src/java.desktop/unix/classes/sun/awt/X11/XSelection.java

/*
 * Copyright (c) 2003, 2014, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.awt.X11;

import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;

import java.io.ByteArrayOutputStream;
import java.io.IOException;

import java.util.Hashtable;
import java.util.Map;

import sun.awt.AppContext;
import sun.awt.SunToolkit;
import sun.awt.UNIXToolkit;

import sun.awt.datatransfer.DataTransferer;

/**
 * A class which interfaces with the X11 selection service.
 */
final class XSelection {

    /* Maps atoms to XSelection instances. */
    private static final Hashtable<XAtom, XSelection> table = new Hashtable<XAtom, XSelection>();
    /* Prevents from parallel selection data request processing. */
    private static final Object lock = new Object();
    /* The property in which the owner should place the requested data. */
    private static final XAtom selectionPropertyAtom = XAtom.get("XAWT_SELECTION");
    /* The maximal length of the property data. */
    public static final long MAX_LENGTH = 1000000;
    /*
     * The maximum data size for ChangeProperty request.
     * 100 is for the structure prepended to the request.
     */
    public static final int MAX_PROPERTY_SIZE;
    static {
        XToolkit.awtLock();
        try {
            MAX_PROPERTY_SIZE =
                (int)(XlibWrapper.XMaxRequestSize(XToolkit.getDisplay()) * 4 - 100);
        } finally {
            XToolkit.awtUnlock();
        }
    }

    /* The PropertyNotify event handler for incremental data transfer. */
    private static final XEventDispatcher incrementalTransferHandler =
        new IncrementalTransferHandler();
    /* The context for the current request - protected with awtLock. */
    private static WindowPropertyGetter propertyGetter = null;

    // The orders of the lock acquisition:
    //   XClipboard -> XSelection -> awtLock.
    //   lock -> awtLock.

    /* The X atom for the underlying selection. */
    private final XAtom selectionAtom;

    /*
     * Owner-related variables - protected with synchronized (this).
     */

    /* The contents supplied by the current owner. */
    private Transferable contents = null;
    /* The format-to-flavor map for the current owner. */
    private Map<Long, DataFlavor> formatMap = null;
    /* The formats supported by the current owner was set. */
    private long[] formats = null;
    /* The AppContext in which the current owner was set. */
    private AppContext appContext = null;
    // The X server time of the last XConvertSelection() call;
    // protected with 'lock' and awtLock.
    private static long lastRequestServerTime;
    /* The time at which the current owner was set. */
    private long ownershipTime = 0;
    // True if we are the owner of this selection.
    private boolean isOwner;
    private OwnershipListener ownershipListener = null;
    private final Object stateLock = new Object();

    static {
        XToolkit.addEventDispatcher(XWindow.getXAWTRootWindow().getWindow(),
                                    new SelectionEventHandler());
    }

    /*
     * Returns the XSelection object for the specified selection atom or
     * {@code null} if none exists.
     */
    static XSelection getSelection(XAtom atom) {
        return table.get(atom);
    }

    /**
     * Creates a selection object.
     *
     * @param  atom the selection atom
     * @throws NullPointerException if atom is {@code null}
     */
    XSelection(XAtom atom) {
        if (atom == null) {
            throw new NullPointerException("Null atom");
        }
        selectionAtom = atom;
        table.put(selectionAtom, this);
    }

    public XAtom getSelectionAtom() {
        return selectionAtom;
    }

    synchronized boolean setOwner(Transferable contents,
                                  Map<Long, DataFlavor> formatMap,
                                  long[] formats, long time) {
        long owner = XWindow.getXAWTRootWindow().getWindow();
        long selection = selectionAtom.getAtom();

        // ICCCM prescribes that CurrentTime should not be used for SetSelectionOwner.
        if (time == XConstants.CurrentTime) {
            time = XToolkit.getCurrentServerTime();
        }

        this.contents = contents;
        this.formatMap = formatMap;
        this.formats = formats;
        this.appContext = AppContext.getAppContext();
        this.ownershipTime = time;

        XToolkit.awtLock();
        try {
            XlibWrapper.XSetSelectionOwner(XToolkit.getDisplay(),
                                           selection, owner, time);
            if (XlibWrapper.XGetSelectionOwner(XToolkit.getDisplay(),
                                               selection) != owner)
            {
                reset();
                return false;
            }
            setOwnerProp(true);
            return true;
        } finally {
            XToolkit.awtUnlock();
        }
    }

