当我的 Java 应用程序退出/崩溃时，如何摆脱 Java 子进程？

Question

I launch a child process in Java as follows:

final String[] cmd = {"<childProcessName>"};
Process process = Runtime.getRuntime().exec(cmd);

It now runs in the background. All good and fine.

If my program now crashes (it is still in dev :-)) the child process still seems to hang around. How can I make it automatically end when the parent Java process dies?

If it helps, I'm using Mac OS X 10.5

Answer 1

I worked it out myself already. I add a shutdown hook, as follows:

final String[] cmd = {"<childProcessName>"};
final Process process = Runtime.getRuntime().exec(cmd);
Runnable runnable = new Runnable() {
    public void run() {
        process.destroy();
    }
};
Runtime.getRuntime().addShutdownHook(new Thread(runnable));

Answer 2

As you said, addShutdownHook is the way to go.

BUT:

• There's no real guarantee that your shutdown hooks are executed if the program terminates. Someone could kill the Java process and in that case your shutdown hook will not be executed. (as said in this SO question )

• some of the standard libraries have their own hooks which may run before yours.

• beware of deadlocks.

Another possibility would be to wrap your java program in a service .

Answer 3

Adding shutdown hook is not a reliable method to kill the child processes. This is because Shutdown hook might not necessarily be executed when a force kill is performed from Task Manager.

One approach would be that the child process can periodically monitor the PID of its parent. This way, Child process can exit itself when the parent exits.