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1   /*
2    * Copyright 2021 TiKV Project Authors.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    * http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   *
16   */
17  
18  package org.tikv.service.failsafe;
19  
20  import java.io.Closeable;
21  
22  public interface CircuitBreaker extends Closeable {
23  
24    enum Status {
25      CLOSED(0),
26      HALF_OPEN(1),
27      OPEN(2);
28  
29      private final int value;
30  
31      private Status(int value) {
32        this.value = value;
33      }
34  
35      public int getValue() {
36        return value;
37      }
38    }
39  
40    /**
41     * Every requests asks this if it is allowed to proceed or not. It is idempotent and does not
42     * modify any internal state.
43     *
44     * @return boolean whether a request should be permitted
45     */
46    boolean allowRequest();
47  
48    /**
49     * Invoked at start of command execution to attempt an execution. This is non-idempotent - it may
50     * modify internal state.
51     */
52    boolean attemptExecution();
53  
54    /** Invoked on successful executions as part of feedback mechanism when in a half-open state. */
55    void recordAttemptSuccess();
56  
57    /** Invoked on unsuccessful executions as part of feedback mechanism when in a half-open state. */
58    void recordAttemptFailure();
59  
60    /** Get the Circuit Breaker Metrics Object. */
61    CircuitBreakerMetrics getMetrics();
62  }