Creating new objects in Thread.run(), when are they garbage collected?

Question

Within a class that extends Thread, consider the following example:

public void run() {
   while (workToDo) {
        JSONObject json = new JSONObject(getNextMap());
        publishJSON(json.toString());
        //  thread sleep
   }
}

Is each instance of json still referenced as long as the thread is running, or are they freed each time new is called? Should this be moved to a method, i.e. publishJSON(getJson(getNextMap())?

After every loop iteration, it will be available for GC as it goes out of scope. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Aug 1, 2013 at 14:25
They are freed when the GC thinks they should be. Note that when reaching the last sentence of the while loop, the object reference hold by json variable will be marked for garbage collection. — Luiggi Mendoza
– Luiggi Mendoza, Commented Aug 1, 2013 at 14:26
@SotiriosDelimanolis there are weird border cases where an out-of-scope, unreachable variable can't be collected. See for example: stackoverflow.com/questions/13531004/… - note that I don't think that other post applies to the OP's case. — assylias
– assylias, Commented Aug 1, 2013 at 14:34
@assylias Right. invisible state. In that case, always safer to null the variable. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Aug 1, 2013 at 14:56

Jack · Accepted Answer · 2013-08-01 14:27:43Z

4

To have a reference to object then it must be a local used variable (while in local scope) or contained in a member variable of a class instance.

I don't see any of the two in your example since after each while iteration the local variable can't be referenced anymore. So, unless you do something with json that saves a reference to it elsewhere, they are eligible for garbage collection.

Mind that this doesn't imply that the GC will collect the no-more-referenced instances after every iteration since its behavior is not predictable from a developer point of view. You just know that eventually they'll be collected.

answered Aug 1, 2013 at 14:27

Jack

134k33 gold badges252 silver badges349 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

coolhouse Over a year ago

Thanks, I wasn't sure if scope changed each pass through the loop.

user207421 Over a year ago

You don't know that. GC may never run at all. You know that the object is eligible for connection under the conditions stated.

Collectives™ on Stack Overflow

Creating new objects in Thread.run(), when are they garbage collected?

1 Answer 1

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Linked

Related