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.kafka.common.memory;
  
  import org.apache.kafka.common.metrics.Sensor;
  import org.apache.kafka.common.utils.Utils;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.nio.ByteBuffer;
  import java.util.concurrent.atomic.AtomicLong;
  
  
  /**
   * a simple pool implementation. this implementation just provides a limit on the total outstanding memory.
   * any buffer allocated must be release()ed always otherwise memory is not marked as reclaimed (and "leak"s)
   */
  public class SimpleMemoryPool implements MemoryPool {
      protected final Logger log = LoggerFactory.getLogger(getClass()); //subclass-friendly
  
      protected final long sizeBytes;
      protected final boolean strict;
      protected final AtomicLong availableMemory;
      protected final int maxSingleAllocationSize;
      protected final AtomicLong startOfNoMemPeriod = new AtomicLong(); //nanoseconds
      protected volatile Sensor oomTimeSensor;
  
      public SimpleMemoryPool(long sizeInBytes, int maxSingleAllocationBytes, boolean strict, Sensor oomPeriodSensor) {
          if (sizeInBytes <= 0 || maxSingleAllocationBytes <= 0 || maxSingleAllocationBytes > sizeInBytes)
              throw new IllegalArgumentException("must provide a positive size and max single allocation size smaller than size."
                  + "provided " + sizeInBytes + " and " + maxSingleAllocationBytes + " respectively");
          this.sizeBytes = sizeInBytes;
          this.strict = strict;
          this.availableMemory = new AtomicLong(sizeInBytes);
          this.maxSingleAllocationSize = maxSingleAllocationBytes;
          this.oomTimeSensor = oomPeriodSensor;
      }
  
      @Override
      public ByteBuffer tryAllocate(int sizeBytes) {
          if (sizeBytes < 1)
              throw new IllegalArgumentException("requested size " + sizeBytes + "<=0");
          if (sizeBytes > maxSingleAllocationSize)
              throw new IllegalArgumentException("requested size " + sizeBytes + " is larger than maxSingleAllocationSize " + maxSingleAllocationSize);
  
          long available;
          boolean success = false;
          //in strict mode we will only allocate memory if we have at least the size required.
          //in non-strict mode we will allocate memory if we have _any_ memory available (so available memory
          //can dip into the negative and max allocated memory would be sizeBytes + maxSingleAllocationSize)
          long threshold = strict ? sizeBytes : 1;
          while ((available = availableMemory.get()) >= threshold) {
              success = availableMemory.compareAndSet(available, available - sizeBytes);
              if (success)
                  break;
          }
  
          if (success) {
              maybeRecordEndOfDrySpell();
          } else {
              if (oomTimeSensor != null) {
                  startOfNoMemPeriod.compareAndSet(0, System.nanoTime());
              }
              log.trace("refused to allocate buffer of size {}", sizeBytes);
              return null;
          }
  
          ByteBuffer allocated = ByteBuffer.allocate(sizeBytes);
          bufferToBeReturned(allocated);
          return allocated;
      }
  
      @Override
      public void release(ByteBuffer previouslyAllocated) {
          if (previouslyAllocated == null)
              throw new IllegalArgumentException("provided null buffer");
  
          bufferToBeReleased(previouslyAllocated);
          availableMemory.addAndGet(previouslyAllocated.capacity());
          maybeRecordEndOfDrySpell();
      }
  
      @Override
      public long size() {
          return sizeBytes;
      }
  
      @Override
      public long availableMemory() {
          return availableMemory.get();
      }
  
      @Override
      public boolean isOutOfMemory() {
          return availableMemory.get() <= 0;
      }
  
      //allows subclasses to do their own bookkeeping (and validation) _before_ memory is returned to client code.
      protected void bufferToBeReturned(ByteBuffer justAllocated) {
          log.trace("allocated buffer of size {} ", justAllocated.capacity());
      }
  
      //allows subclasses to do their own bookkeeping (and validation) _before_ memory is marked as reclaimed.
      protected void bufferToBeReleased(ByteBuffer justReleased) {
          log.trace("released buffer of size {}", justReleased.capacity());
      }
  
      @Override
      public String toString() {
          long allocated = sizeBytes - availableMemory.get();
          return "SimpleMemoryPool{" + Utils.formatBytes(allocated) + "/" + Utils.formatBytes(sizeBytes) + " used}";
      }
  
      protected void maybeRecordEndOfDrySpell() {
          if (oomTimeSensor != null) {
              long startOfDrySpell = startOfNoMemPeriod.getAndSet(0);
              if (startOfDrySpell != 0) {
                  //how long were we refusing allocation requests for
                  oomTimeSensor.record((System.nanoTime() - startOfDrySpell) / 1000000.0); //fractional (double) millis
              }
          }
      }
  }
  