feature #41989 [Cache] make LockRegistry use semaphores when possible (nicolas-grekas)

fabpot · fabpot · commit 479919d4d5cb · 2021-07-08T11:26:17.000+02:00
This PR was merged into the 5.4 branch. Discussion ---------- [Cache] make `LockRegistry` use semaphores when possible | Q | A | ------------- | --- | Branch? | 5.4 | Bug fix? | no | New feature? | yes | Deprecations? | no | Tickets | - | License | MIT | Doc PR | - Commits ------- 87632b7 [Cache] make `LockRegistry` use semaphores when possible
diff --git a/src/Symfony/Component/Cache/CHANGELOG.md b/src/Symfony/Component/Cache/CHANGELOG.md
@@ -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
diff --git a/src/Symfony/Component/Cache/LockRegistry.php b/src/Symfony/Component/Cache/LockRegistry.php
@@ -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.
@@ -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);
 
@@ -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:{}}");
@@ -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;
         }
