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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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
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package sun.lwawt.macosx;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

Safely holds and disposes of native AppKit resources, using the
correct AppKit threading and Objective-C GC semantics.
/**
 * Safely holds and disposes of native AppKit resources, using the
 * correct AppKit threading and Objective-C GC semantics.
 */
public class CFRetainedResource {
    private static native void nativeCFRelease(final long ptr, final boolean disposeOnAppKitThread);

    private final boolean disposeOnAppKitThread;
    // TODO this pointer should be private and accessed via CFNativeAction class
    protected volatile long ptr;

    private final ReadWriteLock lock = new ReentrantReadWriteLock();
    private final Lock writeLock = lock.writeLock();
    private final Lock readLock = lock.readLock();

    
Params:
ptr – CFRetained native object pointer
disposeOnAppKitThread – is the object needs to be CFReleased on the main thread/**
     * @param ptr CFRetained native object pointer
     * @param disposeOnAppKitThread is the object needs to be CFReleased on the main thread
     */
    protected CFRetainedResource(final long ptr, final boolean disposeOnAppKitThread) {
        this.disposeOnAppKitThread = disposeOnAppKitThread;
        this.ptr = ptr;
    }

    
CFReleases previous resource and assigns new pre-retained resource.
Params:
ptr – CFRetained native object pointer/**
     * CFReleases previous resource and assigns new pre-retained resource.
     * @param ptr CFRetained native object pointer
     */
    protected void setPtr(final long ptr) {
        writeLock.lock();
        try {
            if (this.ptr != 0) {
                dispose();
            }
            this.ptr = ptr;
        } finally {
            writeLock.unlock();
        }
    }

    
Manually CFReleases the native resource.
/**
     * Manually CFReleases the native resource.
     */
    protected void dispose() {
        long oldPtr = 0L;
        writeLock.lock();
        try {
            if (ptr == 0) {
                return;
            }
            oldPtr = ptr;
            ptr = 0;
        } finally {
            writeLock.unlock();
        }

        nativeCFRelease(oldPtr, disposeOnAppKitThread); // perform outside of the synchronized block
    }

    
The interface which allows to execute some native operations with
assumption that the native pointer will be valid till the end.
/**
     * The interface which allows to execute some native operations with
     * assumption that the native pointer will be valid till the end.
     */
    public interface CFNativeAction {

        
The native operation should be called from this method.
Params:
ptr – the pointer to the native data/**
         * The native operation should be called from this method.
         *
         * @param  ptr the pointer to the native data
         */
        void run(long ptr);
    }

    
The interface which allows to execute some native operations and get a
result with assumption that the native pointer will be valid till the
end.
/**
     * The interface which allows to execute some native operations and get a
     * result with assumption that the native pointer will be valid till the
     * end.
     */
    interface CFNativeActionGet {

        
The native operation should be called from this method.
Params:
ptr – the pointer to the native data
Returns:
result of the native operation/**
         * The native operation should be called from this method.
         *
         * @param  ptr the pointer to the native data
         * @return result of the native operation
         */
        long run(long ptr);
    }

    
This is utility method which should be used instead of the direct access to the ptr, because this method guaranteed that the pointer will not be zero and will be valid till the end of the operation.It is highly recomended to not use any external lock in action. If the current ptr is 0 then action will be ignored. 
Params:
action – The native operation/**
     * This is utility method which should be used instead of the direct access
     * to the {@link #ptr}, because this method guaranteed that the pointer will
     * not be zero and will be valid till the end of the operation.It is highly
     * recomended to not use any external lock in action. If the current
     * {@link #ptr} is {@code 0} then action will be ignored.
     *
     * @param  action The native operation
     */
    public final void execute(final CFNativeAction action) {
        readLock.lock();
        try {
            if (ptr != 0) {
                action.run(ptr);
            }
        } finally {
            readLock.unlock();
        }
    }

    
This is utility method which should be used instead of the direct access to the ptr, because this method guaranteed that the pointer will not be zero and will be valid till the end of the operation. It is highly recomended to not use any external lock in action. If the current ptr is 0 then action will be ignored and  is returned. 
Params:
action – the native operation
Returns:
result of the native operation, usually the native pointer to
        some other data/**
     * This is utility method which should be used instead of the direct access
     * to the {@link #ptr}, because this method guaranteed that the pointer will
     * not be zero and will be valid till the end of the operation. It is highly
     * recomended to not use any external lock in action. If the current
     * {@link #ptr} is {@code 0} then action will be ignored and {@code} is
     * returned.
     *
     * @param  action the native operation
     * @return result of the native operation, usually the native pointer to
     *         some other data
     */
    final long executeGet(final CFNativeActionGet action) {
        readLock.lock();
        try {
            if (ptr != 0) {
                return action.run(ptr);
            }
        } finally {
            readLock.unlock();
        }
        return 0;
    }

    @Override
    protected final void finalize() throws Throwable {
        dispose();
    }
}