Fescar - RM Executor执行过程介绍

开篇

 这篇文章的目的是介绍ExecuteTemplate中调用的Executor的执行过程。

Executor的类图

Executor.png

说明：

• BaseTransactionalExecutor提供解析SQL语句获取元数据的功能。
• AbstractDMLBaseExecutor提供执行SQL的功能包括doExecute。
• Insert/Delete/UpdateExecutor提供SQL执行前后镜像获取功能。

InsertExecutor执行过程

InsertExecutor.jpg

说明：

• Executor的整个执行的过程(以InsertExecutor为例)，整个是父类调用子类的过程。
• 对比InsertExecutor的类图的接口能够更好的理解整个调用过程。

Executor源码介绍 - 执行过程

StatementProxy

public class StatementProxy extends AbstractStatementProxy {

    @Override
    public ResultSet executeQuery(String sql) throws SQLException {
        this.targetSQL = sql;
        return ExecuteTemplate.execute(this, new StatementCallback() {
            @Override
            public ResultSet execute(Statement statement, Object... args) throws SQLException {
                return statement.executeQuery((String) args[0]);
            }
        }, sql);
    }
}

说明：

• StatementProxy的核心调用逻辑。
• ExecuteTemplate.execute负责调用ExecuteTemplate。
• StatementCallback()负责在Executor当中被回调。

ExecuteTemplate

public class ExecuteTemplate {

    public static  T execute(StatementProxy statementProxy,
                                                     StatementCallback statementCallback,
                                                     Object... args) throws SQLException {
        return execute(null, statementProxy, statementCallback, args);
    }


    public static  T execute(SQLRecognizer sqlRecognizer,
                                                     StatementProxy statementProxy,
                                                     StatementCallback statementCallback,
                                                     Object... args) throws SQLException {

        if (!RootContext.inGlobalTransaction()) {
            // Just work as original statement
            return statementCallback.execute(statementProxy.getTargetStatement(), args);
        }

        // sqlRecognizer 执行过程中传入值为null，走的分支代码
        if (sqlRecognizer == null) {

           //  SQLVisitorFactory.get是一个核心代码，会具体分析
            sqlRecognizer = SQLVisitorFactory.get(
                statementProxy.getTargetSQL(),
                statementProxy.getConnectionProxy().getDbType());
        }
        Executor executor = null;
        if (sqlRecognizer == null) {
            executor = new PlainExecutor(statementProxy, statementCallback);
        } else {
            switch (sqlRecognizer.getSQLType()) {
                case INSERT:
                    executor = new InsertExecutor(statementProxy, statementCallback, sqlRecognizer);
                    break;
                case UPDATE:
                    executor = new UpdateExecutor(statementProxy, statementCallback, sqlRecognizer);
                    break;
                case DELETE:
                    executor = new DeleteExecutor(statementProxy, statementCallback, sqlRecognizer);
                    break;
                case SELECT_FOR_UPDATE:
                    executor = new SelectForUpdateExecutor(statementProxy, statementCallback, sqlRecognizer);
                    break;
                default:
                    executor = new PlainExecutor(statementProxy, statementCallback);
                    break;
            }
        }
        T rs = null;
        try {
            rs = executor.execute(args);

        } catch (Throwable ex) {
            if (ex instanceof SQLException) {
                throw (SQLException) ex;
            } else {
                // Turn everything into SQLException
                new SQLException(ex);
            }
        }
        return rs;
    }
}

说明：

• ExecuteTemplate 执行InsertExecutor的整个过程如上述代码。
• 获取SQLRecognizer sqlRecognizer对象，sqlRecognizer = SQLVisitorFactory.get()。
• 创建InsertExecutor对象，executor = new InsertExecutor()。
• 执行InsertExecutor对象并返回结果，rs = executor.execute(args);

BaseTransactionalExecutor

public abstract class BaseTransactionalExecutor implements Executor {

    protected StatementProxy statementProxy;
    protected StatementCallback statementCallback;
    protected SQLRecognizer sqlRecognizer;
    private TableMeta tableMeta;

    public BaseTransactionalExecutor(StatementProxy statementProxy, 
                   StatementCallback statementCallback, SQLRecognizer sqlRecognizer) {
        this.statementProxy = statementProxy;
        this.statementCallback = statementCallback;
        this.sqlRecognizer = sqlRecognizer;
    }

