fix: Introducing initializers for handling lock cleanup on start

RELEASE_NOTES.md

@@ -39,7 +39,17 @@ The following changes are relevant for v4 custom configs that replaced certain f
 - The `IdentityProviderFactory` inputs have been extended.
   - `/identity/handler/provider-factory/identity.json`
 - LDP components have slightly changed so the preference parser is in a separate config file.
-  - `/config/ldp/handler/*`
+  - `/ldp/handler/*`
+- Restructured the init configs.
+  - `/app/init/base/init.json`
+  - `/app/main/default.json`
+- Added lock cleanup on server start (and updated existing finalization).
+  - `/util/resource-locker/file.json`
+  - `/util/resource-locker/redis.json`
+- Updated finalizers.
+  - `/app/identity/handler/account-store/default.json` 
+  - `/identity/ownership/token.json`
+  - `/ldp/authorization/readers/access-checkers/agent-group.json`
 
 ### Interface changes
 These changes are relevant if you wrote custom modules for the server that depend on existing interfaces.
@@ -49,6 +59,12 @@ These changes are relevant if you wrote custom modules for the server that depen
 - Both `TemplateEngine` implementations now take a `baseUrl` parameter as input.
 - The `IdentityProviderFactory` and `ConvertingErrorHandler` now additionally take a `PreferenceParser` as input.
 - Error handlers now take the incoming HttpRequest as input instead of just the preferences.
+- Extended the initialization/finalization system:
+  * Introduced `Initializable` interface and `InitializableHandler` wrapper class.
+  * Introduced `Finalizer` abstract class and `FinalizableHandler` wrapper class.
+  * Changed type for `finalizer` attribute in `App` from `Finalizable` to `Finalizer` and updated the calling code in `App.stop()`.
+  * Removed the now obsolete `ParallelFinalizer` util class.
+- Added a lock cleanup on initialize for lock implementations `RedisLocker` and `FileSystemResourceLocker`.
 
 A new interface `SingleThreaded` has been added. This empty interface can be implemented to mark a component as not-threadsafe. When the CSS starts in multithreaded mode, it will error and halt if any SingleThreaded components are instantiated.
 

config/app/init/base/init.json

@@ -30,6 +30,7 @@
         "@id": "urn:solid-server:default:PrimarySequenceInitializer",
         "@type":"SequenceHandler",
         "handlers": [
+          { "@id": "urn:solid-server:default:CleanupInitializer"},
           { "@id": "urn:solid-server:default:BaseUrlVerifier" },
           { "@id": "urn:solid-server:default:PrimaryParallelInitializer" },
           { "@id": "urn:solid-server:default:SeededPodInitializer" },
@@ -53,6 +54,13 @@
           { "@id": "urn:solid-server:default:ServerInitializer" }
         ]
       }
+    },
+    {
+      "comment": "Initializers that need to cleanup or do anything else before something writes to the backend should be added here.",
+      "@id": "urn:solid-server:default:CleanupInitializer",
+      "@type":"SequenceHandler",
+      "handlers": [
+      ]
     }
   ]
 }

config/app/main/default.json

@@ -7,11 +7,11 @@
       "@type": "App",
       "initializer": { "@id": "urn:solid-server:default:Initializer" },
       "finalizer": {
-        "comment": "This is going to contain the list of finalizers that need to be called. These should be added in the configs where such classes are configured.",
-        "@id": "urn:solid-server:default:Finalizer",
-        "@type": "ParallelFinalizer",
-        "finalizers": [
-          { "@id": "urn:solid-server:default:ServerInitializer" }
+        "comment": "Is executed when the server is stopped.",
+        "@type": "SequenceHandler",
+        "handlers": [
+          { "@id": "urn:solid-server:default:Finalizer" },
+          { "@id": "urn:solid-server:default:CleanupFinalizer" }
         ]
       },
       "clusterManager": {
@@ -19,6 +19,24 @@
         "@type": "ClusterManager",
         "workers": { "@id": "urn:solid-server:default:variable:workers" }
        }
+    },
+    {
+      "comment": "This is going to contain the list of finalizers that need to be called. These should be added in the configs where such classes are configured.",
+      "@id": "urn:solid-server:default:Finalizer",
+      "@type": "ParallelHandler",
+      "handlers": [
+        {
+          "@type": "FinalizableHandler",
+          "finalizable": { "@id": "urn:solid-server:default:ServerInitializer" }
+        }
+      ]
+    },
+    {
+      "comment": "Finalizers that need to cleanup once no more data will be written to the backend should be added here.",
+      "@id": "urn:solid-server:default:CleanupFinalizer",
+      "@type":"SequenceHandler",
+      "handlers": [
+      ]
     }
   ]
 }

