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/*
* Copyright (C) 2018 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.os;
/**
* Tracks who triggered the work currently executed on this thread.
*
* <p>ThreadLocalWorkSource is automatically updated inside system server for incoming/outgoing
* binder calls and messages posted to handler threads.
*
* <p>ThreadLocalWorkSource can also be set manually if needed to refine the WorkSource.
*
* <p>Example:
* <ul>
* <li>Bluetooth process calls {@link PowerManager#isInteractive()} API on behalf of app foo.
* <li>ThreadLocalWorkSource will be automatically set to the UID of foo.
* <li>Any code on the thread handling {@link PowerManagerService#isInteractive()} can call
* {@link ThreadLocalWorkSource#getUid()} to blame any resource used to handle this call.
* <li>If a message is posted from the binder thread, the code handling the message can also call
* {@link ThreadLocalWorkSource#getUid()} and it will return the UID of foo since the work source is
* automatically propagated.
* </ul>
*
* @hide Only for use within system server.
*/
public final class ThreadLocalWorkSource {
public static final int UID_NONE = Message.UID_NONE;
private static final ThreadLocal<Integer> sWorkSourceUid =
ThreadLocal.withInitial(() -> UID_NONE);
/**
* Returns the UID to blame for the code currently executed on this thread.
*
* <p>This UID is set automatically by common frameworks (e.g. Binder and Handler frameworks)
* and automatically propagated inside system server.
* <p>It can also be set manually using {@link #setUid(int)}.
*/
public static int getUid() {
return sWorkSourceUid.get();
}
/**
* Sets the UID to blame for the code currently executed on this thread.
*
* <p>Inside system server, this UID will be automatically propagated.
* <p>It will be used to attribute future resources used on this thread (e.g. binder
* transactions or processing handler messages) and on any other threads the UID is propagated
* to.
*
* @return a token that can be used to restore the state.
*/
public static long setUid(int uid) {
final long token = getToken();
sWorkSourceUid.set(uid);
return token;
}
/**
* Restores the state using the provided token.
*/
public static void restore(long token) {
sWorkSourceUid.set(parseUidFromToken(token));
}
/**
* Clears the stored work source uid.
*
* <p>This method should be used when we do not know who to blame. If the UID to blame is the
* UID of the current process, it is better to attribute the work to the current process
* explicitly instead of clearing the work source:
*
* <pre>
* ThreadLocalWorkSource.setUid(Process.myUid());
* </pre>
*
* @return a token that can be used to restore the state.
**/
public static long clear() {
return setUid(UID_NONE);
}
private static int parseUidFromToken(long token) {
return (int) token;
}
private static long getToken() {
return sWorkSourceUid.get();
}
private ThreadLocalWorkSource() {
}
}
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