[FLINK-40524][network] Skip the recoveredBuffers monitor on the getNextBuffer hot path for channels that never recover

[1996fanrui]

What is the purpose of the change

LocalInputChannel.getNextBuffer() always entered synchronized (recoveredBuffers) to check recovery
state, even for channels that never needed recovery (where inRecovery is always false and
recoveredBuffers always empty, so the block is dead). needsRecovery is a final field, so gating the
recovery block on it lets steady-state non-recovery channels skip the monitor on the hot path.

Brief change log

• [FLINK-40524] Wrap the recovery block in LocalInputChannel#getNextBuffer in an if (needsRecovery) gate so channels that never recover skip the recoveredBuffers monitor.

Verifying this change

This change is a trivial rework / code cleanup without any test coverage. Behavior is identical when
needsRecovery is true; the only change is the added gate (the wrapped block is reindented accordingly).

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): yes (removes a lock acquisition on the getNextBuffer hot path)
• Anything that affects deployment or recovery: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

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CI report:

• bc80c80 Azure: SUCCESS

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[1996fanrui]

FYI: just wrap inRecovery with if (needsRecovery) {