TimerTask 并发问题

Question

我有一个计时器，它应该告诉我的应用程序是时候读取一些数据了

new Timer().schedule(new TimerTask() {
        @Override
        public void run() {
            try {
                    states[PICK_FRAME_STATE]=true;
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }, 1000/fRate);

状态数组其 final boolean[]

绘制循环中读取的数据所在

  if(lastFrame!=null&&states[PICK_FRAME_STATE]){
      father.image(lastFrame, 500, 200,VRes,HRes);
      buff.add(lastFrame);
      //states[PICK_FRAME_STATE]=false;
      System.out.println(is++);
  }

不过指令

states[PICK_FRAME_STATE]=false;

如果没有注释会使应用程序崩溃。

我希望能够检测到循环中至少传递了 1000/fRate 毫秒，一般来说，它比 1000/fRate 更快。

我认为 TimerTask 每个时间间隔至少准许执行一次，但我遇到了此实现的并发问题（不出所料），有什么解决方法吗？

java.lang.NullPointerException
    at processing.opengl.Texture.copyBufferFromSource(Texture.java:859)
    at sun.reflect.GeneratedMethodAccessor15.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at processing.video.Capture.read(Unknown Source)
    at aaa.view.video.CameraWindow.draw(CameraWindow.java:78)
    at aaa.view.video.CameraWindow.render(CameraWindow.java:99)
    at aaa.desktop.view.ProfileView.render(ProfileView.java:55)
    at aaa.desktop.view.MainView.draw(MainView.java:385)
    at processing.core.PApplet.handleDraw(PApplet.java:2386)
    at processing.opengl.PJOGL$PGLListener.display(PJOGL.java:862)
    at jogamp.opengl.GLDrawableHelper.displayImpl(GLDrawableHelper.java:665)
    at jogamp.opengl.GLDrawableHelper.display(GLDrawableHelper.java:649)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1289)
    at jogamp.opengl.GLDrawableHelper.invokeGLImpl(GLDrawableHelper.java:1119)
    at jogamp.opengl.GLDrawableHelper.invokeGL(GLDrawableHelper.java:994)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1300)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:301)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
    at java.awt.EventQueue.access0(EventQueue.java:97)
    at java.awt.EventQueue.run(EventQueue.java:709)
    at java.awt.EventQueue.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

（根据 Tobias 的回答编辑）

long time=System.currentTimeMillis();
public void draw() {
  if (video.available()) {
    video.read(); // Read a new video frame
    lastFrame=video;
  }
  if(lastFrame!=null && System.currentTimeMillis() - time >= 1000){
      time = System.currentTimeMillis();
      father.image(lastFrame, 500, 200,VRes,HRes);
      buff.add(lastFrame);
      System.out.println(is++);
  }
}

工作起来甚至很艰难，它像以前一样给出了 3 个例外，但后来一切都很好。奇怪的是，如果我评论这条线

time = System.currentTimeMillis();

