David Su | 0c472ad | 2019-12-06 15:14:17 -0800 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2019 The Android Open Source Project |
| 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 | package android.util; |
| 18 | |
| 19 | import android.annotation.NonNull; |
| 20 | |
| 21 | /** |
| 22 | * CloseGuard is a mechanism for flagging implicit finalizer cleanup of |
| 23 | * resources that should have been cleaned up by explicit close |
| 24 | * methods (aka "explicit termination methods" in Effective Java). |
| 25 | * <p> |
| 26 | * A simple example: <pre> {@code |
| 27 | * class Foo { |
| 28 | * |
David Su | ab2c291b | 2020-01-27 14:41:16 -0800 | [diff] [blame] | 29 | * private final CloseGuard guard = new CloseGuard(); |
David Su | 0c472ad | 2019-12-06 15:14:17 -0800 | [diff] [blame] | 30 | * |
| 31 | * ... |
| 32 | * |
| 33 | * public Foo() { |
| 34 | * ...; |
| 35 | * guard.open("cleanup"); |
| 36 | * } |
| 37 | * |
| 38 | * public void cleanup() { |
| 39 | * guard.close(); |
| 40 | * ...; |
David Su | 0def143 | 2019-12-12 18:24:52 -0800 | [diff] [blame] | 41 | * if (Build.VERSION.SDK_INT >= 28) { |
| 42 | * Reference.reachabilityFence(this); |
| 43 | * } |
| 44 | * // For full correctness in the absence of a close() call, other methods may also need |
| 45 | * // reachabilityFence() calls. |
David Su | 0c472ad | 2019-12-06 15:14:17 -0800 | [diff] [blame] | 46 | * } |
| 47 | * |
| 48 | * protected void finalize() throws Throwable { |
| 49 | * try { |
| 50 | * // Note that guard could be null if the constructor threw. |
| 51 | * if (guard != null) { |
| 52 | * guard.warnIfOpen(); |
| 53 | * } |
| 54 | * cleanup(); |
| 55 | * } finally { |
| 56 | * super.finalize(); |
| 57 | * } |
| 58 | * } |
| 59 | * } |
| 60 | * }</pre> |
| 61 | * |
| 62 | * In usage where the resource to be explicitly cleaned up is |
| 63 | * allocated after object construction, CloseGuard protection can |
| 64 | * be deferred. For example: <pre> {@code |
| 65 | * class Bar { |
| 66 | * |
David Su | ab2c291b | 2020-01-27 14:41:16 -0800 | [diff] [blame] | 67 | * private final CloseGuard guard = new CloseGuard(); |
David Su | 0c472ad | 2019-12-06 15:14:17 -0800 | [diff] [blame] | 68 | * |
| 69 | * ... |
| 70 | * |
| 71 | * public Bar() { |
| 72 | * ...; |
| 73 | * } |
| 74 | * |
| 75 | * public void connect() { |
| 76 | * ...; |
| 77 | * guard.open("cleanup"); |
| 78 | * } |
| 79 | * |
| 80 | * public void cleanup() { |
| 81 | * guard.close(); |
| 82 | * ...; |
David Su | 0def143 | 2019-12-12 18:24:52 -0800 | [diff] [blame] | 83 | * if (Build.VERSION.SDK_INT >= 28) { |
| 84 | * Reference.reachabilityFence(this); |
| 85 | * } |
David Su | 0c472ad | 2019-12-06 15:14:17 -0800 | [diff] [blame] | 86 | * // For full correctness in the absence of a close() call, other methods may also need |
| 87 | * // reachabilityFence() calls. |
| 88 | * } |
| 89 | * |
| 90 | * protected void finalize() throws Throwable { |
| 91 | * try { |
| 92 | * // Note that guard could be null if the constructor threw. |
| 93 | * if (guard != null) { |
| 94 | * guard.warnIfOpen(); |
| 95 | * } |
| 96 | * cleanup(); |
| 97 | * } finally { |
| 98 | * super.finalize(); |
| 99 | * } |
| 100 | * } |
| 101 | * } |
| 102 | * }</pre> |
| 103 | * |
| 104 | * When used in a constructor, calls to {@code open} should occur at |
| 105 | * the end of the constructor since an exception that would cause |
| 106 | * abrupt termination of the constructor will mean that the user will |
| 107 | * not have a reference to the object to cleanup explicitly. When used |
| 108 | * in a method, the call to {@code open} should occur just after |
| 109 | * resource acquisition. |
| 110 | */ |
| 111 | public final class CloseGuard { |
| 112 | private final dalvik.system.CloseGuard mImpl; |
| 113 | |
| 114 | /** |
| 115 | * Constructs a new CloseGuard instance. |
| 116 | * {@link #open(String)} can be used to set up the instance to warn on failure to close. |
| 117 | */ |
| 118 | public CloseGuard() { |
| 119 | mImpl = dalvik.system.CloseGuard.get(); |
| 120 | } |
| 121 | |
| 122 | /** |
| 123 | * Initializes the instance with a warning that the caller should have explicitly called the |
| 124 | * {@code closeMethodName} method instead of relying on finalization. |
| 125 | * |
| 126 | * @param closeMethodName non-null name of explicit termination method. Printed by warnIfOpen. |
| 127 | * @throws NullPointerException if closeMethodName is null. |
| 128 | */ |
| 129 | public void open(@NonNull String closeMethodName) { |
| 130 | mImpl.open(closeMethodName); |
| 131 | } |
| 132 | |
| 133 | /** Marks this CloseGuard instance as closed to avoid warnings on finalization. */ |
| 134 | public void close() { |
| 135 | mImpl.close(); |
| 136 | } |
| 137 | |
| 138 | /** |
| 139 | * Logs a warning if the caller did not properly cleanup by calling an explicit close method |
| 140 | * before finalization. |
| 141 | */ |
| 142 | public void warnIfOpen() { |
| 143 | mImpl.warnIfOpen(); |
| 144 | } |
| 145 | } |