zkpython: add_auth can deadlock the interpreter
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Key: ZOOKEEPER-1023
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1023
Project: ZooKeeper
Issue Type: Bug
Components: contrib-bindings
Affects Versions: 3.3.2
Reporter: Botond Hejj
Priority: Minor
Fix For: 3.4.0
If the add_auth method has a callback and we execute another command just after
it than we can deadlock the python api.
Example:
def deadlock(a, b):
pass
def watcher(zh, type, state, path):
if(state == zookeeper.CONNECTED_STATE):
zookeeper.add_auth(zh, 'test', 'test', deadlock)
zookeeper.get_children(zh, '/')
zh = zookeeper.init("np801c3n10:9221,np801c3n10:9331,np801c3n10:9441", watcher)
Looking at the code the problem looks like the following:
get_children sync call is running on the main thread and have the GIL it blocks
until the get_children finished. Meantime on the other thread the callback of
add_auth is called and that tries to get the GIL to call the python callback.
So this thread is waiting for the main thread to release the GIL but the main
thread is waiting for the other thread to process the reply of get_children.
I am not an expert on python binding but I think it can be solved if the GIL
would be release before synchronous c api calls.
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