path: root/src/classes/javax/media/opengl/Threading.java

/*
 * Copyright (c) 2003 Sun Microsystems, Inc. All Rights Reserved.
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
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 * This software is provided "AS IS," without a warranty of any kind. ALL
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 */

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.*;

/** This API provides access to 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 often necessary to limit the multithreading 
    occurring in the typical application using the OpenGL API. 

    <P>

    In the current reference implementation, for instance, multithreading 
    has been limited 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 an implementation that uses the single-threaded model, this
    class provides public access to the mechanism used by the implementation.

    <P>

    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.  In the current reference 
    implementation 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 -- on a newly-created worker thread)
    -Dopengl.1thread=auto      Select default single-threading behavior (currently on)
    -Dopengl.1thread=awt       Enable single-threading of OpenGL work on AWT event dispatch thread (current default on all
                                 platforms, and also the default behavior older releases)
    -Dopengl.1thread=worker    Enable single-threading of OpenGL work on newly-created worker thread (not suitable for Mac
                                 OS X or X11 platforms, and risky on Windows in applet environments)
    </PRE>    
*/

public class Threading {
  private static boolean singleThreaded = true;
  private static final int AWT    = 1;
  private static final int WORKER = 2;
  private static int mode;
  
  static {
    AccessController.doPrivileged(new PrivilegedAction() {
        public Object run() {
          String workaround = System.getProperty("opengl.1thread");
          // Default to using the AWT thread on all platforms except
          // Windows. On OS X there is instability apparently due to
          // using the JAWT on non-AWT threads. On X11 platforms there
          // are potential deadlocks which can be caused if the AWT
          // EventQueue thread hands work off to the GLWorkerThread
          // while holding the AWT lock. The optimization of
          // makeCurrent / release calls isn't worth these stability
          // problems.
          boolean isWindows = System.getProperty("os.name").startsWith("Windows");
          // int defaultMode = (isWindows ? WORKER : AWT);
          int defaultMode = AWT;
          mode = defaultMode;
          if (workaround != null) {
            workaround = workaround.toLowerCase();
            if (workaround.equals("true") ||
                workaround.equals("auto")) {
              // Nothing to do; singleThreaded and mode already set up
            } else if (workaround.equals("worker")) {
              singleThreaded = true;
              mode = WORKER;
            } else if (workaround.equals("awt")) {
              singleThreaded = true;
              mode = AWT;
            } else {
              singleThreaded = false;
            }
          }
          printWorkaroundNotice();
          return null;
        }
      });
  }

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

  /** If an implementation of the javax.media.opengl APIs offers a 
      multithreading option but the default behavior is single-threading, 
      this API provides a mechanism for end users to disable single-threading 
      in this implementation.  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
      single-threading, for example, may 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. This method should be called as early as possible in an
      application. */ 
  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 in this implementation. */
  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");
    }

    switch (mode) {
      case AWT:
        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();
        }
      case WORKER:
        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
          // worker thread, except when we're already on the QFT.
          return (Java2D.isQueueFlusherThread() ||
                  GLWorkerThread.isWorkerThread());
        } else {
          return GLWorkerThread.isWorkerThread();
        }
      default:
        throw new InternalError("Illegal single-threading mode " + mode);
    }
  }

  /** 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");
    }    

    switch (mode) {
      case AWT:
        // 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);
        }
        //    }    
        break;

      case WORKER:
        if (!GLWorkerThread.isStarted()) {
          synchronized (GLWorkerThread.class) {
            if (!GLWorkerThread.isStarted()) {
              GLWorkerThread.start();
            }
          }
        }
        try {
          GLWorkerThread.invokeAndWait(r);
        } catch (InvocationTargetException e) {
          throw new GLException(e.getTargetException());
        } catch (InterruptedException e) {
          throw new GLException(e);
        }
        break;

      default:
        throw new InternalError("Illegal single-threading mode " + mode);
    }
  }

  /** This is a workaround for AWT-related deadlocks which only seem
      to show up in the context of applets */
  static boolean isAWTMode() {
    return (mode == AWT);
  }

  private static void printWorkaroundNotice() {
    if (singleThreaded && Debug.verbose()) {
      System.err.println("Using " +
                         (mode == AWT ? "AWT" : "OpenGL worker") +
                         " thread for performing OpenGL work in javax.media.opengl implementation");
    }
  }
}