Reputation: 1423
My question is related to thread safety of static variables.
Class A{
private static int test=0;
public static void synchronized m1(){
test=test+1;
}
public void synchronized m2(){
test=test+1;
}
}
If two threads, t1 having static lock and t2 having object lock, can continue simultaneously, then how will state test of class A will be thread safe?
May be , I am missing something very basic, but not sure how it works.
Based on below answers, I get the impression that if such states have to be made thread safe, then either both locks should be held by a thread which is updating this state, or make sure it is being accessed by either only static methods or only non-static methods. right?
Upvotes: 0
Views: 4515
Reputation: 5502
Its not thread-safe, and you (the question author) explained very well why.
Upvotes: 0
Reputation: 6618
This is not thread safe. The methods use different monitor objects: the static method uses the class, and the instance method synchronizes using the object instance. You can make the instance method use the class as the monitor object by:
synchronized (A.class) {
...
if you need to. I'd consider making both methods static though, unless you need to access instance variables.
Upvotes: 5