config/identity/handler/account-store/default.json

@@ -28,8 +28,13 @@
     {
       "comment": "Makes sure the expiring storage cleanup timer is stopped when the application needs to stop.",
       "@id": "urn:solid-server:default:Finalizer",
-      "@type": "ParallelFinalizer",
-      "finalizers": [ { "@id": "urn:solid-server:default:ExpiringForgotPasswordStorage" } ]
+      "@type": "ParallelHandler",
+      "handlers": [ 
+        { 
+          "@type": "FinalizableHandler",
+          "finalizable": { "@id": "urn:solid-server:default:ExpiringForgotPasswordStorage" }
+        }
+      ]
     }
   ]
 }

config/identity/ownership/token.json

@@ -21,8 +21,13 @@
     {
       "comment": "Makes sure the expiring storage cleanup timer is stopped when the application needs to stop.",
       "@id": "urn:solid-server:default:Finalizer",
-      "@type": "ParallelFinalizer",
-      "finalizers": [ { "@id": "urn:solid-server:default:ExpiringTokenStorage" } ]
+      "@type": "ParallelHandler",
+      "handlers": [ 
+        { 
+          "@type": "FinalizableHandler",
+          "finalizable": { "@id": "urn:solid-server:default:ExpiringTokenStorage" }
+        } 
+      ]
     }
   ]
 }

config/ldp/authorization/readers/access-checkers/agent-group.json

@@ -14,8 +14,13 @@
     {
       "comment": "Makes sure the expiring storage cleanup timer is stopped when the application needs to stop.",
       "@id": "urn:solid-server:default:Finalizer",
-      "@type": "ParallelFinalizer",
-      "finalizers": [ { "@id": "urn:solid-server:default:ExpiringAclCache" } ]
+      "@type": "ParallelHandler",
+      "handlers": [ 
+        { 
+          "@type": "FinalizableHandler",
+          "finalizable": { "@id": "urn:solid-server:default:ExpiringAclCache" }
+        } 
+      ]
     }
   ]
 }

config/util/resource-locker/file.json

@@ -22,11 +22,25 @@
       "expiration": 3000
     },
     {
-      "comment": "Makes sure the lock folder is cleared and delete when the application needs to stop.",
-      "@id": "urn:solid-server:default:Finalizer",
-      "@type": "ParallelFinalizer",
-      "finalizers": [
-        { "@id": "urn:solid-server:default:FileSystemResourceLocker" }
+      "@id": "urn:solid-server:default:CleanupInitializer",
+      "@type": "SequenceHandler",
+      "handlers": [
+        {
+          "comment": "Makes sure the FileSystemResourceLocker starts with a clean slate when the application is started.",
+          "@type": "InitializableHandler",
+          "initializable": { "@id": "urn:solid-server:default:FileSystemResourceLocker" }
+        }
+      ]
+    },
+    {
+      "@id": "urn:solid-server:default:CleanupFinalizer",
+      "@type": "SequenceHandler",
+      "handlers": [
+        {
+          "comment": "Makes sure the lock folder is removed when the application stops.",
+          "@type": "FinalizableHandler",
+          "finalizable": { "@id": "urn:solid-server:default:FileSystemResourceLocker" }
+        }
       ]
     }
   ]

config/util/resource-locker/redis.json

@@ -12,12 +12,24 @@
       "expiration": 3000
     },
     {
-      "comment": "Makes sure the redis connection is closed when the application needs to stop. Also deletes still-existing locks and counters.",
-      "@id": "urn:solid-server:default:Finalizer",
-      "@type": "ParallelFinalizer",
-      "finalizers": [
+      "@id": "urn:solid-server:default:CleanupInitializer",
+      "@type": "SequenceHandler",
+      "handlers": [
         {
-          "@id": "urn:solid-server:default:RedisLocker"
+          "comment": "Makes sure the RedisLocker starts with a clean slate when the application is started.",
+          "@type": "InitializableHandler",
+          "initializable": { "@id": "urn:solid-server:default:RedisLocker" }
+        }
+      ]
+    },
+    {
+      "@id": "urn:solid-server:default:CleanupFinalizer",
+      "@type": "SequenceHandler",
+      "handlers": [
+        {
+          "comment": "Makes sure the redis connection is closed when the application needs to stop. Also deletes still-existing locks and counters.",
+          "@type": "FinalizableHandler",
+          "finalizable": { "@id": "urn:solid-server:default:RedisLocker" }
         }
       ]
     }

package.json

@@ -57,6 +57,7 @@
     "release": "standard-version",
     "start": "node ./bin/server.js",
     "start:file": "node ./bin/server.js -c config/file.json -f ./data",
+    "start:file-no-setup": "node ./bin/server.js -c config/file-no-setup.json -f ./data",
     "test": "npm run test:ts && npm run jest",
     "test:deploy": "test/deploy/validate-configs.sh",
     "test:ts": "tsc -p test --noEmit",

src/index.ts

@@ -194,7 +194,8 @@ export * from './init/cluster/WorkerManager';
 
 // Init/Final
 export * from './init/final/Finalizable';
-export * from './init/final/ParallelFinalizer';
+export * from './init/final/FinalizableHandler';
+export * from './init/final/Finalizer';
 
