DeviceStorageManagerService学习

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DeviceStorageManagerService部分源码：

/*DeviceStorageManagerService构造方法*/public DeviceStorageManagerService(Context context){mLastReportedFreeMemTime = 0;mContext = context;/*数据共享*/mContentResolver = mContext.getContentResolver();/*获取data分区信息*/mDataFileStats = new StatFs(DATA_PATH);/*获取System分区信息*/mSystemFileStats = new StatFs(SYSTEM_PATH);/*获取Cache信息*/mCacheFileStats = new StatFs(CACHE_PATH);/*获得data分区的总大小*/mTotalMemory = ((long)mDataFileStats.getBlockCount() * mDataFileStats.getBlockSize()) / 100L;/*Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFOR_BOOT在boot完成前发送广播，只能由系统服务接收*//*用于通知存储空间不足*/mStorageLowIntent = new Intent(Intent.ACTION_DEVICE_STORAGE_LOW);mStorageLoaIntent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFOR_BOOT);/*用于通知存储空间恢复正常*/mStorageOkIntent = new Intent(Intent.ACTION_DEVICE_STORAGE_OK);mStorageOkIntent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFOR_BOOT);/*存储空间满*/mStorageFullIntent = new Intent(Intent.ACTION_DEVICE_STORAGE_FULL);mStorageFullIntent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFOR_BOOT);mStorageNotFullIntent = new Intent(Intent.ACTION_DEVICE_STORAGE_NOT_FULL);mStorageNotFullIntent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFOR_BOOT);/*Threshold: 极限查询Settings数据库中sys_storage_threshold_percentage的值，默认值是10%，当data空间只剩下10%的时候，认为空间不足*/mMemLowThreshold = getMemThreshold();/*查询Settings数据库中sys_storage_full_threshold_bytes的值，默认是1MB当data空间只剩1MB时，就认为空间已满，剩下1MB供系统使用*/mMemFullThreshold = getMemFullThreshold();/*检查内存*/checkMemory(true);}private final void checkMemory(boolean checkCache) {        //if the thread that was started to clear cache is still running do nothing till its        //finished clearing cache. Ideally this flag could be modified by clearCache        // and should be accessed via a lock but even if it does this test will fail now and        //hopefully the next time this flag will be set to the correct value./*如果正在清理，则不作处理*/        if(mClearingCache) {            if(localLOGV) Slog.i(TAG, "Thread already running just skip");            //make sure the thread is not hung for too long            long diffTime = System.currentTimeMillis() - mThreadStartTime;            if(diffTime > (10*60*1000)) {                Slog.w(TAG, "Thread that clears cache file seems to run for ever");            }        } else {/*重新计算3个分区的大小*/            restatDataDir();            if (localLOGV)  Slog.v(TAG, "freeMemory="+mFreeMem);            //post intent to NotificationManager to display icon if necessary            if (mFreeMem < mMemLowThreshold) {                if (!mLowMemFlag) {                    if (checkCache) {                        // See if clearing cache helps                        // Note that clearing cache is asynchronous and so we do a                        // memory check again once the cache has been cleared.                        mThreadStartTime = System.currentTimeMillis();                        mClearSucceeded = false;/*尝试清除缓存*/                        clearCache();                    } else {                        Slog.i(TAG, "Running low on memory. Sending notification");/*清除后，空间仍不足，发送广播*/                        sendNotification();                        mLowMemFlag = true;                    }                } else {                    if (localLOGV) Slog.v(TAG, "Running low on memory " +                            "notification already sent. do nothing");                }            } else {                if (mLowMemFlag) {                    Slog.i(TAG, "Memory available. Cancelling notification");                    cancelNotification();                    mLowMemFlag = false;                }            }            if (mFreeMem < mMemFullThreshold) {                if (!mMemFullFlag) {/*如果空间已满，发送存储已满广播*/                    sendFullNotification();                    mMemFullFlag = true;                }            } else {                if (mMemFullFlag) {                    cancelFullNotification();                    mMemFullFlag = false;                }            }        }        if(localLOGV) Slog.i(TAG, "Posting Message again");        //keep posting messages to itself periodically/*private static final long DEFAULT_CHECK_INTERVAL = MONITOR_INTERVAL*60*1000;默认检查时间为1分钟*/        postCheckMemoryMsg(true, DEFAULT_CHECK_INTERVAL);}

清理缓存涉及的部分源代码：

Handler mHandler = new Handler() {        @Override        public void handleMessage(Message msg) {            //don't handle an invalid message            if (msg.what != DEVICE_MEMORY_WHAT) {                Slog.e(TAG, "Will not process invalid message");                return;            }/*收到后checkMemory*/            checkMemory(msg.arg1 == _TRUE);        }};private void postCheckMemoryMsg(boolean clearCache, long delay) {        // Remove queued messages        mHandler.removeMessages(DEVICE_MEMORY_WHAT);/*发送消息给handler*/        mHandler.sendMessageDelayed(mHandler.obtainMessage(DEVICE_MEMORY_WHAT,                clearCache ?_TRUE : _FALSE, 0),                delay);}class CachePackageDataObserver extends IPackageDataObserver.Stub {        public void onRemoveCompleted(String packageName, boolean succeeded) {            mClearSucceeded = succeeded;            mClearingCache = false;            if(localLOGV) Slog.i(TAG, " Clear succeeded:"+mClearSucceeded                    +", mClearingCache:"+mClearingCache+" Forcing memory check");           /*   发送消息重新checkMemory   */postCheckMemoryMsg(false, 0);        }}private final void clearCache() {        if (mClearCacheObserver == null) {            // Lazy instantiation/*创建一个CachePackageDataObserver对象，当PackageManagerService清理完空间时会回调该对象的onRemoveCompleted方法*/            mClearCacheObserver = new CachePackageDataObserver();        }        mClearingCache = true;        try {            if (localLOGV) Slog.i(TAG, "Clearing cache");            IPackageManager.Stub.asInterface(ServiceManager.getService("package")).                    freeStorageAndNotify(mMemLowThreshold, mClearCacheObserver);        } catch (RemoteException e) {            Slog.w(TAG, "Failed to get handle for PackageManger Exception: "+e);            mClearingCache = false;            mClearSucceeded = false;        }}

总结：

1. 构造方法：

1>. 构造方法中会获取3个分区的信息，包括，data，System，Cache；
2>. 创建4个intent，分别用于通知内存不足，内存恢复正常，内存已满，内存不满；
3>. 查询Settings数据获取最小，最大的内存限定(mMaxLowThreshold, mMemFullThreshold)；
4>. 检查内存

2. checkMemory:

1>. 如果正在清理缓存，do nothing；
2>. 重新计算3个分区的剩余空间大小；
3>. 如果内存不足，先尝试清除缓存，再重新计算分区大小，如果仍然不足，发送相应的广播；
4>. 如果内存已满，直接发送内存已满广播；

3. clearCache:

1>. 创建一个CachePackageDataObserver对象，当PackageManagerSevice清理完毕后回调onRemoveCompleted方法；
2>. onRemoveCompleted方法中调用postCheckMemoryMsg(false, 0)，给handler发送消息，调用checkMemory重新计算3个分区的大小；

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