How can I make sure a method is only called once by multiple threads?

Question

I have the following structure:

public void someMethod(){  
   //DO SOME STUFF
   try{  
    doSomeProcessing();  
   }  
   catch (Exception e){  
                


        

Answer 1

We wrote a library that includes a utility lazily load/call a method. It guarantees single usage semantics and preserves any thrown exceptions as you'd expect.

Usage is simple:

LazyReference heavyThing = new LazyReference() {
  protected Thing create() {
    return loadSomeHeavyData();
  }
};

public void someMethod(){  
  //DO SOME STUFF
  try{  
    doSomeProcessing();  
  }  
  catch (Exception e){  
    heavyThing.get();  
    doSomeProcessing();      
  }    
}  

All threads block on the get() and wait for the producer thread (the first caller) to complete.