 // Init/Setup
 export * from './init/setup/SetupHandler';
@@ -221,6 +222,8 @@ export * from './init/BaseUrlVerifier';
 export * from './init/CliResolver';
 export * from './init/ConfigPodInitializer';
 export * from './init/ContainerInitializer';
+export * from './init/Initializable';
+export * from './init/InitializableHandler';
 export * from './init/Initializer';
 export * from './init/LoggerInitializer';
 export * from './init/ModuleVersionVerifier';

src/init/App.ts

@@ -1,5 +1,5 @@
 import type { ClusterManager } from './cluster/ClusterManager';
-import type { Finalizable } from './final/Finalizable';
+import type { Finalizer } from './final/Finalizer';
 import type { Initializer } from './Initializer';
 
 /**
@@ -7,10 +7,10 @@ import type { Initializer } from './Initializer';
  */
 export class App {
   private readonly initializer: Initializer;
-  private readonly finalizer: Finalizable;
+  private readonly finalizer: Finalizer;
   public readonly clusterManager: ClusterManager;
 
-  public constructor(initializer: Initializer, finalizer: Finalizable, clusterManager: ClusterManager) {
+  public constructor(initializer: Initializer, finalizer: Finalizer, clusterManager: ClusterManager) {
     this.initializer = initializer;
     this.finalizer = finalizer;
     this.clusterManager = clusterManager;
@@ -27,6 +27,6 @@ export class App {
    * Stops the application and handles cleanup.
    */
   public async stop(): Promise<void> {
-    await this.finalizer.finalize();
+    await this.finalizer.handleSafe();
   }
 }

src/init/Initializable.ts

@@ -0,0 +1,8 @@
+/**
+ * Allows for initializing state or executing logic when the application is started.
+ * Use this interface to add initialization logic to classes that already extend some other type.
+ * NOTE: classes without an existing extends-relation should extend from Initializer instead!
+ */
+export interface Initializable {
+  initialize: () => Promise<void>;
+}

src/init/InitializableHandler.ts

@@ -0,0 +1,18 @@
+import type { Initializable } from './Initializable';
+import { Initializer } from './Initializer';
+
+/**
+ * Allows using an Initializable as an Initializer Handler.
+ */
+export class InitializableHandler extends Initializer {
+  protected readonly initializable: Initializable;
+
+  public constructor(initializable: Initializable) {
+    super();
+    this.initializable = initializable;
+  }
+
+  public async handle(): Promise<void> {
+    return this.initializable.initialize();
+  }
+}

src/init/Initializer.ts

@@ -1,3 +1,6 @@
 import { AsyncHandler } from '../util/handlers/AsyncHandler';
 
+/**
+ * Initializer is used to indicate an AsyncHandler that performs initialization logic.
+ */
 export abstract class Initializer extends AsyncHandler {}

src/init/final/Finalizable.ts

@@ -1,5 +1,7 @@
 /**
  * Allows for cleaning up an object and stopping relevant loops when the application needs to be stopped.
+ * Use this interface to add finalization logic to classes that already extend some other type.
+ * NOTE: classes without an existing extends-relation should extend from Finalizer instead!
  */
 export interface Finalizable {
   finalize: () => Promise<void>;

src/init/final/FinalizableHandler.ts

@@ -0,0 +1,18 @@
+import type { Finalizable } from './Finalizable';
+import { Finalizer } from './Finalizer';
+
+/**
+ * Allows using a Finalizable as a Finalizer Handler.
+ */
+export class FinalizableHandler extends Finalizer {
+  protected readonly finalizable: Finalizable;
+
+  public constructor(finalizable: Finalizable) {
+    super();
+    this.finalizable = finalizable;
+  }
+
+  public async handle(): Promise<void> {
+    return this.finalizable.finalize();
+  }
+}

src/init/final/Finalizer.ts

@@ -0,0 +1,6 @@
+import { AsyncHandler } from '../../util/handlers/AsyncHandler';
+
+/**
+ * Finalizer is used to indicate an AsyncHandler that performs finalization logic.
+ */
+export abstract class Finalizer extends AsyncHandler {}

src/init/final/ParallelFinalizer.ts

@@ -1,16 +0,0 @@
-import type { Finalizable } from './Finalizable';
-
-/**
- * Finalizes all the injected Finalizable classes in parallel.
- */
-export class ParallelFinalizer implements Finalizable {
-  private readonly finalizers: Finalizable[];
-
-  public constructor(finalizers: Finalizable[] = []) {
-    this.finalizers = finalizers;
-  }
-
-  public async finalize(): Promise<void> {
-    await Promise.all(this.finalizers.map(async(finalizer): Promise<void> => finalizer.finalize()));
-  }
-}

