Even the jvm gets synchronization wrong sometimes
The JVM has the following code in DeleteOnExit.
static void add(String file) {
synchronized(files) {
if(files == null)
throw new IllegalStateException("Shutdown in progress");
files.add(file);
}
}
What would you expect to happen if files was null?
Sadly, it's not the useful error message telling you that a shutdown is in progress.
Instead you get a NullPointerException because you can't synchronize on null, it just doesn't work.
I suspect someone has just gone about adding synchronized blocks to all the methods in the object without looking at what they do.
Update: Ah, there's a bug about it, and it's fixed with newer JVMs, jolly good. http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6526376
static void add(String file) {
synchronized(files) {
if(files == null)
throw new IllegalStateException("Shutdown in progress");
files.add(file);
}
}
What would you expect to happen if files was null?
Sadly, it's not the useful error message telling you that a shutdown is in progress.
Instead you get a NullPointerException because you can't synchronize on null, it just doesn't work.
I suspect someone has just gone about adding synchronized blocks to all the methods in the object without looking at what they do.
Update: Ah, there's a bug about it, and it's fixed with newer JVMs, jolly good. http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6526376