/**
	 * 验证并发update mysql数据库记录
	 * @param args
	 * @throws SQLException
	 * @throws IOException
	 * @throws InterruptedException
	 */
	public static void main(String[] args) throws SQLException, IOException, InterruptedException {
		String url = "jdbc:mysql://localhost:3306/test";
		String user = "root";
		String password = "123456";

		int nThreads = 140; //不要超过数据库最大连接数 : max_connections  151
		ExecutorService pool = Executors.newFixedThreadPool(nThreads);
		CountDownLatch startLatch = new CountDownLatch(nThreads);
		CountDownLatch endLatch = new CountDownLatch(nThreads);

		for (int i = 0; i < nThreads; i++) {
			pool.submit(() -> {
				startLatch.countDown();
				try { startLatch.await(); } catch (Exception e1) { } //等待所有任务都提交了再往下执行 保证并发

				String sql = "update t set count = count-1 where id =1 and count>0";
				try {
					Connection connection = DriverManager.getConnection(url, user, password);
					Statement stat = connection.createStatement();
					stat.execute(sql);
					endLatch.countDown();
				} catch (Exception e) {
					e.printStackTrace();
				}
			});
		}
		endLatch.await(); //等待所有的任务都完成
		System.out.println("done");
		System.exit(0);
	}