java - In Brian Goetz Concurrency In Practice, why is there a while(true) in the final example of a scalable cache? -

in code listing 5.19 of brian goetz book concurrency in practice, presents finished thread safe memoizer class.

i thought understood code in example, except don't understand

while ( true ) 

is @ start of

public v compute(final arg) throws interruptedexception 

method.

why code need while loop?

here entire code sample

public class memoizer<a, v> implements computable<a, v> {     private final concurrentmap<a, future<v>> cache         = new concurrenthashmap<a, future<v>>();     private final computable<a, v> c;      public memoizer(computable<a, v> c) { this.c = c; }      public v compute(final arg) throws interruptedexception {         while (true) {             future<v> f = cache.get(arg);             if (f == null) {                 callable<v> eval = new callable<v>() {                     public v call() throws interruptedexception {                         return c.compute(arg);                     }                 };                 futuretask<v> ft = new futuretask<v>(eval);                 f = cache.putifabsent(arg, ft);                 if (f == null) { f = ft; ft.run(); }             }             try {                 return f.get();             } catch (cancellationexception e) {                 cache.remove(arg, f);             } catch (executionexception e) {                 throw launderthrowable(e.getcause());             }         }     } } 

eternal loop retries on cancellationexception. if other exception being thrown execution stopped.

biotext dot org has blog entry on same issue.