我也不例外

0 <=first frame added
java.lang.NullPointerException
    at processing.opengl.Texture.copyBufferFromSource(Texture.java:859)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at processing.video.Capture.read(Unknown Source)
    at ygg.view.video.CameraWindow.draw(CameraWindow.java:81)
    at ygg.view.video.CameraWindow.render(CameraWindow.java:101)
    at ygg.desktop.view.ProfileView.render(ProfileView.java:55)
    at ygg.desktop.view.MainView.draw(MainView.java:385)
    at processing.core.PApplet.handleDraw(PApplet.java:2386)
    at processing.opengl.PJOGL$PGLListener.display(PJOGL.java:862)
    at jogamp.opengl.GLDrawableHelper.displayImpl(GLDrawableHelper.java:665)
    at jogamp.opengl.GLDrawableHelper.display(GLDrawableHelper.java:649)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1289)
    at jogamp.opengl.GLDrawableHelper.invokeGLImpl(GLDrawableHelper.java:1119)
    at jogamp.opengl.GLDrawableHelper.invokeGL(GLDrawableHelper.java:994)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1300)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:301)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
    at java.awt.EventQueue.access0(EventQueue.java:97)
    at java.awt.EventQueue.run(EventQueue.java:709)
    at java.awt.EventQueue.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
java.lang.NullPointerException
    at processing.opengl.Texture.copyBufferFromSource(Texture.java:859)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at processing.video.Capture.read(Unknown Source)
    at ygg.view.video.CameraWindow.draw(CameraWindow.java:81)
    at ygg.view.video.CameraWindow.render(CameraWindow.java:101)
    at ygg.desktop.view.ProfileView.render(ProfileView.java:55)
    at ygg.desktop.view.MainView.draw(MainView.java:385)
    at processing.core.PApplet.handleDraw(PApplet.java:2386)
    at processing.opengl.PJOGL$PGLListener.display(PJOGL.java:862)
    at jogamp.opengl.GLDrawableHelper.displayImpl(GLDrawableHelper.java:665)
    at jogamp.opengl.GLDrawableHelper.display(GLDrawableHelper.java:649)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1289)
    at jogamp.opengl.GLDrawableHelper.invokeGLImpl(GLDrawableHelper.java:1119)
    at jogamp.opengl.GLDrawableHelper.invokeGL(GLDrawableHelper.java:994)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1300)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:301)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
    at java.awt.EventQueue.access0(EventQueue.java:97)
    at java.awt.EventQueue.run(EventQueue.java:709)
    at java.awt.EventQueue.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
java.lang.NullPointerException
    at processing.opengl.Texture.copyBufferFromSource(Texture.java:859)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at processing.video.Capture.read(Unknown Source)
    at ygg.view.video.CameraWindow.draw(CameraWindow.java:81)
    at ygg.view.video.CameraWindow.render(CameraWindow.java:101)
    at ygg.desktop.view.ProfileView.render(ProfileView.java:55)
    at ygg.desktop.view.MainView.draw(MainView.java:385)
    at processing.core.PApplet.handleDraw(PApplet.java:2386)
    at processing.opengl.PJOGL$PGLListener.display(PJOGL.java:862)
    at jogamp.opengl.GLDrawableHelper.displayImpl(GLDrawableHelper.java:665)
    at jogamp.opengl.GLDrawableHelper.display(GLDrawableHelper.java:649)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1289)
    at jogamp.opengl.GLDrawableHelper.invokeGLImpl(GLDrawableHelper.java:1119)
    at jogamp.opengl.GLDrawableHelper.invokeGL(GLDrawableHelper.java:994)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1300)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:301)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
    at java.awt.EventQueue.access0(EventQueue.java:97)
    at java.awt.EventQueue.run(EventQueue.java:709)
    at java.awt.EventQueue.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
java.lang.NullPointerException
    at processing.opengl.Texture.copyBufferFromSource(Texture.java:859)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at processing.video.Capture.read(Unknown Source)
    at ygg.view.video.CameraWindow.draw(CameraWindow.java:81)
    at ygg.view.video.CameraWindow.render(CameraWindow.java:101)
    at ygg.desktop.view.ProfileView.render(ProfileView.java:55)
    at ygg.desktop.view.MainView.draw(MainView.java:385)
