PoemThread.java
/*
* $Source$
* $Revision$
*
* Copyright (C) 2000 William Chesters
*
* Part of Melati (http://melati.org), a framework for the rapid
* development of clean, maintainable web applications.
*
* Melati is free software; Permission is granted to copy, distribute
* and/or modify this software under the terms either:
*
* a) the GNU General Public License as published by the Free Software
* Foundation; either version 2 of the License, or (at your option)
* any later version,
*
* or
*
* b) any version of the Melati Software License, as published
* at http://melati.org
*
* You should have received a copy of the GNU General Public License and
* the Melati Software License along with this program;
* if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA to obtain the
* GNU General Public License and visit http://melati.org to obtain the
* Melati Software License.
*
* Feel free to contact the Developers of Melati (http://melati.org),
* if you would like to work out a different arrangement than the options
* outlined here. It is our intention to allow Melati to be used by as
* wide an audience as possible.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* Contact details for copyright holder:
*
* William Chesters <williamc At paneris.org>
* http://paneris.org/~williamc
* Obrechtstraat 114, 2517VX Den Haag, The Netherlands
*/
package org.melati.poem;
import java.util.Vector;
import java.util.Enumeration;
import java.util.Map;
import java.util.HashMap;
import org.melati.poem.transaction.ToTidyList;
/**
* A Poem Thread.
*
*/
public final class PoemThread {
private PoemThread() {
}
private static Vector<SessionToken> sessionTokens = new Vector<SessionToken>();
private static Vector<Integer> freeSessionTokenIndices = new Vector<Integer>();
/**
* The maximum number of Threads. Must be < Char.MAX_VALUE = 64k
*/
public static final int threadsMax = 100;
static Integer allocatedSessionToken(AccessToken accessToken,
PoemTransaction transaction, PoemTask task) {
synchronized (freeSessionTokenIndices) {
Integer index;
if (freeSessionTokenIndices.size() == 0) {
int i = sessionTokens.size();
if (i >= threadsMax)
throw new TooManyThreadsPoemException();
sessionTokens.setSize(i + 1);
index = new Integer(i);
} else {
index = (Integer)freeSessionTokenIndices.lastElement();
freeSessionTokenIndices.setSize(freeSessionTokenIndices.size() - 1);
}
SessionToken token = new SessionToken(Thread.currentThread(),
transaction, accessToken, task);
sessionTokens.setElementAt(token, index.intValue());
return index;
}
}
/** Keep track of the old thread names. */
private static Map<Integer, String> threadOldNames = new HashMap<Integer, String>();
/**
* Do the processing to start a db session.
*
* @param accessToken
* The session's token
* @param transaction
* The PoemTransaction to run in
* @param task
* The PoemTask to run
* @throws PoemException
* if we are already in a Session
*/
static void beginSession(AccessToken accessToken,
PoemTransaction transaction, PoemTask task) throws PoemException {
if (inSession())
throw new AlreadyInSessionPoemException();
Integer token = allocatedSessionToken(accessToken, transaction, task);
String oldname = Thread.currentThread().getName();
Thread.currentThread().setName("" + (char)token.intValue());
// Save the old thread name for later use
threadOldNames.put(token, oldname);
}
static void beginSession(AccessToken accessToken, PoemTransaction transaction)
throws PoemException {
beginSession(accessToken, transaction, null);
}
/**
* End a db session.
*
* @throws PoemException
* if we are not in a Session
*/
static void endSession() throws PoemException {
char tokenChar = Thread.currentThread().getName().charAt(0);
Integer token = new Integer(tokenChar);
String oldname = (String)threadOldNames.get(token);
if (oldname == null)
throw new NotInSessionPoemException(Thread.currentThread().getName()
+ " has null old name");
Thread.currentThread().setName(oldname);
synchronized (freeSessionTokenIndices) {
((SessionToken)sessionTokens.elementAt(token.intValue())).close();
sessionTokens.setElementAt(null, token.intValue());
freeSessionTokenIndices.addElement(token);
}
}
/**
* Perform the specified task in the current thread session.
*
* @throws PoemException
* if there is a problem starting or ending the session or if there
* is a problem running the task.
