package jsr166
Type Members
- class LongAdder extends Striped64 with Serializable
Written by Doug Lea with assistance from members of JCP JSR-166 Expert Group and released to the public domain, as explained at http://creativecommons.org/publicdomain/zero/1.0/
Written by Doug Lea with assistance from members of JCP JSR-166 Expert Group and released to the public domain, as explained at http://creativecommons.org/publicdomain/zero/1.0/
One or more variables that together maintain an initially zero
long
sum. When updates (method#add
) are contended across threads, the set of variables may grow dynamically to reduce contention. Method#sum
(or, equivalently,#longValue
) returns the current total combined across the variables maintaining the sum.This class is usually preferable to
java.util.concurrent.atomic.AtomicLong
when multiple threads update a common sum that is used for purposes such as collecting statistics, not for fine-grained synchronization control. Under low update contention, the two classes have similar characteristics. But under high contention, expected throughput of this class is significantly higher, at the expense of higher space consumption.LongAdders can be used with a
java.util.concurrent.ConcurrentHashMap
to maintain a scalable frequency map (a form of histogram or multiset). For example, to add a count to aConcurrentHashMap
, initializing if not already present, you can usefreqs freqs.computeIfAbsent(key, k -> new LongAdder()).increment();
This class extends
Number
, but does not define methods such asequals
,hashCode
andcompareTo
because instances are expected to be mutated, and so are not useful as collection keys.- Since
1.8