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package org.hsqldb;
import org.hsqldb.HsqlNameManager.HsqlName;
import org.hsqldb.lib.IntKeyHashMap;
import org.hsqldb.lib.LongKeyHashMap;
import org.hsqldb.lib.LongValueHashMap;
import org.hsqldb.result.Result;
/**
* This class manages the reuse of Statement objects for prepared
* statements for a Session instance.<p>
*
* A compiled statement is registered by a session to be managed. Once
* registered, it is linked with one or more sessions.<p>
*
* The sql statement text distinguishes different compiled statements and acts
* as lookup key when a session initially looks for an existing instance of
* the compiled sql statement.<p>
*
* Once a session is linked with a statement, it uses the uniqe compiled
* statement id for the sql statement to access the statement.<p>
*
* Changes to database structure via DDL statements, will result in all
* registered Statement objects to become invalidated. This is done by
* comparing the schema change and compile timestamps. When a session
* subsequently attempts to use an invalidated Statement via its id, it will
* reinstantiate the Statement using its sql statement still held by this class.<p>
*
* This class keeps count of the number of time each registered compiled
* statement is linked to a session. It unregisters a compiled statement when
* no session remains linked to it.<p>
*
* Modified by fredt@users from the original by boucherb@users to simplify,
* support multiple identical prepared statements per session, and avoid
* memory leaks. Modified further to support schemas. Changed implementation
* in 1.9 as a session object<p>
*
* @author Campbell Boucher-Burnett (boucherb@users dot sourceforge.net)
* @author Fred Toussi (fredt@users dot sourceforge.net)
*
* @version 1.9.0
* @since 1.7.2
*/
public final class StatementManager {
/**
* The Database for which this object is managing
* CompiledStatement objects.
*/
private Database database;
/** Map: Schema id (int) => {Map: SQL String => Compiled Statement id (long)} */
private IntKeyHashMap schemaMap;
/** Map: Compiled Statement id (int) => SQL String */
private LongKeyHashMap sqlLookup;
/** Map: Compiled statment id (int) => CompiledStatement object. */
private LongKeyHashMap csidMap;
/**
* Monotonically increasing counter used to assign unique ids to compiled
* statements.
*/
private long next_cs_id;
/**
* Constructs a new instance of <code>CompiledStatementManager</code>.
*
* @param database the Database instance for which this object is to
* manage compiled statement objects.
*/
StatementManager(Database database) {
this.database = database;
schemaMap = new IntKeyHashMap();
sqlLookup = new LongKeyHashMap();
csidMap = new LongKeyHashMap();
next_cs_id = 0;
}
/**
* Clears all internal data structures, removing any references to compiled statements.
*/
synchronized void reset() {
schemaMap.clear();
sqlLookup.clear();
csidMap.clear();
next_cs_id = 0;
}
/**
* Retrieves the next compiled statement identifier in the sequence.
*
* @return the next compiled statement identifier in the sequence.
*/
private long nextID() {
next_cs_id++;
return next_cs_id;
}
/**
* Retrieves the registered compiled statement identifier associated with
* the specified SQL String, or a value less than zero, if no such
* statement has been registered.
*
* @param schema the schema id
* @param sql the SQL String
* @return the compiled statement identifier associated with the
* specified SQL String
*/
private long getStatementID(HsqlName schema, String sql) {
LongValueHashMap sqlMap =
(LongValueHashMap) schemaMap.get(schema.hashCode());
if (sqlMap == null) {
return -1;
}
return sqlMap.get(sql, -1);
}
/**
* Returns an existing CompiledStatement object with the given
* statement identifier. Returns null if the CompiledStatement object
* has been invalidated and cannot be recompiled
*
* @param session the session
* @param csid the identifier of the requested CompiledStatement object
* @return the requested CompiledStatement object
*/
public synchronized Statement getStatement(Session session, long csid) {
Statement cs = (Statement) csidMap.get(csid);
if (cs == null) {
return null;
}
if (cs.getCompileTimestamp()
< database.schemaManager.getSchemaChangeTimestamp()) {
String sql = (String) sqlLookup.get(csid);
HsqlName oldSchema = session.getCurrentSchemaHsqlName();
// revalidate with the original schema
try {
HsqlName schema = cs.getSchemaName();
session.setSchema(schema.name);
StatementInsert si = null;
if (cs.generatedResultMetaData() != null) {
si = (StatementInsert) cs;
}
cs = session.compileStatement(sql, cs.getResultProperties());
cs.setID(csid);
cs.setCompileTimestamp(
database.txManager.getGlobalChangeTimestamp());
if (si != null) {
cs.setGeneratedColumnInfo(si.generatedType,
si.generatedInputMetaData);
}
csidMap.put(csid, cs);
} catch (Throwable t) {
freeStatement(csid);
return null;
} finally {
session.setSchema(oldSchema.name);
}
}
return cs;
}
/**
* Registers a compiled statement to be managed.
*
* The only caller should be a Session that is attempting to prepare
* a statement for the first time or process a statement that has been
* invalidated due to DDL changes.
*
* @param csid existing id or negative if the statement is not yet managed
* @param cs The CompiledStatement to add
* @return The compiled statement id assigned to the CompiledStatement
* object
*/
private long registerStatement(long csid, Statement cs) {
if (csid < 0) {
csid = nextID();
int schemaid = cs.getSchemaName().hashCode();
LongValueHashMap sqlMap =
(LongValueHashMap) schemaMap.get(schemaid);
if (sqlMap == null) {
sqlMap = new LongValueHashMap();
schemaMap.put(schemaid, sqlMap);
}
sqlMap.put(cs.getSQL(), csid);
sqlLookup.put(csid, cs.getSQL());
}
cs.setID(csid);
cs.setCompileTimestamp(database.txManager.getGlobalChangeTimestamp());
csidMap.put(csid, cs);
return csid;
}
/**
* Removes one (or all) of the links between a session and a compiled
* statement. If the statement is not linked with any other session, it is
* removed from management.
*
* @param csid the compiled statment identifier
* @param sessionID the session identifier
* @param freeAll if true, remove all links to the session
*/
synchronized void freeStatement(long csid) {
if (csid == -1) {
// statement was never added
return;
}
Statement cs = (Statement) csidMap.remove(csid);
if (cs != null) {
int schemaid = cs.getSchemaName().hashCode();
LongValueHashMap sqlMap =
(LongValueHashMap) schemaMap.get(schemaid);
String sql = (String) sqlLookup.remove(csid);
sqlMap.remove(sql);
}
}
/**
* Compiles an SQL statement and returns a CompiledStatement Object
*
* @param session the session
* @throws Throwable
* @return CompiledStatement
*/
synchronized Statement compile(Session session,
Result cmd) throws Throwable {
String sql = cmd.getMainString();
long csid = getStatementID(session.currentSchema, sql);
Statement cs = (Statement) csidMap.get(csid);
int props;
if (cs == null || !cs.isValid()
|| cs.getCompileTimestamp()
< database.schemaManager.getSchemaChangeTimestamp()) {
props = cmd.getExecuteProperties();
cs = session.compileStatement(sql, props);
csid = registerStatement(csid, cs);
}
cs.setGeneratedColumnInfo(cmd.getGeneratedResultType(),
cmd.getGeneratedResultMetaData());
return cs;
}
}