上一篇博文我介绍了账号与同步的同步实现过程，当中提供了一个工系统进程调用的服务，那么这个服务究竟是怎么被启动和使用的呢？这篇博文我就大体梳理一下启动过程。
事实上作为一个一般开发者，我们仅仅要知道要想知道被监听的ContentProvider有变动，首先那个ContentProvider必须使用ContentResolver.notifyChange(android.net.Uri,
android.database.ContentObserver, boolean)这种方法来通知我们。我们知道这种方法会通知监听这个ContentProvider的ContentObserver数据有变化，可是ContentObserver须要在一个执行这个的进程中注冊，假设这个进程死掉了ContentObserver也须要取消注冊监听，这样就没法监听了。只是值得注意的是，这个notifyChange方法还有另外一个作用，就是配合实现android的同步框架，通知SyncManager启动对应账号的同步。
ContentResolver.java首先我们来看看ContentResolver的notifyChange源代码，例如以下：
public void notifyChange(Uri uri, ContentObserver observer) {
notifyChange(uri, observer, true /* sync to network */);
}
public void notifyChange(Uri uri, ContentObserver observer, boolean syncToNetwork) {
notifyChange(uri, observer, syncToNetwork, UserHandle.getCallingUserId());
}
public void notifyChange(Uri uri, ContentObserver observer, boolean syncToNetwork,
int userHandle) {
try {
getContentService().notifyChange(
uri, observer == null ? null : observer.getContentObserver(),
observer != null && observer.deliverSelfNotifications(), syncToNetwork,
userHandle);
} catch (RemoteException e) {
}
}
上面重载的三个notifyChange方法，终于调用的都是ContentService中的notifyChange方法，getContentService()方法例如以下：
public static IContentService getContentService() {
if (sContentService != null) {
return sContentService;
}
IBinder b = ServiceManager.getService(CONTENT_SERVICE_NAME);
if (false) Log.v("ContentService", "default service binder = " + b);
sContentService = IContentService.Stub.asInterface(b);
if (false) Log.v("ContentService", "default service = " + sContentService);
return sContentService;
}
ContentService是对存根类IContentService.Stub的实现，它提供一系列数据同步及数据訪问等相关的操作,源代码例如以下：
public final class ContentService extends IContentService.Stub
此类中的两个重载的notifyChange方法例如以下：
public void notifyChange(Uri uri, IContentObserver observer,
boolean observerWantsSelfNotifications, boolean syncToNetwork) {
notifyChange(uri, observer, observerWantsSelfNotifications, syncToNetwork,
UserHandle.getCallingUserId());
}
@Override
public void notifyChange(Uri uri, IContentObserver observer,
boolean observerWantsSelfNotifications, boolean syncToNetwork,
int userHandle) {
...
最重要的一句，就是启动ContentObserver的onChange方法
oc.mObserver.onChange(oc.mSelfChange, uri);
...
最重要的还有一句，就是启动同步
if (syncToNetwork) {
SyncManager syncManager = getSyncManager();
if (syncManager != null) {
syncManager.scheduleLocalSync(null /* all accounts */, callingUserHandle, uid,
uri.getAuthority());
}
}
} finally {
restoreCallingIdentity(identityToken);
}
}
//获取SyncManager 的方法
private SyncManager getSyncManager() {
if (SystemProperties.getBoolean("config.disable_network", false)) {
return null;
}
synchronized(mSyncManagerLock) {
try {
// Try to create the SyncManager, return null if it fails (e.g. the disk is full).
