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/*******************************************************************************
 * Copyright (c) 2011 Wind River Systems and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     Wind River Systems - initial API and implementation
 *******************************************************************************/
//#ifdef exercises
package org.eclipse.cdt.examples.dsf.dataviewer;
//#else

//#package org.eclipse.cdt.examples.dsf.dataviewer.answers;
//#endif

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

import org.eclipse.cdt.dsf.concurrent.ConfinedToDsfExecutor;
import org.eclipse.cdt.dsf.concurrent.CountingRequestMonitor;
import org.eclipse.cdt.dsf.concurrent.DataRequestMonitor;
import org.eclipse.cdt.dsf.concurrent.DefaultDsfExecutor;
import org.eclipse.cdt.dsf.concurrent.DsfExecutor;
import org.eclipse.cdt.dsf.concurrent.ICache;
import org.eclipse.cdt.dsf.concurrent.ImmediateExecutor;
import org.eclipse.cdt.dsf.concurrent.ImmediateInDsfExecutor;
import org.eclipse.cdt.dsf.concurrent.Query;
import org.eclipse.cdt.dsf.concurrent.ThreadSafe;
import org.eclipse.cdt.dsf.concurrent.Transaction;
import org.eclipse.cdt.dsf.ui.concurrent.DisplayDsfExecutor;
import org.eclipse.core.runtime.CoreException;
import org.eclipse.jface.viewers.ILazyContentProvider;
import org.eclipse.jface.viewers.TableViewer;
import org.eclipse.jface.viewers.Viewer;
import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.Font;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Table;

/**
 * Data viewer based on a table, which reads data from multiple data
 * providers using ACPM methods and performs a computation on the
 * retrieved data.
 * <p>
 * This example builds on the {@link AsyncSumDataViewer} example.  It
 * demonstrates using ACPM to solve the data consistency problem when
 * retrieving data from multiple sources asynchronously.
 * </p>
 */
@ConfinedToDsfExecutor("fDisplayExecutor")
public class ACPMSumDataViewer implements ILazyContentProvider {
	/** View update frequency interval. */
	final private static int UPDATE_INTERVAL = 10000;

	/** Executor to use instead of Display.asyncExec(). **/
	@ThreadSafe
	final private DsfExecutor fDisplayExecutor;

	/** Executor to use when retrieving data from data providers */
	@ThreadSafe
	final private ImmediateInDsfExecutor fDataExecutor;

	// The viewer and generator that this content provider using.
	final private TableViewer fViewer;
	final private DataGeneratorCacheManager[] fDataGeneratorCMs;
	final private DataGeneratorCacheManager fSumGeneratorCM;

	// Fields used in request cancellation logic.
	private List<ValueRequestMonitor> fItemDataRequestMonitors = new LinkedList<ValueRequestMonitor>();
	private Set<Integer> fIndexesToCancel = new HashSet<Integer>();
	private int fCancelCallsPending = 0;
	private Future<?> fRefreshFuture;

	public ACPMSumDataViewer(TableViewer viewer, ImmediateInDsfExecutor dataExecutor, IDataGenerator[] generators,
			IDataGenerator sumGenerator) {
		fViewer = viewer;
		fDisplayExecutor = DisplayDsfExecutor.getDisplayDsfExecutor(fViewer.getTable().getDisplay());
		fDataExecutor = dataExecutor;

		// Create wrappers for data generators.  Don't need to register as
		// listeners to generator events because the cache managers ensure data
		// are already registered for them.
		fDataGeneratorCMs = new DataGeneratorCacheManager[generators.length];
		for (int i = 0; i < generators.length; i++) {
			fDataGeneratorCMs[i] = new DataGeneratorCacheManager(fDataExecutor, generators[i]);
		}
		fSumGeneratorCM = new DataGeneratorCacheManager(fDataExecutor, sumGenerator);

