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package org.hsqldb;
import org.hsqldb.HsqlNameManager.HsqlName;
import org.hsqldb.lib.IntKeyHashMap;
import org.hsqldb.lib.Iterator;
import org.hsqldb.lib.LongKeyHashMap;
import org.hsqldb.lib.LongKeyIntValueHashMap;
import org.hsqldb.lib.LongValueHashMap;
import org.hsqldb.result.Result;
/**
* This class manages the reuse of Statement objects for prepared
* statements for a Database 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 CompiledStatement objects to become invalidated. This is done by
* setting to null all the managed CompiledStatement instances, while keeping
* their id and sql string. When a session subsequently attempts to use an
* invalidated (null) CompiledStatement 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 different sessions that are linked
* to each registered compiled statement, and the number of times each session
* is linked. 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
* keeping references to Statement objects after DDL changes which
* could result in memory leaks. Modified further to support schemas.<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;
/** Map: Session id (long) => {Map: compiled statement id (long) => use count in session} */
private LongKeyHashMap sessionUseMap;
/** Map: Compiled statment id (int) => number of sessions that use the statement */
private LongKeyIntValueHashMap useMap;
/**
* 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();
sessionUseMap = new LongKeyHashMap();
useMap = new LongKeyIntValueHashMap();
next_cs_id = 0;
}
/**
* Clears all internal data structures, removing any references to compiled statements.
*/
synchronized void reset() {
schemaMap.clear();
sqlLookup.clear();
csidMap.clear();
sessionUseMap.clear();
useMap.clear();
next_cs_id = 0;
}
/**
* Used after a DDL change that could impact the compiled statements.
* Clears references to CompiledStatement objects while keeping the counts
* and references to the sql strings.
*/
synchronized void resetStatements() {
Iterator it = csidMap.values().iterator();
while (it.hasNext()) {
Statement cs = (Statement) it.next();
cs.clearVariables();
}
}
/**
* 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.isValid()) {
String sql = (String) sqlLookup.get(csid);
// revalidate with the original schema
try {
Session sys = database.sessionManager.getSysSession(
session.currentSchema.name, session.getUser());
cs = sys.compileStatement(sql);
cs.setID(csid);
csidMap.put(csid, cs);
} catch (Throwable t) {
freeStatement(csid, session.getId(), true);
return null;
}
}
return cs;
}
/**
* Links a session with a registered compiled statement. If this session has
* not already been linked with the given statement, then the statement use
* count is incremented.
*
* @param csid the compiled statement identifier
* @param sessionID the session identifier
*/
private void linkSession(long csid, long sessionID) {
LongKeyIntValueHashMap scsMap;
scsMap = (LongKeyIntValueHashMap) sessionUseMap.get(sessionID);
if (scsMap == null) {
scsMap = new LongKeyIntValueHashMap();
sessionUseMap.put(sessionID, scsMap);
}
int count = scsMap.get(csid, 0);
scsMap.put(csid, count + 1);
if (count == 0) {
useMap.put(csid, useMap.get(csid, 0) + 1);
}
}
/**
* 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.getSchemalName().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);
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, long sessionID,
boolean freeAll) {
if (csid == -1) {
// statement was never added
return;
}
LongKeyIntValueHashMap scsMap =
(LongKeyIntValueHashMap) sessionUseMap.get(sessionID);
if (scsMap == null) {
// statement already removed due to invalidation
return;
}
int sessionUseCount = scsMap.get(csid, 0);
if (sessionUseCount == 0) {
// statement already removed due to invalidation
} else if (sessionUseCount == 1 || freeAll) {
scsMap.remove(csid);
int usecount = useMap.get(csid, 0);
if (usecount == 0) {
// statement already removed due to invalidation
} else if (usecount == 1) {
Statement cs = (Statement) csidMap.remove(csid);
if (cs != null) {
int schemaid = cs.getSchemalName().hashCode();
LongValueHashMap sqlMap =
(LongValueHashMap) schemaMap.get(schemaid);
String sql = (String) sqlLookup.remove(csid);
sqlMap.remove(sql);
}
useMap.remove(csid);
} else {
useMap.put(csid, usecount - 1);
}
} else {
scsMap.put(csid, sessionUseCount - 1);
}
}
/**
* Releases the link betwen the session and all compiled statement objects
* it is linked to. If any such statement is not linked with any other
* session, it is removed from management.
*
* @param sessionID the session identifier
*/
synchronized void removeSession(long sessionID) {
LongKeyIntValueHashMap scsMap;
long csid;
Iterator i;
scsMap = (LongKeyIntValueHashMap) sessionUseMap.remove(sessionID);
if (scsMap == null) {
return;
}
i = scsMap.keySet().iterator();
while (i.hasNext()) {
csid = i.nextLong();
int usecount = useMap.get(csid, 1) - 1;
if (usecount == 0) {
Statement cs = (Statement) csidMap.remove(csid);
if (cs != null) {
int schemaid = cs.getSchemalName().hashCode();
LongValueHashMap sqlMap =
(LongValueHashMap) schemaMap.get(schemaid);
String sql = (String) sqlLookup.remove(csid);
sqlMap.remove(sql);
}
useMap.remove(csid);
} else {
useMap.put(csid, usecount);
}
}
}
/**
* 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);
if (cs == null || !cs.isValid() || !session.isAdmin()) {
Session sys = database.sessionManager.getSysSession(
session.currentSchema.name, session.getUser());
cs = sys.compileStatement(sql);
csid = registerStatement(csid, cs);
}
linkSession(csid, session.getId());
return cs;
}
}