/*
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* Copyright (C) 2019 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.am;
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import com.android.internal.annotations.GuardedBy;
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/**
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* Detects low memory using PSI.
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*
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* If the kernel doesn't support PSI, then this class is not available.
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*/
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public final class LowMemDetector {
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private static final String TAG = "LowMemDetector";
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private final ActivityManagerService mAm;
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private final LowMemThread mLowMemThread;
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private boolean mAvailable;
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private final Object mPressureStateLock = new Object();
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@GuardedBy("mPressureStateLock")
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private int mPressureState = MEM_PRESSURE_NONE;
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/* getPressureState return values */
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public static final int MEM_PRESSURE_NONE = 0;
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public static final int MEM_PRESSURE_LOW = 1;
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public static final int MEM_PRESSURE_MEDIUM = 2;
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public static final int MEM_PRESSURE_HIGH = 3;
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LowMemDetector(ActivityManagerService am) {
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mAm = am;
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mLowMemThread = new LowMemThread();
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if (init() != 0) {
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mAvailable = false;
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} else {
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mAvailable = true;
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mLowMemThread.start();
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}
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}
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public boolean isAvailable() {
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return mAvailable;
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}
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/**
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* Returns the current mem factor.
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* Note that getMemFactor returns LowMemDetector.MEM_PRESSURE_XXX
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* which match ProcessStats.ADJ_MEM_FACTOR_XXX values. If they deviate
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* there should be conversion performed here to translate pressure state
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* into memFactor.
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*/
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public int getMemFactor() {
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synchronized (mPressureStateLock) {
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return mPressureState;
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}
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}
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private native int init();
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private native int waitForPressure();
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private final class LowMemThread extends Thread {
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public void run() {
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while (true) {
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// sleep waiting for a PSI event
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int newPressureState = waitForPressure();
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if (newPressureState == -1) {
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// epoll broke, tear this down
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mAvailable = false;
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break;
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}
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// got a PSI event? let's update lowmem info
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synchronized (mPressureStateLock) {
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mPressureState = newPressureState;
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}
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}
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}
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}
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}
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