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[Cache] make LockRegistry use semaphores when possible #41989

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Merged
merged 1 commit into from
Jul 8, 2021
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[Cache] make LockRegistry use semaphores when possible #41989

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1 change: 1 addition & 0 deletions src/Symfony/Component/Cache/CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@ CHANGELOG
5.4
---

* Make `LockRegistry` use semaphores when possible
* Deprecate `DoctrineProvider` because this class has been added to the `doctrine/cache` package

5.3
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45 changes: 34 additions & 11 deletions src/Symfony/Component/Cache/LockRegistry.php
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,7 @@
final class LockRegistry
{
private static $openedFiles = [];
private static $lockedFiles;
private static $lockedKeys;

/**
* The number of items in this list controls the max number of concurrent processes.
Expand Down Expand Up @@ -75,32 +75,40 @@ public static function setFiles(array $files): array
fclose($file);
}
}
self::$openedFiles = self::$lockedFiles = [];
self::$openedFiles = self::$lockedKeys = [];

return $previousFiles;
}

public static function compute(callable $callback, ItemInterface $item, bool &$save, CacheInterface $pool, \Closure $setMetadata = null, LoggerInterface $logger = null)
{
if ('\\' === \DIRECTORY_SEPARATOR && null === self::$lockedFiles) {
if ('\\' === \DIRECTORY_SEPARATOR && null === self::$lockedKeys) {
// disable locking on Windows by default
self::$files = self::$lockedFiles = [];
self::$files = self::$lockedKeys = [];
}

$key = self::$files ? abs(crc32($item->getKey())) % \count(self::$files) : -1;
$key = unpack('i', md5($item->getKey(), true))[1];

if ($key < 0 || (self::$lockedFiles[$key] ?? false) || !$lock = self::open($key)) {
if (!\function_exists('sem_get')) {
$key = self::$files ? abs($key) % \count(self::$files) : null;
}

if (null === $key || (self::$lockedKeys[$key] ?? false) || !$lock = self::open($key)) {
return $callback($item, $save);
}

while (true) {
try {
// race to get the lock in non-blocking mode
$locked = flock($lock, \LOCK_EX | \LOCK_NB, $wouldBlock);
if ($wouldBlock = \function_exists('sem_get')) {
$locked = @sem_acquire($lock, true);
} else {
$locked = flock($lock, \LOCK_EX | \LOCK_NB, $wouldBlock);
}

if ($locked || !$wouldBlock) {
$logger && $logger->info(sprintf('Lock %s, now computing item "{key}"', $locked ? 'acquired' : 'not supported'), ['key' => $item->getKey()]);
self::$lockedFiles[$key] = true;
self::$lockedKeys[$key] = true;

$value = $callback($item, $save);

Expand All @@ -115,12 +123,23 @@ public static function compute(callable $callback, ItemInterface $item, bool &$s

return $value;
}

// if we failed the race, retry locking in blocking mode to wait for the winner
$logger && $logger->info('Item "{key}" is locked, waiting for it to be released', ['key' => $item->getKey()]);
flock($lock, \LOCK_SH);

if (\function_exists('sem_get')) {
$lock = sem_get($key);
@sem_acquire($lock);
} else {
flock($lock, \LOCK_SH);
}
} finally {
flock($lock, \LOCK_UN);
unset(self::$lockedFiles[$key]);
if (\function_exists('sem_get')) {
sem_remove($lock);
} else {
flock($lock, \LOCK_UN);
}
unset(self::$lockedKeys[$key]);
}
static $signalingException, $signalingCallback;
$signalingException = $signalingException ?? unserialize("O:9:\"Exception\":1:{s:16:\"\0Exception\0trace\";a:0:{}}");
Expand All @@ -145,6 +164,10 @@ public static function compute(callable $callback, ItemInterface $item, bool &$s

private static function open(int $key)
{
if (\function_exists('sem_get')) {
return sem_get($key);
}

if (null !== $h = self::$openedFiles[$key] ?? null) {
return $h;
}
Expand Down