ben-manes commented on code in PR #1155:
URL: https://github.com/apache/solr/pull/1155#discussion_r1044281175
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solr/core/src/java/org/apache/solr/core/TransientSolrCoreCacheDefault.java:
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@@ -70,10 +80,15 @@ public TransientSolrCoreCacheDefault(CoreContainer
coreContainer) {
Caffeine<String, SolrCore> transientCoresCacheBuilder =
Caffeine.newBuilder()
.initialCapacity(initialCapacity)
- // Use the current thread to queue evicted cores for closing. This
ensures the
- // cache max size is respected (with a different thread the max
size would be
- // respected asynchronously only eventually).
- .executor(Runnable::run)
+ // Do NOT use the current thread to queue evicted cores for
closing. Although this
+ // ensures the cache max size is respected only eventually, it
should be a very
+ // short period of time until the cache maintenance task kicks in.
+ // The onEvict method needs the writeLock from SolrCores to
operate safely.
+ // However, the current thread most probably has acquired a
read-lock already
+ // somewhere up the call stack and would deadlock.
+ // Note that Caffeine cache has an internal maintenance task
rescheduling logic which
+ // explicitly checks on the common pool.
+ .executor(ForkJoinPool.commonPool())
Review Comment:
Caffeine only uses amortized O(1) data structures so it is relatively cheap.
The entry is on an lru doubly linked list that is managed in a non-blocking
fashion. Currently the zero weights are left on the lru and skipped over during
eviction, but they could later be moved on/off if that traversal became an
issue. The modifying of an entry’s weight is done only by write operations,
e.g. on a put, so more expensive that a read but still [very
fast](https://github.com/ben-manes/caffeine/wiki/Benchmarks#write-100-1)
(45M/s).
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