I am using node-zookeeper-client for java script as a zookeeper client.
I have something like this:
const setWatch = (path, functionToExecuteOnTrigger) => {
client.getData(path, (event) => {
// watcher set here
functionToExecuteOnTrigger(event);
}, null)
// null because we are only setting watch here and do not need data
}
This function will set a watch at a path in the zookeeper. Once a watch is triggered, the watcher callback will be called and an appropriate function to be called on the watch is called.
for watches set like this:
setWatch('/data1', function1);
setWatch('/data2', function2);
so function1 is executed for watch triggered in data1 node and function2 executed for watch triggered in data2 node
Now if I have to continuously keep watch at the nodes so that each time something is changed, I would have to re-register the watches immediately after they are triggered:
const setWatch = (path, functionToExecuteOnTrigger) => {
client.getData(path, (event) => {
// watcher set here
// immediately set another watch for the same function
setWatch(path, functionToExecuteOnTrigger);
functionToExecuteOnTrigger(event);
}, null)
// null because we are only setting watch here and do not need data
}
Now the things I know about zookeeper watches are:
- There are 3 types of watches; data, children and exist
- Watchers are one time trigger, i.e. once they are triggered, one has to re-register them to obtain further triggers.
Because of the 2nd point mentioned above, there is a chance of missing changes that occur between the period of watch triggered and re-registering the watch. As mentioned in the official documentation of zookeeper.
So I was wondering if there is a way in which we could actually set multiple watches for the same node (in a queue sort of way) and for each time a watch is triggered, only a single trigger callback is called. Something like this:
setWatch(node, functionToTrigger, noOfWatchesInQueue)
So we will be setting multiple watch for the same node and for a trigger, only one of those set watches are triggered. Hence, if I set 3 watches in queue for the same node i.e
for trigger 1, watch1 is activated
for trigger 2, watch 2 and so on...
That way no event is missed during the time taken to re-register the watch.
Is there a way to obtain this ?? I do not know if this is already been done somewhere, any kind of research material or implementations regarding the issue would be helpful as well.