Question

I’m new to the Java threading and have only recently started to read up on the Memory Model. From my understanding the Java Memory Model as it stands allows the compiler to make optimizations.

This can complicate multi-threaded code and synchronization but my question is for something much simpler. Take this example since the two statements are not dependent on each other, is it possible that the compiler could change the ordering of the code in the try statement and therefore break the check?

boolean success = false;
try{
 MyClass.someFunction();
 success = true;
}
catch(Exception e){

}

if(success){    
    System.out.println("Sucess!");
}
else{
    System.out.println("Fail!");
}

Answer 1

As Java cannot understand what MyClass.someFunction() does, it cannot safely reorder this statement. In fact, most data dependency checkers are completely incapable of moving outside of a function boundary due to side-effects.

Threads are a special case, and not unique to Java – data ends up in registers, and won’t be refetched from memory unless needed. Java’s solution is the transient keyword (similar to volatile in other languages).