Make sure the cache is only reset once at a time

Signed-off-by: Julius Härtl <jus@bitgrid.net>

Author: juliusknorr

lib/private/Template/SCSSCacher.php

@@ -269,8 +269,8 @@ private function isCached(string $fileNameCSS, string $app) {
 	private function variablesChanged(): bool {
 		$injectedVariables = $this->getInjectedVariables();
 		if ($this->config->getAppValue('core', 'theming.variables') !== md5($injectedVariables)) {
-			$this->resetCache();
 			$this->config->setAppValue('core', 'theming.variables', md5($injectedVariables));
+			$this->resetCache();
 			return true;
 		}
 		return false;
@@ -364,6 +364,9 @@ private function cache(string $path, string $fileNameCSS, string $fileNameSCSS,
 	 * We need to regenerate all files when variables change
 	 */
 	public function resetCache() {
+		if (!$this->lockingCache->add('resetCache', 'locked!', 120)) {
+			return;
+		}
 		$this->injectedVariables = null;
 
 		// do not clear locks
@@ -381,6 +384,7 @@ public function resetCache() {
 			}
 		}
 		$this->logger->debug('SCSSCacher: css cache cleared!');
+		$this->lockingCache->remove('resetCache');
 	}
 
 	/**