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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   * The argument determines which lock guards the annotated field or method:
41   * <ul>
42   * <li>
43   * <code>this</code> : The intrinsic lock of the object in whose class the field is defined.
44   * </li>
45   * <li>
46   * <code>class-name.this</code> : For inner classes, it may be necessary to disambiguate 'this';
47   * the <em>class-name.this</em> designation allows you to specify which 'this' reference is intended
48   * </li>
49   * <li>
50   * <code>itself</code> : For reference fields only; the object to which the field refers.
51   * </li>
52   * <li>
53   * <code>field-name</code> : The lock object is referenced by the (instance or static) field
54   * specified by <em>field-name</em>.
55   * </li>
56   * <li>
57   * <code>class-name.field-name</code> : The lock object is reference by the static field specified
58   * by <em>class-name.field-name</em>.
59   * </li>
60   * <li>
61   * <code>method-name()</code> : The lock object is returned by calling the named nil-ary method.
62   * </li>
63   * <li>
64   * <code>class-name.class</code> : The Class object for the specified class should be used as the lock object.
65   * </li>
66   * <p>
67   * Based on code developed by Brian Goetz and Tim Peierls and concepts
68   * published in 'Java Concurrency in Practice' by Brian Goetz, Tim Peierls,
69   * Joshua Bloch, Joseph Bowbeer, David Holmes and Doug Lea.
70   */
71  @Documented
72  @Target({ElementType.FIELD, ElementType.METHOD})
73  @Retention(RetentionPolicy.CLASS) // The original version used RUNTIME
74  public @interface GuardedBy {
75      String value();
76  }