# The parallel\Future class

(0.8.0)

## Futures

A Future represents the return value or uncaught exception from a task, and exposes an API for cancellation.

示例 #1 Example showing Future as return value

    <?php
    $runtime = new \parallel\Runtime;
    $future  = $runtime->run(function(){
        return "World";
    });
    printf("Hello %s\n", $future->value());
    ?>

以上示例的输出类似于：

    Hello World

The behaviour of a future also allows it to be used as a simple synchronization point even where the task does not return a value explicitly.

示例 #2 Example showing Future as synchronization point

    <?php
    $runtime = new \parallel\Runtime;
    $future  = $runtime->run(function(){
        echo "in child ";
        for ($i = 0; $i < 500; $i++) {
            if ($i % 10 == 0) {
                echo ".";
            }
        }
        echo " leaving child";
    });

    $future->value();
    echo "\nparent continues\n";
    ?>

以上示例的输出类似于：

    in child .................................................. leaving child
    parent continues

## 类摘要

final class parallel\Future {
/* Resolution */
public function value(): mixed
/* State */
public function cancelled(): bool
public function done(): bool
/* Cancellation */
public function cancel(): bool
}

## 目录

- parallel\Future::cancel — Cancellation
- parallel\Future::cancelled — State Detection
- parallel\Future::done — State Detection
- parallel\Future::value — Resolution

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