		// Schedule a task to refresh the viewer periodically.
		fRefreshFuture = fDisplayExecutor.scheduleAtFixedRate(new Runnable() {
			@Override
			public void run() {
				queryItemCount();
			}
		}, UPDATE_INTERVAL, UPDATE_INTERVAL, TimeUnit.MILLISECONDS);
	}

	@Override
	public void dispose() {
		// Cancel the periodic task of refreshing the view.
		fRefreshFuture.cancel(false);

		// Need to dispose cache managers that were created in this class.  This
		// needs to be done on the cache manager's thread.
		Query<Object> disposeCacheManagersQuery = new Query<Object>() {
			@Override
			protected void execute(DataRequestMonitor<Object> rm) {
				fSumGeneratorCM.dispose();
				for (DataGeneratorCacheManager dataGeneratorCM : fDataGeneratorCMs) {
					dataGeneratorCM.dispose();
				}
				rm.setData(new Object());
				rm.done();
			}
		};
		fDataExecutor.execute(disposeCacheManagersQuery);
		try {
			disposeCacheManagersQuery.get();
		} catch (InterruptedException e) {
		} catch (ExecutionException e) {
		}

		// Cancel any outstanding data requests.
		for (ValueRequestMonitor rm : fItemDataRequestMonitors) {
			rm.cancel();
		}
		fItemDataRequestMonitors.clear();
	}

	@Override
	public void inputChanged(Viewer viewer, Object oldInput, Object newInput) {
		// Set the initial count to the viewer after the input is set.
		queryItemCount();
	}

	@Override
	public void updateElement(final int index) {
		// Calculate the visible index range.
		final int topIdx = fViewer.getTable().getTopIndex();
		final int botIdx = topIdx + getVisibleItemCount(topIdx);

		// Request the item for the given index.
		queryValue(index);

		// Invoke a cancel task with a delay.  The delay allows multiple cancel
		// calls to be combined together improving performance of the viewer.
		fCancelCallsPending++;
		fDisplayExecutor.execute(new Runnable() {
			@Override
			public void run() {
				cancelStaleRequests(topIdx, botIdx);
			}
		});
	}

	/**
	 * Calculates the number of visible items based on the top item index and
	 * table bounds.
	 * @param top Index of top item.
	 * @return calculated number of items in viewer
	 */
	private int getVisibleItemCount(int top) {
		Table table = fViewer.getTable();
		int itemCount = table.getItemCount();
		return Math.min((table.getBounds().height / table.getItemHeight()) + 2, itemCount - top);
	}

	/**
	 * Retrieve the current count.  When a new count is set to viewer, the viewer
	 * will refresh all items as well.
	 */
	private void queryItemCount() {
		// Create the request monitor to collect the count.  This request
		// monitor will be completed by the following transaction.
		final DataRequestMonitor<Integer> rm = new DataRequestMonitor<Integer>(fDisplayExecutor, null) {
			@Override
			protected void handleSuccess() {
				setCountToViewer(getData());
			}

			@Override
			protected void handleRejectedExecutionException() {
			} // Shutting down, ignore.
		};

		// Use a transaction, even with a single cache.  This will ensure that
		// if the cache is reset during processing by an event.  The request
		// for data will be re-issued.
		fDataExecutor.execute(new Runnable() {
			@Override
			public void run() {
				new Transaction<Integer>() {
					@Override
					protected Integer process() throws Transaction.InvalidCacheException, CoreException {
						return processCount(this);
					}
				}.request(rm);
			}
		});
	}

	/**
	 * Perform the count retrieval from the sum data generator.
	 * @param transaction The ACPM transaction to use for calculation.
	 * @return Calculated count.
	 * @throws Transaction.InvalidCacheException {@link Transaction#process}
	 * @throws CoreException See {@link Transaction#process}
	 */
	private Integer processCount(Transaction<Integer> transaction)
			throws Transaction.InvalidCacheException, CoreException {
		ICache<Integer> countCache = fSumGeneratorCM.getCount();
		transaction.validate(countCache);
		return countCache.getData();
	}

