[fix][broker] Fix get owned service units NPE

[Demogorgon314]

Motivation

When using KoP protocol, the KoP will NamespaceService#addNamespaceBundleOwnershipListener before the broker start, however, at this time, the ExtensibleLoadManagerImpl not start yet. So it will cause NPE.

We should return an empty set when ExtensibleLoadManagerImpl does not start.

Modifications

• Add a check when getOwnedServiceUnits.
• Add units test to cover this case.

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

[Demogorgon314]

@heesung-sn Please help review this PR

[codecov-commenter]

Codecov Report

Merging #20625 (dfaa8f9) into master (677d160) will increase coverage by 41.11%.
The diff coverage is 100.00%.

@@              Coverage Diff              @@
##             master   #20625       +/-   ##
=============================================
+ Coverage     31.93%   73.04%   +41.11%     
- Complexity    11779    31998    +20219     
=============================================
  Files          1498     1867      +369     
  Lines        114595   138663    +24068     
  Branches      12428    15237     +2809     
=============================================
+ Hits          36591   101290    +64699     
+ Misses        73158    29354    -43804     
- Partials       4846     8019     +3173     

Flag	Coverage Δ
inttests	24.13% <0.00%> (?)
systests	24.87% <0.00%> (?)
unittests	72.34% <100.00%> (+40.41%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...dbalance/extensions/ExtensibleLoadManagerImpl.java	78.62% <100.00%> (+76.50%)	⬆️

... and 1552 files with indirect coverage changes

[tisonkun]

Looks good.

... while I wonder what the caller does after get an empty set from getOwnedServiceUnits? Retry?

[tisonkun]

Merging...

[Demogorgon314]

@tisonkun

    public void addNamespaceBundleOwnershipListener(NamespaceBundleOwnershipListener... listeners) {
        Objects.requireNonNull(listeners);
        for (NamespaceBundleOwnershipListener listener : listeners) {
            if (listener != null) {
                bundleOwnershipListeners.add(listener);
            }
        }
        getOwnedServiceUnits().forEach(bundle -> notifyNamespaceBundleOwnershipListener(bundle, listeners)); // <-- caller
    }

If the load manager has not started yet, it means we don’t have any ownership in the current broker, so it is fine to get an empty set here. After the load manager starts and has owned the bundle, it will notify all the listeners when they have ownership acquired by the current broker.

[tisonkun]

@Demogorgon314 Thanks for your explanation!