It turns out kazoo always uses async:
http://kazoo.readthedocs.org/en/latest/_modules/kazoo/client.html#KazooClient.get
I tried calling "sync(path)", but it didn't help.
I believe that is used only to sync data between
zookeeper servers anyway (and I am trying it all
on a single, local server)
J.
On 05/13/2014 09:25 PM, Jacek Becla wrote:
> Serge at al,
>
> I am trying to implement code to avoid race conditions in zookeeper.
> I figured I'd create an ephemeral node "/LOCKS/<dbName>" and proceed
> with sensitive things only after creating such node successfully.
> However, I have the impression zookeeper will allow multiple jobs
> to create the same node, even in synchronous mode. Here is a test
> I'm using (see below), if I run it concurrently (just two instances),
> I'm typically seeing a collision (pasted below).
>
> Can you have a look, think about it, and let's discuss tomorrow.
> Thanks!
>
>
> ===================================
>
> import os
> import socket
> import time
> from random import randint
>
>
> from kazoo.client import KazooClient
> from kazoo.exceptions import NodeExistsError, NoNodeError
>
> def sleepABit():
> v = randint(1,100) / 1000.0
> print "sleep ", v
> time.sleep(v)
>
>
> def createIt(zk, k, v):
> while True:
> try:
> print "create ", v
> zk.create(k, v, ephemeral=True, makepath=True)
> except:
> print "create failed"
> sleepABit()
> finally:
> print "create ok"
> return
>
>
> k = "/LOCKS/x"
> zk = KazooClient(hosts="127.0.0.1:12181")
> zk.start()
>
> for i in range(0,100):
> v = str(socket.gethostbyname(socket.gethostname())) + '_' +
> str(os.getpid()) + '_' + str(i)
>
> createIt(zk, k, v)
>
> sleepABit()
>
> d, s = zk.get(k)
> print "got ", d
>
> print "delete"
> zk.delete(k)
>
> print "---"
>
>
> =====================
>
> create 141.142.225.179_8831_29
> create ok
> sleep 0.04
> got 141.142.225.179_8839_16
> delete
> Traceback (most recent call last):
> File "quickTest.py", line 45, in <module>
> zk.delete(k)
> File
> "/usr/local/home/becla/qserv/1/stack/Linux64/kazoo/1.3.1/lib/python/kazoo-1.3.1-py2.6.egg/kazoo/client.py",
> line 1159, in delete
> return self.delete_async(path, version).get()
> File
> "/usr/local/home/becla/qserv/1/stack/Linux64/kazoo/1.3.1/lib/python/kazoo-1.3.1-py2.6.egg/kazoo/handlers/threading.py",
> line 107, in get
> raise self._exception
> kazoo.exceptions.NoNodeError: ((), {})
>
>
> See? the node has pid 8831 and successfully created the node,
> but the other job (pid 8839) managed to create it OK as well
> before job with pid 8831 deleted it.
>
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