SharePreference源码
ContextImpl getSharedPreferences方法， mSharedPrefsPaths 是个集合ArrayMap<String, File>，根据名称缓存了文件
public SharedPreferences getSharedPreferences(String name, int mode) {
// At least one application in the world actually passes in a null
// name. This happened to work because when we generated the file name
// we would stringify it to "null.xml". Nice.
if (mPackageInfo.getApplicationInfo().targetSdkVersion <
Build.VERSION_CODES.KITKAT) {
if (name == null) {
name = "null";
}
}
File file;
synchronized (ContextImpl.class) {
if (mSharedPrefsPaths == null) {
mSharedPrefsPaths = new ArrayMap<>();
}
file = mSharedPrefsPaths.get(name);
if (file == null) {
// 1如果不存在，则创建
file = getSharedPreferencesPath(name);
mSharedPrefsPaths.put(name, file);
}
}
//这个时候已经有文件了
return getSharedPreferences(file, mode);
}
//注释 1 /baoming/data/shared_prefs目录下
public File getSharedPreferencesPath(String name) {
return makeFilename(getPreferencesDir(), name + ".xml");
}
private File getPreferencesDir() {
synchronized (mSync) {
if (mPreferencesDir == null) {
mPreferencesDir = new File(getDataDir(), "shared_prefs");
}
return ensurePrivateDirExists(mPreferencesDir);
}
}
@Override
public SharedPreferences getSharedPreferences(File file, int mode) {
SharedPreferencesImpl sp;
synchronized (ContextImpl.class) {
//1 从缓存中获取SharedPreferencesImpl对象。根据进程名获取当前进程的
final ArrayMap<File, SharedPreferencesImpl> cache = getSharedPreferencesCacheLocked();
sp = cache.get(file);
if (sp == null) {
//检查mode
checkMode(mode);
if (getApplicationInfo().targetSdkVersion >= android.os.Build.VERSION_CODES.O) {
if (isCredentialProtectedStorage()
&& !getSystemService(UserManager.class)
.isUserUnlockingOrUnlocked(UserHandle.myUserId())) {
throw new IllegalStateException("SharedPreferences in credential encrypted "
+ "storage are not available until after user is unlocked");
}
}
//2 生成一个SharedPreferencesImpl，放入缓存
sp = new SharedPreferencesImpl(file, mode);
cache.put(file, sp);
return sp;
}
}
if ((mode & Context.MODE_MULTI_PROCESS) != 0 ||
getApplicationInfo().targetSdkVersion < android.os.Build.VERSION_CODES.HONEYCOMB) {
// If somebody else (some other process) changed the prefs
// file behind our back, we reload it. This has been the
// historical (if undocumented) behavior.
sp.startReloadIfChangedUnexpectedly();
}
return sp;
}
//注释1 。根据包名，也就是进程名获取缓存。
private ArrayMap<File, SharedPreferencesImpl> getSharedPreferencesCacheLocked() {
if (sSharedPrefsCache == null) {
sSharedPrefsCache = new ArrayMap<>();
}
final String packageName = getPackageName();
ArrayMap<File, SharedPreferencesImpl> packagePrefs = sSharedPrefsCache.get(packageName);
if (packagePrefs == null) {
packagePrefs = new ArrayMap<>();
sSharedPrefsCache.put(packageName, packagePrefs);
}
return packagePrefs;
}
//注释2 生成一个实现类
SharedPreferencesImpl(File file, int mode) {
mFile = file;
mBackupFile = makeBackupFile(file);
mMode = mode;
mLoaded = false;
mMap = null;
startLoadFromDisk();
}
//从磁盘上加载
private void startLoadFromDisk() {
synchronized (mLock) {
mLoaded = false;
}
new Thread("SharedPreferencesImpl-load") {
public void run() {
loadFromDisk();
}
}.start();
}
private void loadFromDisk() {
synchronized (mLock) {
if (mLoaded) {
return;
}
//如果备份文件存在
if (mBackupFile.exists()) {
mFile.delete();
mBackupFile.renameTo(mFile);
}
}
// Debugging
if (mFile.exists() && !mFile.canRead()) {
Log.w(TAG, "Attempt to read preferences file " + mFile + " without permission");
}
Map map = null;
StructStat stat = null;
try {
stat = Os.stat(mFile.getPath());
if (mFile.canRead()) {
BufferedInputStream str = null;
try {
str = new BufferedInputStream(
new FileInputStream(mFile), 16*1024);
//xml文件格式。用Pull方式去解析
map = XmlUtils.readMapXml(str);
} catch (Exception e) {
Log.w(TAG, "Cannot read " + mFile.getAbsolutePath(), e);
} finally {
IoUtils.closeQuietly(str);
}
}
} catch (ErrnoException e) {
/* ignore */
}
synchronized (mLock) {
mLoaded = true;
if (map != null) {
mMap = map;
mStatTimestamp = stat.st_mtim;
mStatSize = stat.st_size;
} else {
mMap = new HashMap<>();
}
mLock.notifyAll();
}
}
public Editor edit() {
// TODO: remove the need to call awaitLoadedLocked() when
// requesting an editor. will require some work on the
// Editor, but then we should be able to do:
//
// context.getSharedPreferences(..).edit().putString(..).apply()
//
// ... all without blocking.
