Twisted will not send data back only if I use async DB ops - redis

Question

After struggling with inlineCallbacks and yield of twisted/txredisapi, I can save my data into redis. Thanks to author of txredisapi. Now I met a new issue, socket server will not send back to client before/after saving into DB.
Twisted offers simple socket server as following:
from twisted.internet import protocol, reactor
class Echo(protocol.Protocol):
def dataReceived(self, data):
self.transport.write(data) ### write back
class EchoFactory(protocol.Factory):
def buildProtocol(self, addr):
return Echo()
reactor.listenTCP(8000, EchoFactory)
recctor.run()
My code is similiar, only with additional DB ops.
#!/usr/bin/env python
import time
import binascii
import txredisapi
from twisted.internet import defer
from twisted.internet import protocol, reactor
from twisted.internet.protocol import Factory
from twisted.enterprise import adbapi
from twisted.python import log
from dmpack import Dmpack
from dmdb import Dmdb
from dmconfig import DmConf
dm = Dmpack()
conf = DmConf().loadConf()
rcs = txredisapi.lazyConnection(password=conf['RedisPassword'])
dbpool = adbapi.ConnectionPool("MySQLdb",db=conf['DbName'],user=conf['DbAccount'],\
passwd=conf['DbPassword'],host=conf['DbHost'],\
use_unicode=True,charset=conf['DbCharset'])
def getDataParsed(data):
realtime = None
period = None
self.snrCode = dm.snrToAscii(data[2:7])
realtime = data[7:167] # save it into redis
period = data[167:-2] # save it into SQL
return (snrCode, realtime, period)
class PlainTCP(protocol.Protocol):
def __init__(self, factory):
self.factory = factory
self.factory.numConnections = 0
self.snrCode = None
self.rData = None
self.pData = None
self.err = None
def connectionMade(self):
self.factory.numConnections += 1
print "Nr. of connections: %d\n" %(self.factory.numConnections)
self.transport.write("Hello remote\r\n") # it only prints very 5 connections.
def connectionLost(self, reason):
self.factory.numConnections -= 1
print "Nr. of connections: %d\n" %(self.factory.numConnections)
#defer.inlineCallbacks
def dataReceived(self, data):
global dbpool, rcs
(self.snrCode,rDat,pDat) = getDataParsed(data)
if self.snrCode == None or rDat == None or pDat == None:
err = "Bad format"
else:
err = "OK"
print "err:%s"%(err) # debug print to show flow control
self.err = err
self.transport.write(self.snrCode)
self.transport.write(self.err)
self.transport.write(rDat)
self.transport.write(pDat)
self.transport.loseConnection()
if self.snrCode != None and rDat != None and pDat != None:
res = yield self.saveRealTimeData(rcs, rDat)
res = yield self.savePeriodData(dbpool, pDat, conf)
print "err2:%s"%(err) # debug print to show flow control
#defer.inlineCallbacks
def saveRealTimeData(self, rc, dat):
key = "somekey"
val = "somedata"
yield rc.set(key,val)
yield rc.expire(key,30)
#defer.inlineCallbacks
def savePeriodData(self,rc,dat,conf):
query = "some SQL statement"
yield rc.runQuery(query)
class PlainTCPFactory(protocol.Factory):
def buildProtocol(self, addr):
return PlainTCP(self)
def main():
dmdb = Dmdb()
if not dmdb.detectDb():
print "Please run MySQL RDBS first."
sys.exit()
log.startLogging(sys.stdout)
reactor.listenTCP(8080, PlainTCPFactory())
reactor.run()
if __name__ == "__main__":
main()
And clip of my client, which is a simple client:
def connectSend(host="127.0.0.1",port=8080):
global packet
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try:
s.connect((host, port))
s.sendall(''.join(packet))
data = s.recv(1024)
s.close()
print 'Received', repr(data)
except socket.error, err:
print "Remote socket is not available: %s"%str(err)
sys.exit(1)
The current status is:
If disable #defer.inlineCallbacks and yield opertions of dataReceived(), both self.transport.write() inside of connectionMode() and dataReceived() can output data to clients.
If we enabled #defer.inlineCallbacks and two yield DB ops of SQL/Redis, then self.transport.write() inside of connectionMode() prints every 5 connections, and dataReceived() will not output any data to clients.
the debug print statements will print on log regardless of #defer.inlineCallbacks anyway.
I was told that dataReceived() should not be #defer.inlineCallbacks. But it doesn't change anything if I removed that decoration.
I am thinking if gevent can help me out of this unpredicted behavior. I am twisted into an endless tornado, cyclone .....
Anyone who has similiar experience, please help me. Thanks.

Answer 1

By changing function as following, the code works.
#COMMENT OUT decorator of #defer.inlineCallbacks
def dataReceived(self, data):
global dbpool, rcs
(self.snrCode,rDat,pDat) = getDataParsed(data)
if self.snrCode == None or rDat == None or pDat == None:
err = "Bad format"
else:
err = "OK"
print "err:%s"%(err) # debug print to show flow control
self.err = err
self.transport.write(self.snrCode)
self.transport.write(self.err)
self.transport.write(rDat)
self.transport.write(pDat)
self.transport.loseConnection()
if self.snrCode != None and rDat != None and pDat != None:
self.saveRealTimeData(rcs, rDat)
self.savePeriodData(dbpool, pDat, conf)
# Removing yield before DB ops
print "err2:%s"%(err) # debug print to show flow control
#defer.inlineCallbacks
def saveRealTimeData(self, rc, dat):
print "saveRedis"
key = "somekey"
val = "somedata"
yield rc.set(key,val)
yield rc.expire(key,30)
#defer.inlineCallbacks
def savePeriodData(self,rc,dat,conf):
print "save SQL"
query = "some SQL statement"
yield rc.runQuery(query)
If we keep #defer.inlineCallbacks and yield in dataReceived. The connection is closed before second DB op. Therefore no data is output to connection. Maybe is caused by inlineCallbacks decorator.
By removing this, the flow control is simple and straightforward.
However, I still can get why I can not add inlineCallbacks if there are two deferred DB ops. This time they don't need deferred?