# 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 value(): mixed
/* State */
public cancelled(): bool
public done(): bool
/* Cancellation */
public 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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