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 com.datastax.oss.driver.api.core.session.throttling;
  
  import edu.umd.cs.findbugs.annotations.NonNull;
  import java.io.Closeable;
  
  /**
   * Limits the number of concurrent requests executed by the driver.
   *
   * <p>Usage in non-blocking applications: beware that some implementations of this interface use
   * locks for internal coordination, and do not qualify as lock-free. If your application enforces
   * strict lock-freedom, then you should use the {@code PassThroughRequestThrottler} or the {@code
   * ConcurrencyLimitingRequestThrottler}.
   */
  public interface RequestThrottler extends Closeable {
  
    /**
     * Registers a new request to be throttled. The throttler will invoke {@link
     * Throttled#onThrottleReady(boolean)} when the request is allowed to proceed.
     */
    void register(@NonNull Throttled request);
  
    /**
     * Signals that a request has succeeded. This indicates to the throttler that another request
     * might be started.
     */
    void signalSuccess(@NonNull Throttled request);
  
    /**
     * Signals that a request has failed. This indicates to the throttler that another request might
     * be started.
     */
    void signalError(@NonNull Throttled request, @NonNull Throwable error);
  
    /**
     * Signals that a request has timed out. This indicates to the throttler that this request has
     * stopped (if it was running already), or that it doesn't need to be started in the future.
     *
     * <p>Note: requests are responsible for handling their own timeout. The throttler does not
     * perform time-based eviction on pending requests.
     */
    void signalTimeout(@NonNull Throttled request);
  
    /**
     * Signals that a request has been cancelled. This indicates to the throttler that another request
     * might be started.
     */
    default void signalCancel(@NonNull Throttled request) {
      // no-op for backward compatibility purposes
    }
  }
  