content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package accord.local;
  
  import java.util.concurrent.atomic.AtomicLong;
  
  import accord.utils.Invariants;
  
  public interface UniqueTimeService
  {
      /**
       * Expected to provide a value > all prior values
       */
      default long uniqueNow() { return uniqueNow(0); }
  
      /**
       * Expected to provide a value > all prior values, and greater than the parameter
       */
      long uniqueNow(long greaterThan);
  
      default long uniqueStale(long greaterThan) { return uniqueNow(greaterThan); }
  
      class AtomicUniqueTime extends AtomicLong implements UniqueTimeService
      {
          final TimeService time;
  
          public AtomicUniqueTime(TimeService time)
          {
              this.time = time;
          }
  
          @Override
          public long uniqueNow(long greaterThan)
          {
              long now = time.now();
              return accumulateAndGet(Math.max(now - 1, greaterThan), (a, b) -> Math.max(a, b) + 1);
          }
      }
  
      class AtomicUniqueTimeWithStaleReservation extends AtomicLong implements UniqueTimeService
      {
          // 1 in every ~1k hlc are reserved for stale hlc by default
          private static final long RESERVATION_MASK = 0x3ff;
          final TimeService time;
          final AtomicLong lastStale = new AtomicLong();
  
          public AtomicUniqueTimeWithStaleReservation(TimeService time)
          {
              this.time = time;
          }
  
          @Override
          public long uniqueNow(long greaterThan)
          {
              long now = time.now();
              long min = Math.max(now, greaterThan + 1);
              while (true)
              {
                  long cur = get();
                  if (cur >= min)
                      break;
  
                  long next = Math.max(min, cur + 1);
                  if (!isSafeNow(next))
                      ++next;
  
                  if (compareAndSet(cur, next))
                      return next;
              }
  
              while (true)
              {
                  long result = incrementAndGet();
                  if (isSafeNow(result))
                      return result;
              }
          }
  
          @Override
          public long uniqueStale(long greaterThan)
          {
              long now = time.now();
              long min = greaterThan + 1;
              while (true)
              {
                  long cur = lastStale.get();
                  if (cur >= now)
                      return uniqueNow(greaterThan);
  
                  long next = ensureStale(Math.max(min, cur + 1));
                  if (lastStale.compareAndSet(cur, next))
                      return next;
              }
          }
  
          protected long ensureStale(long stale)
          {
              if ((stale & RESERVATION_MASK) == 0)
                  return stale;
  
              stale += 1 + RESERVATION_MASK - (stale & RESERVATION_MASK);
              Invariants.require((stale & RESERVATION_MASK) == 0);
              return stale;
          }
  
          protected boolean isSafeNow(long now)
          {
              return (now & RESERVATION_MASK) != 0;
          }
      }
  }
  