Java8InAction学习笔记(四) - 18965050/Java8InAction GitHub Wiki
- Stream.parallel()用于线程并行计算
- Stream.sequential()用于串行计算
线程池线程数大小默认为可用的CPU数(Runtime.getRuntime().availableProcessors()), 可通过类似
System.setProperty("java.util.concurrent.ForkJoinPool.common.parallelism", "12");
这种方式修改.
使用parallel这种方式要注意:
- 并行的并非比串行的性能好. 存在线程切换的开销, unbox转换等
- 并行的操作应该是无状态的
集合Stream来源对Parallel友好程度:
Fork/Join框架是Java7中引入的. 其逻辑为:
if (task is small enough or no longer divisible) {
compute task sequentially
} else {
split task in two subtasks
call this method recursively possibly further splitting each subtask
wait for the completion of all subtasks
combine the results of each subtask
}
Spliterator全称为"splitable iterator", 作为parallel的chunk分割器.
public interface Spliterator<T> {
boolean tryAdvance(Consumer<? super T> action);
Spliterator<T> trySplit();
long estimateSize();
int characteristics();
}
Spliterator调用trySplit()方法, 如果有Spliterator对象返回, 则可以再分隔;如果返回null, 则不能在进行分割了.
characteristics()方法返回结果含义:
