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1   /*
2    * ====================================================================
3    * Licensed to the Apache Software Foundation (ASF) under one
4    * or more contributor license agreements.  See the NOTICE file
5    * distributed with this work for additional information
6    * regarding copyright ownership.  The ASF licenses this file
7    * to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance
9    * with the License.  You may obtain a copy of the License at
10   *
11   *   http://www.apache.org/licenses/LICENSE-2.0
12   *
13   * Unless required by applicable law or agreed to in writing,
14   * software distributed under the License is distributed on an
15   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
16   * KIND, either express or implied.  See the License for the
17   * specific language governing permissions and limitations
18   * under the License.
19   * ====================================================================
20   *
21   * This software consists of voluntary contributions made by many
22   * individuals on behalf of the Apache Software Foundation.  For more
23   * information on the Apache Software Foundation, please see
24   * <http://www.apache.org/>.
25   *
26   */
27  package org.apache.http.annotation;
28  
29  import java.lang.annotation.Documented;
30  import java.lang.annotation.ElementType;
31  import java.lang.annotation.Retention;
32  import java.lang.annotation.RetentionPolicy;
33  import java.lang.annotation.Target;
34  
35  /**
36   * The field or method to which this annotation is applied can only be accessed
37   * when holding a particular lock, which may be a built-in (synchronization) lock,
38   * or may be an explicit java.util.concurrent.Lock.
39   *
40   * <p>
41   * The argument determines which lock guards the annotated field or method:
42   * </p>
43   * <ul>
44   * <li>
45   * {@code this} : The intrinsic lock of the object in whose class the field is defined.
46   * </li>
47   * <li>
48   * {@code class-name.this} : For inner classes, it may be necessary to disambiguate 'this';
49   * the <em>class-name.this</em> designation allows you to specify which 'this' reference is intended
50   * </li>
51   * <li>
52   * {@code itself} : For reference fields only; the object to which the field refers.
53   * </li>
54   * <li>
55   * {@code field-name} : The lock object is referenced by the (instance or static) field
56   * specified by <em>field-name</em>.
57   * </li>
58   * <li>
59   * {@code class-name.field-name} : The lock object is reference by the static field specified
60   * by <em>class-name.field-name</em>.
61   * </li>
62   * <li>
63   * {@code method-name()} : The lock object is returned by calling the named nil-ary method.
64   * </li>
65   * <li>
66   * {@code class-name.class} : The Class object for the specified class should be used as the lock object.
67   * </li>
68   * </ul>
69   * <p>
70   * Based on code developed by Brian Goetz and Tim Peierls and concepts
71   * published in 'Java Concurrency in Practice' by Brian Goetz, Tim Peierls,
72   * Joshua Bloch, Joseph Bowbeer, David Holmes and Doug Lea.
73   * </p>
74   */
75  @Documented
76  @Target({ElementType.FIELD, ElementType.METHOD})
77  @Retention(RetentionPolicy.CLASS) // The original version used RUNTIME
78  public @interface GuardedBy {
79      String value();
80  }