1u0 commented on a change in pull request #8523: [FLINK-12481][runtime] Invoke
timer callback in task thread (via mailbox)
URL: https://github.com/apache/flink/pull/8523#discussion_r288254960
##########
File path:
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java
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@@ -1358,4 +1358,19 @@ public void actionsUnavailable() throws
InterruptedException {
mailbox.putMail(actionUnavailableLetter);
}
}
+
+ private class TimerInvocationContext implements
SystemProcessingTimeService.ScheduledCallbackExecutionContext {
Review comment:
I don't think that the mailbox is exposed to the
`SystemProcessingTimeService` at all here. On the contrary.
The `TimerInvocationContext` is in fact a "mailbox sender" (implementation
detail, that doesn't matter for the timer service). I'm not using the real
`MailboxSender` interface, because it would involve somehow adapting
`ProcessingTimeCallback` interface to `Runnable`. Or changing all implementers
of `ProcessingTimeCallback` to new api - this may be quite involving and may
conflict with others' changes.
Imo, things like `SystemProcessingTimeService` can be neutral about use
cases. The fact that it already had checkpoint lock and error handler callback,
I find as incidental, rather by design.
Having additional transformation of `ProcessingTimeCallback` in the time
service, into a mailbox letter (`Runnable`), would make things even more
coupled.
An alternative could be, that there are no newly introduced
`SystemProcessingTimeService.ScheduledCallbackExecutionContext`, but keeping
`SystemProcessingTimeService` implementation clean (not coupled with
`StreamTask`).
Add a proxy `ProcessingTimeService` implementation that would be exposed for
others to register timers, but upon registration, the proxy would register it's
own callback, which when fired, places the original `ProcessingTimeCallback` as
a letter into the mailbox.
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