src/util/locking/FileSystemResourceLocker.ts

@@ -1,9 +1,10 @@
 import { createHash } from 'crypto';
-import { ensureDirSync, pathExists, readdir, rmdir } from 'fs-extra';
+import { ensureDir, remove } from 'fs-extra';
 import type { LockOptions, UnlockOptions } from 'proper-lockfile';
 import { lock, unlock } from 'proper-lockfile';
 import type { ResourceIdentifier } from '../../http/representation/ResourceIdentifier';
 import type { Finalizable } from '../../init/final/Finalizable';
+import type { Initializable } from '../../init/Initializable';
 import { getLoggerFor } from '../../logging/LogUtil';
 import { createErrorMessage } from '../errors/ErrorUtil';
 import { InternalServerError } from '../errors/InternalServerError';
@@ -34,9 +35,12 @@ const attemptDefaults: Required<AttemptSettings> = { retryCount: -1, retryDelay:
  * Argument interface of the FileSystemResourceLocker constructor.
  */
 interface FileSystemResourceLockerArgs {
-  /** The rootPath of the filesystem */
+  /** The rootPath of the filesystem _[default is the current dir `./`]_ */
   rootFilePath?: string;
-  /** The path to the directory where locks will be stored (appended to rootFilePath) */
+  /**
+   * The path to the directory where locks will be stored (appended to rootFilePath)
+   * _[default is `/.internal/locks`]_
+   */
   lockDirectory?: string;
   /** Custom settings concerning retrying locks */
   attemptSettings?: AttemptSettings;
@@ -54,24 +58,22 @@ function isCodedError(err: unknown): err is { code: string } & Error {
  * either resolve successfully or reject immediately with the causing error. The retry function of the library
  * however will be ignored and replaced by our own LockUtils' {@link retryFunctionUntil} function.
  */
-export class FileSystemResourceLocker implements ResourceLocker, Finalizable {
+export class FileSystemResourceLocker implements ResourceLocker, Initializable, Finalizable {
   protected readonly logger = getLoggerFor(this);
   private readonly attemptSettings: Required<AttemptSettings>;
   /** Folder that stores the locks */
   private readonly lockFolder: string;
+  private finalized = false;
 
   /**
    * Create a new FileSystemResourceLocker
-   * @param rootFilePath - The rootPath of the filesystem _[default is the current dir `./`]_
-   * @param lockDirectory - The path to the directory where locks will be stored (appended to rootFilePath)
-                            _[default is `/.internal/locks`]_
-   * @param attemptSettings - Custom settings concerning retrying locks
+   * @param args - Configures the locker using the specified FileSystemResourceLockerArgs instance.
    */
   public constructor(args: FileSystemResourceLockerArgs = {}) {
     const { rootFilePath, lockDirectory, attemptSettings } = args;
+    defaultLockOptions.onCompromised = this.customOnCompromised.bind(this);
     this.attemptSettings = { ...attemptDefaults, ...attemptSettings };
     this.lockFolder = joinFilePath(rootFilePath ?? './', lockDirectory ?? '/.internal/locks');
-    ensureDirSync(this.lockFolder);
   }
 
   /**
@@ -149,13 +151,36 @@ export class FileSystemResourceLocker implements ResourceLocker, Finalizable {
     };
   }
 
+  /**
+   * Initializer method to be executed on server start. This makes sure that no pre-existing (dangling) locks
+   * remain on disk, so that request will not be blocked because a lock was acquired in the previous server instance.
+   *
+   * NOTE: this also removes locks created by the GreedyReadWriteLocker.
+   * (See issue: https://github.com/CommunitySolidServer/CommunitySolidServer/issues/1358)
+   */
+  public async initialize(): Promise<void> {
+    // Remove all existing (dangling) locks so new requests are not blocked (by removing the lock folder).
+    await remove(this.lockFolder);
+    // Put the folder back since `proper-lockfile` depends on its existence.
+    return ensureDir(this.lockFolder);
+  }
+
   public async finalize(): Promise<void> {
-    // Delete lingering locks in the lockFolder.
-    if (await pathExists(this.lockFolder)) {
-      for (const dir of await readdir(this.lockFolder)) {
-        await rmdir(joinFilePath(this.lockFolder, dir));
-      }
-      await rmdir(this.lockFolder);
+    // Register that finalize was called by setting a state variable.
+    this.finalized = true;
+    // NOTE: in contrast with initialize(), the lock folder is not cleared here, as the proper-lock library
+    // manages these files and will attempt to clear existing files when the process is shutdown gracefully.
   }
+
+  /**
+   * This function is used to override the proper-lock onCompromised function.
+   * Once the locker was finalized, it will log the provided error instead of throwing it
+   * This allows for a clean shutdown procedure.
+   */
+  private customOnCompromised(err: any): void {
+    if (!this.finalized) {
+      throw err;
+    }
+    this.logger.warn(`onCompromised was called with error: ${err.message}`);
   }
 }

