`
jayjayjaylun
  • 浏览: 89782 次
  • 性别: Icon_minigender_1
  • 来自: 广州
社区版块
存档分类
最新评论

runtime shutdown hook

    博客分类:
  • java
阅读更多

 

void java.lang.Runtime .addShutdownHook(Thread hook)

Registers a new virtual-machine shutdown hook.

The Java virtual machine shuts down in response to two kinds of events:

     

  • The program exits normally, when the last non-daemon thread exits or when the exit (equivalently, System.exit ) method is invoked, or
  • The virtual machine is terminated in response to a user interrupt, such as typing ^C , or a system-wide event, such as user logoff or system shutdown.

A shutdown hook is simply an initialized but unstarted thread. When the virtual machine begins its shutdown sequence it will start all registered shutdown hooks in some unspecified order and let them run concurrently. When all the hooks have finished it will then run all uninvoked finalizers if finalization-on-exit has been enabled. Finally, the virtual machine will halt. Note that daemon threads will continue to run during the shutdown sequence, as will non-daemon threads if shutdown was initiated by invoking the exit method.

Once the shutdown sequence has begun it can be stopped only by invoking the halt method, which forcibly terminates the virtual machine.

Once the shutdown sequence has begun it is impossible to register a new shutdown hook or de-register a previously-registered hook. Attempting either of these operations will cause an IllegalStateException to be thrown.

Shutdown hooks run at a delicate time in the life cycle of a virtual machine and should therefore be coded defensively. They should, in particular, be written to be thread-safe and to avoid deadlocks insofar as possible. They should also not rely blindly upon services that may have registered their own shutdown hooks and therefore may themselves in the process of shutting down.

Shutdown hooks should also finish their work quickly. When a program invokes exit the expectation is that the virtual machine will promptly shut down and exit. When the virtual machine is terminated due to user logoff or system shutdown the underlying operating system may only allow a fixed amount of time in which to shut down and exit. It is therefore inadvisable to attempt any user interaction or to perform a long-running computation in a shutdown hook.

Uncaught exceptions are handled in shutdown hooks just as in any other thread, by invoking the uncaughtException method of the thread's ThreadGroup object. The default implementation of this method prints the exception's stack trace to System.err and terminates the thread; it does not cause the virtual machine to exit or halt.

In rare circumstances the virtual machine may abort , that is, stop running without shutting down cleanly. This occurs when the virtual machine is terminated externally, for example with the SIGKILL signal on Unix or the TerminateProcess call on Microsoft Windows. The virtual machine may also abort if a native method goes awry by, for example, corrupting internal data structures or attempting to access nonexistent memory. If the virtual machine aborts then no guarantee can be made about whether or not any shutdown hooks will be run.

 

Parameters:
hook An initialized but unstarted Thread object
Throws:
IllegalArgumentException - If the specified hook has already been registered, or if it can be determined that the hook is already running or has already been run
IllegalStateException - If the virtual machine is already in the process of shutting down
SecurityException - If a security manager is present and it denies RuntimePermission ("shutdownHooks")
Since:
1.3
See Also:
removeShutdownHook
halt(int)
exit(int)


public class ShutdownHook {
	public static void main(String[] args) {
		
		Thread  hook= new Thread(){
			@Override
			public void run() {
				System.out.println("shutdown hook end!");
				//super.run();
			}
		};
		Runtime.getRuntime().addShutdownHook(hook);

		
		Object f  =new Object(){
			@Override
			protected void finalize() throws Throwable {
				System.out.println("free Object!!!");
				//super.finalize();
			}
		};
		
		f=null;
		
		
		System.gc();
		
		System.out.println(" main exit (0)!");
		//cause shutdown hook invoking.
		System.exit(0);
		//Runtime.getRuntime().removeShutdownHook(hook);
		System.out.println(" end main string ");
		
		try {
			Thread.sleep(5000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		 
		//throw new RuntimeException("a");
//If  you enter ^C it will cause shutdown too. 
//		D:\develop\workspace\test\src>java ShutdownHook
//		 main exit (0)!
//		shutdown hook end!
	}
}



 

分享到:
评论

相关推荐

    解析Runtime中shutdown hook的使用详解

    通过调用`Runtime.getRuntime().addShutdownHook(Thread t)`方法,可以将一个已经初始化但尚未开始执行的线程作为`shutdown hook`注册到JVM中。 以下是一个简单的`shutdown hook`实现示例: ```java public class ...

    JVM问题诊断常用命令

    - `java.runtime.name=Java(TM) SE Runtime Environment` 指出了Java运行环境的名称。 - `java.vm.name=Java HotSpot(TM) Server VM` 显示了JVM的名字。 这些信息对于定位问题和优化程序具有重要作用。比如,如果...

    java 程序的退出的资源

    你可以通过`Runtime.getRuntime().addShutdownHook(Thread hook)`注册自定义的`Thread`,在程序退出前进行必要的清理工作,如关闭文件流、释放网络连接等。 此外,Java还提供了`Thread.stop()`和`Thread.interrupt...

    shutdown-app

    可以使用`Runtime.getRuntime().addShutdownHook(Thread hook)`来添加一个钩子。 5. **Spring Boot应用关闭**: - 如果"shutdown-app"是在Spring Boot环境下,那么可能涉及到`@PreDestroy`注解,它标记在方法上,...

    JAVA并发编程实践-线程的关闭与取消-学习笔记

    15. **关闭钩子(Shutdown Hook)**:通过`Runtime.getRuntime().addShutdownHook(Thread hook)`注册自定义的关闭钩子,这些钩子在JVM关闭时执行,用于清理资源。 16. **精灵线程(Daemon Thread)**:精灵线程是不...

    C# 截获关机、注销、重启的消息

    在`WndProc`方法中,添加对`WM_SHUTDOWN_HOOK`消息的处理代码。当接收到该消息时,启动宣传Logo动画,然后在动画结束后调用对应的API函数执行实际的关机、注销或重启操作。可以使用`ExitWindowsEx`或`...

    Java应用中使用ShutdownHook友好地清理现场

     JDK在1.3之后提供了Java Runtime.addShutdownHook(Thread hook)方法,可以注册一个JVM关闭的钩子,这个钩子可以在以下几种场景被调用:  1)程序正常退出  2)使用System.exit()  3)终端使用Ctrl+C触发的...

    通过JDK源码分析关闭钩子详解

    为了应对这种情况,Java提供了一个优雅的解决方案——Shutdown Hook。Java虚拟机(JVM)在接收到退出指令时,会尝试执行所有注册的关闭钩子,这些钩子通常是实现`Runnable`接口的线程对象。 **关闭钩子的生成步骤**...

    Java利用WatchService监听文件变化示例

    最后,为了确保在Java虚拟机关闭的时候能够释放资源并关闭WatchService,应该在程序中增加一个关闭钩子(shutdown hook),确保在JVM关闭的时候能够执行资源释放的相关操作,特别是关闭WatchService。 下面是一个...

    VB编程资源大全(英文源码 其它)

    in "random number table....)<END><br>37,rptparam.zip This program generates datareport with two parameter values set during runtime - using dataenvironment and Microsoft Jet.OLEDB 3.51<END><br>38,...

Global site tag (gtag.js) - Google Analytics