Package org.apache.gobblin.util.callbacks

This package provides some simple instrumentation to handling callback execution.

See: Description

Class Summary

Class	Description
Callback<L,R>	A helper class to wrap a function and provide a name for logging purposes
CallbackResult<R>	A helper class to simplify the access the result of a callback (if any)
CallbacksDispatcher<L>	A helper to dispatch callbacks to a set of listeners.
CallbacksDispatcher.CallbackResults<L,R>

Package org.apache.gobblin.util.callbacks Description

This package provides some simple instrumentation to handling callback execution.

Listeners

Listeners are the object to which the callbacks are sent. This package does not impose too many restrictions on what listeners should look like. For a given CallbacksDispatcher, they should all implement the same interface.

Callbacks

Callbacks are represented as Function instances which take one L parameter, the listener to be applied on, and can return a result of type R. If no meaningful result is returned, R should be Void. There is a helper class Callback which allows to assign a meaningful string to the callback. Typically, this is the name of the callback and short description of any bound arguments.

Note that callback instances as defined above can't take any arguments to be passed to the listeners. They should be viewed as a binding of the actual callback method call to a specific set of arguments.

For example, if we want to define a callback void onNewJob(JobSpec newJob) to be sent to JobCatalogListener interface, we need:

• Define the NewJobCallback implements Callback
• In the constructor, the above class should take and save a parameter for the JobSpec.
• The apply method, should look something like input.onNewJob(this.newJob)

Callbacks Dispatcher

The CallbacksDispatcher is responsible for:

• Maintaining a list of listeners of type L.
• Dispatch callbacks invoked through CallbacksDispatcher.execCallbacks(com.google.common.base.Function) to each of the above listeners.
• Provide parallelism of the callbacks if necessary.
• Guarantee isolation of failures in callbacks.
• Provide logging for debugging purposes.
• Classify callback results in CallbacksDispatcher.CallbackResults for easier upstream processing.