事件调度线程的确切时间何时开始? [英] When exactly is the Event Dispatch Thread started?
问题描述
EDT确切何时开始?哪一行代码负责?
When exactly is the EDT started? What line of code is responsible of it?
我的猜测是"someSwingComponent.setVisible(true)"可以解决问题，但我不确定.
My guess is that "someSwingComponent.setVisible(true)" does the trick, but I'm not sure.
谢谢！
推荐答案
问:EDT确切何时开始?哪一行代码负责[f]?
Swing的内部工作方式是特定于JVM的.不同的JVM基于不同的条件启动事件调度线程(EDT).一般而言:
Q: When exactly is the EDT started? What line of code is responsible [f]of it?
The inner workings of Swing are JVM-specific. Different JVMs start the Event Dispatch Thread (EDT) based on differing criteria. In general though:
EDT在收到其第一个
AWTEvent时启动.
下面的堆栈跟踪重申了这一点.以下面的 main 方法为例.
The stack traces below reaffirm this point. Take for example the following main method.
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setVisible(true);
}
在上面的示例中，负责启动EDT的代码行为 frame.setVisible(true);
In the example above, the line of code responsible for starting the EDT is frame.setVisible(true);
上面的 main 方法是在两个不同的JVM上执行的.在 EventQueue.initDispatchThread 处放置了一个断点.当达到断点时，将记录以下堆栈跟踪.
The above main method was executed on two different JVMs. A breakpoint was placed at EventQueue.initDispatchThread. When the breakpoint was hit, the following stack traces were noted.
在 AWT-AppKit 线程上使用Mac的JDK:
Using the Mac's JDK on the AWT-AppKit thread:
EventQueue.initDispatchThread() line: 906
EventQueue.wakeup(boolean) line: 1109
NativeMethodAccessorImpl.invoke0(Method, Object, Object[]) line: not available [native method]
NativeMethodAccessorImpl.invoke(Object, Object[]) line: 39
DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 25
Method.invoke(Object, Object...) line: 597
SunToolkit.wakeupEventQueue(EventQueue, boolean) line: 348
PostEventQueue.postEvent(AWTEvent) line: 2137
SunToolkit.postEvent(AppContext, AWTEvent) line: 583
SunToolkit.executeOnEventHandlerThread(PeerEvent) line: 654
SunToolkit.executeOnEventHandlerThread(Object, Runnable) line: 631
EventFactoryProxy.windowMoved(CWindow) line: 89
在主线程上使用Oracle的Windows JDK:
Using Oracle's JDK for Windows on the main thread:
java.awt.EventQueue.initDispatchThread() line: 861
java.awt.EventQueue.postEventPrivate(java.awt.AWTEvent) line: 199
java.awt.EventQueue.postEvent(java.awt.AWTEvent) line: 180
javax.swing.RepaintManager.scheduleProcessingRunnable(sun.awt.AppContext) line: 1369
javax.swing.RepaintManager.nativeAddDirtyRegion(sun.awt.AppContext, java.awt.Container, int, int, int, int) line: 548
javax.swing.SwingPaintEventDispatcher.createPaintEvent(java.awt.Component, int, int, int, int) line: 45
sun.awt.windows.WFramePeer(sun.awt.windows.WComponentPeer).postPaintIfNecessary(int, int, int, int) line: 741
sun.awt.windows.WFramePeer(sun.awt.windows.WComponentPeer).handlePaint(int, int, int, int) line: 736
sun.java2d.d3d.D3DScreenUpdateManager.repaintPeerTarget(sun.awt.windows.WComponentPeer) line: 274
sun.java2d.d3d.D3DScreenUpdateManager.createScreenSurface(sun.awt.Win32GraphicsConfig, sun.awt.windows.WComponentPeer, int, boolean) line: 175
...
sun.awt.windows.WToolkit.createFrame(java.awt.Frame) line: 383
javax.swing.JFrame(java.awt.Frame).addNotify() line: 460
javax.swing.JFrame(java.awt.Window).show() line: 859
javax.swing.JFrame(java.awt.Component).show(boolean) line: 1584
javax.swing.JFrame(java.awt.Component).setVisible(boolean) line: 1536
javax.swing.JFrame(java.awt.Window).setVisible(boolean) line: 842
Example.main(java.lang.String[]) line: 113
在Mac上，调用 PostEventQueue.postEvent(AWTEvent).类似地，在Windows上，也会调用 java.awt.EventQueue.postEvent(java.awt.AWTEvent).两者最终都调用 EventQueue.initDispatchThread .
On the Mac, a call to PostEventQueue.postEvent(AWTEvent) is made. Similarly on Windows, a call to java.awt.EventQueue.postEvent(java.awt.AWTEvent) is made. Both eventually call EventQueue.initDispatchThread.
作为另一个示例，请考虑以下 main 方法:
As another example, consider the following main method:
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
System.out.println("Start!");
}
});
}
在主线程上使用Mac的JDK:
Using the Mac's JDK on the main thread:
EventQueue.initDispatchThread() line: 906 [local variables unavailable]
EventQueue.postEventPrivate(AWTEvent) line: 227
EventQueue.postEvent(AWTEvent) line: 208
EventQueue.invokeLater(Runnable) line: 1048
SwingUtilities.invokeLater(Runnable) line: 1267
Example.main(String[]) line: 31
在主线程上使用Oracle的Windows JDK:
Using Oracle's JDK for Windows on the main thread:
java.awt.EventQueue.initDispatchThread() line: 861
java.awt.EventQueue.postEventPrivate(java.awt.AWTEvent) line: 199
java.awt.EventQueue.postEvent(java.awt.AWTEvent) line: 180
java.awt.EventQueue.invokeLater(java.lang.Runnable) line: 999
javax.swing.SwingUtilities.invokeLater(java.lang.Runnable) line: 1267
对 SwingUtilties.invokeLater 的调用负责启动EDT.再次在这里，调用 EventQueue.postEvent(AWTEvent).
The call to SwingUtilties.invokeLater is responsible for starting the EDT. Here again, calls to EventQueue.postEvent(AWTEvent) are made.
不仅对 someSwingComponent.setVisible(true)的任何调用都会启动EDT.例如，执行以下 main 方法不会创建 AWT-Event-Queue-0 线程:
Not just any call to someSwingComponent.setVisible(true) will start the EDT. For example, executing the following main method does not create the AWT-Event-Queue-0 thread:
public static void main(String[] args) {
JLabel label = new JLabel();
label.setVisible(true);
}
资源
当然，在线上有许多有关EDT的资源.
Resources
Of course, there are many resources online about the EDT.
- Java的
- 事件调度线程" 教程的课程:Swing中的并发"
- 线程和摆动" 来自Sun Developer Network
- "Swing Threads" (来自Java词汇表，网址为mindprod.com)
- 事件分配线程如何工作?" 堆栈溢出
- "The Event Dispatch Thread" from The Java Tutorials's "Lesson: Concurrency in Swing"
- "Threads and Swing" from the Sun Developer Network
- "Swing Threads" from the Java Glossary at mindprod.com
- "How does the event dispatch thread work?" on Stack Overflow
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