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Comment regarding synchronization in Cache#computeIfAbsent

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This commit is contained in:
Jason Tedor 2015-10-08 18:15:52 -04:00
parent 881593eea9
commit a6abb4fcdd
1 changed files with 4 additions and 0 deletions
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4
core/src/main/java/org/elasticsearch/common/cache/Cache.java vendored
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@ -300,6 +300,10 @@ public class Cache<K, V> {
V value = get(key, now);
if (value == null) {
CacheSegment<K, V> segment = getCacheSegment(key);
// we synchronize against the segment lock; this is to avoid a scenario where another thread is inserting
// a value for the same key via put which would not be observed on this thread without a mechanism
// synchronizing the two threads; it is possible that the segment lock will be too expensive here (it blocks
// readers too!) so consider this as a possible place to optimize should contention be observed
try (ReleasableLock ignored = segment.writeLock.acquire()) {
value = get(key, now);
if (value == null) {