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

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

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7 changes: 7 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 +1,7 @@
<?php

namespace Symfony\Component\HttpKernel\HttpCache;

class CacheWasLockedException extends \Exception
{
}
16 changes: 6 additions & 10 deletions src/Symfony/Component/HttpKernel/HttpCache/HttpCache.php
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Expand Up @@ -219,7 +219,11 @@ 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);
try {
$response = $this->lookup($request, $catch);
} catch (CacheWasLockedException) {
$response = $this->lookup($request, $catch);
}
Comment on lines +222 to +226
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This allows to restart the process only once.

In fact, the old code would wait for the lock to be released, but only try to acquire it later on. That could, in theory, allow for repeated cycles without actually reaching the 503 condition in lock().

Maybe it is even better this way to fail with the exception instead of silenty retrying over and over again?

}

$this->restoreResponseBody($request, $response);
Expand Down Expand Up @@ -576,15 +580,7 @@ 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');
}
}
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