src/util/locking/RedisLocker.ts

@@ -1,6 +1,7 @@
 import Redis from 'ioredis';
 import type { ResourceIdentifier } from '../../http/representation/ResourceIdentifier';
 import type { Finalizable } from '../../init/final/Finalizable';
+import type { Initializable } from '../../init/Initializable';
 import { getLoggerFor } from '../../logging/LogUtil';
 import type { AttemptSettings } from '../LockUtils';
 import { retryFunction } from '../LockUtils';
@@ -42,13 +43,14 @@ const PREFIX_LOCK = '__L__';
  * * @see [Redis Lua scripting documentation](https://redis.io/docs/manual/programmability/)
  * * @see [ioredis Lua scripting API](https://github.com/luin/ioredis#lua-scripting)
  */
-export class RedisLocker implements ReadWriteLocker, ResourceLocker, Finalizable {
+export class RedisLocker implements ReadWriteLocker, ResourceLocker, Initializable, Finalizable {
   protected readonly logger = getLoggerFor(this);
 
   private readonly redis: Redis;
   private readonly redisRw: RedisReadWriteLock;
   private readonly redisLock: RedisResourceLock;
   private readonly attemptSettings: Required<AttemptSettings>;
+  private finalized = false;
 
   public constructor(redisClient = '127.0.0.1:6379', attemptSettings: AttemptSettings = {}) {
     this.redis = this.createRedisClient(redisClient);
@@ -113,6 +115,9 @@ export class RedisLocker implements ReadWriteLocker, ResourceLocker, Finalizable
    * @param fn - The function reference to swallow false from.
    */
   private swallowFalse(fn: () => Promise<RedisAnswer>): () => Promise<unknown> {
+    if (this.finalized) {
+      throw new Error('Invalid state: cannot execute Redis operation once finalize() has been called.');
+    }
     return async(): Promise<unknown> => {
       const result = await fromResp2ToBool(fn());
       // Swallow any result resolving to `false`
@@ -172,13 +177,28 @@ export class RedisLocker implements ReadWriteLocker, ResourceLocker, Finalizable
     );
   }
 
-  /* Finalizer methods */
+  /* Initializer & Finalizer methods */
+
+  public async initialize(): Promise<void> {
+    // On server start: remove all existing (dangling) locks, so new requests are not blocked.
+    return this.clearLocks();
+  }
 
   public async finalize(): Promise<void> {
-    // This for loop is an extra failsafe,
-    // this extra code won't slow down anything, this function will only be called to shut down in peace
+    this.finalized = true;
     try {
-      // Remove any lock still open, since once closed, they should no longer be held.
+      // On controlled server shutdown: clean up all existing locks.
+      return await this.clearLocks();
+    } finally {
+      // Always quit the redis client
+      await this.redis.quit();
+    }
+  }
+
+  /**
+   * Remove any lock still open
+   */
+  private async clearLocks(): Promise<void> {
     const keysRw = await this.redisRw.keys(`${PREFIX_RW}*`);
     if (keysRw.length > 0) {
       await this.redisRw.del(...keysRw);
@@ -188,8 +208,5 @@ export class RedisLocker implements ReadWriteLocker, ResourceLocker, Finalizable
     if (keysLock.length > 0) {
       await this.redisLock.del(...keysLock);
     }
-    } finally {
-      await this.redis.quit();
-    }
   }
 }

test/integration/RedisLocker.test.ts

@@ -10,7 +10,7 @@ import { getDefaultVariables, getTestConfigPath, instantiateFromConfig } from '.
 /**
  * Test the general functionality of the server using a RedisLocker with Read-Write strategy.
  */
-describeIf('docker', 'A server with a RedisLocker', (): void => {
+describeIf('docker')('A server with a RedisLocker', (): void => {
   const port = getPort('RedisLocker');
   const baseUrl = `http://localhost:${port}/`;
   let app: App;

