| /* |
| * Copyright (C) 2020 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package android.media.permission; |
| |
| import android.annotation.NonNull; |
| import android.annotation.Nullable; |
| |
| /** |
| * An RAII-style object, used to establish a scope in which a single identity is part of the |
| * context. This is used in order to avoid having to explicitly pass identity information through |
| * deep call-stacks. |
| * <p> |
| * Intended usage: |
| * <pre> |
| * void caller() { |
| * Identity originator = ...; |
| * try (SafeCloseable ignored = IdentityContext.create(originator)) { |
| * // Within this scope the context is established. |
| * callee(); |
| * } |
| * // Outside the scope the context is restored to its prior state. |
| * |
| * void callee() { |
| * // Here we can access the identity without having to explicitly take it as an argument. |
| * // This is true even if this were a deeply nested call. |
| * Identity originator = IdentityContext.getNonNull(); |
| * ... |
| * } |
| * </pre> |
| * |
| * @hide |
| */ |
| public class IdentityContext implements SafeCloseable { |
| private static ThreadLocal<Identity> sThreadLocalIdentity = new ThreadLocal<>(); |
| private @Nullable Identity mPrior = get(); |
| |
| /** |
| * Create a scoped identity context. |
| * |
| * @param identity The identity to establish with the scope. |
| * @return A {@link SafeCloseable}, to be used in a try-with-resources block to establish a |
| * scope. |
| */ |
| public static @NonNull |
| SafeCloseable create(@Nullable Identity identity) { |
| return new IdentityContext(identity); |
| } |
| |
| /** |
| * Get the current identity context. |
| * |
| * @return The identity, or null if it has not been established. |
| */ |
| public static @Nullable |
| Identity get() { |
| return sThreadLocalIdentity.get(); |
| } |
| |
| /** |
| * Get the current identity context. Throws a {@link NullPointerException} if it has not been |
| * established. |
| * |
| * @return The identity. |
| */ |
| public static @NonNull |
| Identity getNonNull() { |
| Identity result = get(); |
| if (result == null) { |
| throw new NullPointerException("Identity context is not set"); |
| } |
| return result; |
| } |
| |
| private IdentityContext(@Nullable Identity identity) { |
| set(identity); |
| } |
| |
| @Override |
| public void close() { |
| set(mPrior); |
| } |
| |
| private static void set(@Nullable Identity identity) { |
| sThreadLocalIdentity.set(identity); |
| } |
| } |