waterWang opened a new pull request, #1306:
URL: https://github.com/apache/curator/pull/1306
## Summary
When a `CuratorCache` is built with the `SINGLE_NODE_CACHE` option, only one
node is ever cached (the root path). Today the cache still uses a
`ConcurrentHashMap`-backed `StandardCuratorCacheStorage`, which is overkill and
wastes memory for this case. This PR adds a dedicated
`SingleNodeCuratorCacheStorage` implementation backed by a single
`AtomicReference` and switches the default storage selection to it whenever
`SINGLE_NODE_CACHE` is set.
Fixes #1304
## Changes
- **New `SingleNodeCuratorCacheStorage`** — implements `CuratorCacheStorage`
with a single `AtomicReference<ChildData>`. All interface methods (`put`,
`remove`, `get`, `size`, `stream`, `clear`) behave identically to
`StandardCuratorCacheStorage` for the single-node case:
- `size()` returns `0` or `1`
- `stream()` yields at most one element
- `put`/`get`/`remove` match on the stored node's path, so a single-node
cache can never hold entries for multiple paths.
- Honors the `cacheBytes` flag the same way `StandardCuratorCacheStorage`
does.
- **`CuratorCacheStorage.java`** — adds two factory methods: `singleNode()`
and `singleNodeDataNotCached()`.
- **`CuratorCacheImpl.java`** — the constructor now selects
`CuratorCacheStorage.singleNode()` (instead of `standard()`) when
`SINGLE_NODE_CACHE` is set and no explicit storage was provided by the caller.
Calling `builder(client, path).withStorage(...)` still takes precedence.
## Behavioral compatibility
- `CuratorCacheStorage` is a public interface and the storage is only
switched when the caller did **not** supply a custom storage. Explicit
`withStorage()` calls are unchanged.
- The `SINGLE_NODE_CACHE` option previously only controlled watcher
recursion (`recursive = !options.contains(SINGLE_NODE_CACHE)`); this PR
additionally optimizes the backing store without changing any observable
semantics — `get`, `size`, `stream`, and events all behave the same.
## Test plan
Existing `TestCuratorCache` (incl. `testClearOnClose`,
`testGreaterThan64kZNodes`) and related cache tests cover the standard path and
should remain green. Single-node behavior is exercised by tests that build
caches with `SINGLE_NODE_CACHE` and verify `get`/`size`/stream semantics.
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