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An implementation of Fibonacci
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private BigInteger f(int n, Map<Integer, BigInteger> cache) { | |
BigInteger result = cache.putIfAbsent(n, RESERVED); | |
if (result == null) { | |
int half = (n + 1) / 2; | |
CompletableFuture<BigInteger> completableFuture = new CompletableFuture<>(); | |
CompletableFuture<BigInteger> futureResult = CompletableFuture.supplyAsync(() -> f(half - 1, cache)); | |
futureResult.thenAcceptBothAsync(CompletableFuture.supplyAsync( | |
() -> f(half, cache)), | |
(s1, s2) -> { | |
BigInteger result1 = null; | |
if (n % 2 == 1) { | |
result1 = s1.multiply(s1).add(s2.multiply(s2)); | |
} else { | |
result1 = s1.shiftLeft(1).add(s2).multiply(s2); | |
} | |
synchronized (RESERVED) { | |
cache.put(n, result1); | |
RESERVED.notifyAll(); | |
completableFuture.complete(result1); | |
} | |
}); | |
try { | |
return completableFuture.get(); | |
} catch (InterruptedException | ExecutionException e) { | |
e.printStackTrace(); | |
} | |
} else if (result == RESERVED) { | |
try { | |
ReservedBlocker blocker = new ReservedBlocker(n, cache); | |
ForkJoinPool.managedBlock(blocker); | |
result = blocker.result; | |
} catch (InterruptedException e) { | |
throw new CancellationException("interrupted"); | |
} | |
} | |
return result; | |
} |
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