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[HttpCache] Hit the backend only once after waiting for the cache lock #60502

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Merged
merged 1 commit into from
Jun 13, 2025
+96 −12
Merged

[HttpCache] Hit the backend only once after waiting for the cache lock #60502

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19 changes: 19 additions & 0 deletions src/Symfony/Component/HttpKernel/HttpCache/CacheWasLockedException.php
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Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
<?php

/*
* This file is part of the Symfony package.
*
* (c) Fabien Potencier <fabien@symfony.com>
*
* For the full copyright and license information, please view the LICENSE
* file that was distributed with this source code.
*/

namespace Symfony\Component\HttpKernel\HttpCache;

/**
* @internal
*/
class CacheWasLockedException extends \Exception
{
}
18 changes: 8 additions & 10 deletions src/Symfony/Component/HttpKernel/HttpCache/HttpCache.php
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Expand Up @@ -219,7 +219,13 @@ public function handle(Request $request, int $type = HttpKernelInterface::MAIN_R
$this->record($request, 'reload');
$response = $this->fetch($request, $catch);
} else {
$response = $this->lookup($request, $catch);
$response = null;
do {
try {
$response = $this->lookup($request, $catch);
} catch (CacheWasLockedException) {
}
} while (null === $response);
}

$this->restoreResponseBody($request, $response);
Expand Down Expand Up @@ -576,15 +582,7 @@ protected function lock(Request $request, Response $entry): bool

// wait for the lock to be released
if ($this->waitForLock($request)) {
// replace the current entry with the fresh one
$new = $this->lookup($request);
$entry->headers = $new->headers;
$entry->setContent($new->getContent());
$entry->setStatusCode($new->getStatusCode());
$entry->setProtocolVersion($new->getProtocolVersion());
foreach ($new->headers->getCookies() as $cookie) {
$entry->headers->setCookie($cookie);
}
throw new CacheWasLockedException(); // unwind back to handle(), try again
} else {
// backend is slow as hell, send a 503 response (to avoid the dog pile effect)
$entry->setStatusCode(503);
Expand Down
60 changes: 60 additions & 0 deletions src/Symfony/Component/HttpKernel/Tests/HttpCache/HttpCacheTest.php
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Expand Up @@ -18,6 +18,7 @@
use Symfony\Component\HttpKernel\Event\TerminateEvent;
use Symfony\Component\HttpKernel\HttpCache\Esi;
use Symfony\Component\HttpKernel\HttpCache\HttpCache;
use Symfony\Component\HttpKernel\HttpCache\Store;
use Symfony\Component\HttpKernel\HttpCache\StoreInterface;
use Symfony\Component\HttpKernel\HttpKernelInterface;
use Symfony\Component\HttpKernel\Kernel;
Expand Down Expand Up @@ -717,6 +718,7 @@ public function testDegradationWhenCacheLocked()
*/
sleep(10);

$this->store = $this->createStore(); // create another store instance that does not hold the current lock
$this->request('GET', '/');
$this->assertHttpKernelIsNotCalled();
$this->assertEquals(200, $this->response->getStatusCode());
Expand All @@ -735,6 +737,64 @@ public function testDegradationWhenCacheLocked()
$this->assertEquals('Old response', $this->response->getContent());
}

public function testHitBackendOnlyOnceWhenCacheWasLocked()
{
// Disable stale-while-revalidate, it circumvents waiting for the lock
$this->cacheConfig['stale_while_revalidate'] = 0;

$this->setNextResponses([
[
'status' => 200,
'body' => 'initial response',
'headers' => [
'Cache-Control' => 'public, no-cache',
'Last-Modified' => 'some while ago',
],
],
[
'status' => 304,
'body' => '',
'headers' => [
'Cache-Control' => 'public, no-cache',
'Last-Modified' => 'some while ago',
],
],
[
'status' => 500,
'body' => 'The backend should not be called twice during revalidation',
'headers' => [],
],
]);

$this->request('GET', '/'); // warm the cache

// Use a store that simulates a cache entry being locked upon first attempt
$this->store = new class(sys_get_temp_dir() . '/http_cache') extends Store {
private bool $hasLock = false;

public function lock(Request $request): bool
{
$hasLock = $this->hasLock;
$this->hasLock = true;

return $hasLock;
}

public function isLocked(Request $request): bool
{
return false;
}
};

$this->request('GET', '/'); // hit the cache with simulated lock/concurrency block

$this->assertEquals(200, $this->response->getStatusCode());
$this->assertEquals('initial response', $this->response->getContent());

$traces = $this->cache->getTraces();
$this->assertSame(['stale', 'valid', 'store'], current($traces));
}

public function testHitsCachedResponseWithSMaxAgeDirective()
{
$time = \DateTimeImmutable::createFromFormat('U', time() - 5);
Expand Down
11 changes: 9 additions & 2 deletions src/Symfony/Component/HttpKernel/Tests/HttpCache/HttpCacheTestCase.php
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Expand Up @@ -30,7 +30,7 @@ abstract class HttpCacheTestCase extends TestCase
protected $responses;
protected $catch;
protected $esi;
protected Store $store;
protected ?Store $store = null;

protected function setUp(): void
{
Expand Down Expand Up @@ -115,7 +115,9 @@ public function request($method, $uri = '/', $server = [], $cookies = [], $esi =

$this->kernel->reset();

$this->store = new Store(sys_get_temp_dir().'/http_cache');
if (! $this->store) {
$this->store = $this->createStore();
}

if (!isset($this->cacheConfig['debug'])) {
$this->cacheConfig['debug'] = true;
Expand Down Expand Up @@ -183,4 +185,9 @@ public static function clearDirectory($directory)

closedir($fp);
}

protected function createStore(): Store
{
return new Store(sys_get_temp_dir() . '/http_cache');
}
}