if (mSyncManager == null) mSyncManager = new SyncManager(mContext, mFactoryTest);
} catch (SQLiteException e) {
Log.e(TAG, "Can't create SyncManager", e);
}
return mSyncManager;
}
}
这是一个同步机制中最核心的类，承载了基本的功能实现，本人仅仅大体介绍一下主要代码，以求打通整个流程。首先来看上面那个类调用的方法scheduleLocalSync：
public void scheduleLocalSync(Account account, int userId, int reason, String authority) {
final Bundle extras = new Bundle();
extras.putBoolean(ContentResolver.SYNC_EXTRAS_UPLOAD, true);
scheduleSync(account, userId, reason, authority, extras,
LOCAL_SYNC_DELAY /* earliest run time */,
2 * LOCAL_SYNC_DELAY /* latest sync time. */,
false /* onlyThoseWithUnkownSyncableState */);
}
scheduleLocalSync方法主要调用了scheduleSync方法，其大体内容例如以下：
public void scheduleSync(Account requestedAccount, int userId, int reason,
String requestedAuthority, Bundle extras, long beforeRuntimeMillis,
long runtimeMillis, boolean onlyThoseWithUnkownSyncableState) {
boolean isLoggable = Log.isLoggable(TAG, Log.VERBOSE);
final boolean backgroundDataUsageAllowed = !mBootCompleted ||
getConnectivityManager().getBackgroundDataSetting();
if (extras == null) {
extras = new Bundle();
}
if (isLoggable) {
Log.d(TAG, "one-time sync for: " + requestedAccount + " " + extras.toString() + " "
+ requestedAuthority);
}
//假设是加速模式则把延迟时间设置为-1，runtimeMillis在较早的版本号中是叫做delay的，就是当你调用这种方法后多久启动同步任务。
Boolean expedited = extras.getBoolean(ContentResolver.SYNC_EXTRAS_EXPEDITED, false);
if (expedited) {
runtimeMillis = -1; // this means schedule at the front of the queue
}
//获取手机中全部加入过的账号信息
AccountAndUser[] accounts;
if (requestedAccount != null && userId != UserHandle.USER_ALL) {
accounts = new AccountAndUser[] { new AccountAndUser(requestedAccount, userId) };
} else {
// if the accounts aren't configured yet then we can't support an account-less
// sync request
accounts = mRunningAccounts;
if (accounts.length == 0) {
if (isLoggable) {
Log.v(TAG, "scheduleSync: no accounts configured, dropping");
}
return;
}
}
//
final boolean uploadOnly = extras.getBoolean(ContentResolver.SYNC_EXTRAS_UPLOAD, false);
final boolean manualSync = extras.getBoolean(ContentResolver.SYNC_EXTRAS_MANUAL, false);
if (manualSync) {
extras.putBoolean(ContentResolver.SYNC_EXTRAS_IGNORE_BACKOFF, true);
extras.putBoolean(ContentResolver.SYNC_EXTRAS_IGNORE_SETTINGS, true);
}
final boolean ignoreSettings =
extras.getBoolean(ContentResolver.SYNC_EXTRAS_IGNORE_SETTINGS, false);
int source;
if (uploadOnly) {
source = SyncStorageEngine.SOURCE_LOCAL;
} else if (manualSync) {
source = SyncStorageEngine.SOURCE_USER;
} else if (requestedAuthority == null) {
source = SyncStorageEngine.SOURCE_POLL;
} else {
// this isn't strictly server, since arbitrary callers can (and do) request
// a non-forced two-way sync on a specific url
source = SyncStorageEngine.SOURCE_SERVER;
}
for (AccountAndUser account : accounts) {
// Compile a list of authorities that have sync adapters. For each authority sync each account that matches a sync adapter.