    at processing.core.PApplet.handleDraw(PApplet.java:2386)
    at processing.opengl.PJOGL$PGLListener.display(PJOGL.java:862)
    at jogamp.opengl.GLDrawableHelper.displayImpl(GLDrawableHelper.java:665)
    at jogamp.opengl.GLDrawableHelper.display(GLDrawableHelper.java:649)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1289)
    at jogamp.opengl.GLDrawableHelper.invokeGLImpl(GLDrawableHelper.java:1119)
    at jogamp.opengl.GLDrawableHelper.invokeGL(GLDrawableHelper.java:994)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1300)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:301)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
    at java.awt.EventQueue.access0(EventQueue.java:97)
    at java.awt.EventQueue.run(EventQueue.java:709)
    at java.awt.EventQueue.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
java.lang.NullPointerException
    at processing.opengl.Texture.copyBufferFromSource(Texture.java:859)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at processing.video.Capture.read(Unknown Source)
    at ygg.view.video.CameraWindow.draw(CameraWindow.java:81)
    at ygg.view.video.CameraWindow.render(CameraWindow.java:101)
    at ygg.desktop.view.ProfileView.render(ProfileView.java:55)
    at ygg.desktop.view.MainView.draw(MainView.java:385)
    at processing.core.PApplet.handleDraw(PApplet.java:2386)
    at processing.opengl.PJOGL$PGLListener.display(PJOGL.java:862)
    at jogamp.opengl.GLDrawableHelper.displayImpl(GLDrawableHelper.java:665)
    at jogamp.opengl.GLDrawableHelper.display(GLDrawableHelper.java:649)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1289)
    at jogamp.opengl.GLDrawableHelper.invokeGLImpl(GLDrawableHelper.java:1119)
    at jogamp.opengl.GLDrawableHelper.invokeGL(GLDrawableHelper.java:994)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1300)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:301)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
    at java.awt.EventQueue.access0(EventQueue.java:97)
    at java.awt.EventQueue.run(EventQueue.java:709)
    at java.awt.EventQueue.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
java.lang.NullPointerException
    at processing.opengl.Texture.copyBufferFromSource(Texture.java:859)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at processing.video.Capture.read(Unknown Source)
    at ygg.view.video.CameraWindow.draw(CameraWindow.java:81)
    at ygg.view.video.CameraWindow.render(CameraWindow.java:101)
    at ygg.desktop.view.ProfileView.render(ProfileView.java:55)
    at ygg.desktop.view.MainView.draw(MainView.java:385)
    at processing.core.PApplet.handleDraw(PApplet.java:2386)
    at processing.opengl.PJOGL$PGLListener.display(PJOGL.java:862)
    at jogamp.opengl.GLDrawableHelper.displayImpl(GLDrawableHelper.java:665)
    at jogamp.opengl.GLDrawableHelper.display(GLDrawableHelper.java:649)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1289)
    at jogamp.opengl.GLDrawableHelper.invokeGLImpl(GLDrawableHelper.java:1119)
    at jogamp.opengl.GLDrawableHelper.invokeGL(GLDrawableHelper.java:994)
    at javax.media.opengl.awt.GLCanvas.run(GLCanvas.java:1300)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:301)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
    at java.awt.EventQueue.access0(EventQueue.java:97)
    at java.awt.EventQueue.run(EventQueue.java:709)
    at java.awt.EventQueue.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
1 
2
3

ecc...每 1000 毫秒

Answer 1

试试这个

private long time = System.currentTimeMillis();

//...

// draw call:
if(lastFrame != null && System.currentTimeMillis() - time >= 1000){
    // do stuff
    time = System.currentTimeMillis();
}

// do stuff 最多每 1000 毫秒调用一次。没有任何 TimerTask 魔法。

编辑

试试这个捕捉 "missed" 帧：

private long time = System.currentTimeMillis();

//...

// draw call:
long delta = System.currentTimeMillis() - time;
if(lastFrame != null && delta >= 1000){
    int framesMissed = delta / 1000; // rounds to full seconds
    for(int i=0;i<framesMissed;i++){
        // do stuff for each missed frame/picture
    }
    // apply "overlap" so we actually carry the right result to the next call
    time = System.currentTimeMillis() - (delta-(1000*framesMissed));
}

// do stuff 现在每经过一秒就会调用一次，忽略绘制调用的频率（它们可能比 1000 毫秒快或慢）

TimerTask 并发问题

TimerTask concurrency issue

java

concurrency

timertask

编辑