[jira] [Resolved] (FLINK-40524) LocalInputChannel.getNextBuffer takes the recoveredBuffers monitor on every buffer even when the channel never needed recovery

["Rui Fan (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-40524?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Rui Fan resolved FLINK-40524.
-----------------------------
    Fix Version/s: 2.4.0
       Resolution: Fixed

Merged to master(2.4.0) via: 9bd05c557c74c21e68faa6f5a11e47c6c513c025

> LocalInputChannel.getNextBuffer takes the recoveredBuffers monitor on every buffer even when the channel never needed recovery
> ------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: FLINK-40524
>                 URL: https://issues.apache.org/jira/browse/FLINK-40524
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Runtime / Checkpointing
>            Reporter: Rui Fan
>            Assignee: Rui Fan
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 2.4.0
>
>
> CDR added an unconditional `synchronized (recoveredBuffers)` to the local-consume hot path [1], but for channels built with `needsRecovery=false` (all local channels when CDR is off) `inRecovery` is always false and `recoveredBuffers` always empty, so the block is dead yet still costs a monitor acquire per buffer. Fix: since `needsRecovery` is final, gate the recovery block on it so the steady-state path skips the monitor entirely.
> [1] https://github.com/apache/flink/blob/76e774e04ff84ea305714153c5f4790fff98437c/flink-runtime/src/main/java/org/apache/flink/runtime/io/network/partition/consumer/LocalInputChannel.java#L566



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