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https://issues.apache.org/jira/browse/FLINK-5929?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15897444#comment-15897444
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ASF GitHub Bot commented on FLINK-5929:
---------------------------------------
Github user aljoscha commented on the issue:
https://github.com/apache/flink/pull/3479
One quick initial remark: instead of each time having an anonymous inner
class for the `Context` you can create a reusable class for that like this:
```
class InternalProcessWindowContext<IN, OUT, KEY, W extends Window>
extends ProcessWindowFunction<IN, OUT, KEY, W>.Context {
W window;
InternalWindowFunction.InternalWindowContext internalContext;
InternalProcessWindowContext(ProcessWindowFunction<IN, OUT, KEY, W>
function) {
function.super();
}
@Override
public W window() {
return window;
}
@Override
public KeyedStateStore windowState() {
return internalContext.windowState();
}
@Override
public KeyedStateStore globalState() {
return internalContext.globalState();
}
}
```
The `function.super()` call in there makes it work even though `Context` is
itself defined as an inner abstract class of `ProcessWindowFunction`. It's a
bit of black magic and not really too well known, I think. 😉
> Allow Access to Per-Window State in ProcessWindowFunction
> ---------------------------------------------------------
>
> Key: FLINK-5929
> URL: https://issues.apache.org/jira/browse/FLINK-5929
> Project: Flink
> Issue Type: Improvement
> Components: DataStream API
> Reporter: Aljoscha Krettek
>
> Right now, the state that a {{WindowFunction}} or {{ProcessWindowFunction}}
> can access is scoped to the key of the window but not the window itself. That
> is, state is global across all windows for a given key.
> For some use cases it is beneficial to keep state scoped to a window. For
> example, if you expect to have several {{Trigger}} firings (due to early and
> late firings) a user can keep state per window to keep some information
> between those firings.
> The per-window state has to be cleaned up in some way. For this I see two
> options:
> - Keep track of all state that a user uses and clean up when we reach the
> window GC horizon.
> - Add a method {{cleanup()}} to {{ProcessWindowFunction}} which is called
> when we reach the window GC horizon that users can/should use to clean up
> their state.
> On the API side, we can add a method {{windowState()}} on
> {{ProcessWindowFunction.Context}} that retrieves the per-window state and
> {{globalState()}} that would allow access to the (already available) global
> state. The {{Context}} would then look like this:
> {code}
> /**
> * The context holding window metadata
> */
> public abstract class Context {
> /**
> * @return The window that is being evaluated.
> */
> public abstract W window();
> /**
> * State accessor for per-key and per-window state.
> */
> KeyedStateStore windowState();
> /**
> * State accessor for per-key global state.
> */
> KeyedStateStore globalState();
> }
> {code}
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