获取getSharedPreferences(String name, int mode)
先取了缓存, 如果缓存未命中, 才构造对象
@Override
public SharedPreferences getSharedPreferences(File file, int mode) {
SharedPreferencesImpl sp;
synchronized (ContextImpl.class) {
final ArrayMap cache = getSharedPreferencesCacheLocked();
sp = cache.get(file);
if (sp == null) {
....
sp = new SharedPreferencesImpl(file, mode);
cache.put(file, sp);
return sp;
}
}
....
return sp;
}
private ArrayMap getSharedPreferencesCacheLocked() {
if (sSharedPrefsCache == null) {
sSharedPrefsCache = new ArrayMap<>();
}
final String packageName = getPackageName();
ArrayMap packagePrefs = sSharedPrefsCache.get(packageName);
if (packagePrefs == null) {
packagePrefs = new ArrayMap<>();
sSharedPrefsCache.put(packageName, packagePrefs);
}
return packagePrefs;
}
构造SharedPreferencesImpl(File file, int mode)
开启线程，从disk加载数据到内存
SharedPreferencesImpl(File file, int mode) {
mFile = file;
mBackupFile = makeBackupFile(file);//.bak备份文件
mMode = mode;
mLoaded = false; //预防重复加载
mMap = null; //内存数据存储
mThrowable = null;
startLoadFromDisk();
}
private void startLoadFromDisk() {
synchronized (mLock) {
mLoaded = false;
}
new Thread("SharedPreferencesImpl-load") {
public void run() {
loadFromDisk();
}
}.start();
}
数据加载loadFromDisk()
private void loadFromDisk() {
synchronized (mLock) {
if (mLoaded) {
return;
}
if (mBackupFile.exists()) {
mFile.delete();
mBackupFile.renameTo(mFile);
}
}
....//xml文件读取到map
Map map = null;
StructStat stat = null;
Throwable thrown = null;
try {
stat = Os.stat(mFile.getPath());
if (mFile.canRead()) {
BufferedInputStream str = null;
try {
str = new BufferedInputStream(
new FileInputStream(mFile), 16 * 1024);
map = (Map) XmlUtils.readMapXml(str);
} catch (Exception e) {
Log.w(TAG, "Cannot read " + mFile.getAbsolutePath(), e);
} finally {
IoUtils.closeQuietly(str);
}
}
} catch (ErrnoException e) {
} catch (Throwable t) {
thrown = t;
}
....//mLoaded 标记已加载到内存，数据赋值到mMap，释放锁
synchronized (mLock) {
mLoaded = true;
mThrowable = thrown;
try {
if (thrown == null) {
if (map != null) {
mMap = map;
mStatTimestamp = stat.st_mtim;
mStatSize = stat.st_size;
} else {
mMap = new HashMap<>();
}
}
} catch (Throwable t) {
mThrowable = t;
} finally {
mLock.notifyAll();//通知所有持有mLock线程释放
}
}
}
使用sp获取getString(String key)
由下面代码看，获取value前会等待loadFromDisk()的锁释放，首次getSharedPreferences()后立马getString(key)，会阻塞当前线程
public String getString(String key, @Nullable String defValue) {
synchronized (mLock) {
awaitLoadedLocked();//等待锁
String v = (String)mMap.get(key);//直接mMap内存获取value
return v != null ? v : defValue;
}
}
private void awaitLoadedLocked() {
if (!mLoaded) {
BlockGuard.getThreadPolicy().onReadFromDisk();
}
while (!mLoaded) {
try {
mLock.wait();//mLock锁等待
} catch (InterruptedException unused) {
}
}
if (mThrowable != null) {
throw new IllegalStateException(mThrowable);
}
}
使用sp存数据putString(String key,String value)
private final Map mModified = new HashMap<>();
public Editor putString(String key, @Nullable String value) {
synchronized (mEditorLock) {
mModified.put(key, value);//数据放入Map
return this;
}
}
调用commit()或apply()，将mModified 数据先提交到内存中，再同步等待或异步写入disk
//异步不阻塞
public void apply() {
final MemoryCommitResult mcr = commitToMemory();//提交到内存
final Runnable awaitCommit = new Runnable() {
@Override
public void run() {
mcr.writtenToDiskLatch.await();
....
}
};
QueuedWork.addFinisher(awaitCommit);
Runnable postWriteRunnable = new Runnable() {
@Override
public void run() {
awaitCommit.run();
QueuedWork.removeFinisher(awaitCommit);
}
};
SharedPreferencesImpl.this.enqueueDiskWrite(mcr, postWriteRunnable);//添加写disk的任务到LinkedList中
.....
}
//同步CountDownLatch阻塞
public boolean commit() {
long startTime = 0;
....
