一、SharedPreferences构建:
1.1 ContextImpl.getSharedPreferences:
private static ArrayMap> sSharedPrefs;
@Override
public SharedPreferences getSharedPreferences(String name, int mode) {
SharedPreferencesImpl sp;
synchronized (ContextImpl.class) {
if (sSharedPrefs == null) {
sSharedPrefs = new ArrayMap>();
}
final String packageName = getPackageName();
ArrayMap packagePrefs = sSharedPrefs.get(packageName);
if (packagePrefs == null) {
packagePrefs = new ArrayMap();
sSharedPrefs.put(packageName, packagePrefs);
}
/**
* api19以下支持name = null;
*/
if (mPackageInfo.getApplicationInfo().targetSdkVersion < Build.VERSION_CODES.KITKAT) {
if (name == null) {
name = "null";
}
}
sp = packagePrefs.get(name);
if (sp == null) {
/**
* 1. 一个name对应一个SharedPreferencesImpl;
* 2. 将File缓存在SharedPreferencesImpl中;
*/
File prefsFile = getSharedPrefsFile(name); 模块<1.2>
sp = new SharedPreferencesImpl(prefsFile, mode); 模块<1.3>
packagePrefs.put(name, sp);
return sp;
}
}
return sp;
}
1.2 ContextImpl.getSharedPrefsFile:
/**
* 构建对应的File文件;
*/
@Override
public File getSharedPrefsFile(String name) {
return makeFilename(getPreferencesDir(), name + ".xml");
}
private File makeFilename(File base, String name) {
if (name.indexOf(File.separatorChar) < 0) {
return new File(base, name);
}
}
1.3 SharedPreferencesImpl构造函数:
SharedPreferencesImpl(File file, int mode) {
mFile = file;
mBackupFile = makeBackupFile(file);
mMode = mode;
mLoaded = false;
mMap = null;
/**
* 1. 结合模块<1.4>可知, 在使用Sp时, 需要先根据name将指定目录下的文件中的内容全部
* 加载进内存中, 然后在进行读写操作;
* 2. 数据量越大, 加载就越耗时, 所以这也就是为什么一直强调尽量不要在一个sp中存储大量数据;
*/
startLoadFromDisk(); 模块<1.4>
}
1.4 SharedPreferencesImpl.startLoadFromDisk:
private void startLoadFromDisk() {
synchronized (this) {
mLoaded = false;
}
new Thread("SharedPreferencesImpl-load") {
public void run() {
synchronized (SharedPreferencesImpl.this) {
/**
* File中的数据加载进Map是在子线程中进行, 与putXXX操作如何进行同步? 模块<二>
*/
loadFromDiskLocked();
}
}
}.start();
}
private void loadFromDiskLocked() {
if (mLoaded) {
return;
}
if (mBackupFile.exists()) {
mFile.delete();
mBackupFile.renameTo(mFile);
}
Map map = null;
StructStat stat = null;
stat = Os.stat(mFile.getPath());
if (mFile.canRead()) {
/**
* 数据量越大, 这一块就越耗时, 进行get/edit操作时如果加载没完成会处于阻塞状态;
*/
BufferedInputStream str = null;
str = new BufferedInputStream(new FileInputStream(mFile), 16*1024);
map = XmlUtils.readMapXml(str);
}
mLoaded = true;
if (map != null) {
mMap = map;
mStatTimestamp = stat.st_mtime;
mStatSize = stat.st_size;
} else {
mMap = new HashMap();
}
notifyAll();
}
二、SharedPreferencesImpl.edit:
public Editor edit() {
/**
* 这里的插入操作与初始化Sp时磁盘数据加载到内存共用同一把锁, 如果初始化时的数据加载
* 耗时过长, 这里就会被一直阻塞;
*/
synchronized (this) {
awaitLoadedLocked();
}
return new EditorImpl();
}
private void awaitLoadedLocked() {
while (!mLoaded) {
wait();
}
}
三、EditorImpl.putXXX:
public Editor putInt(String key, int value) {
synchronized (this) {
/**
* 对于指定name的Sp, 由于sp与EditorImpl都是单例, 在结合这里的锁对象, 所以Sp是线程安全的;
*/
mModified.put(key, value);
return this;
}
}
四、EditorImpl.commit:
4.1 EditorImpl.commit:
public boolean commit() {
/**
* 将数据从缓存集合mModified读取到mMap中, 然后将mMap赋值给MCR;
*/
MemoryCommitResult mcr = commitToMemory(); 模块<4.2>
/**
* 将数据从mcr.mapToWriteToDisk中写入到磁盘中;
*/
SharedPreferencesImpl.this.enqueueDiskWrite(mcr, null); 模块<4.3>
try {
mcr.writtenToDiskLatch.await();
} catch (InterruptedException e) {
return false;
}
notifyListeners(mcr);
return mcr.writeToDiskResult;
}
4.2 EditorImpl.commitToMemory:
private MemoryCommitResult commitToMemory() {
MemoryCommitResult mcr = new MemoryCommitResult();
synchronized (SharedPreferencesImpl.this) {
if (mDiskWritesInFlight > 0) {
mMap = new HashMap(mMap);
}
mcr.mapToWriteToDisk = mMap;
mDiskWritesInFlight++;
boolean hasListeners = mListeners.size() > 0;
if (hasListeners) {
mcr.keysModified = new ArrayList();
mcr.listeners = new HashSet(mListeners.keySet());
}
synchronized (this) {
for (Map.Entry e : mModified.entrySet()) {
String k = e.getKey();
Object v = e.getValue();
...
