スレッドセーフな連想カウンタをリセットしたい人生だった ref: https://qiita.com/piyo7/items/81d1d395733b3cea072c

file0.scala

val counter = TrieMap[Key, LongAdder]()

file1.scala

counter.getOrElseUpdate(key, new LongAdder()).increment()

file2.scala

for (key <- counter.keys) {
  val sum = counter.remove(key).sum()
  logger.debug(s"$key: $sum")
}

file3.scala

for {
  key <- counter.keys
  value <- counter.get(key)
} {
  val sum = value.sumThenReset()
  logger.debug(s"$key: $sum")
}

file4.scala

val counter = TrieMap[Key, AtomicLong]()

file5.scala

for {
  key <- counter.keys
  value <- counter.get(key)
} {
  val v = value.getAndSet(0)
  logger.debug(s"$key: $v")
}

file6.scala

for {
  key <- counter.keys
  value <- counter.get(key)
} {
  val v = value.get()
  if (v == 0) counter.remove(key)
}

file7.scala

scala> new AtomicLong(0) == new AtomicLong(0)
res0: Boolean = false

file8.java

public final class AtomicLongMap<K> implements Serializable {
  private final ConcurrentHashMap<K, Long> map;

file9.java

public final class AtomicLongMap<K> {
  private final ConcurrentHashMap<K, AtomicLong> map;