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      1 /*
      2  * Copyright (C) 2016 The Android Open Source Project
      3  *
      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
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     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.
     15  */
     16 
     17 package com.android.server.pm;
     18 
     19 import android.os.Environment;
     20 import android.os.SystemClock;
     21 import android.util.AtomicFile;
     22 
     23 import java.io.File;
     24 import java.util.concurrent.atomic.AtomicBoolean;
     25 import java.util.concurrent.atomic.AtomicLong;
     26 
     27 /**
     28  * A simple base class for statistics that need to be saved/restored from a dedicated file. This
     29  * class provides a base implementation that:
     30  * <ul>
     31  * <li>Provide an AtomicFile to the actual read/write code
     32  * <li>A background-thread write and a synchronous write
     33  * <li>Write-limiting for the background-thread (by default writes are at least 30 minutes apart)
     34  * <li>Can lock on the provided data object before writing
     35  * </ul>
     36  * For completion, a subclass needs to implement actual {@link #writeInternal(Object) writing} and
     37  * {@link #readInternal(Object) reading}.
     38  */
     39 public abstract class AbstractStatsBase<T> {
     40 
     41     private static final int WRITE_INTERVAL_MS =
     42             (PackageManagerService.DEBUG_DEXOPT) ? 0 : 30*60*1000;
     43     private final Object mFileLock = new Object();
     44     private final AtomicLong mLastTimeWritten = new AtomicLong(0);
     45     private final AtomicBoolean mBackgroundWriteRunning = new AtomicBoolean(false);
     46     private final String mFileName;
     47     private final String mBackgroundThreadName;
     48     private final boolean mLock;
     49 
     50     protected AbstractStatsBase(String fileName, String threadName, boolean lock) {
     51         mFileName = fileName;
     52         mBackgroundThreadName = threadName;
     53         mLock = lock;
     54     }
     55 
     56     protected AtomicFile getFile() {
     57         File dataDir = Environment.getDataDirectory();
     58         File systemDir = new File(dataDir, "system");
     59         File fname = new File(systemDir, mFileName);
     60         return new AtomicFile(fname);
     61     }
     62 
     63     protected void writeNow(final T data) {
     64         writeImpl(data);
     65         mLastTimeWritten.set(SystemClock.elapsedRealtime());
     66     }
     67 
     68     protected boolean maybeWriteAsync(final T data) {
     69         if (SystemClock.elapsedRealtime() - mLastTimeWritten.get() < WRITE_INTERVAL_MS
     70             && !PackageManagerService.DEBUG_DEXOPT) {
     71             return false;
     72         }
     73 
     74         if (mBackgroundWriteRunning.compareAndSet(false, true)) {
     75             new Thread(mBackgroundThreadName) {
     76                 @Override
     77                 public void run() {
     78                     try {
     79                         writeImpl(data);
     80                         mLastTimeWritten.set(SystemClock.elapsedRealtime());
     81                     } finally {
     82                         mBackgroundWriteRunning.set(false);
     83                     }
     84                 }
     85             }.start();
     86             return true;
     87         }
     88 
     89         return false;
     90     }
     91 
     92     private void writeImpl(T data) {
     93         if (mLock) {
     94             synchronized (data) {
     95                 synchronized (mFileLock) {
     96                     writeInternal(data);
     97                 }
     98             }
     99         } else {
    100             synchronized (mFileLock) {
    101                 writeInternal(data);
    102             }
    103         }
    104     }
    105 
    106     protected abstract void writeInternal(T data);
    107 
    108     protected void read(T data) {
    109         if (mLock) {
    110             synchronized (data) {
    111                 synchronized (mFileLock) {
    112                     readInternal(data);
    113                 }
    114             }
    115         } else {
    116             synchronized (mFileLock) {
    117                 readInternal(data);
    118             }
    119         }
    120         // We use the current time as last-written. read() is called on system server startup
    121         // (current situation), and we want to postpone I/O at boot.
    122         mLastTimeWritten.set(SystemClock.elapsedRealtime());
    123     }
    124 
    125     protected abstract void readInternal(T data);
    126 }
    127