github.com/zacharyvoase/gevent-psycopg2/blob/master/lib/gevent_psycopg2.py
	while True:
		state = conn.poll()
		if state == psycopg2.extensions.POLL_OK:
			break
		elif state == psycopg2.extensions.POLL_READ:
			wait_read(conn.fileno(), timeout=timeout)
		elif state == psycopg2.extensions.POLL_WRITE:
			wait_write(conn.fileno(), timeout=timeout)
		else:
			raise psycopg2.OperationalError('unhandled state: %r' % state)

psycopg2.extensions.set_wait_callback(gevent_wait_callback)

pool = gevent.queue.Queue(maxsize=4)
for _ in xrange(4):
	pool.put(psycopg2.connect('dbname=%s user=%s' % ('sysvitals', 'sysvitals')))

@contextlib.contextmanager
def cursor(): # https://code.google.com/p/gevent/source/browse/examples/psycopg2_pool.py?name=1.0b4#88
	conn = pool.get(timeout=1)
	try:
		yield conn.cursor(cursor_factory=psycopg2.extras.DictCursor)
	except:
		if not conn.closed:
			try:
				conn.rollback()
			except:
				gevent.get_hub().handle_error(conn, *sys.exc_info())
		raise
	else:
		conn.commit()
	finally:
		if conn.closed:
			raise Exception('cursor context manager got back closed connection')
		pool.put_nowait(conn)

def query_one(cur, sql, *args):
	cur.execute(sql, args)
	rval = cur.fetchone()
	if cur.fetchone() is not None:
		raise Exception('got more than one value for query', sql, args)
	return rval

def create_server(group_id, hostname):
	with cursor() as cur:
		server_id = query_one(cur, 'INSERT INTO servers (group_id, hostname) VALUES(%s, %s) RETURNING id',
				group_id, hostname)[0]
	return server_id