Re: JavaMemoryModel: Thread starting in constructors

From: Jeremy Manson (
Date: Tue Mar 12 2002 - 10:54:17 EST

> How about:
> f) the thread will be SUSPENDED and RESUMED automatically
> on exit from the most-derived class constructor (exceptions
> aside);

That doesn't solve the problem in terms of the semantics. There is no
implicit synchronzation associated with Thread.suspend() and
Thread.resume() (nor should there be, I suspect; it's good to stay away
from those methods). Even if you were to use wait/notify, it isn't a good
idea because the constructor may never end (unless you mean that this only
applies to threads started on the last line of the constructor), viz.:

class A {
         int x;
         final int y;
         Object lock = new Object();
         public A(int a, int b) {
                 x = a;
                 y = b;
                 new Thread() {
                     public void run() {
                         System.out.println("x = " + x + ", y = " + y);
                while (true) {

More realistically, there could be a wait in the constructor dependent on
a notify in the thread. This is left as an exercise for the reader.

> or, even better:
> g) a rather simple mechanism of POST-constructors could be
> introduced to SAFELY/MEANINGFULLY exploit the polymorphic
> behavior (publish this, start threads, etc) at "construction"
> time without all those silly "manual" init()s/factories/final
> wrappers, etc.

That would be nice, but it wouldn't help existing code. That probably
needs its own JSR, too.

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