	/**
	 * Set the givne count to the viewer.  This will cause the viewer will
	 * refresh all items' data as well.
	 * <p>Note: This method must be called in the display thread. </p>
	 * @param count New count to set to viewer.
	 */
	private void setCountToViewer(int count) {
		if (!fViewer.getTable().isDisposed()) {
			fViewer.setItemCount(count);
			fViewer.getTable().clearAll();
		}
	}

	/**
	 * Retrieve the current value for given index.
	 */
	private void queryValue(final int index) {
		// Create the request monitor to collect the value.  This request
		// monitor will be completed by the following transaction.
		final ValueRequestMonitor rm = new ValueRequestMonitor(index) {
			@Override
			protected void handleCompleted() {
				fItemDataRequestMonitors.remove(this);
				if (isSuccess()) {
					setValueToViewer(index, getData());
				}
			}

			@Override
			protected void handleRejectedExecutionException() {
				// Shutting down, ignore.
			}
		};

		// Save the value request monitor, to cancel it if the view is
		// scrolled.
		fItemDataRequestMonitors.add(rm);

		// Use a transaction, even with a single cache.  This will ensure that
		// if the cache is reset during processing by an event.  The request
		// for data will be re-issued.
		fDataExecutor.execute(new Runnable() {
			@Override
			public void run() {
				new Transaction<String>() {
					@Override
					protected String process() throws Transaction.InvalidCacheException, CoreException {
						return processValue(this, index);
					}
				}.request(rm);
			}
		});
	}

	/**
	 * Write the view value to the viewer.
	 * <p>Note: This method must be called in the display thread. </p>
	 * @param index Index of value to set.
	 * @param value New value.
	 */
	private void setValueToViewer(int index, String value) {
		if (!fViewer.getTable().isDisposed()) {
			fViewer.replace(value, index);
		}
	}

	/**
	 * Perform the calculation compose the string with data provider values
	 * and the sum.  This implementation also validates the result.
	 * @param transaction The ACPM transaction to use for calculation.
	 * @param index Index of value to calculate.
	 * @return Calculated value.
	 * @throws Transaction.InvalidCacheException {@link Transaction#process}
	 * @throws CoreException See {@link Transaction#process}
	 */
	private String processValue(Transaction<String> transaction, int index)
			throws Transaction.InvalidCacheException, CoreException {
		List<ICache<Integer>> valueCaches = new ArrayList<ICache<Integer>>(fDataGeneratorCMs.length);
		for (DataGeneratorCacheManager dataGeneratorCM : fDataGeneratorCMs) {
			valueCaches.add(dataGeneratorCM.getValue(index));
		}
		// Validate all value caches at once.  This executes needed requests
		// in parallel.
		transaction.validate(valueCaches);

		// TODO: evaluate sum generator cache in parallel with value caches.
		ICache<Integer> sumCache = fSumGeneratorCM.getValue(index);
		transaction.validate(sumCache);

		// Compose the string with values, sum, and validation result.
		StringBuilder result = new StringBuilder();
		int calcSum = 0;
		for (ICache<Integer> valueCache : valueCaches) {
			if (result.length() != 0)
				result.append(" + ");
			result.append(valueCache.getData());
			calcSum += valueCache.getData();
		}
		result.append(" = ");
		result.append(sumCache.getData());
		if (calcSum != sumCache.getData()) {
			result.append(" !INCORRECT! ");
		}

		return result.toString();
	}

	/**
	 * Dedicated class for data item requests.  This class holds the index
	 * argument so it can be examined when canceling stale requests.
	 */
	private class ValueRequestMonitor extends DataRequestMonitor<String> {
		/** Index is used when canceling stale requests. */
		int fIndex;

		ValueRequestMonitor(int index) {
			super(fDisplayExecutor, null);
			fIndex = index;
		}

		@Override
		protected void handleRejectedExecutionException() {
			// Shutting down, ignore.
		}
	}

	/**
	 * Cancels any outstanding value requests for items which are no longer
	 * visible in the viewer.
	 *
	 * @param topIdx Index of top visible item in viewer.
	 * @param botIdx Index of bottom visible item in viewer.
	 */
	private void cancelStaleRequests(int topIdx, int botIdx) {
		// Decrement the count of outstanding cancel calls.
		fCancelCallsPending--;

