1、模式定义

对象池（也称为资源池）被用来管理对象缓存。对象池是一组已经初始化过且可以直接使用的对象集合，用户在使用对象时可以从对象池中获取对象，对其进行操作处理，并在不需要时归还给对象池而非销毁它。

若对象初始化、实例化的代价高，且需要经常实例化，但每次实例化的数量较少的情况下，使用对象池可以获得显著的性能提升。常见的使用对象池模式的技术包括 线程池 、 数据库连接池 、任务队列池、图片资源对象池等。

当然，如果要实例化的对象较小，不需要多少资源开销，就没有必要使用对象池模式了，这非但不会提升性能，反而浪费内存空间，甚至降低性能。

2、UML类图

3、示例代码

Pool.php

<?php
namespace DesignPatterns\Creational\Pool;
class Pool
{
 private $instances = array();
 private $class;
 public function __construct($class)
 {
 $this->class = $class;
 }
 public function get()
 {
 if (count($this->instances) > 0) {
 return array_pop($this->instances);
 }
 return new $this->class();
 }
 public function dispose($instance)
 {
 $this->instances[] = $instance;
 }
}
 

Processor.php

<?php
namespace DesignPatterns\Creational\Pool;
class Processor
{
 private $pool;
 private $processing = 0;
 private $maxProcesses = 3;
 private $waitingQueue = [];
 public function __construct(Pool $pool)
 {
 $this->pool = $pool;
 }
 public function process($image)
 {
 if ($this->processing++ < $this->maxProcesses) {
 $this->createWorker($image);
 } else {
 $this->pushToWaitingQueue($image);
 }
 }
 private function createWorker($image)
 {
 $worker = $this->pool->get();
 $worker->run($image, array($this, 'processDone'));
 }
 public function processDone($worker)
 {
 $this->processing--;
 $this->pool->dispose($worker);
 if (count($this->waitingQueue) > 0) {
 $this->createWorker($this->popFromWaitingQueue());
 }
 }
 private function pushToWaitingQueue($image)
 {
 $this->waitingQueue[] = $image;
 }
 private function popFromWaitingQueue()
 {
 return array_pop($this->waitingQueue);
 }
}
 

Worker.php

<?php
namespace DesignPatterns\Creational\Pool;
class Worker
{
 public function __construct()
 {
 // let's say that constuctor does really expensive work...
 // for example creates "thread"
 }
 public function run($image, array $ callback )
 {
 // do something with $image...
 // and when it's done, execute callback
 call_user_func($callback, $this);
 }
}
 

4、测试代码

Tests/PoolTest.php

<?php
namespace DesignPatterns\Creational\Pool\Tests;
use DesignPatterns\Creational\Pool\Pool;
class PoolTest extends \PHPUnit_Framework_TestCase
{
 public function testPool()
 {
 $pool = new Pool('DesignPatterns\Creational\Pool\Tests\TestWorker');
 $worker = $pool->get();
 $this->assertEquals(1, $worker->id);
 $worker->id = 5;
 $pool->dispose($worker);
 $this->assertEquals(5, $pool->get()->id);
 $this->assertEquals(1, $pool->get()->id);
 }
}
 

Tests/TestWorker.php

<?php
namespace DesignPatterns\Creational\Pool\Tests;
class TestWorker
{
 public $id = 1;
}