kill,就是這個人還可以掙扎的出來,給他家人打個電話,告訴他們他就要死了,不能回家吃晚飯了.
kill -9,就是那個人死在馬桶上,隔間還鎖着,外面等候的人也不知道他死了.
kill -0 PID 向某一進程發送一個無效的信號，如果該進程存在（能夠接收信號），echo $?爲0，否則爲1，已證明此進程是否存在（<pre name="code" class="plain">The signals listed below may be available for use with kill. When known constant, numbers and default behavior are shown.
Name Num Action Description
0 0 n/a exit code indicates if a signal may be sent測試用的java類，該類會等待30*6秒，在線程結束或者中斷時等待6秒後輸出"exit"
public class TestShutdownHook {
static{
Runtime.getRuntime().addShutdownHook(new Thread(){
public void run(){
Thread.sleep(6000);
System.out.println("exit!");
}
});
}
public static void main(String[] args) {
// TODO Auto-generated method stub
Thread thread = new MyThread();
thread.start();
}
static class MyThread extends Thread{
private int i = 30;
public MyThread(){
}
public void run(){
while(i > 0){
i--;
System.out.println("running...");
try {
Thread.sleep(6000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}核心方法是 Runtime.getRuntime().addShutdownHook
關於這個方法的java官方說明
Open Declaration void java.lang.Runtime.addShutdownHook(Thread hook)
addShutdownHook
public void 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. Attempts to use other thread-based services such as the AWT event-dispatch thread, for example, may lead to deadlocks.
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 objectThrows: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 runIllegalStateException - If the virtual machine is already in the process of shutting downSecurityException - If a security manager is present and it denies RuntimePermission("shutdownHooks")Since:1.3See Also:removeShutdownHook(java.lang.Thread), halt(int), exit(int)
java啓動該進程後，如果使用kill的話等待6秒後輸出exit
如果kill -9 改進程，不會輸出exit，程序直接退出
如果想讓程序在退出時有一定時間處理善後工作，但又想控制時間，可以在這樣做
kill 進程號 &
sleep 時間(秒)
kill -9 進程號