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//Copyright 2015 Erik De Rijcke
//
//Licensed under the Apache License,Version2.0(the"License");
//you may not use this file except in compliance with the License.
//You may obtain a copy of the License at
//
//http://www.apache.org/licenses/LICENSE-2.0
//
//Unless required by applicable law or agreed to in writing,software
//distributed under the License is distributed on an"AS IS"BASIS,
//WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,either express or implied.
//See the License for the specific language governing permissions and
//limitations under the License.
package org.freedesktop.wayland.server;

import org.freedesktop.jaccall.JNI;
import org.freedesktop.wayland.server.jaccall.WaylandServerCore;

import java.nio.ByteBuffer;

public class ShmBuffer {

    public final Long pointer;

    /**
     * Create a new underlying WlBufferResource with the constructed ShmBuffer as it's implementation.
     * 
     * {@code ShmBuffer} should never be stored in a compositor instead it should always be queried from a
     * {@code WlBufferResource}. Listening for the resource's destruction can be done when the buffer
     * resource is attached to a surface.
     *
     * @param client
     * @param id
     * @param width
     * @param height
     * @param stride
     * @param format
     */
    public ShmBuffer(final Client client,
                     final int id,
                     final int width,
                     final int height,
                     final int stride,
                     final int format) {
        this(WaylandServerCore.INSTANCE()
                              .wl_shm_buffer_create(client.pointer,
                                                    id,
                                                    width,
                                                    height,
                                                    stride,
                                                    format));
    }

    protected ShmBuffer(final Long pointer) {
        this.pointer = pointer;
    }

    public static ShmBuffer get(final Resource resource) {
        final long wlShmBuffer = WaylandServerCore.INSTANCE()
                                                  .wl_shm_buffer_get(resource.pointer);

        final ShmBuffer buffer;
        if (wlShmBuffer == 0L) {
            buffer = null;
        }
        else {
            buffer = new ShmBuffer(wlShmBuffer);
        }
        return buffer;
    }

    /**
     * Mark that the given SHM buffer is about to be accessed
     * 

     * An SHM buffer is a memory-mapped file given by the client.
     * According to POSIX, reading from a memory-mapped region that
     * extends off the end of the file will cause a SIGBUS signal to be
     * generated. Normally this would cause the compositor to terminate.
     * In order to make the compositor robust against clients that change
     * the size of the underlying file or lie about its size, you should
     * protect access to the buffer by calling this function before
     * reading from the memory and call {@link #endAccess()}
     * afterwards. This will install a signal handler for SIGBUS which
     * will prevent the compositor from crashing.
     * 

     * After calling this function the signal handler will remain
     * installed for the lifetime of the compositor process. Note that
     * this function will not work properly if the compositor is also
     * installing its own handler for SIGBUS.
     * 

     * If a SIGBUS signal is received for an address within the range of
     * the SHM pool of the given buffer then the client will be sent an
     * error event when {@link #endAccess()} is called. If the signal
     * is for an address outside that range then the signal handler will
     * reraise the signal which would will likely cause the compositor to
     * terminate.
     * 

     * It is safe to nest calls to these functions as long as the nested
     * calls are all accessing the same buffer. The number of calls to
     * wl_shm_buffer_end_access must match the number of calls to
     * {@code beginAccess()}. These functions are thread-safe and it
     * is allowed to simultaneously access different buffers or the same
     * buffer from multiple threads.
     */
    public void beginAccess() {
        WaylandServerCore.INSTANCE()
                         .wl_shm_buffer_begin_access(this.pointer);
    }

    /**
     * Ends the access to a buffer started by {@link #beginAccess()}.
     * 

     * This should be called after {@link #beginAccess()} once the
     * buffer is no longer being accessed. If a SIGBUS signal was
     * generated in-between these two calls then the resource for the
     * given buffer will be sent an error.
     */
    public void endAccess() {
        WaylandServerCore.INSTANCE()
                         .wl_shm_buffer_end_access(this.pointer);
    }

    /**
     * /** Get a pointer to the memory for the SHM buffer
     * 

     * Returns a pointer which can be used to read the data contained in
     * the given SHM buffer.
     *