2 * Copyright (C) 2017 The Android Open Source Project
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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
17 package com.android.server;
19 import static android.os.Process.getThreadPriority;
20 import static android.os.Process.myTid;
21 import static android.os.Process.setThreadPriority;
24 * Utility class to boost threads in sections where important locks are held.
26 public class ThreadPriorityBooster {
28 private volatile int mBoostToPriority;
29 private final int mLockGuardIndex;
31 private final ThreadLocal<PriorityState> mThreadState = new ThreadLocal<PriorityState>() {
32 @Override protected PriorityState initialValue() {
33 return new PriorityState();
37 public ThreadPriorityBooster(int boostToPriority, int lockGuardIndex) {
38 mBoostToPriority = boostToPriority;
39 mLockGuardIndex = lockGuardIndex;
43 final int tid = myTid();
44 final int prevPriority = getThreadPriority(tid);
45 final PriorityState state = mThreadState.get();
46 if (state.regionCounter == 0) {
47 state.prevPriority = prevPriority;
48 if (prevPriority > mBoostToPriority) {
49 setThreadPriority(tid, mBoostToPriority);
52 state.regionCounter++;
53 if (LockGuard.ENABLED) {
54 LockGuard.guard(mLockGuardIndex);
59 final PriorityState state = mThreadState.get();
60 state.regionCounter--;
61 final int currentPriority = getThreadPriority(myTid());
62 if (state.regionCounter == 0 && state.prevPriority != currentPriority) {
63 setThreadPriority(myTid(), state.prevPriority);
68 * Updates the priority we boost the threads to, and updates the current thread's priority if
71 protected void setBoostToPriority(int priority) {
73 // We don't care about the other threads here, as long as they see the update of this
74 // variable immediately.
75 mBoostToPriority = priority;
76 final PriorityState state = mThreadState.get();
77 final int tid = myTid();
78 final int prevPriority = getThreadPriority(tid);
79 if (state.regionCounter != 0 && prevPriority != priority) {
80 setThreadPriority(tid, priority);
84 private static class PriorityState {
87 * Acts as counter for number of synchronized region that needs to acquire 'this' as a lock
88 * the current thread is currently in. When it drops down to zero, we will no longer boost
89 * the thread's priority.
94 * The thread's previous priority before boosting.