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.distributedlog.common.util;
  
  /**
   * Permit manager for managing permits.
   */
  public interface PermitManager {
  
      /**
       * A class present a permit managed by a permit manager.
       */
      interface Permit {
          Permit ALLOWED = () -> true;
          boolean isAllowed();
      }
  
      PermitManager UNLIMITED_PERMIT_MANAGER = new PermitManager() {
          @Override
          public Permit acquirePermit() {
              return Permit.ALLOWED;
          }
  
          @Override
          public void releasePermit(Permit permit) {
              // nop
          }
  
          @Override
          public boolean allowObtainPermits() {
              return true;
          }
  
          @Override
          public boolean disallowObtainPermits(Permit permit) {
              return false;
          }
  
          @Override
          public void close() {
              // nop
          }
  
      };
  
      /**
       * Obetain a permit from permit manager.
       *
       * @return permit.
       */
      Permit acquirePermit();
  
      /**
       * Release a given permit.
       *
       * @param permit
       *          permit to release
       */
      void releasePermit(Permit permit);
  
      /**
       * Allow obtaining permits.
       */
      boolean allowObtainPermits();
  
      /**
       * Disallow obtaining permits. Disallow needs to be performed under the context
       * of <i>permit</i>.
       *
       * @param permit
       *          permit context to disallow
       */
      boolean disallowObtainPermits(Permit permit);
  
      /**
       * Release the resources.
       */
      void close();
  }
  