aspose file tools*
The moose likes Java in General and the fly likes when are static ThreadLocal variables intialized Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login
JavaRanch » Java Forums » Java » Java in General
Bookmark "when are static ThreadLocal variables intialized" Watch "when are static ThreadLocal variables intialized" New topic
Author

when are static ThreadLocal variables intialized

Yan Zhou
Ranch Hand

Joined: Sep 02, 2003
Posts: 137
The following code is from ThreadLocal's JavaDoc.

All static variables are initialized when classes are loaded, before the main() even starts. I wonder whether static ThreadLocal variables are so, too.

I do not think that ThreadLocal variables would be initialized before threads are created, may be they are initialized when threads are created?

public class SerialNum {
// The next serial number to be assigned
private static int nextSerialNum = 0;

private static ThreadLocal serialNum = new ThreadLocal() {
protected synchronized Object initialValue() {
return new Integer(nextSerialNum++);
}
};

public static int get() {
return ((Integer) (serialNum.get())).intValue();
}
}
Peter Chase
Ranch Hand

Joined: Oct 30, 2001
Posts: 1970
I think you are imagining ThreadLocal to be somehow "magic", but in fact it is a pure Java class. It has no native methods and no special hooks into the JVM. You can look at its source, in the JDK.

When the class, containing a static field that is a reference to a ThreadLocal, is loaded, that field is initialised.

In your example, the initialisation of the static field involves constructing an instance of ThreadLocal().

When you first use methods on your instance of ThreadLocal, in a particular thread, the ThreadLocal's value for that thread is initialised to whatever the initialValue() method returns.


Betty Rubble? Well, I would go with Betty... but I'd be thinking of Wilma.
Maulin Vasavada
Ranch Hand

Joined: Nov 04, 2001
Posts: 1871
Hi Yan,

1. http://java.sun.com/developer/JDCTechTips/2003/tt1208.html#2
2. http://www-106.ibm.com/developerworks/java/library/j-threads3.html

These links should be good for help. I read it carefully and I got how it works. Also, at the end of the techtip article they recommend to look at LogRecord and Charset classes in the JDK API and I looked at their sources to see how they are using ThreadLocal..

Though I found IBM's article with more insights.

Thanks
Maulin
 
I agree. Here's the link: http://aspose.com/file-tools
 
subject: when are static ThreadLocal variables intialized