/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License
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*/
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package com.android.server;
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import static android.os.Process.getThreadPriority;
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import static android.os.Process.myTid;
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import static android.os.Process.setThreadPriority;
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/**
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* Utility class to boost threads in sections where important locks are held.
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*/
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public class ThreadPriorityBooster {
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private static final boolean ENABLE_LOCK_GUARD = false;
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private static final int PRIORITY_NOT_ADJUSTED = Integer.MAX_VALUE;
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private volatile int mBoostToPriority;
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private final int mLockGuardIndex;
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private final ThreadLocal<PriorityState> mThreadState = new ThreadLocal<PriorityState>() {
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@Override protected PriorityState initialValue() {
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return new PriorityState();
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}
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};
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public ThreadPriorityBooster(int boostToPriority, int lockGuardIndex) {
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mBoostToPriority = boostToPriority;
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mLockGuardIndex = lockGuardIndex;
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}
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public void boost() {
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final PriorityState state = mThreadState.get();
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if (state.regionCounter == 0) {
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final int prevPriority = getThreadPriority(state.tid);
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if (prevPriority > mBoostToPriority) {
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setThreadPriority(state.tid, mBoostToPriority);
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state.prevPriority = prevPriority;
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}
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}
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state.regionCounter++;
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if (ENABLE_LOCK_GUARD) {
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LockGuard.guard(mLockGuardIndex);
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}
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}
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public void reset() {
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final PriorityState state = mThreadState.get();
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state.regionCounter--;
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if (state.regionCounter == 0 && state.prevPriority != PRIORITY_NOT_ADJUSTED) {
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setThreadPriority(state.tid, state.prevPriority);
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state.prevPriority = PRIORITY_NOT_ADJUSTED;
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}
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}
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/**
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* Updates the priority we boost the threads to, and updates the current thread's priority if
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* necessary.
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*/
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protected void setBoostToPriority(int priority) {
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// We don't care about the other threads here, as long as they see the update of this
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// variable immediately.
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mBoostToPriority = priority;
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final PriorityState state = mThreadState.get();
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if (state.regionCounter != 0) {
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final int prevPriority = getThreadPriority(state.tid);
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if (prevPriority != priority) {
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setThreadPriority(state.tid, priority);
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}
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}
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}
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private static class PriorityState {
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final int tid = myTid();
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/**
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* Acts as counter for number of synchronized region that needs to acquire 'this' as a lock
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* the current thread is currently in. When it drops down to zero, we will no longer boost
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* the thread's priority.
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*/
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int regionCounter;
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/**
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* The thread's previous priority before boosting.
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*/
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int prevPriority = PRIORITY_NOT_ADJUSTED;
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}
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}
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