synchronized (mLock) {
//如果前面的xml文件没有加载完成。等待。。
awaitLoadedLocked();
}
//返回一个新的EditorImpl对象
return new EditorImpl();
}
小结:SharedPreferencesImpl初始化的时候会创建一个线程把文件加载进来。如果文件还没加载进来调用edit方法则会阻塞当前调用线程。
//put的数据都放在mModified map集合中。
public Editor putString(String key, @Nullable String value) {
synchronized (mLock) {
mModified.put(key, value);
return this;
}
}
public boolean commit() {
long startTime = 0;
if (DEBUG) {
startTime = System.currentTimeMillis();
}
//注释1 把mModefied的里面的值放到mMap里面
MemoryCommitResult mcr = commitToMemory();
//注释2 放入QueuedWork队列。QueuedWork是HandlerThread实现的单线程。
SharedPreferencesImpl.this.enqueueDiskWrite(
mcr, null /* sync write on this thread okay */);
try {
//阻塞当前线程，直到写入文件完成
mcr.writtenToDiskLatch.await();
} catch (InterruptedException e) {
return false;
} finally {
if (DEBUG) {
Log.d(TAG, mFile.getName() + ":" + mcr.memoryStateGeneration
+ " committed after " + (System.currentTimeMillis() - startTime)
+ " ms");
}
}
notifyListeners(mcr);
//3 返回是否写入成功
return mcr.writeToDiskResult;
}
//注释1 把mModefied的里面的值放到mMap里面
private MemoryCommitResult commitToMemory() {
...
synchronized (mLock) {
boolean changesMade = false;
//如果调用了clear方法。则mClear为true.
if (mClear) {
if (!mMap.isEmpty()) {
changesMade = true;
mMap.clear();
}
mClear = false;
}
//把mModefied的里面的值放到mMap里面。mModefied是当前Editor调用putXXX的集合。mMap则是所有数据的集合。
for (Map.Entry<String, Object> e : mModified.entrySet()) {
String k = e.getKey();
Object v = e.getValue();
if (v == this || v == null) {
if (!mMap.containsKey(k)) {
continue;
}
mMap.remove(k);
} else {
if (mMap.containsKey(k)) {
Object existingValue = mMap.get(k);
if (existingValue != null && existingValue.equals(v)) {
continue;
}
}
mMap.put(k, v);
}
changesMade = true;
if (hasListeners) {
keysModified.add(k);
}
}
mModified.clear();
if (changesMade) {
mCurrentMemoryStateGeneration++;
}
memoryStateGeneration = mCurrentMemoryStateGeneration;
}
}
return new MemoryCommitResult(memoryStateGeneration, keysModified, listeners,
mapToWriteToDisk);
}
//注释2 最终会调用如下方法 写入文件,并且写入结果在MemoryCommitResult对象
private void writeToFile(MemoryCommitResult mcr, boolean isFromSyncCommit) {
...
// Attempt to write the file, delete the backup and return true as atomically as
// possible. If any exception occurs, delete the new file; next time we will restore
// from the backup.
try {
//获取输入流
FileOutputStream str = createFileOutputStream(mFile);
//同样用Pull写入
XmlUtils.writeMapXml(mcr.mapToWriteToDisk, str);
writeTime = System.currentTimeMillis();
//刷新
FileUtils.sync(str);
fsyncTime = System.currentTimeMillis();
//关闭流
str.close();
//写入成功了。释放
mcr.setDiskWriteResult(true, true);
long fsyncDuration = fsyncTime - writeTime;
mSyncTimes.add((int) fsyncDuration);
mNumSync++;
//返回。
return;
} catch (XmlPullParserException e) {
Log.w(TAG, "writeToFile: Got exception:", e);
} catch (IOException e) {
Log.w(TAG, "writeToFile: Got exception:", e);
}
//如果写入失败。释放
mcr.setDiskWriteResult(false, false);
}
小结：commit方法运行在当前调用的线程中。如果未写入文件，则阻塞当前进程等待写入文件数据完成才会返回。
apply方法
public void apply() {
final long startTime = System.currentTimeMillis();
//把mModefied的里面的值放到mMap里面
final MemoryCommitResult mcr = commitToMemory();
final Runnable awaitCommit = new Runnable() {
public void run() {
try {
//阻塞
mcr.writtenToDiskLatch.await();
} catch (InterruptedException ignored) {
}
if (DEBUG && mcr.wasWritten) {
Log.d(TAG, mFile.getName() + ":" + mcr.memoryStateGeneration
+ " applied after " + (System.currentTimeMillis() - startTime)
+ " ms");
}
}
};
//添加到sFinishers当中
QueuedWork.addFinisher(awaitCommit);
Runnable postWriteRunnable = new Runnable() {
public void run() {
awaitCommit.run();
QueuedWork.removeFinisher(awaitCommit);
}
};
//放入QueuedWork队列
SharedPreferencesImpl.this.enqueueDiskWrite(mcr, postWriteRunnable);
// Okay to notify the listeners before it's hit disk
// because the listeners should always get the same
// SharedPreferences instance back, which has the
// changes reflected in memory.
