關於Java-CountDownLatch

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關於Java-CountDownLatch

CountDownLatch 可以看作一個計數器，不過計數是原子操作，
也就是說同一時間只有一個執行緒能夠操作該計數器。

常用方法介紹

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Public constructors
CountDownLatch(int count)
-------------------
Public methods
void await()
boolean await(long timeout, TimeUnit unit)
void countDown()
long getCount()
String toString()

example

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private static ExecutorService exec;

public static void setUpBeforeClass() {
	exec = Executors.newFixedThreadPool(1000);
}

final CountDownLatch latch = new CountDownLatch(13 * 13 * 14 * 13 * 13 * 14);

for (int i = 0; i <= 12; i++) {
	for (int j = 0; j <= 12; j++) {
		for (int k = 0; k <= 13; k++) {
			for (int l = 0; l <= 12; l++) {
				for (int m = 0; m <= 12; m++) {
					for (int n = 0; n <= 13; n++) {
						Runnable task = new Runnable() {

							@Override
							public void run() {
								try {
									//To do something
								} catch (Exception e) {
									LogUtils.error.error("Failure!!! type:" + type, e);
								} finally {
									latch.countDown();
								}
							}
						};
						exec.execute(task);
					}
				}
			}
		}
	}
}
latch.await();
System.out.println("All tasks are already finish!!");
此例子會使用1000個執行緒跑13 * 13 * 14 * 13 * 13 * 14個task
因為有使用CountDownLatch 每執行一個task會使用latch.countDown();去減1
最後latch.await(); 變成0時就代表所有執行緒皆已完成。