mMap.put(k, v);
mcr.changesMade = true;
if (hasListeners) {
mcr.keysModified.add(k);
}
}
mModified.clear();
}
}
return mcr;
}
- 简而言之, EditorImpl.putXXX方法将数据缓存进mModified中, 然后调用commit将mModified数据读取到mMap中, 然后赋值给MemoryCommitResult.mapToWriteToDisk, 同时情况mModified;
4.3 SharedPreferencesImpl.enqueueDiskWrite:
private void enqueueDiskWrite(final MemoryCommitResult mcr, final Runnable postWriteRunnable) {
final Runnable writeToDiskRunnable = new Runnable() {
public void run() {
// 全局共用一把锁, 写入磁盘操作是线程同步的;
synchronized (mWritingToDiskLock) {
writeToFile(mcr); 模块<4.4>
}
synchronized (SharedPreferencesImpl.this) {
mDiskWritesInFlight--;
}
if (postWriteRunnable != null) {
postWriteRunnable.run();
}
}
};
/**
* commit方式 ---> isFromSyncCommit = true;
* apply方式 ---> isFromSyncCommit = false;
*/
final boolean isFromSyncCommit = (postWriteRunnable == null);
if (isFromSyncCommit) {
boolean wasEmpty = false;
synchronized (SharedPreferencesImpl.this) {
/**
* 1. 结合模块<4.2>可知, mDiskWritesInFlight默认为0, 调用一次commit, 触发一次
* mDiskWritesInFlight++ = 1操作, 然后在writeToDiskRunnable.run中又重置
* mDiskWritesInFlight = 0操作;
* 2. 所以调用一次commit时, mDiskWritesInFlight == 1, empty = true;
*/
wasEmpty = mDiskWritesInFlight == 1;
}
if (wasEmpty) {
/**
* 调用commit时会跳转到这里, 触发writeToDiskRunnable.run;
*/
writeToDiskRunnable.run();
return;
}
}
/**
* 如果是apply方式, 则会执行到这里, 可知, writeToDiskRunnable被运行在子线程中, 然后
* 触发writeToFile在子线程中执行;
*/
QueuedWork.singleThreadExecutor().execute(writeToDiskRunnable); 模块<5.2>
}
4.4 SharedPreferencesImpl.writeToFile:
private void writeToFile(MemoryCommitResult mcr) {
if (mFile.exists()) {
if (!mcr.changesMade) {
/**
* 正如文章所说, changesMade默认为false, mModified数据被写入到mMap时将changesMade
* 置为true, 所以如果数据没有发生变化, 则不对File做任何处理;
*/
mcr.setDiskWriteResult(true);
return;
}
}
try {
FileOutputStream str = createFileOutputStream(mFile);
if (str == null) {
mcr.setDiskWriteResult(false);
return;
}
XmlUtils.writeMapXml(mcr.mapToWriteToDisk, str);
FileUtils.sync(str);
str.close();
/**
* 设置文件的读写权限;
*/
ContextImpl.setFilePermissionsFromMode(mFile.getPath(), mMode, 0);
final StructStat stat = Os.stat(mFile.getPath());
synchronized (this) {
mStatTimestamp = stat.st_mtime;
mStatSize = stat.st_size;
}
mBackupFile.delete();
mcr.setDiskWriteResult(true);
return;
}
catch (XmlPullParserException e) {...}
catch (IOException e) {...}
mcr.setDiskWriteResult(false);
}
五、EditorImpl.apply:
5.1 EditorImpl.apply:
public void apply() {
/**
* 将mModified数据写入到MemoryCommitResult中;
*/
final MemoryCommitResult mcr = commitToMemory();
final Runnable awaitCommit = new Runnable() {
public void run() {
mcr.writtenToDiskLatch.await();
}
};
QueuedWork.add(awaitCommit);
Runnable postWriteRunnable = new Runnable() {
public void run() {
awaitCommit.run();
QueuedWork.remove(awaitCommit);
}
};
/**
* 将MemoryCommitResult中缓存的数据写入到磁盘中;
*/
SharedPreferencesImpl.this.enqueueDiskWrite(mcr, postWriteRunnable); 模块<4.3>
notifyListeners(mcr);
}