目录

目的UML 类图代码测试
目的

在初始化实例成本高，实例化率高，可用实例不足的情况下，对象池可以极大地提升性能。在创建对象（尤其是通过网络）时间花销不确定的情况下，通过对象池在可期时间内就可以获得所需的对象。

无论如何，对象池模式在需要耗时创建对象方面，例如创建数据库连接，套接字连接，线程和大型图形对象（比方字体或位图等），使用起来都是大有裨益的。在某些情况下，简单的对象池（无外部资源，只占内存）可能效率不高，甚至会有损性能。

UML 类图代码

WorkerPool.php

<?php
 
namespace DesignPatterns\Creational\Pool;
 
class WorkerPool implements \Countable
{
    /**
    * @var StringReverseWorker[]
    */
    private $occupiedWorkers = [];
 
    /**
    * @var StringReverseWorker[]
    */
    private $freeWorkers = [];
 
    public function get(): StringReverseWorker
    {
        if (count($this->freeWorkers) == 0) {
            $worker = new StringReverseWorker();
        } else {
            $worker = array_pop($this->freeWorkers);
        }
 
        $this->occupiedWorkers[spl_object_hash($worker)] = $worker;
 
        return $worker;
    }
 
    public function dispose(StringReverseWorker $worker)
    {
        $key = spl_object_hash($worker);
 
        if (isset($this->occupiedWorkers[$key])) {
            unset($this->occupiedWorkers[$key]);
            $this->freeWorkers[$key] = $worker;
        }
    }
 
    public function count(): int
    {
        return count($this->occupiedWorkers) + count($this->freeWorkers);
    }
}

StringReverseWorker.php

<?php
 
namespace DesignPatterns\Creational\Pool;
 
class StringReverseWorker
{
    /**
    * @var \DateTime
    */
    private $createdAt;
 
    public function __construct()
    {
        $this->createdAt = new \DateTime();
    }
 
    public function run(string $text)
    {
        return strrev($text);
    }
}
测试

Tests/PoolTest.php

<?php
 
namespace DesignPatterns\Creational\Pool\Tests;
 
use DesignPatterns\Creational\Pool\WorkerPool;
use PHPUnit\Framework\TestCase;
 
class PoolTest extends TestCase
{
    public function testCanGetNewInstancesWithGet()
    {
        $pool = new WorkerPool();
        $worker1 = $pool->get();
        $worker2 = $pool->get();
 
        $this->assertCount(2, $pool);
        $this->assertNotSame($worker1, $worker2);
    }
 
    public function testCanGetSameInstanceTwiceWhenDisposingItFirst()
    {
        $pool = new WorkerPool();
        $worker1 = $pool->get();
        $pool->dispose($worker1);
        $worker2 = $pool->get();
 
        $this->assertCount(1, $pool);
        $this->assertSame($worker1, $worker2);
    }
}

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