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 org.apache.cassandra.utils.memory;
  
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  import java.util.concurrent.atomic.AtomicLongFieldUpdater;
  
  import com.google.common.annotations.VisibleForTesting;
  import com.google.common.base.Preconditions;
  
  import com.codahale.metrics.Gauge;
  import com.codahale.metrics.Timer;
  import org.apache.cassandra.metrics.CassandraMetricsRegistry;
  import org.apache.cassandra.metrics.DefaultNameFactory;
  import org.apache.cassandra.metrics.MetricNameFactory;
  import org.apache.cassandra.utils.concurrent.WaitQueue;
  import org.apache.cassandra.utils.ExecutorUtils;
  
  import static org.apache.cassandra.utils.concurrent.WaitQueue.newWaitQueue;
  
  
  /**
   * Represents an amount of memory used for a given purpose, that can be allocated to specific tasks through
   * child MemtableAllocator objects.
   */
  public abstract class MemtablePool
  {
      public static final String TYPE_NAME = "MemtablePool";
      final MemtableCleanerThread<?> cleaner;
  
      // the total memory used by this pool
      public final SubPool onHeap;
      public final SubPool offHeap;
  
      public final Timer blockedOnAllocating;
      public final Gauge<Long> numPendingTasks;
  
      final WaitQueue hasRoom = newWaitQueue();
  
      MemtablePool(long maxOnHeapMemory, long maxOffHeapMemory, float cleanThreshold, MemtableCleaner cleaner)
      {
          Preconditions.checkArgument(cleaner != null, "Cleaner should not be null");
  
          this.onHeap = getSubPool(maxOnHeapMemory, cleanThreshold);
          this.offHeap = getSubPool(maxOffHeapMemory, cleanThreshold);
          this.cleaner = getCleaner(cleaner);
          MetricNameFactory nameFactory = new DefaultNameFactory(TYPE_NAME);
          blockedOnAllocating = CassandraMetricsRegistry.Metrics.timer(nameFactory.createMetricName("BlockedOnAllocation"));
          numPendingTasks = CassandraMetricsRegistry.Metrics.register(nameFactory.createMetricName("PendingFlushTasks"),
                                                                      () -> (long) this.cleaner.numPendingTasks());
      }
  
      SubPool getSubPool(long limit, float cleanThreshold)
      {
          return new SubPool(limit, cleanThreshold);
      }
  
      MemtableCleanerThread<?> getCleaner(MemtableCleaner cleaner)
      {
          return cleaner == null ? null : new MemtableCleanerThread<>(this, cleaner);
      }
  
      @VisibleForTesting
      public void shutdownAndWait(long timeout, TimeUnit unit) throws InterruptedException, TimeoutException
      {
          ExecutorUtils.shutdownNowAndWait(timeout, unit, cleaner);
      }
  
      public abstract MemtableAllocator newAllocator(String table);
  
      public boolean needsCleaning()
      {
          return onHeap.needsCleaning() || offHeap.needsCleaning();
      }
  
      public Long getNumPendingtasks()
      {
          return numPendingTasks.getValue();
      }
  
      /**
       * Note the difference between acquire() and allocate(); allocate() makes more resources available to all owners,
       * and acquire() makes shared resources unavailable but still recorded. An Owner must always acquire resources,
       * but only needs to allocate if there are none already available. This distinction is not always meaningful.
       */
      public class SubPool
      {
  
          // total memory/resource permitted to allocate
          public final long limit;
  
          // ratio of used to spare (both excluding 'reclaiming') at which to trigger a clean
          public final float cleanThreshold;
  
          // total bytes allocated and reclaiming
          volatile long allocated;
          volatile long reclaiming;
  
          // a cache of the calculation determining at what allocation threshold we should next clean
          volatile long nextClean;
  
          public SubPool(long limit, float cleanThreshold)
          {
              this.limit = limit;
              this.cleanThreshold = cleanThreshold;
          }
  
          /** Methods for tracking and triggering a clean **/
  
          boolean needsCleaning()
          {
              // use strictly-greater-than so we don't clean when limit is 0
              return used() > nextClean && updateNextClean();
          }
  
          void maybeClean()
          {
              if (needsCleaning() && cleaner != null)
                  cleaner.trigger();
          }
  
          private boolean updateNextClean()
          {
              while (true)
              {
                  long current = nextClean;
                  long reclaiming = this.reclaiming;
                  long next =  reclaiming + (long) (this.limit * cleanThreshold);
                  if (current == next || nextCleanUpdater.compareAndSet(this, current, next))
                      return used() > next;
              }
          }
  
          /** Methods to allocate space **/
  
          boolean tryAllocate(long size)
          {
              while (true)
              {
                  long cur;
                  if ((cur = allocated) + size > limit)
                      return false;
                  if (allocatedUpdater.compareAndSet(this, cur, cur + size))
                      return true;
              }
          }
  
          /**
           * apply the size adjustment to allocated, bypassing any limits or constraints. If this reduces the
           * allocated total, we will signal waiters
           */
          private void adjustAllocated(long size)
          {
              while (true)
              {
                  long cur = allocated;
                  if (allocatedUpdater.compareAndSet(this, cur, cur + size))
                      return;
              }
          }
  
          void allocated(long size)
          {
              assert size >= 0;
              if (size == 0)
                  return;
  
              adjustAllocated(size);
              maybeClean();
          }
  
          void acquired()
          {
              maybeClean();
          }
  
          void released(long size)
          {
              assert size >= 0 : "Negative released: " + size;
              adjustAllocated(-size);
              hasRoom.signalAll();
          }
  
          void reclaiming(long size)
          {
              if (size == 0)
                  return;
              reclaimingUpdater.addAndGet(this, size);
          }
  
          void reclaimed(long size)
          {
              if (size == 0)
                  return;
  
              reclaimingUpdater.addAndGet(this, -size);
              if (updateNextClean() && cleaner != null)
                  cleaner.trigger();
          }
  
          public long used()
          {
              return allocated;
          }
  
          public long getReclaiming()
          {
              return reclaiming;
          }
  
          public float reclaimingRatio()
          {
              float r = reclaiming / (float) limit;
              if (Float.isNaN(r))
                  return 0;
              return r;
          }
  
          public float usedRatio()
          {
              float r = allocated / (float) limit;
              if (Float.isNaN(r))
                  return 0;
              return r;
          }
  
          public MemtableAllocator.SubAllocator newAllocator()
          {
              return new MemtableAllocator.SubAllocator(this);
          }
  
          public WaitQueue hasRoom()
          {
              return hasRoom;
          }
  
          public Timer.Context blockedTimerContext()
          {
              return blockedOnAllocating.time();
          }
      }
  
      private static final AtomicLongFieldUpdater<SubPool> reclaimingUpdater = AtomicLongFieldUpdater.newUpdater(SubPool.class, "reclaiming");
      private static final AtomicLongFieldUpdater<SubPool> allocatedUpdater = AtomicLongFieldUpdater.newUpdater(SubPool.class, "allocated");
      private static final AtomicLongFieldUpdater<SubPool> nextCleanUpdater = AtomicLongFieldUpdater.newUpdater(SubPool.class, "nextClean");
  
  }
  