| /* |
| * Copyright (C) 2017 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 com.android.server; |
| |
| import static android.os.Process.getThreadPriority; |
| import static android.os.Process.myTid; |
| import static android.os.Process.setThreadPriority; |
| |
| /** |
| * Utility class to boost threads in sections where important locks are held. |
| */ |
| public class ThreadPriorityBooster { |
| |
| private static final boolean ENABLE_LOCK_GUARD = false; |
| |
| private volatile int mBoostToPriority; |
| private final int mLockGuardIndex; |
| |
| private final ThreadLocal<PriorityState> mThreadState = new ThreadLocal<PriorityState>() { |
| @Override protected PriorityState initialValue() { |
| return new PriorityState(); |
| } |
| }; |
| |
| public ThreadPriorityBooster(int boostToPriority, int lockGuardIndex) { |
| mBoostToPriority = boostToPriority; |
| mLockGuardIndex = lockGuardIndex; |
| } |
| |
| public void boost() { |
| final int tid = myTid(); |
| final int prevPriority = getThreadPriority(tid); |
| final PriorityState state = mThreadState.get(); |
| if (state.regionCounter == 0) { |
| state.prevPriority = prevPriority; |
| if (prevPriority > mBoostToPriority) { |
| setThreadPriority(tid, mBoostToPriority); |
| } |
| } |
| state.regionCounter++; |
| if (ENABLE_LOCK_GUARD) { |
| LockGuard.guard(mLockGuardIndex); |
| } |
| } |
| |
| public void reset() { |
| final PriorityState state = mThreadState.get(); |
| state.regionCounter--; |
| final int currentPriority = getThreadPriority(myTid()); |
| if (state.regionCounter == 0 && state.prevPriority != currentPriority) { |
| setThreadPriority(myTid(), state.prevPriority); |
| } |
| } |
| |
| /** |
| * Updates the priority we boost the threads to, and updates the current thread's priority if |
| * necessary. |
| */ |
| protected void setBoostToPriority(int priority) { |
| |
| // We don't care about the other threads here, as long as they see the update of this |
| // variable immediately. |
| mBoostToPriority = priority; |
| final PriorityState state = mThreadState.get(); |
| final int tid = myTid(); |
| final int prevPriority = getThreadPriority(tid); |
| if (state.regionCounter != 0 && prevPriority != priority) { |
| setThreadPriority(tid, priority); |
| } |
| } |
| |
| private static class PriorityState { |
| |
| /** |
| * Acts as counter for number of synchronized region that needs to acquire 'this' as a lock |
| * the current thread is currently in. When it drops down to zero, we will no longer boost |
| * the thread's priority. |
| */ |
| int regionCounter; |
| |
| /** |
| * The thread's previous priority before boosting. |
| */ |
| int prevPriority; |
| } |
| } |