一種高併發流控程序的簡單輕量實現

實現一個流控程序，控制客戶端每秒調用某個遠程服務不超過N次，客戶端是會多線程併發調用。

import java.util.Date;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

public class FlowConcurrentController {
	// 每秒併發訪問控制數量
	final static int MAX_QPS = 10;
	// 併發控制信號量
	final static Semaphore semaphore = new Semaphore(MAX_QPS);
	// 監控每秒併發訪問次數（理論上accessCount.get() <= 10）
	final static AtomicInteger accessCount = new AtomicInteger(0);

	// 模擬遠程訪問
	private static void remoteCall(int i, int j) {
		System.out.println(String.format("%s - %s: %d %d", new Date(), Thread.currentThread(), i, j));
	}

	private static void releaseWork() { // 每秒release一次
		// release semaphore thread
		Executors.newScheduledThreadPool(1).scheduleAtFixedRate(new Runnable() {
			@Override
			public void run() {
				semaphore.release(accessCount.get());
				accessCount.set(0);
			}
		}, 1000, 1000, TimeUnit.MILLISECONDS);
	}

	// 模擬併發訪問控制
	private static void simulateAccess(final int m, final int n)
			throws Exception { // m : 線程數；n : 調用數
		ExecutorService pool = Executors.newFixedThreadPool(100);
		for (int i = m; i > 0; i--) {
			final int x = i;
			pool.submit(new Runnable() {
				@Override
				public void run() {
					for (int j = n; j > 0; j--) {
						try {
							Thread.sleep(5);
						} catch (InterruptedException e) {
							e.printStackTrace();
						}

						semaphore.acquireUninterruptibly(1);
						accessCount.incrementAndGet();
						remoteCall(x, j);
					}
				}
			});
		}

		pool.shutdown();
		pool.awaitTermination(1, TimeUnit.HOURS);
	}

	public static void main(String[] args) throws Exception {
		// 開啓releaseWork
		releaseWork();
		
		// 開始模擬lots of concurrent calls: 100 * 1000
		simulateAccess(100, 1000);
	}

}

上面的代碼中存在一個小問題，就是accessCount的釋放後，存在負數的情況，也就是說高併發的情況下每秒會存在>MAX_QPS次的併發訪問次數，還不能做到非常精確控制。

期待大家更加簡單和輕量的方式。