Hi Ulf,
Ulf Zibis said the following on 10/08/09 20:07:
Am 08.10.2009 06:35, David Holmes - Sun Microsystems schrieb:
Ulf Zibis said the following on 10/08/09 08:58:
For my better understanding:
Can you explain me the real bug in
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6881442.
In my understanding, loading the "name" field twice is too only a
performance bug. Please correct me!
Class.getName() could in theory return null and this is not allowed,
hence this was a functional correctness issue.
Hm, my problem is, I can't see any condition, how Class.getName() could
return null, except native method getName0() would return null.
But if native getName0() could return null, I can't see how the new code
would prevent method Class.getName() from returning null.
It's a memory model issue. The code is like this:
public String getName() {
if (name == null)
name = getName0();
return name;
}
but in theory, accoridng to the JMM experts, it could act as if it does
this:
public String getName() {
String tmp1 = name; // sees null
String tmp2 = name; // sees non-null
if (tmp2 == null)
tmp1 = name = getName0();
return tmp1;
}
imagine the temporaries are registers.
David
