簡介¶

public abstract class Number implements java.io.Serializable - Striped64(Striped64是在java8中添加用来支持累加器的并发组件，它可以在并发环境下使用来做某种计数) java.lang.Runtime

內容¶

Striped64(lock-free and Still Remain thread-safe.)¶

• LongAdder-LongAccumulator
• DoubleAdder-DoubleAccumulator

The call {@code new LongAdder()} is equivalent to {@code new LongAccumulator((x, y) -> x + y, 0L)} The call {@code new DoubleAdder()} is equivalent to {@code new DoubleAccumulator((x, y) -> x + y, 0.0)}

LongAdder¶

LongAdder counter = new LongAdder();
ExecutorService executorService = Executors.newFixedThreadPool(8);

int numberOfThreads = 4;
int numberOfIncrements = 100;

Runnable incrementAction = () -> IntStream
  .range(0, numberOfIncrements)
  .forEach(i -> counter.increment());

for (int i = 0; i < numberOfThreads; i++) {
    executorService.execute(incrementAction);
}

LongAccumulator¶

LongAccumulator accumulator = new LongAccumulator(Long::sum, 0L);
int numberOfThreads = 4;
int numberOfIncrements = 100;

Runnable accumulateAction = () -> IntStream
  .rangeClosed(0, numberOfIncrements)
  .forEach(accumulator::accumulate);

for (int i = 0; i < numberOfThreads; i++) {
    executorService.execute(accumulateAction);
}

Runtime¶

public static void main(String[] args) {
    try {
        Runtime runtime = Runtime.getRuntime();
        System.out.println(runtime.freeMemory());
        System.out.println(runtime.maxMemory());
        System.out.println(runtime.totalMemory());
        System.out.println(runtime.maxMemory());
        System.out.println(runtime.availableProcessors());

        Thread thread1 = new Thread(() -> {
            System.out.println("Runtime.addShutdownHook 1");
            // runtime.halt(1);
            // 强行终止当前正在运行的Java虚拟机
            // addShutdownHook不會起作用
        });
        Thread thread2 = new Thread(() -> {
            System.out.println("Runtime.addShutdownHook 2");
        });
        Thread thread3 = new Thread(() -> {
            System.out.println("Runtime.addShutdownHook 3");
        });

        // 可以添加多個addShutdownHook
        runtime.addShutdownHook(thread3);
        runtime.addShutdownHook(thread2);
        runtime.addShutdownHook(thread1);

        TimeUnit.SECONDS.sleep(1);

        runtime.removeShutdownHook(thread2);

        System.out.println("main.end");
    } catch (Exception e) {
        e.printStackTrace();
    }

}

參考資料¶