package simple2;
import test.Test;

// @NotThreadSafe
public class SingleUpdatePerThread {

	private static long result;

	private SingleUpdatePerThread() {
		// Cannot be instantiated
	}

	private static void addPartialResult(long partial) {
		result += partial;
	}

	public static long sum(int[] nums) throws Exception {
		result = 0;
		Thread[] threads = new Thread[Test.NUM_THREADS];
		int size = (int) Math.ceil((double) nums.length / Test.NUM_THREADS);
		for (int i = 0; i < Test.NUM_THREADS; i++) {
			threads[i] = new Thread(
					new SumSingleUpdate(nums, i * size, (i + 1) * size));
			threads[i].start();
		}
		for (Thread thread : threads) {
			thread.join();
		}
		return result;
	}

	static class SumSingleUpdate implements Runnable {
		private final int[] nums;
		private final int low;
		private final int high;

		public SumSingleUpdate(int[] nums, int low, int high) {
			this.nums = nums;
			this.low = low;
			this.high = Math.min(high, nums.length);
		}

		public void run() {
			long partialSum = 0;
			for (int i = low; i < high; i++) {
				partialSum += nums[i];
			}
			SingleUpdatePerThread.addPartialResult(partialSum);
		}
	}
}