notifyListeners(mcr);
}
//QueuedWork.queue先执行writeToDiskRunnable里面的run方法。而后执行postWriteRunnable里面的run方法
private void enqueueDiskWrite(final MemoryCommitResult mcr,
final Runnable postWriteRunnable) {
final boolean isFromSyncCommit = (postWriteRunnable == null);
final Runnable writeToDiskRunnable = new Runnable() {
public void run() {
synchronized (mWritingToDiskLock) {
//1 执行完写入文件的操作
writeToFile(mcr, isFromSyncCommit);
}
synchronized (mLock) {
mDiskWritesInFlight--;
}
//2 执行postWriteRunnable的方法
if (postWriteRunnable != null) {
postWriteRunnable.run();
}
}
};
// Typical #commit() path with fewer allocations, doing a write on
// the current thread.
if (isFromSyncCommit) {
boolean wasEmpty = false;
synchronized (mLock) {
wasEmpty = mDiskWritesInFlight == 1;
}
if (wasEmpty) {
writeToDiskRunnable.run();
return;
}
}
QueuedWork.queue(writeToDiskRunnable, !isFromSyncCommit);
}
小结:apply方法放入列队中等待执行，不会影响当前线程
在apply里面看到，添加了一个阻塞的任务到QueuedWork的sFinishers里面，
public void apply() {
final long startTime = System.currentTimeMillis();
//把mModefied的里面的值放到mMap里面
final MemoryCommitResult mcr = commitToMemory();
final Runnable awaitCommit = new Runnable() {
public void run() {
try {
//阻塞
mcr.writtenToDiskLatch.await();
} catch (InterruptedException ignored) {
}
if (DEBUG && mcr.wasWritten) {
Log.d(TAG, mFile.getName() + ":" + mcr.memoryStateGeneration
+ " applied after " + (System.currentTimeMillis() - startTime)
+ " ms");
}
}
};
//添加到sFinishers当中
QueuedWork.addFinisher(awaitCommit);
...
}
而QueueWork里面还有个触发sFinishers执行的，这个方法在哪里执行的呢
public static void waitToFinish() {
long startTime = System.currentTimeMillis();
boolean hadMessages = false;
Handler handler = getHandler();
synchronized (sLock) {
if (handler.hasMessages(QueuedWorkHandler.MSG_RUN)) {
// Delayed work will be processed at processPendingWork() below
handler.removeMessages(QueuedWorkHandler.MSG_RUN);
if (DEBUG) {
hadMessages = true;
Log.d(LOG_TAG, "waiting");
}
}
// We should not delay any work as this might delay the finishers
sCanDelay = false;
}
StrictMode.ThreadPolicy oldPolicy = StrictMode.allowThreadDiskWrites();
try {
processPendingWork();
} finally {
StrictMode.setThreadPolicy(oldPolicy);
}
try {
while (true) {
Runnable finisher;
synchronized (sLock) {
finisher = sFinishers.poll();
}
if (finisher == null) {
break;
}
finisher.run();
}
} finally {
sCanDelay = true;
}
synchronized (sLock) {
long waitTime = System.currentTimeMillis() - startTime;
if (waitTime > 0 || hadMessages) {
mWaitTimes.add(Long.valueOf(waitTime).intValue());
mNumWaits++;
if (DEBUG || mNumWaits % 1024 == 0 || waitTime > MAX_WAIT_TIME_MILLIS) {
mWaitTimes.log(LOG_TAG, "waited: ");
}
}
}
}
Service和,Activity的生命周期方法里面会调用。为什么会在Service和Activity的生命周期里面调用这些方法？如果耗时操作岂不会阻塞主线程？因为都在stop或者pause和stop里面执行了。可能是保证内存中的数据存入文件中。
private void handleStopService(IBinder token) {
...
QueuedWork.waitToFinish();
try {
ActivityManager.getService().serviceDoneExecuting(
token, SERVICE_DONE_EXECUTING_STOP, 0, 0);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
...
}
private void handlePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges, boolean dontReport, int seq) {
ActivityClientRecord r = mActivities.get(token);
...
QueuedWork.waitToFinish();
}
// Tell the activity manager we have paused.
if (!dontReport) {
try {
ActivityManager.getService().activityPaused(token);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
...
}
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