[Zookeeper-developer] [ zookeeper-Patches-1937078 ] Passing a watch object to read requests

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Patches item #1937078, was opened at 2008-04-07 14:21
Message generated for change (Settings changed) made by phunt
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>Category: java client
>Group: 3.0.0
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Benjamin Reed (breed)
Assigned to: Benjamin Reed (breed)
Summary: Passing a watch object to read requests

Initial Comment:
When using a libraries for higher order synchronization primitives it gets hard to coordinate interests in watch events. It would be much more convenient if a Watcher object could be passed to the getData, getChildren, or exists methods.

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Comment By: Patrick Hunt (phunt)
Date: 2008-05-22 14:09

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Here's the patch, assigning to Ben for further review.

Please pay particular attention to the handling of state changes - I clear
the watch table when we are not sync'd to the server. Verify my workflow.

File Added: watcherobj.patch

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Comment By: Patrick Hunt (phunt)
Date: 2008-05-20 23:18

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I've implemented this for Java. I overloaded the respective methods with
signatures that take watcher object instead of watch boolean. I added new
methods rather than replacing -- this maintains b/w compatibility.

1) should I mark the old methods as deprecated or should we just support
both method types (newer signature w/ explicit watcher object && old watch
boolean which directs to the "global" watcher.)

2) I see this is listed as category "java client" so I'm assuming there is
no need for this feature in c code interface.


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Comment By: Patrick Hunt (phunt)
Date: 2008-05-20 17:52

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I was specifically referring to the client api, not the protocol -- should
I assume that that last watcher on a particular node "wins". What I mean is
if a client calls "getChildren(path, watcherobj1); getChildren(path,
watcherobj2);" (notice same patch) what should the client lib do? I'm
assuming use the last watcher, but wanted to verify.


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Comment By: Benjamin Reed (breed)
Date: 2008-05-19 19:05

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The client will need to track the multiple watcher objects to invoke when
it gets the callback. The client server protocol doesn't change, this is
just a client side thing. We should add the ability to remove watches as a
separate feature request.

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Comment By: Patrick Hunt (phunt)
Date: 2008-05-14 00:21

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What should we do if the user calls getData multiple times with different
watcher objects? Remove previous watch and replace with new watcher, throw
error, or allow multiple watchers on particular node? How about removing a
watch by calling method on particular node with null watcher?


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