Synnefo

/*

 * Copyright 2009 Electronic Business Systems Ltd.

 *

 * This file is part of GSS.

 *

 * GSS is free software: you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation, either version 3 of the License, or

 * (at your option) any later version.

 *

 * GSS 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.

 *

 * You should have received a copy of the GNU General Public License

 * along with GSS.  If not, see <http://www.gnu.org/licenses/>.

 */

package gr.ebs.gss.server.ejb;

import java.util.concurrent.Callable;

import java.util.concurrent.ExecutionException;

import java.util.concurrent.Executors;

import java.util.concurrent.ScheduledExecutorService;

import java.util.concurrent.ScheduledFuture;

import java.util.concurrent.TimeUnit;

import javax.ejb.EJBTransactionRolledbackException;

import org.apache.commons.logging.Log;

import org.apache.commons.logging.LogFactory;

/**

 * A helper class that provides a method for repeatedly trying a transaction

 * that is rolled back due to optimistic locking exceptions.

 *

 * @author  past

 */

public class TransactionHelper<T> {

	/**

	 * The logger.

	 */

	private static Log logger = LogFactory.getLog(TransactionHelper.class);

	/**

	 * Number of times to retry a transaction that was rolled back due to

	 * optimistic locking.

	 */

	private static final int TRANSACTION_RETRIES = 10;

	/**

	 * The minimum retry timeout in milliseconds.

	 */

	private static final int MIN_TIMEOUT = 100;

	/**

	 * Execute the supplied command until it completes, ignoring transaction

	 * rollbacks. Try at least TRANSACTION_RETRIES times before giving up,

	 * each time waiting a random amount of time, using an exponential

	 * backoff scheme. See http://en.wikipedia.org/wiki/Exponential_backoff

	 * for the basic idea.

	 *

	 * @param command the command to execute

	 * @return the value returned by the command

	 * @throws Exception any other exception thrown by the command

	 */

	public T tryExecute(final Callable<T> command) throws Exception {

		T returnValue = null;

		// Schedule a Future task to call the command after delay milliseconds.

		int delay = 0;

		ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);

		for (int i = 0; i < TRANSACTION_RETRIES; i++) {

			final int retry = i;

			ScheduledFuture<T> future = executor.schedule(new Callable<T>() {

				@Override

				public T call() throws Exception {

					return command.call();

				}

			}, delay, TimeUnit.MILLISECONDS);

			try {

				returnValue = future.get();

				break;

			} catch (ExecutionException e) {

				Throwable cause = e.getCause();

				if (!(cause instanceof EJBTransactionRolledbackException) ||

							retry == TRANSACTION_RETRIES - 1) {

					executor.shutdownNow();

					throw new Exception(cause);

				}

				delay = MIN_TIMEOUT + (int) (MIN_TIMEOUT * Math.random() * (i + 1));

				String origCause = cause.getCause() == null ?

							cause.getClass().getName() :

							cause.getCause().getClass().getName();

				logger.info("Transaction retry #" + (i+1) + " scheduled in " + delay +

							" msec due to " + origCause);

			}

		}

		executor.shutdownNow();

		return returnValue;

	}

}

import gr.ebs.gss.server.ejb.TransactionHelper;

import gr.ebs.gss.server.ejb.TransactionHelper;

import gr.ebs.gss.server.ejb.TransactionHelper;

import gr.ebs.gss.server.ejb.TransactionHelper;

import gr.ebs.gss.server.ejb.TransactionHelper;

		final User user = getUser(req);

			final FolderDTO folder = (FolderDTO) parent;

			final String name = getLastElement(path);

			final String mimeType = getServletContext().getMimeType(name);

			final FileHeaderDTO f = file;

			final File uf = uploadedFile;

				fileDTO = new TransactionHelper<FileHeaderDTO>().tryExecute(new Callable<FileHeaderDTO>() {

					@Override

					public FileHeaderDTO call() throws Exception {

						return getService().updateFileContents(user.getId(), f.getId(), mimeType, uf.length(), uf.getAbsolutePath());

					}

				});

				fileDTO = new TransactionHelper<FileHeaderDTO>().tryExecute(new Callable<FileHeaderDTO>() {

					@Override

					public FileHeaderDTO call() throws Exception {

						return getService().createFile(user.getId(), folder.getId(), name, mimeType, uf.length(), uf.getAbsolutePath());

					}

				});

		} catch (Exception e) {

			resp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, path);

			return;

		final String path = getRelativePath(req);

		final User user = getUser(req);

				final FolderDTO folder = (FolderDTO) parent;

				new TransactionHelper<Void>().tryExecute(new Callable<Void>() {

					@Override

					public Void call() throws Exception {

						getService().createFolder(user.getId(), folder.getId(), getLastElement(path));

						return null;

					}

				});

		} catch (Exception e) {

			resp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, path);

			return;

		final User user = getUser(req);

			final FolderDTO folder = (FolderDTO) object;

				final String des = dest;

				new TransactionHelper<Void>().tryExecute(new Callable<Void>() {

					@Override

					public Void call() throws Exception {

						getService().copyFolder(user.getId(), folder.getId(), des);

						return null;

					}

				});

			} catch (Exception e) {

				errorList.put(dest, new Integer(WebdavStatus.SC_INTERNAL_SERVER_ERROR));

				return false;

			final FileHeaderDTO file = (FileHeaderDTO) object;

				final String des = dest;

				new TransactionHelper<Void>().tryExecute(new Callable<Void>() {

					@Override

					public Void call() throws Exception {

						getService().copyFile(user.getId(), file.getId(), des);

						return null;

					}

				});

			} catch (Exception e) {

				errorList.put(dest, new Integer(WebdavStatus.SC_INTERNAL_SERVER_ERROR));

				return false;

		final User user = getUser(req);

				final FileHeaderDTO f = file;

				new TransactionHelper<Void>().tryExecute(new Callable<Void>() {

					@Override

					public Void call() throws Exception {

						getService().deleteFile(user.getId(), f.getId());

						return null;

					}

				});

			} catch (Exception e) {

				resp.sendError(WebdavStatus.SC_INTERNAL_SERVER_ERROR);

				return false;

				final FolderDTO f = folder;

				new TransactionHelper<Void>().tryExecute(new Callable<Void>() {

					@Override

					public Void call() throws Exception {

						getService().deleteFolder(user.getId(), f.getId());

						return null;

					}

				});

			} catch (Exception e) {

				errorList.put(path, new Integer(WebdavStatus.SC_INTERNAL_SERVER_ERROR));

					final User user = getUser(req);

						final FolderDTO cf = childFolder;

						new TransactionHelper<Void>().tryExecute(new Callable<Void>() {

							@Override

							public Void call() throws Exception {

								getService().deleteFolder(user.getId(), cf.getId());

								return null;

							}

						});

					} else if (childFile != null) {

						final FileHeaderDTO cf = childFile;

						new TransactionHelper<Void>().tryExecute(new Callable<Void>() {

							@Override

							public Void call() throws Exception {

								getService().deleteFile(user.getId(), cf.getId());

								return null;

							}

						});

					}

				} catch (Exception e) {

					errorList.put(childName, new Integer(WebdavStatus.SC_INTERNAL_SERVER_ERROR));