always use lock when writing/reading cache data to/from file

vimeo · Aug 5, 2022 · fd76799 · fd76799
1 parent 1ef3851
commit fd76799
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Showing 4 changed files with 227 additions and 112 deletions.
diff --git a/src/Psalm/Internal/Provider/ClassLikeStorageCacheProvider.php b/src/Psalm/Internal/Provider/ClassLikeStorageCacheProvider.php
@@ -8,10 +8,14 @@
 
 use function array_merge;
 use function dirname;
+use function fclose;
 use function file_exists;
-use function file_get_contents;
 use function file_put_contents;
 use function filemtime;
+use function filesize;
+use function flock;
+use function fopen;
+use function fread;
 use function get_class;
 use function hash;
 use function igbinary_serialize;
@@ -23,8 +27,11 @@
 use function strtolower;
 use function unlink;
 use function unserialize;
+use function usleep;
 
 use const DIRECTORY_SEPARATOR;
+use const LOCK_EX;
+use const LOCK_SH;
 use const PHP_VERSION_ID;
 
 /**
@@ -72,6 +79,35 @@ public function __construct(Config $config)
         $this->modified_timestamps .= $this->config->computeHash();
     }
 
+    protected function safeFileGetContents(string $path): string
+    {
+        // no readable validation as that must be done in the caller
+        $fp = fopen($path, 'r');
+        if ($fp === false) {
+            return '';
+        }
+        $max_wait_cycles = 5;
+        $has_lock = false;
+        while ($max_wait_cycles > 0) {
+            if (flock($fp, LOCK_SH)) {
+                $has_lock = true;
+                break;
+            }
+            $max_wait_cycles--;
+            usleep(50000);
+        }
+
+        if (!$has_lock) {
+            fclose($fp);
+            throw new UnexpectedValueException('Could not aquire lock for ' . $path);
+        }
+
+        $content = (string) fread($fp, filesize($path));
+        fclose($fp);
+
+        return $content;
+    }
+
     public function writeToCache(ClassLikeStorage $storage, string $file_path, string $file_contents): void
     {
         $fq_classlike_name_lc = strtolower($storage->name);
@@ -86,9 +122,9 @@ public function writeToCache(ClassLikeStorage $storage, string $file_path, strin
 
         $cache_location = $this->getCacheLocationForClass($fq_classlike_name_lc, $file_path, true);
         if ($this->config->use_igbinary) {
-            file_put_contents($cache_location, igbinary_serialize($storage));
+            file_put_contents($cache_location, igbinary_serialize($storage), LOCK_EX);
         } else {
-            file_put_contents($cache_location, serialize($storage));
+            file_put_contents($cache_location, serialize($storage), LOCK_EX);
         }
     }
 
@@ -132,7 +168,7 @@ private function loadFromCache(string $fq_classlike_name_lc, ?string $file_path)
 
         if (file_exists($cache_location)) {
             if ($this->config->use_igbinary) {
-                $storage = igbinary_unserialize((string)file_get_contents($cache_location));
+                $storage = igbinary_unserialize($this->safeFileGetContents($cache_location));
 
                 if ($storage instanceof ClassLikeStorage) {
                     return $storage;
@@ -141,7 +177,7 @@ private function loadFromCache(string $fq_classlike_name_lc, ?string $file_path)
                 return null;
             }
 
-            $storage = unserialize((string)file_get_contents($cache_location));
+            $storage = unserialize($this->safeFileGetContents($cache_location));
 
             if ($storage instanceof ClassLikeStorage) {
                 return $storage;