public boolean containsValue(@Nullable Object value) {
if (value == null) {
return false;
}
long now = ticker.read();
final Segment<K, V>[] segments = this.segments;
long last = -1L;
for (int i = 0; i < CONTAINS_VALUE_RETRIES; i++) {
long sum = 0L;
for (Segment<K, V> segment : segments) {
// ensure visibility of most recent completed write
int unused = segment.count; // read-volatile
AtomicReferenceArray<ReferenceEntry<K, V>> table = segment.table;
for (int j = 0; j < table.length(); j++) {
for (ReferenceEntry<K, V> e = table.get(j); e != null; e = e.getNext()) {
V v = segment.getLiveValue(e, now);
if (v != null && valueEquivalence.equivalent(value, v)) {
return true;
}
}
}
sum += segment.modCount;
}
if (sum == last) {
break;
}
last = sum;
}
return false;
}
guava将containsValue设计成不加锁的操作。并且使用modCount检测在执行方法期间cache有没有变化。我的疑问是，modCount貌似只是对执行put操作做了检测，如果在该方法执行中在return true之前其他线程做了一个remove操作，是否该方法返回值就是错的。如果改为无论如何都检测modCount的次数如何？