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package com.android.providers.contacts;import com.google.android.collect.Lists;import com.google.android.collect.Maps;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteTransactionListener;import java.util.List;import java.util.Map;/** * A transaction for interacting with a Contacts provider. This is used to pass state around * throughout the operations comprising the transaction, including which databases the overall * transaction is involved in, and whether the operation being performed is a batch operation. * * 和ContactProvider交互的事务。在包含事务（Transaction）的整个过程中用来传递状态信息，例如：全部的事务涉及那个数据库以及当前 * 正在处理的数据库是否为批处理等。 * * 本事务用于管理在事务操作中涉及到的数据库。加入到集合，从集合中删除等。 */public class ContactsTransaction { /** * Whether this transaction is encompassing a batch of operations. If we're in batch mode, * transactional operations from non-batch callers are ignored. * 当前的事务是否包含一个批处理操作，如果我们当前处在批处理模式，非批处理事务性请求会忽略。 */ private final boolean mBatch; /** * The list of databases that have been enlisted in this transaction. * 在当前事务中还没有建立的数据库列表 */ private List mDatabasesForTransaction; /** * The mapping of tags to databases involved in this transaction. * 事务中涉及到的数据库tags的map集合 */ private Map mDatabaseTagMap; /** * Whether any actual changes have been made successfully in this transaction. * 在当前事务中，是否发生了任何实际的变化（数据是否发生改变） */ private boolean mIsDirty; /** * Whether a yield operation failed with an exception. If this occurred, we may not have a * lock on one of the databases that we started the transaction with (the yield code cleans * that up itself), so we should do an extra check before ending transactions. * 是否一个yield操作由于异常而失败。如果发生了这种情况，yield code会自己 * 处理，不会在事务（Transaction）要处理的数据库上加锁。 * 但我们应该在终止事务之前额外检查一下。 */ private boolean mYieldFailed; /** * Creates a new transaction object, optionally marked as a batch transaction. * @param batch Whether the transaction is in batch mode. * 创建一个事务。参数：是否标记为批处理 */ public ContactsTransaction(boolean batch) { mBatch = batch; mDatabasesForTransaction = Lists.newArrayList(); mDatabaseTagMap = Maps.newHashMap(); mIsDirty = false; } public boolean isBatch() { return mBatch; } public boolean isDirty() { return mIsDirty; } public void markDirty() { mIsDirty = true; } public void markYieldFailed() { mYieldFailed = true; } /** * If the given database has not already been enlisted in this transaction, adds it to our * list of affected databases and starts a transaction on it. If we already have the given * database in this transaction, this is a no-op. * @param db The database to start a transaction on, if necessary. * @param tag A constant that can be used to retrieve the DB instance in this transaction. * @param listener A transaction listener to attach to this transaction. May be null. * 如果事务作用的数据库没有建立，将数据库增加到（作用列表中）并且对数据库启动事务。 * 如果数据库建立了，这是一个无效的操作。 */ public void startTransactionForDb(SQLiteDatabase db, String tag, SQLiteTransactionListener listener) { if (!hasDbInTransaction(tag)) { mDatabasesForTransaction.add(db); mDatabaseTagMap.put(tag, db); if (listener != null) { db.beginTransactionWithListener(listener); } else { db.beginTransaction(); } } } /** * Returns whether DB corresponding to the given tag is currently enlisted in this transaction. * 返回被事务作用的数据库（DB）是否建立。建立返回true。否则false; */ public boolean hasDbInTransaction(String tag) { return mDatabaseTagMap.containsKey(tag); } /** * Retrieves the database enlisted in the transaction corresponding to the given tag. * @param tag The tag of the database to look up. * @return The database corresponding to the tag, or null if no database with that tag has been * enlisted in this transaction. * 返回 根据tag在列表中查找数据库。列表由事务所涉及到的数据库组成。 * 返回数据库 或者null */ public SQLiteDatabase getDbForTag(String tag) { return mDatabaseTagMap.get(tag); } /** * Removes the database corresponding to the given tag from this transaction. It is now the * caller's responsibility to do whatever needs to happen with this database - it is no longer * a part of this transaction. * @param tag The tag of the database to remove. * @return The database corresponding to the tag, or null if no database with that tag has been * enlisted in this transaction. * 根据tag从集合中移除数据库并返回。 * 前期我们构建了事务涉及的数据库集合，现在是用户的指责去操作这些数据库，在数据库上可以做任何用户想做的事情。 * 移除的数据库不再属于本事务。 */ public SQLiteDatabase removeDbForTag(String tag) { SQLiteDatabase db = mDatabaseTagMap.get(tag); mDatabaseTagMap.remove(tag); mDatabasesForTransaction.remove(db); return db; } /** * Marks all active DB transactions as successful. * @param callerIsBatch Whether this is being performed in the context of a batch operation. * If it is not, and the transaction is marked as batch, this call is a no-op. * 将所有的数据库标记为成功。 * 参数：是否由批处理引发的，如果不是，并且当前事务为批处理（batch标记为true），那么此调用为无用调用。 */ public void markSuccessful(boolean callerIsBatch) { if (!mBatch || callerIsBatch) { for (SQLiteDatabase db : mDatabasesForTransaction) { db.setTransactionSuccessful(); } } } /** * Completes the transaction, ending the DB transactions for all associated databases. * @param callerIsBatch Whether this is being performed in the context of a batch operation. * If it is not, and the transaction is marked as batch, this call is a no-op. * 终止与此事务相关的数据库上的所有事务。 * 根据mYieldFaild决定是否在finish前终止数据库上的事务（db.endTransaction()） * 参数：是否由批处理引发的，如果不是，并且当前事务为批处理（batch标记为true），那么此调用为无用调用。 */ public void finish(boolean callerIsBatch) { if (!mBatch || callerIsBatch) { for (SQLiteDatabase db : mDatabasesForTransaction) { // If an exception was thrown while yielding, it's possible that we no longer have // a lock on this database, so we need to check before attempting to end its // transaction. Otherwise, we should always expect to be in a transaction (and will // throw an exception if this is not the case). if (mYieldFailed && !db.isDbLockedByCurrentThread()) { // We no longer hold the lock, so don't do anything with this database. continue; } db.endTransaction(); } mDatabasesForTransaction.clear(); mDatabaseTagMap.clear(); mIsDirty = false; } }}