    /**
     * Blocks the current thread till SelectionNotify or PropertyNotify (in case of INCR transfer) arrives.
     */
    private static void waitForSelectionNotify(WindowPropertyGetter dataGetter) throws InterruptedException {
        long startTime = System.currentTimeMillis();
        XToolkit.awtLock();
        try {
            do {
                DataTransferer.getInstance().processDataConversionRequests();
                XToolkit.awtLockWait(250);
            } while (propertyGetter == dataGetter && System.currentTimeMillis() < startTime + UNIXToolkit.getDatatransferTimeout());
        } finally {
            XToolkit.awtUnlock();
        }
    }

    /*
     * Returns the list of atoms that represent the targets for which an attempt
     * to convert the current selection will succeed.
     */
    public long[] getTargets(long time) {
        if (XToolkit.isToolkitThread()) {
            throw new Error("UNIMPLEMENTED");
        }

        long[] targets = null;

        synchronized (lock) {
            WindowPropertyGetter targetsGetter =
                new WindowPropertyGetter(XWindow.getXAWTRootWindow().getWindow(),
                                         selectionPropertyAtom, 0, MAX_LENGTH,
                                         true, XConstants.AnyPropertyType);

            try {
                XToolkit.awtLock();
                try {
                    propertyGetter = targetsGetter;
                    lastRequestServerTime = time;

                    XlibWrapper.XConvertSelection(XToolkit.getDisplay(),
                                                  getSelectionAtom().getAtom(),
                                                  XDataTransferer.TARGETS_ATOM.getAtom(),
                                                  selectionPropertyAtom.getAtom(),
                                                  XWindow.getXAWTRootWindow().getWindow(),
                                                  time);

                    // If the owner doesn't respond within the
                    // SELECTION_TIMEOUT, we report conversion failure.
                    try {
                        waitForSelectionNotify(targetsGetter);
                    } catch (InterruptedException ie) {
                        return new long[0];
                    } finally {
                        propertyGetter = null;
                    }
                } finally {
                    XToolkit.awtUnlock();
                }
                targets = getFormats(targetsGetter);
            } finally {
                targetsGetter.dispose();
            }
        }
        return targets;
    }

    static long[] getFormats(WindowPropertyGetter targetsGetter) {
        long[] formats = null;

        if (targetsGetter.isExecuted() && !targetsGetter.isDisposed() &&
                (targetsGetter.getActualType() == XAtom.XA_ATOM ||
                 targetsGetter.getActualType() == XDataTransferer.TARGETS_ATOM.getAtom()) &&
                targetsGetter.getActualFormat() == 32)
        {
            // we accept property with TARGETS type to be compatible with old jdks
            // see 6607163
            int count = targetsGetter.getNumberOfItems();
            if (count > 0) {
                long atoms = targetsGetter.getData();
                formats = new long[count];
                for (int index = 0; index < count; index++) {
                    formats[index] =
                            Native.getLong(atoms+index*XAtom.getAtomSize());
                }
            }
        }

        return formats != null ? formats : new long[0];
    }

    /*
     * Requests the selection data in the specified format and returns
     * the data provided by the owner.
     */
    public byte[] getData(long format, long time) throws IOException {
        if (XToolkit.isToolkitThread()) {
            throw new Error("UNIMPLEMENTED");
        }

        byte[] data = null;

        synchronized (lock) {
            WindowPropertyGetter dataGetter =
                new WindowPropertyGetter(XWindow.getXAWTRootWindow().getWindow(),
                                         selectionPropertyAtom, 0, MAX_LENGTH,
                                         false, // don't delete to handle INCR properly.
                                         XConstants.AnyPropertyType);

            try {
                XToolkit.awtLock();
                try {
                    propertyGetter = dataGetter;
                    lastRequestServerTime = time;

                    XlibWrapper.XConvertSelection(XToolkit.getDisplay(),
                                                  getSelectionAtom().getAtom(),
                                                  format,
                                                  selectionPropertyAtom.getAtom(),
                                                  XWindow.getXAWTRootWindow().getWindow(),
                                                  time);