final HashSet<String> syncableAuthorities = new HashSet<String>();
for (RegisteredServicesCache.ServiceInfo<SyncAdapterType> syncAdapter :
mSyncAdapters.getAllServices(account.userId)) {
syncableAuthorities.add(syncAdapter.type.authority);
}
// if the url was specified then replace the list of authorities with just this authority or clear it if this authority isn't syncable
if (requestedAuthority != null) {
final boolean hasSyncAdapter = syncableAuthorities.contains(requestedAuthority);
syncableAuthorities.clear();
if (hasSyncAdapter) syncableAuthorities.add(requestedAuthority);
}
for (String authority : syncableAuthorities) {
//account账号是否声明同步authority
int isSyncable = getIsSyncable(account.account, account.userId,
authority);
if (isSyncable == 0) {
continue;
}
//一系列的推断，排除一起异常的情况
final RegisteredServicesCache.ServiceInfo<SyncAdapterType> syncAdapterInfo;
syncAdapterInfo = mSyncAdapters.getServiceInfo(
SyncAdapterType.newKey(authority, account.account.type), account.userId);
if (syncAdapterInfo == null) {
continue;
}
final boolean allowParallelSyncs = syncAdapterInfo.type.allowParallelSyncs();
final boolean isAlwaysSyncable = syncAdapterInfo.type.isAlwaysSyncable();
if (isSyncable < 0 && isAlwaysSyncable) {
mSyncStorageEngine.setIsSyncable(account.account, account.userId, authority, 1);
isSyncable = 1;
}
if (onlyThoseWithUnkownSyncableState && isSyncable >= 0) {
continue;
}
if (!syncAdapterInfo.type.supportsUploading() && uploadOnly) {
continue;
}
// always allow if the isSyncable state is unknown
boolean syncAllowed =
(isSyncable < 0)
|| ignoreSettings
|| (backgroundDataUsageAllowed
&& mSyncStorageEngine.getMasterSyncAutomatically(account.userId)
&& mSyncStorageEngine.getSyncAutomatically(account.account,
account.userId, authority));
if (!syncAllowed) {
if (isLoggable) {
Log.d(TAG, "scheduleSync: sync of " + account + ", " + authority
+ " is not allowed, dropping request");
}
continue;
}
//最后进入两种须要通知同步的情况，都调用scheduleSyncOperation方法实现
Pair<Long, Long> backoff = mSyncStorageEngine
.getBackoff(account.account, account.userId, authority);
long delayUntil = mSyncStorageEngine.getDelayUntilTime(account.account,
account.userId, authority);
final long backoffTime = backoff != null ? backoff.first : 0;
if (isSyncable < 0) {
// Initialisation sync.
Bundle newExtras = new Bundle();
newExtras.putBoolean(ContentResolver.SYNC_EXTRAS_INITIALIZE, true);
if (isLoggable) {
Log.v(TAG, "schedule initialisation Sync:"
+ ", delay until " + delayUntil
+ ", run by " + 0
+ ", source " + source
+ ", account " + account
+ ", authority " + authority
+ ", extras " + newExtras);
}
scheduleSyncOperation(
new SyncOperation(account.account, account.userId, reason, source,
authority, newExtras, 0 /* immediate */, 0 /* No flex time*/,
backoffTime, delayUntil, allowParallelSyncs));
}
if (!onlyThoseWithUnkownSyncableState) {
if (isLoggable) {
Log.v(TAG, "scheduleSync:"
+ " delay until " + delayUntil
+ " run by " + runtimeMillis
+ " flex " + beforeRuntimeMillis
+ ", source " + source
+ ", account " + account
+ ", authority " + authority
+ ", extras " + extras);
}
scheduleSyncOperation(
new SyncOperation(account.account, account.userId, reason, source,
authority, extras, runtimeMillis, beforeRuntimeMillis,
backoffTime, delayUntil, allowParallelSyncs));
}
}
}
}
//此方法主要做两件是，一是把要同步的操作加入到队列中，二是发消息
public void scheduleSyncOperation(SyncOperation syncOperation) {
boolean queueChanged;
synchronized (mSyncQueue) {
queueChanged = mSyncQueue.add(syncOperation);
}
if (queueChanged) {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "scheduleSyncOperation: enqueued " + syncOperation);
}
sendCheckAlarmsMessage();
} else {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "scheduleSyncOperation: dropping duplicate sync operation "
+ syncOperation);
}
}
}
//发出MESSAGE_CHECK_ALARMS消息
private void sendCheckAlarmsMessage() {
if (Log.isLoggable(TAG, Log.VERBOSE)) Log.v(TAG, "sending MESSAGE_CHECK_ALARMS");
mSyncHandler.removeMessages(SyncHandler.MESSAGE_CHECK_ALARMS);
mSyncHandler.sendEmptyMessage(SyncHandler.MESSAGE_CHECK_ALARMS);
}
//接收消息并处理
@Override
public void handleMessage(Message msg) {
if (tryEnqueueMessageUntilReadyToRun(msg)) {
return;
}
switch (msg.what) {
case SyncHandler.MESSAGE_CANCEL: {
...
