小细节招致假调用

小细节导致假调用

    private final A9Loader<List<E>> loader;    private final ThreadFactory     factory;    private final int               latch;    private final Semaphore         procOrder = new Semaphore(0, false);    private final ExtedEntryA9cq<E> entryA9cq = new ExtedEntryA9cq<E>(false, 0);    private volatile int            procLatch;    private volatile Future<E>      refFuture;... ...    private Future<E> asyncLoad() {        //check loading        final Future<E> current = refFuture;        if (current != null) return current;                // async load        ExecutorService executor = Executors.newSingleThreadExecutor(factory);        final Future<E> result = executor.submit(new Callable<E>() {                        public E call() throws Exception {                final E nul = null;                try {                    List<E> ls = loader.heavyLoad();                    if (ls != null && ls.size() > 0) {                        entryA9cq.append(ls);                    }                    procLatch = latch;                }                catch (Exception e) {                    if (procLatch > 0) {                        procLatch = -1;                        loader.handleException(e);                    }                    else {                        throw e;                    }                }                finally {                    try {                        procOrder.acquire(); // waiting for 'refFuture = result'                    }                    finally {                        refFuture = null;                    }                }                return nul; // only a blocking mark            }        });        executor.shutdown();        refFuture = result;        procOrder.release();

上面的代码有问题，可能导致外层调用者永远进不到 "// async load 块"。
若是 while(true)调用，那么就死循环了。
（其中：entryA9cq 的方法都能保证原子性）

修改如下：

               finally {                    procOrder.acquireUninterruptibly(); // waiting for 'refFuture = result'                    refFuture = null;                }                return nul; // only a blocking mark            }        });                refFuture = result;        procOrder.release(); // ensure the release.        executor.shutdown();

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