目的
在初始化實例成本高，實例化率高，可用實例不足的情況下，對象池可以極大地提升性能。在創建對象（尤其是通過網絡）時間花銷不確定的情況下，通過對象池在可期時間內就可以獲得所需的對象。
無論如何，對象池模式在需要耗時創建對象方面，例如創建數據庫連接，套接字連接，線程和大型圖形對象（比方字體或位圖等），使用起來都是大有裨益的。在某些情況下，簡單的對象池（無外部資源，只占內存）可能效率不高，甚至會有損性能。
UML 類圖
代碼
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);
}
}
測試
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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