    @Override
    public Object execute(Object... args) throws Throwable {
        String xid = RootContext.getXID();
        statementProxy.getConnectionProxy().bind(xid);
        return doExecute(args);
    }

    protected abstract Object doExecute(Object... args) throws Throwable;
}

说明：

• 关注BaseTransactionalExecutor的构造函数。
• BaseTransactionalExecutor的execute是执行的入口函数，调用抽象方法doExecute()
• BaseTransactionalExecutor的doExecute()在子类中实现。

AbstractDMLBaseExecutor

public abstract class AbstractDMLBaseExecutor extends BaseTransactionalExecutor {

    private static final Logger LOGGER = LoggerFactory.getLogger(AbstractDMLBaseExecutor.class);

    public AbstractDMLBaseExecutor(StatementProxy statementProxy, 
       StatementCallback statementCallback, SQLRecognizer sqlRecognizer) {
        super(statementProxy, statementCallback, sqlRecognizer);
    }

    @Override
    public T doExecute(Object... args) throws Throwable {
        AbstractConnectionProxy connectionProxy = statementProxy.getConnectionProxy();
        if (connectionProxy.getAutoCommit()) {
            return executeAutoCommitTrue(args);
        } else {
            return executeAutoCommitFalse(args);
        }
    }

    protected T executeAutoCommitFalse(Object[] args) throws Throwable {
        TableRecords beforeImage = beforeImage();
        T result = statementCallback.execute(statementProxy.getTargetStatement(), args);
        TableRecords afterImage = afterImage(beforeImage);
        prepareUndoLog(beforeImage, afterImage);
        return result;
    }

    protected T executeAutoCommitTrue(Object[] args) throws Throwable {
        T result = null;
        AbstractConnectionProxy connectionProxy = statementProxy.getConnectionProxy();
        LockRetryController lockRetryController = new LockRetryController();
        try {
            connectionProxy.setAutoCommit(false);
            while (true) {
                try {
                    result = executeAutoCommitFalse(args);
                    connectionProxy.commit();
                    break;
                } catch (LockConflictException lockConflict) {
                    connectionProxy.getTargetConnection().rollback();
                    lockRetryController.sleep(lockConflict);
                }
            }

        } catch (Exception e) {
            // when exception occur in finally,this exception will lost, so just print it here
            LOGGER.error("exception occur", e);
            throw e;
        } finally {
            connectionProxy.setAutoCommit(true);
        }
        return result;
    }
}

说明：

• BaseTransactionalExecutor的调用子类AbstractDMLBaseExecutor的doExecute方法。
• AbstractDMLBaseExecutor的doExecute()执行executeAutoCommitFalse或executeAutoCommitTrue方法。
• executeAutoCommitTrue方法内部也是通过executeAutoCommitFalse实现的。
• executeAutoCommitFalse()按照保存beforeImage()、statementCallback.execute()、afterImage()、prepareUndoLog()顺序执行。
• beforeImage()负责保存执行前镜像、afterImage()负责保存执行后镜像、prepareUndoLog()负责保存回滚日志。
• statementCallback.execute()负责执行statement操作。

InsertExecutor

public class InsertExecutor extends AbstractDMLBaseExecutor {

    public InsertExecutor(StatementProxy statementProxy, 
        StatementCallback statementCallback, SQLRecognizer sqlRecognizer) {
        super(statementProxy, statementCallback, sqlRecognizer);
    }

    @Override
    protected TableRecords beforeImage() throws SQLException {
        return TableRecords.empty(getTableMeta());
    }

    @Override
    protected TableRecords afterImage(TableRecords beforeImage) throws SQLException {
        SQLInsertRecognizer recogizier = (SQLInsertRecognizer)sqlRecognizer;
        List insertColumns = recogizier.getInsertColumns();
        TableMeta tmeta = getTableMeta();
        TableRecords afterImage = null;
        if (tmeta.containsPK(insertColumns)) {
            // insert values including PK
            List