MemoryCommitResult mcr = commitToMemory();
SharedPreferencesImpl.this.enqueueDiskWrite(mcr, null /* sync write on this thread okay */);
mcr.writtenToDiskLatch.await();//直接阻塞当前线程，直至数据写成功释放CountDownLatch
....
notifyListeners(mcr);
return mcr.writeToDiskResult;
}
commitToMemory会将内存mMap集合中的数据转换到mapToWriteToDisk集合里，然后将新put到mModified数据加进来，所以每一次的commit都会将所有的数据提交一遍。
private MemoryCommitResult commitToMemory() {
long memoryStateGeneration;
List keysModified = null;
Set listeners = null;
Map mapToWriteToDisk;
synchronized (SharedPreferencesImpl.this.mLock) {
// We optimistically don't make a deep copy until
// a memory commit comes in when we're already
// writing to disk.
if (mDiskWritesInFlight > 0) {
// We can't modify our mMap as a currently
// in-flight write owns it. Clone it before
// modifying it.
// noinspection unchecked
mMap = new HashMap(mMap);
}
mapToWriteToDisk = mMap;
mDiskWritesInFlight++;
boolean hasListeners = mListeners.size() > 0;
if (hasListeners) {
keysModified = new ArrayList();
listeners = new HashSet(mListeners.keySet());
}
synchronized (mEditorLock) {
boolean changesMade = false;
if (mClear) {
if (!mapToWriteToDisk.isEmpty()) {
changesMade = true;
mapToWriteToDisk.clear();
}
mClear = false;
}
for (Map.Entry e : mModified.entrySet()) {
String k = e.getKey();
Object v = e.getValue();
.....
if (v == this || v == null) {
if (!mapToWriteToDisk.containsKey(k)) {
continue;
}
mapToWriteToDisk.remove(k);
} else {
if (mapToWriteToDisk.containsKey(k)) {
Object existingValue = mapToWriteToDisk.get(k);
if (existingValue != null && existingValue.equals(v)) {
continue;
}
}
mapToWriteToDisk.put(k, v);
}
changesMade = true;
if (hasListeners) {
keysModified.add(k);
}
}
mModified.clear();
if (changesMade) {
mCurrentMemoryStateGeneration++;
}
memoryStateGeneration = mCurrentMemoryStateGeneration;
}
}
return new MemoryCommitResult(memoryStateGeneration, keysModified, listeners,
mapToWriteToDisk);
}
private void enqueueDiskWrite(final MemoryCommitResult mcr,
final Runnable postWriteRunnable) {
final boolean isFromSyncCommit = (postWriteRunnable == null);
final Runnable writeToDiskRunnable = new Runnable() {
@Override
public void run() {
synchronized (mWritingToDiskLock) {
writeToFile(mcr, isFromSyncCommit);
}
synchronized (mLock) {
mDiskWritesInFlight--;
}
if (postWriteRunnable != null) {
postWriteRunnable.run();
}
}
};
....//同步commit时直接当前线程写入
if (isFromSyncCommit) {
boolean wasEmpty = false;
synchronized (mLock) {
wasEmpty = mDiskWritesInFlight == 1;
}
if (wasEmpty) {
writeToDiskRunnable.run();
return;
}
}
QueuedWork.queue(writeToDiskRunnable, !isFromSyncCommit);//加到QueuedWork中的待写入LinkedList中
}
QueuedWork是一个封装了HanderThread单线程writeToDiskRunnable的处理类
public static void queue(Runnable work, boolean shouldDelay) {
Handler handler = getHandler();
synchronized (sLock) {
sWork.add(work);
//MSG_RUN 执行processPendingWork 遍历writeToDiskRunnable执行
if (shouldDelay && sCanDelay) {
handler.sendEmptyMessageDelayed(QueuedWorkHandler.MSG_RUN, DELAY);
} else {
handler.sendEmptyMessage(QueuedWorkHandler.MSG_RUN);
}
}
}
private static void processPendingWork() {
long startTime = 0;
....
synchronized (sProcessingWork) {
.....
if (work.size() > 0) {
for (Runnable w : work) {
w.run();
}
}
}
}
同时在QueuedWork中还有一个waitToFinish()方法，看注释会在Activity onPause;BroadcastReceiver onReceive;Service command 直接当前线程执行等待sWork里的writeToDiskRunnable任务
/**
* Trigger queued work to be processed immediately. The queued work is processed on a separate
* thread asynchronous. While doing that run and process all finishers on this thread. The
* finishers can be implemented in a way to check weather the queued work is finished.
*
* Is called from the Activity base class's onPause(), after BroadcastReceiver's onReceive,
* after Service command handling, etc. (so async work is never lost)
*/
public static void waitToFinish() {
long startTime = System.currentTimeMillis();
boolean hadMessages = false;
Handler handler = getHandler();
synchronized (sLock) {
//移除线程里所有runnable信息，
if (handler.hasMessages(QueuedWorkHandler.MSG_RUN)) {
// Delayed work will be processed at processPendingWork() below
handler.removeMessages(QueuedWorkHandler.MSG_RUN);
...
}
// We should not delay any work as this might delay the finishers
sCanDelay = false;
}
StrictMode.ThreadPolicy oldPolicy = StrictMode.allowThreadDiskWrites();
try {
processPendingWork();//直接当前线程执行写操作
} finally {
StrictMode.setThreadPolicy(oldPolicy);
}
....
}