test/integration/ResourceLockCleanup.test.ts

@@ -0,0 +1,84 @@
+import fetch from 'cross-fetch';
+import type { App, DataAccessorBasedStore, Initializable, ResourceLocker } from '../../src';
+import { readableToString, BasicRepresentation } from '../../src';
+import { describeIf, getPort } from '../util/Util';
+import { getDefaultVariables, getTestConfigPath, getTestFolder, instantiateFromConfig, removeFolder } from './Config';
+
+const port = getPort('ResourceLockCleanup');
+const baseUrl = `http://localhost:${port}/`;
+const rootFilePath = getTestFolder(`resource-lock-cleanup`);
+const resourceIdentifier = { path: `${baseUrl}container1/test.txt` };
+
+const configs: [string, any][] = [
+  [
+    'file-based', {
+      config: 'server-file.json',
+      init: async(initializable: Initializable): Promise<void> => initializable.initialize(),
+      teardown: async(): Promise<void> => removeFolder(rootFilePath),
+    }],
+  [
+    'redis-based', {
+      config: 'server-redis-lock.json',
+      init: jest.fn(),
+      teardown: jest.fn(),
+    }],
+];
+
+describeIf('docker').each(configs)('A server using %s locking', (id, { config, init, teardown }):
+void => {
+  let app: App;
+  let store: DataAccessorBasedStore;
+  let locker: ResourceLocker;
+
+  beforeAll(async(): Promise<void> => {
+    const variables = {
+      ...getDefaultVariables(port, baseUrl),
+      'urn:solid-server:default:variable:rootFilePath': rootFilePath,
+    };
+
+    // Create the server
+    const instances = await instantiateFromConfig(
+      'urn:solid-server:test:Instances',
+      [
+        getTestConfigPath(config),
+      ],
+      variables,
+    ) as Record<string, any>;
+    ({ app, store, locker } = instances);
+    // Create the test resource
+    await store.setRepresentation(resourceIdentifier, new BasicRepresentation('abc', 'text/plain'));
+
+    // Perform additional initialization, if configured
+    await init(locker);
+  });
+
+  afterAll(async(): Promise<void> => {
+    // Stop the server
+    await app.stop();
+
+    // Execute the configured teardown
+    await teardown();
+  });
+
+  it('should not be affected by dangling locks.', async(): Promise<void> => {
+    // Simulate lock existing before server startup, by creating a (write) lock directly
+    await locker.acquire({ path: `${resourceIdentifier.path}.write` });
+    // Start the server
+    await app.start();
+
+    // Updating the resource should succeed (if the server clears dangling locks on startup).
+    const updatedContent = 'def';
+    const result = await fetch(resourceIdentifier.path, {
+      method: 'PUT',
+      headers: {
+        'content-type': 'text/plain',
+      },
+      body: updatedContent,
+    });
+    expect(result.status).toBe(205);
+    // Check if the resource was updated:
+    const representation = await store.getRepresentation(resourceIdentifier);
+    const data = await readableToString(representation.data);
+    expect(data).toEqual(updatedContent);
+  });
+});

test/integration/SparqlStorage.test.ts

@@ -8,7 +8,7 @@ import { getDefaultVariables, getPresetConfigPath, getTestConfigPath, instantiat
 const port = getPort('SparqlStorage');
 const baseUrl = `http://localhost:${port}/`;
 
-describeIf('docker', 'A server with a SPARQL endpoint as storage', (): void => {
+describeIf('docker')('A server with a SPARQL endpoint as storage', (): void => {
   let app: App;
 
   beforeAll(async(): Promise<void> => {

test/integration/config/server-file.json

@@ -27,17 +27,25 @@
     "css:config/util/index/default.json",
     "css:config/util/logging/winston.json",
     "css:config/util/representation-conversion/default.json",
-    "css:config/util/resource-locker/memory.json",
+    "css:config/util/resource-locker/file.json",
     "css:config/util/variables/default.json"
   ],
   "@graph": [
     {
       "@id": "urn:solid-server:test:Instances",
       "@type": "RecordObject",
-      "RecordObject:_record": [
+      "record": [
         {
           "RecordObject:_record_key": "app",
           "RecordObject:_record_value": { "@id": "urn:solid-server:default:App" }
+        },
+        {
+          "RecordObject:_record_key": "store",
+          "RecordObject:_record_value": { "@id": "urn:solid-server:default:ResourceStore_Backend" }
+        },
+        {
+          "RecordObject:_record_key": "locker",
+          "RecordObject:_record_value": { "@id": "urn:solid-server:default:FileSystemResourceLocker" }
         }
       ]
     },

test/integration/config/server-redis-lock.json

@@ -38,6 +38,10 @@
           "RecordObject:_record_key": "app",
           "RecordObject:_record_value": { "@id": "urn:solid-server:default:App" }
         },
+        {
+          "RecordObject:_record_key": "store",
+          "RecordObject:_record_value": { "@id": "urn:solid-server:default:ResourceStore_Backend" }
+        },
         {
           "RecordObject:_record_key": "locker",
           "RecordObject:_record_value": { "@id": "urn:solid-server:default:RedisLocker" }

test/unit/init/App.test.ts

@@ -1,17 +1,17 @@
 import type { ClusterManager } from '../../../src';
 import { App } from '../../../src/init/App';
-import type { Finalizable } from '../../../src/init/final/Finalizable';
+import type { Finalizer } from '../../../src/init/final/Finalizer';
 import type { Initializer } from '../../../src/init/Initializer';
 
 describe('An App', (): void => {
   let initializer: Initializer;
-  let finalizer: Finalizable;
+  let finalizer: Finalizer;
   let clusterManager: ClusterManager;
   let app: App;
 
   beforeEach(async(): Promise<void> => {
     initializer = { handleSafe: jest.fn() } as any;
-    finalizer = { finalize: jest.fn() };
+    finalizer = { handleSafe: jest.fn() } as any;
     clusterManager = {} as any;
     app = new App(initializer, finalizer, clusterManager);
   });
@@ -23,7 +23,7 @@ describe('An App', (): void => {
 
   it('can stop with the finalizer.', async(): Promise<void> => {
     await expect(app.stop()).resolves.toBeUndefined();
-    expect(finalizer.finalize).toHaveBeenCalledTimes(1);
+    expect(finalizer.handleSafe).toHaveBeenCalledTimes(1);
   });
 
