/*

 * Copyright (c) 2005, 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

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 */

package sun.java2d.pipe;

import java.util.HashSet;

import java.util.Set;

import sun.awt.SunToolkit;

/**

 * The RenderQueue class encapsulates a RenderBuffer on which rendering

 * operations are enqueued.  Note that the RenderQueue lock must be acquired

 * before performing any operations on the queue (e.g. enqueuing an operation

 * or flushing the queue).  A sample usage scenario follows:

 *

 *     public void drawSomething(...) {

 *         rq.lock();

 *         try {

 *             ctx.validate(...);

 *             rq.ensureCapacity(4);

 *             rq.getBuffer().putInt(DRAW_SOMETHING);

 *             ...

 *         } finally {

 *             rq.unlock();

 *         }

 *     }

 *

 * If you are enqueuing an operation that involves 8-byte parameters (i.e.

 * long or double values), it is imperative that you ensure proper

 * alignment of the underlying RenderBuffer.  This can be accomplished

 * simply by providing an offset to the first 8-byte parameter in your

 * operation to the ensureCapacityAndAlignment() method.  For example:

 *

 *     public void drawStuff(...) {

 *         rq.lock();

 *         try {

 *             RenderBuffer buf = rq.getBuffer();

 *             ctx.validate(...);

 *             // 28 total bytes in the operation, 12 bytes to the first long

 *             rq.ensureCapacityAndAlignment(28, 12);

 *             buf.putInt(DRAW_STUFF);

 *             buf.putInt(x).putInt(y);

 *             buf.putLong(addr1);

 *             buf.putLong(addr2);

 *         } finally {

 *             rq.unlock();

 *         }

 *     }

 */

public abstract class RenderQueue {

    /** The size of the underlying buffer, in bytes. */

    private static final int BUFFER_SIZE = 32000;

    /** The underlying buffer for this queue. */

    protected RenderBuffer buf;

    /**

     * A Set containing hard references to Objects that must stay alive until

     * the queue has been completely flushed.

     */

    protected RenderQueue() {

        buf = RenderBuffer.allocate(BUFFER_SIZE);

    }

    /**

     * Locks the queue for read/write access.

     */

    public final void lock() {

        /*

         * Implementation note: In theory we should have two separate locks:

         * one lock to synchronize access to the RenderQueue, and then a

         * separate lock (the AWT lock) that only needs to be acquired when

         * we are about to flush the queue (using native windowing system

         * operations).  In practice it has been difficult to enforce the

         * correct lock ordering; sometimes AWT will have already acquired

         * the AWT lock before grabbing the RQ lock (see 6253009), while the

         * expected order should be RQ lock and then AWT lock.  Due to this

         * issue, using two separate locks is prone to deadlocks.  Therefore,

         * to solve this issue we have decided to eliminate the separate RQ

         * lock and instead just acquire the AWT lock here.  (Someday it might

         * be nice to go back to the old two-lock system, but that would

         * require potentially risky changes to AWT to ensure that it never

         * acquires the AWT lock before calling into 2D code that wants to

         * acquire the RQ lock.)

         */

        SunToolkit.awtLock();

    }

    /**

     * Attempts to lock the queue.  If successful, this method returns true,

     * indicating that the caller is responsible for calling

     * <code>unlock</code>; otherwise this method returns false.

     */

    public final boolean tryLock() {

        return SunToolkit.awtTryLock();

    }

    /**

     * Unlocks the queue.

     */

    public final void unlock() {

        SunToolkit.awtUnlock();

    }

    /**

     * Adds the given Object to the set of hard references, which will

     * prevent that Object from being disposed until the queue has been

     * flushed completely.  This is useful in cases where some enqueued

     * data could become invalid if the reference Object were garbage

     * collected before the queue could be processed.  (For example, keeping

     * a hard reference to a FontStrike will prevent any enqueued glyph

     * images associated with that strike from becoming invalid before the

     * queue is flushed.)  The reference set will be cleared immediately

     * after the queue is flushed each time.

     */

    public final void addReference(Object ref) {

        refSet.add(ref);

    }

    /**

     * Returns the encapsulated RenderBuffer object.

     */

    public final RenderBuffer getBuffer() {

        return buf;

    }

    /**

     * Ensures that there will be enough room on the underlying buffer

     * for the following operation.  If the operation will not fit given

     * the remaining space, the buffer will be flushed immediately, leaving

     * an empty buffer for the impending operation.

     *

     * @param opsize size (in bytes) of the following operation

     */

    public final void ensureCapacity(int opsize) {

        if (buf.remaining() < opsize) {

            flushNow();

        }

    }

    /**

     * Convenience method that is equivalent to calling ensureCapacity()

     * followed by ensureAlignment().  The ensureCapacity() call allows for an

     * extra 4 bytes of space in case the ensureAlignment() method needs to

     * insert a NOOP token on the buffer.

     *

     * @param opsize size (in bytes) of the following operation

     * @param first8ByteValueOffset offset (in bytes) from the current

     * position to the first 8-byte value used in the following operation

     */

    public final void ensureCapacityAndAlignment(int opsize,

                                                 int first8ByteValueOffset)

    {

        ensureCapacity(opsize + 4);

        ensureAlignment(first8ByteValueOffset);

    }

    /**

     * Inserts a 4-byte NOOP token when necessary to ensure that all 8-byte

     * parameters for the following operation are added to the underlying

     * buffer with an 8-byte memory alignment.

     *

     * @param first8ByteValueOffset offset (in bytes) from the current

     * position to the first 8-byte value used in the following operation

     */

    public final void ensureAlignment(int first8ByteValueOffset) {

        int first8ByteValuePosition = buf.position() + first8ByteValueOffset;

        if ((first8ByteValuePosition & 7) != 0) {

            buf.putInt(BufferedOpCodes.NOOP);

        }

    }

    /**

     * Immediately processes each operation currently pending on the buffer.

     * This method will block until the entire buffer has been flushed.  The

     * queue lock must be acquired before calling this method.

     */

    public abstract void flushNow();

    /**

     * Immediately processes each operation currently pending on the buffer,

     * and then invokes the provided task.  This method will block until the

     * entire buffer has been flushed and the provided task has been executed.

     * The queue lock must be acquired before calling this method.

     */

    public abstract void flushAndInvokeNow(Runnable task);

    /**

     * Updates the current position of the underlying buffer, and then

     * flushes the queue immediately.  This method is useful when native code

     * has added data to the queue and needs to flush immediately.

     */

    public void flushNow(int position) {

        buf.position(position);

        flushNow();

    }

}