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1   /**
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  package org.apache.hadoop.hbase.ipc;
19  
20  import org.apache.hadoop.hbase.classification.InterfaceAudience;
21  import org.apache.hadoop.hbase.classification.InterfaceStability;
22  import org.apache.hadoop.hbase.HBaseInterfaceAudience;
23  
24  import java.io.IOException;
25  import java.net.InetSocketAddress;
26  
27  /**
28   * An interface for RPC request scheduling algorithm.
29   */
30  @InterfaceAudience.LimitedPrivate({HBaseInterfaceAudience.COPROC, HBaseInterfaceAudience.PHOENIX})
31  @InterfaceStability.Evolving
32  public abstract class RpcScheduler {
33    public static final String IPC_SERVER_MAX_CALLQUEUE_LENGTH =
34        "hbase.ipc.server.max.callqueue.length";
35    public static final String IPC_SERVER_PRIORITY_MAX_CALLQUEUE_LENGTH =
36        "hbase.ipc.server.priority.max.callqueue.length";
37  
38    /** Exposes runtime information of a {@code RpcServer} that a {@code RpcScheduler} may need. */
39    public static abstract class Context {
40      public abstract InetSocketAddress getListenerAddress();
41    }
42  
43    /**
44     * Does some quick initialization. Heavy tasks (e.g. starting threads) should be
45     * done in {@link #start()}. This method is called before {@code start}.
46     *
47     * @param context provides methods to retrieve runtime information from
48     */
49    public abstract void init(Context context);
50  
51    /**
52     * Prepares for request serving. An implementation may start some handler threads here.
53     */
54    public abstract void start();
55  
56    /** Stops serving new requests. */
57    public abstract void stop();
58  
59    /**
60     * Dispatches an RPC request asynchronously. An implementation is free to choose to process the
61     * request immediately or delay it for later processing.
62     *
63     * @param task the request to be dispatched
64     */
65    public abstract boolean dispatch(CallRunner task) throws IOException, InterruptedException;
66  
67    /** Retrieves length of the general queue for metrics. */
68    public abstract int getGeneralQueueLength();
69  
70    /** Retrieves length of the priority queue for metrics. */
71    public abstract int getPriorityQueueLength();
72  
73    /** Retrieves length of the replication queue for metrics. */
74    public abstract int getReplicationQueueLength();
75  
76    /** Retrieves the number of active handler. */
77    public abstract int getActiveRpcHandlerCount();
78  
79    /**
80     * If CoDel-based RPC executors are used, retrieves the number of Calls that were dropped
81     * from general queue because RPC executor is under high load; returns 0 otherwise.
82     */
83    public abstract long getNumGeneralCallsDropped();
84  
85    /**
86     * If CoDel-based RPC executors are used, retrieves the number of Calls that were
87     * picked from the tail of the queue (indicating adaptive LIFO mode, when
88     * in the period of overloade we serve last requests first); returns 0 otherwise.
89     */
90    public abstract long getNumLifoModeSwitches();
91  }