/*
 * Copyright (c) 2003 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * 
 * - Redistribution of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * 
 * - Redistribution in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * 
 * Neither the name of Sun Microsystems, Inc. or the names of
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES,
 * INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN
 * MICROSYSTEMS, INC. ("SUN") AND ITS LICENSORS SHALL NOT BE LIABLE FOR
 * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
 * DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES. IN NO EVENT WILL SUN OR
 * ITS LICENSORS BE LIABLE FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR
 * DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE
 * DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY,
 * ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE, EVEN IF
 * SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 * 
 * You acknowledge that this software is not designed or intended for use
 * in the design, construction, operation or maintenance of any nuclear
 * facility.
 * 
 * Sun gratefully acknowledges that this software was originally authored
 * and developed by Kenneth Bradley Russell and Christopher John Kline.
 */

package javax.media.opengl;

import java.awt.EventQueue;
import java.lang.reflect.InvocationTargetException;
import java.security.AccessController;
import java.security.PrivilegedAction;

import com.sun.opengl.impl.*;

/** Defines the threading model for the implementation of the classes
    in this package.

    <P>

    OpenGL is specified as a thread-safe API, but in practice there
    are multithreading-related issues on most, if not all, of the
    platforms which support it. For example, some OpenGL
    implementations do not behave well when one context is made
    current first on one thread, released, and then made current on a
    second thread, although this is legal according to the OpenGL
    specification. On other platforms there are other problems.

    <P>

    Due to these limitations, and due to the inherent multithreading
    in the Java platform (in particular, in the Abstract Window
    Toolkit), it is necessary to limit the multithreading occurring in
    the typical application using the OpenGL API. This has been done by
    forcing all OpenGL-related work for GLAutoDrawables on to a single
    thread. In other words, if an application uses only the
    GLAutoDrawable and GLEventListener callback mechanism, it is
    guaranteed to have the most correct single-threaded behavior on
    all platforms.

    <P>

    Applications using the GLContext makeCurrent/release API directly
    will inherently break this single-threaded model, as these methods
    require that the OpenGL context be made current on the current
    thread immediately. For applications wishing to integrate better
    with the single-threaded model, this class provides public access
    to the mechanism used by this implementation of the
    javax.media.opengl APIs. Users can execute Runnables on the
    internal thread used for performing OpenGL work, and query whether
    the current thread is already this thread. Using these mechanisms
    the user can move work from the current thread on to the internal
    OpenGL thread if desired.

    <P>

    This class also provides mechanisms for querying whether this
    internal serialization of OpenGL work is in effect, and a
    programmatic way of disabling it. Currently it is enabled by
    default, although it could be disabled in the future if OpenGL
    drivers become more robust on all platforms.

    <P>

    In addition to specifying programmatically whether the single
    thread for OpenGL work is enabled, users may switch it on and off
    using the system property <code>opengl.1thread</code>. Valid values
    for this system property are:

    <PRE>
    -Dopengl.1thread=false     Disable single-threading of OpenGL work
    -Dopengl.1thread=true      Enable single-threading of OpenGL work (default)
    -Dopengl.1thread=auto      Select default single-threading behavior (currently on)
    </PRE>    
*/

public class Threading {
  private static boolean singleThreaded = true;
  
  static {
    AccessController.doPrivileged(new PrivilegedAction() {
        public Object run() {
          String workaround = System.getProperty("opengl.1thread");
          if (workaround != null && (!workaround.equals("auto"))) {
            singleThreaded = Boolean.valueOf(workaround).booleanValue();
          }
          printWorkaroundNotice();
          return null;
        }
      });
  }

  /** No reason to ever instantiate this class */
  private Threading() {}

  /** Provides a mechanism for end users to disable the default
      single-threading of this implementation of the
      javax.media.opengl APIs. Users are strongly discouraged from
      calling this method unless they are aware of all of the
      consequences and are prepared to enforce some amount of
      threading restrictions in their applications. Disabling this
      single-threading, for example, will have unintended consequences
      on GLAutoDrawable implementations such as GLCanvas, GLJPanel and
      GLPbuffer. Currently there is no supported way to re-enable it
      once disabled, partly to discourage careless use of this
      method. */ 
  public static void disableSingleThreading() {
    singleThreaded = false;
    if (Debug.verbose()) {
      System.err.println("Application forced disabling of single-threading of javax.media.opengl implementation");
    }
  }

  /** Indicates whether OpenGL work is being automatically forced to a
      single thread. */
  public static boolean isSingleThreaded() {
    return singleThreaded;
  }

  /** Indicates whether the current thread is the single thread on
      which this implementation of the javax.media.opengl APIs
      performs all of its OpenGL-related work. This method should only
      be called if the single-thread model is in effect. */
  public static boolean isOpenGLThread() throws GLException {
    if (!isSingleThreaded()) {
      throw new GLException("Should only call this in single-threaded mode");
    }

    if (Java2D.isOGLPipelineActive()) {
      // FIXME: ideally only the QFT would be considered to be the
      // "OpenGL thread", but we can not currently run all of JOGL's
      // OpenGL work on that thread. For now, run the GLJPanel's
      // Java2D/JOGL bridge on the QFT but everything else on the
      // EDT, except when we're already on the QFT.
      return (Java2D.isQueueFlusherThread() ||
              EventQueue.isDispatchThread());
    } else {
      return EventQueue.isDispatchThread();
    }
  }

  /** Executes the passed Runnable on the single thread used for all
      OpenGL work in this javax.media.opengl API implementation. It is
      not specified exactly which thread is used for this
      purpose. This method should only be called if the single-thread
      model is in use and if the current thread is not the OpenGL
      thread (i.e., if <code>isOpenGLThread()</code> returns
      false). It is up to the end user to check to see whether the
      current thread is the OpenGL thread and either execute the
      Runnable directly or perform the work inside it. */
  public static void invokeOnOpenGLThread(Runnable r) throws GLException {
    if (!isSingleThreaded()) {
      throw new GLException ("Should only call this in single-threaded mode");
    }

    if (isOpenGLThread()) {
      throw new GLException ("Should only call this from other threads than the OpenGL thread");
    }    

    // FIXME: ideally should run all OpenGL work on the Java2D QFT
    // thread when it's enabled, but there are issues with this when
    // the GLJPanel is not using the Java2D bridge; would like to run
    // its OpenGL work on the QFT, but do the image drawing from the
    // EDT. Other issues still remain with the GLCanvas as well.

    //    if (Java2D.isOGLPipelineActive()) {
    //      Java2D.invokeWithOGLContextCurrent(null, r);
    //    } else {
    try {
      EventQueue.invokeAndWait(r);
    } catch (InvocationTargetException e) {
      throw new GLException(e.getTargetException());
    } catch (InterruptedException e) {
      throw new GLException(e);
    }
    //    }    
  }

  private static void printWorkaroundNotice() {
    if (singleThreaded && Debug.verbose()) {
      System.err.println("Using single thread for performing OpenGL work in javax.media.opengl implementation");
    }
  }
}