PHP异常安全与资源清理模式

PHP异常安全与资源清理模式

异常发生时资源清理很重要。PHP提供了try-finally和RAII模式确保资源释放。今天说说PHP中异常安全和资源清理的最佳实践。

try-finally确保清理。

```php
function processFile(string $path): string
{
$handle = fopen($path, 'r');
if ($handle === false) throw new RuntimeException("无法打开文件");

try {
$content = fread($handle, 1024);
if ($content === false) throw new RuntimeException("读取失败");
return $content;
} finally {
fclose($handle);
}
}

file_put_contents('/tmp/test.txt', 'Hello');
echo processFile('/tmp/test.txt') . "\n";
?>

事务清理。

```php
function withTransaction(PDO $pdo, callable $callback): mixed
{
$pdo->beginTransaction();

try {
$result = $callback($pdo);
$pdo->commit();
return $result;
} catch (Exception $e) {
$pdo->rollBack();
throw $e;
}
}

$pdo = new PDO('mysql:host=localhost;dbname=test', 'root', '');

try {
$result = withTransaction($pdo, function (PDO $pdo) {
$pdo->exec("UPDATE accounts SET balance = balance - 100 WHERE id = 1");
$pdo->exec("UPDATE accounts SET balance = balance + 100 WHERE id = 2");
return '转账成功';
});
echo $result . "\n";
} catch (Exception $e) {
echo "失败: {$e->getMessage()}\n";
}
?>

RAII模式。

```php
class ResourceGuard
{
private $resource;
private string $type;

public function __construct(string $type, $resource)
{
$this->type = $type;
$this->resource = $resource;
}

public function get(): mixed
{
return $this->resource;
}

public function __destruct()
{
if ($this->resource === null) return;

switch ($this->type) {
case 'file':
if (is_resource($this->resource)) fclose($this->resource);
break;
case 'curl':
if (is_resource($this->resource)) curl_close($this->resource);
break;
case 'stream':
if (is_resource($this->resource)) fclose($this->resource);
break;
}

$this->resource = null;
}
}

function readFileRAII(string $path): string
{
$handle = fopen($path, 'r');
if ($handle === false) throw new RuntimeException("打开失败");

$guard = new ResourceGuard('file', $handle);
$content = fread($guard->get(), 1024);

if ($content === false) throw new RuntimeException("读取失败");
return $content;
}

echo readFileRAII('/tmp/test.txt') . "\n";
?>

多个资源的清理。

```php
function processMultipleResources(string $file1, string $file2): array
{
$h1 = fopen($file1, 'r');
$h2 = fopen($file2, 'r');

if ($h1 === false || $h2 === false) {
if ($h1) fclose($h1);
if ($h2) fclose($h2);
throw new RuntimeException("打开文件失败");
}

try {
return [fread($h1, 1024), fread($h2, 1024)];
} finally {
fclose($h1);
fclose($h2);
}
}
?>

异常安全的资源清理是系统稳定性的基础。try-finally确保代码无论是否异常都执行清理。事务在异常时自动回滚。RAII模式将资源绑定到对象生命周期。delete关键字自动处理资源释放。