                    // If the owner doesn't respond within the
                    // SELECTION_TIMEOUT, we report conversion failure.
                    try {
                        waitForSelectionNotify(dataGetter);
                    } catch (InterruptedException ie) {
                        return new byte[0];
                    } finally {
                        propertyGetter = null;
                    }
                } finally {
                    XToolkit.awtUnlock();
                }

                validateDataGetter(dataGetter);

                // Handle incremental transfer.
                if (dataGetter.getActualType() ==
                    XDataTransferer.INCR_ATOM.getAtom()) {

                    if (dataGetter.getActualFormat() != 32) {
                        throw new IOException("Unsupported INCR format: " +
                                              dataGetter.getActualFormat());
                    }

                    int count = dataGetter.getNumberOfItems();

                    if (count <= 0) {
                        throw new IOException("INCR data is missed.");
                    }

                    long ptr = dataGetter.getData();

                    int len = 0;

                    {
                        // Following Xt sources use the last element.
                        long longLength = Native.getLong(ptr, count-1);

                        if (longLength <= 0) {
                            return new byte[0];
                        }

                        if (longLength > Integer.MAX_VALUE) {
                            throw new IOException("Can't handle large data block: "
                                                  + longLength + " bytes");
                        }

                        len = (int)longLength;
                    }

                    dataGetter.dispose();

                    ByteArrayOutputStream dataStream = new ByteArrayOutputStream(len);

                    while (true) {
                        WindowPropertyGetter incrDataGetter =
                            new WindowPropertyGetter(XWindow.getXAWTRootWindow().getWindow(),
                                                     selectionPropertyAtom,
                                                     0, MAX_LENGTH, false,
                                                     XConstants.AnyPropertyType);

                        try {
                            XToolkit.awtLock();
                            XToolkit.addEventDispatcher(XWindow.getXAWTRootWindow().getWindow(),
                                                        incrementalTransferHandler);

                            propertyGetter = incrDataGetter;

                            try {
                                XlibWrapper.XDeleteProperty(XToolkit.getDisplay(),
                                                            XWindow.getXAWTRootWindow().getWindow(),
                                                            selectionPropertyAtom.getAtom());

                                // If the owner doesn't respond within the
                                // SELECTION_TIMEOUT, we terminate incremental
                                // transfer.
                                waitForSelectionNotify(incrDataGetter);
                            } catch (InterruptedException ie) {
                                break;
                            } finally {
                                propertyGetter = null;
                                XToolkit.removeEventDispatcher(XWindow.getXAWTRootWindow().getWindow(),
                                                               incrementalTransferHandler);
                                XToolkit.awtUnlock();
                            }

                            validateDataGetter(incrDataGetter);

                            if (incrDataGetter.getActualFormat() != 8) {
                                throw new IOException("Unsupported data format: " +
                                                      incrDataGetter.getActualFormat());
                            }

                            count = incrDataGetter.getNumberOfItems();

                            if (count == 0) {
                                break;
                            }

                            if (count > 0) {
                                ptr = incrDataGetter.getData();
                                for (int index = 0; index < count; index++) {
                                    dataStream.write(Native.getByte(ptr + index));
                                }
                            }

                            data = dataStream.toByteArray();

                        } finally {
                            incrDataGetter.dispose();
                        }
                    }
                } else {
                    XToolkit.awtLock();
                    try {
                        XlibWrapper.XDeleteProperty(XToolkit.getDisplay(),
                                                    XWindow.getXAWTRootWindow().getWindow(),
                                                    selectionPropertyAtom.getAtom());
                    } finally {
                        XToolkit.awtUnlock();
                    }

                    if (dataGetter.getActualFormat() != 8) {
                        throw new IOException("Unsupported data format: " +
                                              dataGetter.getActualFormat());
                    }

                    int count = dataGetter.getNumberOfItems();
                    if (count > 0) {
                        data = new byte[count];
                        long ptr = dataGetter.getData();
                        for (int index = 0; index < count; index++) {
                            data[index] = Native.getByte(ptr + index);
                        }
                    }
                }
            } finally {
                dataGetter.dispose();
            }
        }

        return data != null ? data : new byte[0];
    }

    private void validateDataGetter(WindowPropertyGetter propertyGetter)
            throws IOException
    {
        // The order of checks is important because a property getter
        // has not been executed in case of timeout as well as in case of
        // changed selection owner.