   it('can check its clusterManager for the threading mode.', async(): Promise<void> => {

test/unit/init/InitializableHandler.test.ts

@@ -0,0 +1,11 @@
+import { InitializableHandler } from '../../../src';
+
+describe('InitializableHandler', (): void => {
+  const initializable = { initialize: jest.fn() };
+  const initializer = new InitializableHandler(initializable);
+
+  it('redirects handle towards initialize.', async(): Promise<void> => {
+    await initializer.handleSafe();
+    expect(initializable.initialize).toHaveBeenCalledTimes(1);
+  });
+});

test/unit/init/final/FinalizableHandler.test.ts

@@ -0,0 +1,11 @@
+import { FinalizableHandler } from '../../../../src';
+
+describe('FinalizableHandler', (): void => {
+  const finalizable = { finalize: jest.fn() };
+  const finalizer = new FinalizableHandler(finalizable);
+
+  it('redirects handle towards finalize.', async(): Promise<void> => {
+    await finalizer.handleSafe();
+    expect(finalizable.finalize).toHaveBeenCalledTimes(1);
+  });
+});

test/unit/init/final/ParallelFinalizer.test.ts

@@ -1,30 +0,0 @@
-import type { Finalizable } from '../../../../src/init/final/Finalizable';
-import { ParallelFinalizer } from '../../../../src/init/final/ParallelFinalizer';
-
-describe('A ParallelFinalizer', (): void => {
-  let finalizers: Finalizable[];
-  let finalizer: ParallelFinalizer;
-  let results: number[];
-
-  beforeEach(async(): Promise<void> => {
-    results = [];
-    finalizers = [
-      { finalize: jest.fn((): any => results.push(0)) },
-      { finalize: jest.fn((): any => results.push(1)) },
-    ];
-
-    finalizer = new ParallelFinalizer(finalizers);
-  });
-
-  it('is finished when all finalizers are finished.', async(): Promise<void> => {
-    await expect(finalizer.finalize()).resolves.toBeUndefined();
-    expect(finalizers[0].finalize).toHaveBeenCalledTimes(1);
-    expect(finalizers[1].finalize).toHaveBeenCalledTimes(1);
-    expect(results).toEqual([ 0, 1 ]);
-  });
-
-  it('works if there are no input finalizers.', async(): Promise<void> => {
-    finalizer = new ParallelFinalizer();
-    await expect(finalizer.finalize()).resolves.toBeUndefined();
-  });
-});

test/unit/util/locking/FileSystemResourceLocker.test.ts

@@ -1,6 +1,5 @@
 import { readdir } from 'fs-extra';
-import { InternalServerError } from '../../../../src/util/errors/InternalServerError';
-import { FileSystemResourceLocker } from '../../../../src/util/locking/FileSystemResourceLocker';
+import { InternalServerError, FileSystemResourceLocker } from '../../../../src';
 
 const lockFolder = './.internal/locks/';
 
@@ -10,6 +9,7 @@ describe('A FileSystemResourceLocker', (): void => {
 
   beforeEach(async(): Promise<void> => {
     locker = new FileSystemResourceLocker({ attemptSettings: { retryCount: 19, retryDelay: 100 }});
+    await locker.initialize();
   });
 
   afterEach(async(): Promise<void> => {
@@ -109,11 +109,18 @@ describe('A FileSystemResourceLocker', (): void => {
     await expect(locker.acquire(identifier)).rejects.toThrow(InternalServerError);
   });
 
-  it('clears the files in de lock directory after calling finalize.', async(): Promise<void> => {
+  it('clears the files in de lock directory upon calling initialize.', async(): Promise<void> => {
     await locker.acquire(identifier);
     await expect(readdir(lockFolder)).resolves.toHaveLength(1);
+    await locker.initialize();
+    await expect(readdir(lockFolder)).resolves.toHaveLength(0);
+  });
+
+  it('stops proper-lock from throwing errors onCompromise after finalize was called.',
+    async(): Promise<void> => {
+      expect((): void => (locker as any).customOnCompromised(new Error('test'))).toThrow();
       await locker.finalize();
-    await expect(readdir(lockFolder)).rejects.toThrow();
+      expect((locker as any).customOnCompromised(new Error('test'))).toBeUndefined();
     });
 
   it('can create a locker with default AttemptSettings.', async(): Promise<void> => {