case SyncHandler.MESSAGE_SYNC_FINISHED:
...
case SyncHandler.MESSAGE_SERVICE_CONNECTED: {
ServiceConnectionData msgData = (ServiceConnectionData)msg.obj;
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.d(TAG, "handleSyncHandlerMessage: MESSAGE_SERVICE_CONNECTED: "
+ msgData.activeSyncContext);
}
// check that this isn't an old message
if (isSyncStillActive(msgData.activeSyncContext)) {
runBoundToSyncAdapter(msgData.activeSyncContext, msgData.syncAdapter);
}
break;
}
case SyncHandler.MESSAGE_SERVICE_DISCONNECTED: {
...
case SyncHandler.MESSAGE_SYNC_ALARM: {
boolean isLoggable = Log.isLoggable(TAG, Log.VERBOSE);
if (isLoggable) {
Log.v(TAG, "handleSyncHandlerMessage: MESSAGE_SYNC_ALARM");
}
mAlarmScheduleTime = null;
try {
nextPendingSyncTime = maybeStartNextSyncLocked();
} finally {
mHandleAlarmWakeLock.release();
}
break;
}
//须要检查时钟任务，有须要通知的同步操作
case SyncHandler.MESSAGE_CHECK_ALARMS:
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "handleSyncHandlerMessage: MESSAGE_CHECK_ALARMS");
}
nextPendingSyncTime = maybeStartNextSyncLocked();
break;
}
} finally {
manageSyncNotificationLocked();
manageSyncAlarmLocked(earliestFuturePollTime, nextPendingSyncTime);
mSyncTimeTracker.update();
mSyncManagerWakeLock.release();
}
}
//检查可能有下一个通知操作
private long maybeStartNextSyncLocked() {
...一堆的推断
for (int i = 0, N = operations.size(); i < N; i++) {
...一堆的推断
// If the next run time is in the future, even given the flexible scheduling, return the time.
if (op.effectiveRunTime - op.flexTime > now) {
if (nextReadyToRunTime > op.effectiveRunTime) {
nextReadyToRunTime = op.effectiveRunTime;
}
if (isLoggable) {
Log.v(TAG, " Dropping sync operation: Sync too far in future.");
}
continue;
}
...一堆的推断
if (toReschedule != null) {
runSyncFinishedOrCanceledLocked(null, toReschedule);
scheduleSyncOperation(toReschedule.mSyncOperation);
}
synchronized (mSyncQueue) {
mSyncQueue.remove(candidate);
}
dispatchSyncOperation(candidate);
}
return nextReadyToRunTime;
}
//正式分发通知同步操作
private boolean dispatchSyncOperation(SyncOperation op) {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "dispatchSyncOperation: we are going to sync " + op);
Log.v(TAG, "num active syncs: " + mActiveSyncContexts.size());
for (ActiveSyncContext syncContext : mActiveSyncContexts) {
Log.v(TAG, syncContext.toString());
}
}
// connect to the sync adapter
SyncAdapterType syncAdapterType = SyncAdapterType.newKey(op.authority, op.account.type);
final RegisteredServicesCache.ServiceInfo<SyncAdapterType> syncAdapterInfo;
syncAdapterInfo = mSyncAdapters.getServiceInfo(syncAdapterType, op.userId);
if (syncAdapterInfo == null) {
Log.d(TAG, "can't find a sync adapter for " + syncAdapterType
+ ", removing settings for it");
mSyncStorageEngine.removeAuthority(op.account, op.userId, op.authority);
return false;
}
//一个SyncManager的内部类