        if (propertyGetter.isDisposed()) {
            throw new IOException("Owner failed to convert data");
        }

        // The owner didn't respond - terminate the transfer.
        if (!propertyGetter.isExecuted()) {
            throw new IOException("Owner timed out");
        }
    }

    // To be MT-safe this method should be called under awtLock.
    boolean isOwner() {
        return isOwner;
    }

    // To be MT-safe this method should be called under awtLock.
    private void setOwnerProp(boolean f) {
        isOwner = f;
        fireOwnershipChanges(isOwner);
    }

    private void lostOwnership() {
        setOwnerProp(false);
    }

    public synchronized void reset() {
        contents = null;
        formatMap = null;
        formats = null;
        appContext = null;
        ownershipTime = 0;
    }

    // Converts the data to the 'format' and if the conversion succeeded stores
    // the data in the 'property' on the 'requestor' window.
    // Returns true if the conversion succeeded.
    private boolean convertAndStore(long requestor, long format, long property) {
        int dataFormat = 8; /* Can choose between 8,16,32. */
        byte[] byteData = null;
        long nativeDataPtr = 0;
        int count = 0;

        try {
            SunToolkit.insertTargetMapping(this, appContext);

            byteData = DataTransferer.getInstance().convertData(this,
                                                                contents,
                                                                format,
                                                                formatMap,
                                                                XToolkit.isToolkitThread());
        } catch (IOException ioe) {
            return false;
        }

        if (byteData == null) {
            return false;
        }

        count = byteData.length;

        try {
            if (count > 0) {
                if (count <= MAX_PROPERTY_SIZE) {
                    nativeDataPtr = Native.toData(byteData);
                } else {
                    // Initiate incremental data transfer.
                    new IncrementalDataProvider(requestor, property, format, 8,
                                                byteData);

                    nativeDataPtr =
                        XlibWrapper.unsafe.allocateMemory(XAtom.getAtomSize());

                    Native.putLong(nativeDataPtr, (long)count);

                    format = XDataTransferer.INCR_ATOM.getAtom();
                    dataFormat = 32;
                    count = 1;
                }

            }

            XToolkit.awtLock();
            try {
                XlibWrapper.XChangeProperty(XToolkit.getDisplay(), requestor, property,
                                            format, dataFormat,
                                            XConstants.PropModeReplace,
                                            nativeDataPtr, count);
            } finally {
                XToolkit.awtUnlock();
            }
        } finally {
            if (nativeDataPtr != 0) {
                XlibWrapper.unsafe.freeMemory(nativeDataPtr);
                nativeDataPtr = 0;
            }
        }

        return true;
    }

    private void handleSelectionRequest(XSelectionRequestEvent xsre) {
        long property = xsre.get_property();
        final long requestor = xsre.get_requestor();
        final long requestTime = xsre.get_time();
        final long format = xsre.get_target();
        boolean conversionSucceeded = false;

        if (ownershipTime != 0 &&
            (requestTime == XConstants.CurrentTime || requestTime >= ownershipTime))
        {
            // Handle MULTIPLE requests as per ICCCM.
            if (format == XDataTransferer.MULTIPLE_ATOM.getAtom()) {
                conversionSucceeded = handleMultipleRequest(requestor, property);
            } else {
                // Support for obsolete clients as per ICCCM.
                if (property == XConstants.None) {
                    property = format;
                }

                if (format == XDataTransferer.TARGETS_ATOM.getAtom()) {
                    conversionSucceeded = handleTargetsRequest(property, requestor);
                } else {
                    conversionSucceeded = convertAndStore(requestor, format, property);
                }
            }
        }

        if (!conversionSucceeded) {
            // None property indicates conversion failure.
            property = XConstants.None;
        }

        XSelectionEvent xse = new XSelectionEvent();
        try {
            xse.set_type(XConstants.SelectionNotify);
            xse.set_send_event(true);
            xse.set_requestor(requestor);
            xse.set_selection(selectionAtom.getAtom());
            xse.set_target(format);
            xse.set_property(property);
            xse.set_time(requestTime);

            XToolkit.awtLock();
            try {
                XlibWrapper.XSendEvent(XToolkit.getDisplay(), requestor, false,
                                       XConstants.NoEventMask, xse.pData);
            } finally {
                XToolkit.awtUnlock();
            }
        } finally {
            xse.dispose();
        }
    }

    private boolean handleMultipleRequest(final long requestor, long property) {
        if (XConstants.None == property) {
            // The property cannot be None for a MULTIPLE request.
            return false;
        }

        boolean conversionSucceeded = false;

