java 8，CompletableFuture

Question

在下面的代码片段中，谁能告诉我当我们调用 CompletableFuture.supplyAsync() 时会发生什么以及返回值时会在单独的线程中返回吗？

// Run a task specified by a Supplier object asynchronously
CompletableFuture<String> future = CompletableFuture.supplyAsync(new Supplier<String>() {
    @Override
    public String get() {
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            throw new IllegalStateException(e);
        }
        return "Result of the asynchronous computation";
    }
});

// Block and get the result of the Future
String result = future.get();
System.out.println(result);

Answer 1

这会返回一个新的Completable Future对象，它基本上得到在借自 ForkJoinPool 的新线程中执行。请引用javadoc -

/**
 * Returns a new CompletableFuture that is asynchronously completed
 * by a task running in the {@link ForkJoinPool#commonPool()} with
 * the value obtained by calling the given Supplier.
 *
 * @param supplier a function returning the value to be used
 * to complete the returned CompletableFuture
 * @param <U> the function's return type
 * @return the new CompletableFuture
 */
public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier) {
    return asyncSupplyStage(asyncPool, supplier);
}