RE: JavaMemoryModel: Java Class initialization can deadlock?

From: Bill Pugh (
Date: Wed Mar 19 2003 - 16:57:32 EST

At 1:27 PM -0800 3/19/03, Boehm, Hans wrote:
>3) This can obviously deadlock even with a single thread, so we
>patch this by detecting the most obvious deadlock case which
>involves a recursive invocation of class initialization from the
>same thread. In that case we allow the (partially) uninitialized
>class to be used instead. This causes some strange behavior, but
>since most classes presumably contain many methods that rely on only
>compile-time initialization, it allows some interesting cases to
>work correctly.

Actually, the spec already handles the potential for deadlock in a
single thread.

class A {
   static int x;
   static {
     System.out.println("B.y = " + B.y);
     x = 1;
class B {
   static int y;
   static {
     System.out.println("A.x = " + A.x);
     y = 1;
class Test {
   public static void main(String args[]) {
         System.out.println("A.x = " + A.x);

Invoking java Test is guaranteed to print:
A.x = 0
B.y = 1
A.x = 1

So initialization circularities experienced by a single thread
can allow a program to see incompletely initialized classes.

But when experienced by multiple threads, you get deadlock rather
than incompletely initialized classes.

So rather than having to worry about two different bad behaviors,
maybe we should have just one.

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