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.
This class extends
Number, but does not define
methods such as
equals,
hashCode and
compareTo because instances are expected to be mutated, and so are
not useful as collection keys.
jsr166e note: This class is targeted to be placed in
java.util.concurrent.atomic.