		// Must check again, in case disposed while re-dispatching.
		if (fDataGeneratorCMs == null || fViewer.getTable().isDisposed()) {
			return;
		}

		// Go through the outstanding requests and cancel any that
		// are not visible anymore.
		for (Iterator<ValueRequestMonitor> itr = fItemDataRequestMonitors.iterator(); itr.hasNext();) {
			ValueRequestMonitor item = itr.next();
			if (item.fIndex < topIdx || item.fIndex > botIdx) {
				// Set the item to canceled status, so that the data provider
				// will ignore it.
				item.cancel();

				// Add the item index to list of indexes that were canceled,
				// which will be sent to the table widget.
				fIndexesToCancel.add(item.fIndex);

				// Remove the item from the outstanding cancel requests.
				itr.remove();
			}
		}
		if (!fIndexesToCancel.isEmpty() && fCancelCallsPending == 0) {
			Set<Integer> canceledIdxs = fIndexesToCancel;
			fIndexesToCancel = new HashSet<Integer>();

			// Clear the indexes of the canceled request, so that the
			// viewer knows to request them again when needed.
			// Note: clearing using TableViewer.clear(int) seems very
			// inefficient, it's better to use Table.clear(int[]).
			int[] canceledIdxsArray = new int[canceledIdxs.size()];
			int i = 0;
			for (Integer index : canceledIdxs) {
				canceledIdxsArray[i++] = index;
			}
			fViewer.getTable().clear(canceledIdxsArray);
		}
	}

	/**
	 * The entry point for the example.
	 * @param args Program arguments.
	 */
	public static void main(String[] args) {
		// Create the shell to hold the viewer.
		Display display = new Display();
		Shell shell = new Shell(display, SWT.SHELL_TRIM);
		shell.setLayout(new GridLayout());
		GridData data = new GridData(GridData.FILL_BOTH);
		shell.setLayoutData(data);
		Font font = new Font(display, "Courier", 10, SWT.NORMAL);

		// Create the table viewer.
		TableViewer tableViewer = new TableViewer(shell, SWT.BORDER | SWT.VIRTUAL);
		tableViewer.getControl().setLayoutData(data);

		DsfExecutor executor = new DefaultDsfExecutor("Example executor");

		// Create the data generator.
		final IDataGenerator[] generators = new IDataGenerator[5];
		for (int i = 0; i < generators.length; i++) {
			generators[i] = new DataGeneratorWithExecutor(executor);
		}
		final IDataGenerator sumGenerator = new ACPMSumDataGenerator(executor, generators);

		// Create the content provider which will populate the viewer.
		ACPMSumDataViewer contentProvider = new ACPMSumDataViewer(tableViewer, new ImmediateInDsfExecutor(executor),
				generators, sumGenerator);
		tableViewer.setContentProvider(contentProvider);
		tableViewer.setInput(new Object());

		// Open the shell and service the display dispatch loop until user
		// closes the shell.
		shell.open();
		while (!shell.isDisposed()) {
			if (!display.readAndDispatch())
				display.sleep();
		}

		// The IDataGenerator.shutdown() method is asynchronous, this requires
		// using a query again in order to wait for its completion.
		Query<Object> shutdownQuery = new Query<Object>() {
			@Override
			protected void execute(DataRequestMonitor<Object> rm) {
				CountingRequestMonitor crm = new CountingRequestMonitor(ImmediateExecutor.getInstance(), rm);
				for (int i = 0; i < generators.length; i++) {
					generators[i].shutdown(crm);
				}
				sumGenerator.shutdown(crm);
				crm.setDoneCount(generators.length);
			}
		};

		executor.execute(shutdownQuery);
		try {
			shutdownQuery.get();
		} catch (Exception e) {
		}

		// Shut down the display.
		font.dispose();
		display.dispose();
	}
}

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