ActiveSyncContext activeSyncContext =
new ActiveSyncContext(op, insertStartSyncEvent(op), syncAdapterInfo.uid);
activeSyncContext.mSyncInfo = mSyncStorageEngine.addActiveSync(activeSyncContext);
mActiveSyncContexts.add(activeSyncContext);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "dispatchSyncOperation: starting " + activeSyncContext);
}
//绑定服务端
if (!activeSyncContext.bindToSyncAdapter(syncAdapterInfo, op.userId)) {
Log.e(TAG, "Bind attempt failed to " + syncAdapterInfo);
closeActiveSyncContext(activeSyncContext);
return false;
}
return true;
}
ActiveSyncContext是SyncManager的内部类，它实现了ServiceConnection，当中的两个重要的方法例如以下：
boolean bindToSyncAdapter(RegisteredServicesCache.ServiceInfo info, int userId) {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.d(TAG, "bindToSyncAdapter: " + info.componentName + ", connection " + this);
}
Intent intent = new Intent();
//还记得上一篇博文中的这个Action吗？android.content.SyncAdapter
intent.setAction("android.content.SyncAdapter");
intent.setComponent(info.componentName);
intent.putExtra(Intent.EXTRA_CLIENT_LABEL,
com.android.internal.R.string.sync_binding_label);
intent.putExtra(Intent.EXTRA_CLIENT_INTENT, PendingIntent.getActivityAsUser(
mContext, 0, new Intent(Settings.ACTION_SYNC_SETTINGS), 0,
null, new UserHandle(userId)));
mBound = true;
final boolean bindResult = mContext.bindServiceAsUser(intent, this,
Context.BIND_AUTO_CREATE | Context.BIND_NOT_FOREGROUND
| Context.BIND_ALLOW_OOM_MANAGEMENT,
new UserHandle(mSyncOperation.userId));
if (!bindResult) {
mBound = false;
}
return bindResult;
}
public void onServiceConnected(ComponentName name, IBinder service) {
Message msg = mSyncHandler.obtainMessage();
msg.what = SyncHandler.MESSAGE_SERVICE_CONNECTED;
msg.obj = new ServiceConnectionData(this, ISyncAdapter.Stub.asInterface(service));
mSyncHandler.sendMessage(msg);
}
//在上面的接收MESSAGE_SERVICE_CONNECTED消息后，运行runBoundToSyncAdapter
private void runBoundToSyncAdapter(final ActiveSyncContext activeSyncContext,
ISyncAdapter syncAdapter) {
activeSyncContext.mSyncAdapter = syncAdapter;
final SyncOperation syncOperation = activeSyncContext.mSyncOperation;
try {
activeSyncContext.mIsLinkedToDeath = true;
syncAdapter.asBinder().linkToDeath(activeSyncContext, 0);
//还记得上一篇博文中有关startSync的介绍吗？
syncAdapter.startSync(activeSyncContext, syncOperation.authority,
syncOperation.account, syncOperation.extras);
} catch (RemoteException remoteExc) {
Log.d(TAG, "maybeStartNextSync: caught a RemoteException, rescheduling", remoteExc);
closeActiveSyncContext(activeSyncContext);
increaseBackoffSetting(syncOperation);
scheduleSyncOperation(new SyncOperation(syncOperation));
} catch (RuntimeException exc) {
closeActiveSyncContext(activeSyncContext);
Log.e(TAG, "Caught RuntimeException while starting the sync " + syncOperation, exc);
}
}
注意，本博文仅仅是简单地抽取了notifyChange分支的流程，给大家看，有兴趣的童鞋能够研究一下requestSync流程。