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/*
* 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 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 (LockGuard.ENABLED) {
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;
}
}
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