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(chuàng)建對象（尤其是通過網(wǎng)絡(luò)）時間花銷不確定的情況下，通過對象池在可期時間內(nèi)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(chuàng)建對象方面，例如創(chuàng)建數(shù)據(jù)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(nèi)存）可能效率不高，甚至?xí)袚p性能。

WorkerPool.php

<?phpnamespace DesignPatternsCreationalPool;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

<?phpnamespace DesignPatternsCreationalPool;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

<?phpnamespace DesignPatternsCreationalPoolTests;use DesignPatternsCreationalPoolWorkerPool;use PHPUnitFrameworkTestCase;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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