java - 在 Java 8 并行流中，终端操作是否在返回之前完成所有计算？

Question

例如，如果类 Foo 有实例方法 bar()，

List<Foo> list = new ArrayList<>();
// ...
list.stream()
    .parallel()
    .forEach(Foo::bar);
doSomething();

是否保证在调用 doSomething() 之前所有对 bar() 的调用都已返回？

Answer 1

是的，除非终端操作是 iterator() 或 spliterator()。

来自java.util.stream package page:

In almost all cases, terminal operations are eager, completing their traversal of the data source and processing of the pipeline before returning. Only the terminal operations iterator() and spliterator() are not; these are provided as an "escape hatch" to enable arbitrary client-controlled pipeline traversals in the event that the existing operations are not sufficient to the task.