*/
static void inSession(PoemTask task, AccessToken accessToken,
PoemTransaction transaction) throws PoemException {
beginSession(accessToken, transaction, task);
try {
task.run();
} finally {
endSession();
}
}
/**
* Retrieve the open sessions.
*
* @return a Vector of open {@link SessionToken}s
*/
public static Vector<SessionToken> openSessions() {
Vector<SessionToken> open = new Vector<SessionToken>();
Enumeration<SessionToken> e = null;
// synchronized(sessionTokens) {
e = sessionTokens.elements();
// }
while (e.hasMoreElements()) {
SessionToken token = e.nextElement();
if (token != null)
open.addElement(token);
}
return open;
}
static SessionToken _sessionToken() {
// If we are not in a PoemThread then the name is likely
// to be "main" or "Thread-1", "Thread-2" etc
if (Thread.currentThread().getName().length() != 1)
return null;
SessionToken context = (SessionToken)sessionTokens.elementAt(Thread
.currentThread().getName().charAt(0));
if (context.thread == Thread.currentThread())
return context;
else
return null;
}
/**
* @return the current SessionToken
* @throws NotInSessionPoemException if there is no current SessionToken
*/
public static SessionToken sessionToken() throws NotInSessionPoemException {
SessionToken it = _sessionToken();
if (it == null)
throw new NotInSessionPoemException();
return it;
}
/**
* Retrieve the {@link ToTidyList} for this session.
*
* @return the {@link ToTidyList} for this {@link PoemThread}.
*/
public static ToTidyList toTidy() throws NotInSessionPoemException {
return sessionToken().toTidy();
}
/**
* Retrieve the {@link PoemTransaction} for this PoemThread.
*
* @return the {@link PoemTransaction} for this {@link PoemThread}.
*/
public static PoemTransaction transaction() {
return sessionToken().transaction;
}
/**
* Whether we are currently in a session.
*
* @return whether we are currently in a session
*/
public static boolean inSession() {
return _sessionToken() != null;
}
/**
* @return the access token under which your thread is running.
* @throws NotInSessionPoemException
* if we are not in a session
* @throws NoAccessTokenPoemException
* if we do not have an AccessToken
*/
public static AccessToken accessToken() throws NotInSessionPoemException,
NoAccessTokenPoemException {
AccessToken it = sessionToken().accessToken;
if (it == null)
throw new NoAccessTokenPoemException();
return it;
}
/**
* Change the access token under which your thread is operating. You can't do
* this unless the current token is <TT>root</TT>.
*
* @see AccessToken#root
*/
public static void setAccessToken(AccessToken token)
throws NonRootSetAccessTokenPoemException {
SessionToken context = sessionToken();
AccessToken old = context.accessToken;
if (old != AccessToken.root)
throw new NonRootSetAccessTokenPoemException(old);
context.accessToken = token;
}
/**
* Run a {@link PoemTask} under a specified {@link AccessToken}, typically
* <tt>Root</tt>.
*
* @param token
* the token to run with
* @param task
* the task to run
*/
public static void withAccessToken(AccessToken token, PoemTask task) {
SessionToken context = sessionToken();
AccessToken old = context.accessToken;
context.accessToken = token;
try {
task.run();
} finally {
context.accessToken = old;
}
}
/**
* Check that we have the given {@link Capability}, throw an
* {@link AccessPoemException} if we don't.
*
* @param capability
* to check
*/
public static void assertHasCapability(Capability capability)
throws NotInSessionPoemException, NoAccessTokenPoemException,
AccessPoemException {
AccessToken token = accessToken();
if (!token.givesCapability(capability))
throw new AccessPoemException(token, capability);
}
/**
* Retrieve the {@link Database} associated with this thread.
*
* @return the {@link Database} associated with this thread.
*/
public static Database database() throws NotInSessionPoemException {
return transaction().getDatabase();
}
/**
* Write to the underlying DBMS.
*
*/
public static void writeDown() {
transaction().writeDown();
}
/**
* Commit to the underlying DBMS.
*
*/
public static void commit() {
SessionToken token = sessionToken();
try {
token.transaction.commit();
} finally {
token.toTidy().close();
}
}
/**
* Rollback the underlying DBMS.
*
*/
public static void rollback() {
SessionToken token = sessionToken();
try {
token.transaction.rollback();
} finally {
token.toTidy().close();
}
}
}