        // First retrieve the list of requested targets.
        WindowPropertyGetter wpg =
                new WindowPropertyGetter(requestor, XAtom.get(property),
                                         0, MAX_LENGTH, false,
                                         XConstants.AnyPropertyType);
        try {
            wpg.execute();

            if (wpg.getActualFormat() == 32 && (wpg.getNumberOfItems() % 2) == 0) {
                final long count = wpg.getNumberOfItems() / 2;
                final long pairsPtr = wpg.getData();
                boolean writeBack = false;

                for (int i = 0; i < count; i++) {
                    long target = Native.getLong(pairsPtr, 2 * i);
                    long prop = Native.getLong(pairsPtr, 2 * i + 1);

                    if (!convertAndStore(requestor, target, prop)) {
                        // To report failure, we should replace the
                        // target atom with 0 in the MULTIPLE property.
                        Native.putLong(pairsPtr, 2 * i, 0);
                        writeBack = true;
                    }
                }
                if (writeBack) {
                    XToolkit.awtLock();
                    try {
                        XlibWrapper.XChangeProperty(XToolkit.getDisplay(),
                                                    requestor,
                                                    property,
                                                    wpg.getActualType(),
                                                    wpg.getActualFormat(),
                                                                XConstants.PropModeReplace,
                                                    wpg.getData(),
                                                    wpg.getNumberOfItems());
                    } finally {
                        XToolkit.awtUnlock();
                    }
                }
                conversionSucceeded = true;
            }
        } finally {
            wpg.dispose();
        }

        return conversionSucceeded;
    }

    private boolean handleTargetsRequest(long property, long requestor)
            throws IllegalStateException
    {
        boolean conversionSucceeded = false;
        // Use a local copy to avoid synchronization.
        long[] formatsLocal = formats;

        if (formatsLocal == null) {
            throw new IllegalStateException("Not an owner.");
        }

        long nativeDataPtr = 0;

        try {
            final int count = formatsLocal.length;
            final int dataFormat = 32;

            if (count > 0) {
                nativeDataPtr = Native.allocateLongArray(count);
                Native.put(nativeDataPtr, formatsLocal);
            }

            conversionSucceeded = true;

            XToolkit.awtLock();
            try {
                XlibWrapper.XChangeProperty(XToolkit.getDisplay(), requestor,
                                            property, XAtom.XA_ATOM, dataFormat,
                                            XConstants.PropModeReplace,
                                            nativeDataPtr, count);
            } finally {
                XToolkit.awtUnlock();
            }
        } finally {
            if (nativeDataPtr != 0) {
                XlibWrapper.unsafe.freeMemory(nativeDataPtr);
                nativeDataPtr = 0;
            }
        }
        return conversionSucceeded;
    }

    private void fireOwnershipChanges(final boolean isOwner) {
        OwnershipListener l = null;
        synchronized (stateLock) {
            l = ownershipListener;
        }
        if (null != l) {
            l.ownershipChanged(isOwner);
        }
    }

    void registerOwershipListener(OwnershipListener l) {
        synchronized (stateLock) {
            ownershipListener = l;
        }
    }

    void unregisterOwnershipListener() {
        synchronized (stateLock) {
            ownershipListener = null;
        }
    }

    private static final class SelectionEventHandler implements XEventDispatcher {
        @Override
        public void dispatchEvent(XEvent ev) {
            switch (ev.get_type()) {
            case XConstants.SelectionNotify: {
                XToolkit.awtLock();
                try {
                    XSelectionEvent xse = ev.get_xselection();
                    // Ignore the SelectionNotify event if it is not the response to our last request.
                    if (propertyGetter != null && xse.get_time() == lastRequestServerTime) {
                        // The property will be None in case of conversion failure.
                        if (xse.get_property() == selectionPropertyAtom.getAtom()) {
                            propertyGetter.execute();
                            propertyGetter = null;
                        } else if (xse.get_property() == 0) {
                            propertyGetter.dispose();
                            propertyGetter = null;
                        }
                    }
                    XToolkit.awtLockNotifyAll();
                } finally {
                    XToolkit.awtUnlock();
                }
                break;
            }
            case XConstants.SelectionRequest: {
                XSelectionRequestEvent xsre = ev.get_xselectionrequest();
                long atom = xsre.get_selection();
                XSelection selection = XSelection.getSelection(XAtom.get(atom));

