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.bifromq.mqtt.session;
  
  import org.apache.bifromq.metrics.ITenantMeter;
  import org.apache.bifromq.metrics.TenantMetric;
  import com.github.benmanes.caffeine.cache.Caffeine;
  import com.github.benmanes.caffeine.cache.LoadingCache;
  import io.micrometer.core.instrument.Meter;
  import io.netty.util.concurrent.FastThreadLocal;
  import java.util.Map;
  import java.util.WeakHashMap;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.atomic.AtomicLong;
  
  public class TenantGauge {
      private final TenantMetric metric;
      private final FastThreadLocal<LoadingCache<String, AtomicLong>> threadLocalTenantMemGauge;
  
      private final Map<String, WeakHashMap<AtomicLong, Object>> tenantMemGauge = new ConcurrentHashMap<>();
  
      public TenantGauge(TenantMetric gaugeMetric) {
          assert gaugeMetric.meterType == Meter.Type.GAUGE;
          this.metric = gaugeMetric;
          this.threadLocalTenantMemGauge = new FastThreadLocal<>() {
              @Override
              protected LoadingCache<String, AtomicLong> initialValue() {
                  return Caffeine.newBuilder().weakValues()
                      .build(key -> {
                          AtomicLong gauge = new AtomicLong();
                          register(key, gauge);
                          return gauge;
                      });
              }
          };
      }
  
      public AtomicLong get(String tenant) {
          return threadLocalTenantMemGauge.get().get(tenant);
      }
  
      private void register(String tenantId, AtomicLong gauge) {
          tenantMemGauge.compute(tenantId, (k, v) -> {
              if (v == null) {
                  WeakHashMap<AtomicLong, Object> threadLocalGauges = new WeakHashMap<>();
                  v = threadLocalGauges;
                  v.put(gauge, new Object());
                  ITenantMeter.gauging(k, metric, () -> {
                      if (threadLocalGauges.isEmpty()) {
                          tenantMemGauge.remove(k, threadLocalGauges);
                          ITenantMeter.stopGauging(tenantId, metric);
                          return 0;
                      } else {
                          return threadLocalGauges.keySet().stream().mapToLong(AtomicLong::get).sum();
                      }
                  });
              } else {
                  v.put(gauge, new Object());
              }
              return v;
          });
      }
  }
  