test/unit/util/locking/RedisLocker.test.ts

@@ -70,8 +70,20 @@ const store = {
 const redis: jest.Mocked<Redis & RedisResourceLock & RedisReadWriteLock> = {
   defineCommand: jest.fn(),
   quit: jest.fn(),
-  keys: jest.fn().mockResolvedValue([]),
-  del: jest.fn(),
+  keys: jest.fn().mockImplementation(async(pattern: string): Promise<string[]> =>
+    Object.keys(store.internal)
+      .filter((value: string): boolean => new RegExp(pattern, 'u').test(value))),
+  del: jest.fn().mockImplementation(async(...keys: string[]): Promise<number> => {
+    let deletedEntries = 0;
+    for (const key of keys) {
+      if (typeof store.internal[key] !== 'undefined') {
+        deletedEntries += 1;
+      }
+      // eslint-disable-next-line @typescript-eslint/no-dynamic-delete
+      delete store.internal[key];
+    }
+    return deletedEntries;
+  }),
   acquireReadLock: jest.fn().mockImplementation(async(key: string): Promise<number> =>
     store.acquireReadLock(key)),
   acquireWriteLock: jest.fn().mockImplementation(async(key: string): Promise<number | null | 'OK'> =>
@@ -407,29 +419,14 @@ describe('A RedisLocker', (): void => {
     });
 
     describe('finalize()', (): void => {
-      it('should quit when there are no more keys when finalize() is called.', async(): Promise<void> => {
-      // This works since the Redis is simply a mock and quit should have cleared the internal store
-        await locker.withWriteLock(resource1, async(): Promise<any> => {
-          await locker.finalize();
-          expect(redis.quit).toHaveBeenCalledTimes(1);
-        });
-      });
-      it('should clear all lock keys when finalize() is called.', async(): Promise<void> => {
-        redis.keys.mockResolvedValueOnce([ '__L__k1', '__L__k2' ]);
-        // This works since the Redis is simply a mock and quit should have cleared the internal store
-        await locker.withWriteLock(resource1, async(): Promise<any> => {
-          await locker.finalize();
-          expect(redis.quit).toHaveBeenCalledTimes(1);
-        });
-      });
-
-      it('should clear all rw keys when finalize() is called.', async(): Promise<void> => {
-        redis.keys.mockResolvedValueOnce([ '__RW__k1', '__RW__k2' ]);
-        // This works since the Redis is simply a mock and quit should have cleared the internal store
-        await locker.withWriteLock(resource1, async(): Promise<any> => {
+      it('should call quit and clear Read-Write locks when finalize() is called.', async(): Promise<void> => {
+        const promise = locker.withWriteLock(resource1, async(): Promise<any> => {
           await locker.finalize();
+          expect(Object.keys(store.internal)).toHaveLength(0);
           expect(redis.quit).toHaveBeenCalledTimes(1);
         });
+        // Auto-release of Read-Write lock should result in an exception, as the Locker has been finalized.
+        await expect(promise).rejects.toThrow(/Invalid state/u);
       });
     });
   });
@@ -521,17 +518,27 @@ describe('A RedisLocker', (): void => {
       });
     });
 
+    describe('initialize()', (): void => {
+      it('should clear all locks when initialize() is called.', async(): Promise<void> => {
+        await locker.acquire({ path: 'path1' });
+        await locker.acquire({ path: 'path2' });
+        await locker.initialize();
+        expect(Object.keys(store.internal)).toHaveLength(0);
+      });
+    });
+
     describe('finalize()', (): void => {
       it('should clear all locks (even when empty) when finalize() is called.', async(): Promise<void> => {
         await locker.finalize();
+        expect(Object.keys(store.internal)).toHaveLength(0);
         expect(redis.quit).toHaveBeenCalledTimes(1);
       });
 
       it('should clear all locks when finalize() is called.', async(): Promise<void> => {
-        redis.keys
-          .mockResolvedValueOnce([ '__L__k1', '__L__k2' ])
-          .mockResolvedValueOnce([ '__L__k1', '__L__k2' ]);
+        await locker.acquire({ path: 'path1' });
+        await locker.acquire({ path: 'path2' });
         await locker.finalize();
+        expect(Object.keys(store.internal)).toHaveLength(0);
         expect(redis.quit).toHaveBeenCalledTimes(1);
       });
     });

test/util/Util.ts

@@ -1,6 +1,7 @@
 import type { Dirent, Stats } from 'fs';
 import { PassThrough, Readable } from 'stream';
 import type { SystemError } from '../../src/util/errors/SystemError';
+import Describe = jest.Describe;
 
 const portNames = [
   // Integration
@@ -19,6 +20,7 @@ const portNames = [
   'PodCreation',
   'PodQuota',
   'RedisLocker',
+  'ResourceLockCleanup',
   'RestrictedIdentity',
   'SeedingPods',
   'ServerFetch',
@@ -40,11 +42,10 @@ export function getPort(name: typeof portNames[number]): number {
   return 6000 + idx;
 }
 
-export function describeIf(envFlag: string, name: string, fn: () => void): void {
+export function describeIf(envFlag: string): Describe {
   const flag = `TEST_${envFlag.toUpperCase()}`;
   const enabled = !/^(|0|false)$/iu.test(process.env[flag] ?? '');
-  // eslint-disable-next-line jest/valid-describe-callback, jest/valid-title, jest/no-disabled-tests
-  return enabled ? describe(name, fn) : describe.skip(name, fn);
+  return enabled ? describe : describe.skip;
 }
 
 /**