                if (selection != null) {
                    selection.handleSelectionRequest(xsre);
                }
                break;
            }
            case XConstants.SelectionClear: {
                XSelectionClearEvent xsce = ev.get_xselectionclear();
                long atom = xsce.get_selection();
                XSelection selection = XSelection.getSelection(XAtom.get(atom));

                if (selection != null) {
                    selection.lostOwnership();
                }

                XToolkit.awtLock();
                try {
                    XToolkit.awtLockNotifyAll();
                } finally {
                    XToolkit.awtUnlock();
                }
                break;
            }
            }
        }
    }

    private static final class IncrementalDataProvider implements XEventDispatcher {
        private final long requestor;
        private final long property;
        private final long target;
        private final int format;
        private final byte[] data;
        private int offset = 0;

        // NOTE: formats other than 8 are not supported.
        public IncrementalDataProvider(long requestor, long property,
                                       long target, int format, byte[] data) {
            if (format != 8) {
                throw new IllegalArgumentException("Unsupported format: " + format);
            }

            this.requestor = requestor;
            this.property = property;
            this.target = target;
            this.format = format;
            this.data = data;

            XWindowAttributes wattr = new XWindowAttributes();
            try {
                XToolkit.awtLock();
                try {
                    XlibWrapper.XGetWindowAttributes(XToolkit.getDisplay(), requestor,
                                                     wattr.pData);
                    XlibWrapper.XSelectInput(XToolkit.getDisplay(), requestor,
                                             wattr.get_your_event_mask() |
                                             XConstants.PropertyChangeMask);
                } finally {
                    XToolkit.awtUnlock();
                }
            } finally {
                wattr.dispose();
            }
            XToolkit.addEventDispatcher(requestor, this);
        }

        @Override
        public void dispatchEvent(XEvent ev) {
            switch (ev.get_type()) {
            case XConstants.PropertyNotify:
                XPropertyEvent xpe = ev.get_xproperty();
                if (xpe.get_window() == requestor &&
                    xpe.get_state() == XConstants.PropertyDelete &&
                    xpe.get_atom() == property) {

                    int count = data.length - offset;
                    long nativeDataPtr = 0;
                    if (count > MAX_PROPERTY_SIZE) {
                        count = MAX_PROPERTY_SIZE;
                    }

                    if (count > 0) {
                        nativeDataPtr = XlibWrapper.unsafe.allocateMemory(count);
                        for (int i = 0; i < count; i++) {
                            Native.putByte(nativeDataPtr+i, data[offset + i]);
                        }
                    } else {
                        assert (count == 0);
                        // All data has been transferred.
                        // This zero-length data indicates end of transfer.
                        XToolkit.removeEventDispatcher(requestor, this);
                    }

                    XToolkit.awtLock();
                    try {
                        XlibWrapper.XChangeProperty(XToolkit.getDisplay(),
                                                    requestor, property,
                                                    target, format,
                                                    XConstants.PropModeReplace,
                                                    nativeDataPtr, count);
                    } finally {
                        XToolkit.awtUnlock();
                    }
                    if (nativeDataPtr != 0) {
                        XlibWrapper.unsafe.freeMemory(nativeDataPtr);
                        nativeDataPtr = 0;
                    }

                    offset += count;
                }
            }
        }
    }

    private static final class IncrementalTransferHandler implements XEventDispatcher {
        @Override
        public void dispatchEvent(XEvent ev) {
            switch (ev.get_type()) {
            case XConstants.PropertyNotify:
                XPropertyEvent xpe = ev.get_xproperty();
                if (xpe.get_state() == XConstants.PropertyNewValue &&
                    xpe.get_atom() == selectionPropertyAtom.getAtom()) {
                    XToolkit.awtLock();
                    try {
                        if (propertyGetter != null) {
                            propertyGetter.execute();
                            propertyGetter = null;
                        }
                        XToolkit.awtLockNotifyAll();
                    } finally {
                        XToolkit.awtUnlock();
                    }
                }
                break;
            }
        }
    }
}