java7-Fork/Join
阿新 • • 發佈:2017-12-26
ddl 般的 tar clas static calc junit java7 new
Fork/Join 框架與傳統線程池的區別采用“工作竊取”模式(work-stealing):當執行新的任務時它可以將其拆分分成更小的任務執行,並將小任務加到線程隊列中,然後再從一個隨機線程的隊列中偷一個並把它放在自己的隊列中。
相對於一般的線程池實現,fork/join框架的優勢體現在對其中包含的任務的處理方式上.在一般的線程池中,如果一個線程正在執行的任務由於某些原因無法繼續運行,那麽該線程會處於等待狀態.而在fork/join框架實現中,如果某個子問題由於等待另外一個子問題的完成而無法繼續運行.那麽處理該子問題的線程會主動尋找其他尚未運行的子問題來執行.這種方式減少了線程的等待時間,提高了性能.
代碼體驗效果:
import java.util.concurrent.RecursiveTask; public class ForkJoinCalculate extends RecursiveTask<Long>{ /** * */ private static final long serialVersionUID = 13475679780L; private long start; private long end; private static finallong THRESHOLD = 10000L; //臨界值 public ForkJoinCalculate(long start, long end) { this.start = start; this.end = end; } @Override protected Long compute() { long length = end - start; if(length <= THRESHOLD){ longsum = 0; for (long i = start; i <= end; i++) { sum += i; } return sum; }else{ long middle = (start + end) / 2; ForkJoinCalculate left = new ForkJoinCalculate(start, middle); left.fork(); //拆分,並將該子任務壓入線程隊列 ForkJoinCalculate right = new ForkJoinCalculate(middle+1, end); right.fork(); return left.join() + right.join(); } } }
測試類:
import java.util.concurrent.ForkJoinPool; import java.util.concurrent.ForkJoinTask; import java.util.stream.LongStream; import org.junit.Test; public class TestForkJoin { static long num = 10000000000000L; @Test public void test1(){ long start = System.currentTimeMillis(); ForkJoinPool pool = new ForkJoinPool(); ForkJoinTask<Long> task = new ForkJoinCalculate(0L, num); long sum = pool.invoke(task); System.out.println(sum); long end = System.currentTimeMillis(); System.out.println("test1耗費的時間為: " + (end - start)); //112-1953-1988-2654-2647-20663-113808 } @Test public void test2(){ long start = System.currentTimeMillis(); long sum = 0L; for (long i = 0L; i <= num; i++) { sum += i; } System.out.println(sum); long end = System.currentTimeMillis(); System.out.println("test2耗費的時間為: " + (end - start)); //34-3174-3132-4227-4223-31583 } @Test public void test3(){ long start = System.currentTimeMillis(); Long sum = LongStream.rangeClosed(0L, num) .parallel() .sum(); System.out.println(sum); long end = System.currentTimeMillis(); System.out.println("test3耗費的時間為: " + (end - start)); //2061-2053-2086-18926 } }
java7-Fork/Join