在catch中开始一个新线程

Question

I have a class ( class A for example) implements Runnable . In run method I have a try catch .I want to start a new thread in catch like this

new Thread(new A()).start();

Is this a true manner to handle exceptions?

I mean maybe its a dangerous way because the heap will get full very soon; in other words garbage collector will not garbage this object because another object has been just created in it.

Answer 1

I mean maybe its a dangerous way because the heap will get full very soon; in other words garbage collector will not garbage this object because another object has been just created in it.

It is not dangerous for that reason. If we assume that new Thread(new A()).start(); is the last thing that the original thread does before it exits, then by the time we need to GC the original thread will have exited, and hence its stack contents won't be reachable. The only thread that will still be reachable will be the one that it still alive.

However, it is dangerous if the new thread is liable to repeat the computation and then throw the same exception again, and again, and again ... So if you do write code like this, it is a good idea for the application to keep a track of how often the thread is being re-launched, and pull the plug if it happens too often.

The other problem with the code as written is that the code that launched the original thread sees it die, but doesn't hear about the new thread. That is problematic if your want to initiate shutdown by interrupting the worker threads.

If you put those two problems (and others) together, it is better for the code that launched the original thread to be responsible for relaunching.

Answer 2

Thread is new parallel light weight process. As soon as its run method completed it will be eligible for GC. I don't think it effects GC life cycle of the object from where it started.

Only one new thing in your case is, handling exceptions with thread. Without knowing more details about why you want this, its hard to tell is it safe/good practice.

Answer 3

This is not a very good way of handling exceptions within a thread. Why would the newly created thread of the same type not have the same exception?

What you should do is have some form of thread manager up a level from the thread that will monitor for, handle, and if necessary recreate new threads when old ones fail.

This will allow you to add more ways to handle the error, and will look a lot neater if you try and debug the threads. instead of having all these hanging threads (cause the parent was cleaned by GC) you'll know all threads have spawned from the same location.

What you are proposing will not clutter the heap because threads will be GC'd when they have finished running.

Answer 4

If you didn't store any references to the thread that you'd created - it will be cleaned by GC when terminated. In your case I think it's pretty safe to start a new thread inside run() method.

Just be sure you are not creating inner classes or storing this thread instance - it can cause memory leak, of course.

Good luck