Introducing PCC locking for DBTransaction

Author: CMCDragonkai

package-lock.json

@@ -28,9 +28,9 @@
   },
   "dependencies": {
     "@matrixai/async-init": "^1.8.1",
-    "@matrixai/async-locks": "^2.3.1",
+    "@matrixai/async-locks": "^3.0.0",
     "@matrixai/errors": "^1.1.2",
-    "@matrixai/logger": "^2.2.2",
+    "@matrixai/logger": "^2.3.0",
     "@matrixai/resources": "^1.1.3",
     "@matrixai/workers": "^1.3.3",
     "node-gyp-build": "4.4.0",

package.json

@@ -1,4 +1,5 @@
 import type { ResourceAcquire } from '@matrixai/resources';
+import type { RWLockWriter } from '@matrixai/async-locks';
 import type {
   KeyPath,
   LevelPath,
@@ -20,6 +21,7 @@ import {
   CreateDestroyStartStop,
   ready,
 } from '@matrixai/async-init/dist/CreateDestroyStartStop';
+import { LockBox } from '@matrixai/async-locks';
 import DBIterator from './DBIterator';
 import DBTransaction from './DBTransaction';
 import { rocksdbP } from './rocksdb';
@@ -69,6 +71,7 @@ class DB {
   protected fs: FileSystem;
   protected logger: Logger;
   protected workerManager?: DBWorkerManagerInterface;
+  protected _lockBox: LockBox<RWLockWriter> = new LockBox();
   protected _db: RocksDBDatabase;
   /**
    * References to iterators
@@ -97,6 +100,10 @@ class DB {
     return this._transactionRefs;
   }
 
+  get lockBox(): Readonly<LockBox<RWLockWriter>> {
+    return this._lockBox;
+  }
+
   constructor({
     dbPath,
     crypto,
@@ -193,6 +200,7 @@ class DB {
     return async () => {
       const tran = new DBTransaction({
         db: this,
+        lockBox: this._lockBox,
         logger: this.logger,
       });
       return [

src/DB.ts

@@ -1,10 +1,17 @@
+import type { ResourceRelease } from '@matrixai/resources';
+import type {
+  LockBox,
+  MultiLockRequest as AsyncLocksMultiLockRequest,
+} from '@matrixai/async-locks';
 import type DB from './DB';
 import type {
+  ToString,
   KeyPath,
   LevelPath,
   DBIteratorOptions,
   DBClearOptions,
   DBCountOptions,
+  MultiLockRequest,
 } from './types';
 import type {
   RocksDBTransaction,
@@ -13,6 +20,7 @@ import type {
 } from './rocksdb/types';
 import Logger from '@matrixai/logger';
 import { CreateDestroy, ready } from '@matrixai/async-init/dist/CreateDestroy';
+import { RWLockWriter } from '@matrixai/async-locks';
 import DBIterator from './DBIterator';
 import { rocksdbP } from './rocksdb';
 import * as utils from './utils';
@@ -21,37 +29,44 @@ import * as errors from './errors';
 interface DBTransaction extends CreateDestroy {}
 @CreateDestroy()
 class DBTransaction {
+  public readonly id: number;
+
   protected _db: DB;
   protected logger: Logger;
-
+  protected lockBox: LockBox<RWLockWriter>;
+  protected _locks: Map<
+    string,
+    {
+      lock: RWLockWriter;
+      type: 'read' | 'write';
+      release: ResourceRelease;
+    }
+  > = new Map();
   protected _options: RocksDBTransactionOptions;
   protected _transaction: RocksDBTransaction;
-  protected _id: number;
   protected _snapshot: RocksDBTransactionSnapshot;
-
+  protected _iteratorRefs: Set<DBIterator<any, any>> = new Set();
   protected _callbacksSuccess: Array<() => any> = [];
   protected _callbacksFailure: Array<(e?: Error) => any> = [];
   protected _callbacksFinally: Array<(e?: Error) => any> = [];
   protected _committed: boolean = false;
   protected _rollbacked: boolean = false;
 
-  /**
-   * References to iterators
-   */
-  protected _iteratorRefs: Set<DBIterator<any, any>> = new Set();
-
   public constructor({
     db,
+    lockBox,
     logger,
     ...options
   }: {
     db: DB;
+    lockBox: LockBox<RWLockWriter>;
     logger?: Logger;
   } & RocksDBTransactionOptions) {
     logger = logger ?? new Logger(this.constructor.name);
     logger.debug(`Constructing ${this.constructor.name}`);
     this.logger = logger;
     this._db = db;
+    this.lockBox = lockBox;
     const options_ = {
       ...options,
       // Transactions should be synchronous
@@ -61,21 +76,24 @@ class DBTransaction {
     this._options = options_;
     this._transaction = rocksdbP.transactionInit(db.db, options_);
     db.transactionRefs.add(this);
-    this._id = rocksdbP.transactionId(this._transaction);
-    logger.debug(`Constructed ${this.constructor.name} ${this._id}`);
+    this.id = rocksdbP.transactionId(this._transaction);
+    logger.debug(`Constructed ${this.constructor.name} ${this.id}`);
   }
 
   /**
    * Destroy the transaction
    * This cannot be called until the transaction is committed or rollbacked
    */
   public async destroy() {
-    this.logger.debug(`Destroying ${this.constructor.name} ${this._id}`);
-    this._db.transactionRefs.delete(this);
+    this.logger.debug(`Destroying ${this.constructor.name} ${this.id}`);
     if (!this._committed && !this._rollbacked) {
       throw new errors.ErrorDBTransactionNotCommittedNorRollbacked();
     }
-    this.logger.debug(`Destroyed ${this.constructor.name} ${this._id}`);
+    this._db.transactionRefs.delete(this);
+    // Unlock all locked keys in reverse
+    const lockedKeys = [...this._locks.keys()].reverse();
+    await this.unlock(...lockedKeys);
+    this.logger.debug(`Destroyed ${this.constructor.name} ${this.id}`);
   }
 
   get db(): Readonly<DB> {
@@ -86,17 +104,6 @@ class DBTransaction {
     return this._transaction;
   }
 
-  get id(): number {
-    return this._id;
-  }
-
-  /**
-   * @internal
-   */
-  get iteratorRefs(): Readonly<Set<DBIterator<any, any>>> {
-    return this._iteratorRefs;
-  }
-
   get callbacksSuccess(): Readonly<Array<() => any>> {
     return this._callbacksSuccess;
   }
@@ -117,6 +124,98 @@ class DBTransaction {
     return this._rollbacked;
   }
 
+  get locks(): ReadonlyMap<
+    string,
+    {
+      lock: RWLockWriter;
+      type: 'read' | 'write';
+      release: ResourceRelease;
+    }
+  > {
+    return this._locks;
+  }
+
+  /**
+   * @internal
+   */
+  get iteratorRefs(): Readonly<Set<DBIterator<any, any>>> {
+    return this._iteratorRefs;
+  }
+
+  /**
+   * Lock a sequence of lock requests
+   * If the lock request doesn't specify, it
+   * defaults to using `RWLockWriter` with `write` type
+   * Keys are locked in string sorted order
+   * Even though keys can be arbitrary strings, by convention, you should use
+   * keys that correspond to keys in the database
+   * Locking with the same key is idempotent therefore lock re-entrancy is enabled
+   * Keys are automatically unlocked in reverse sorted order
+   * when the transaction is destroyed
+   * There is no support for lock upgrading or downgrading
+   * There is no deadlock detection
+   */
+  public async lock(
+    ...requests: Array<MultiLockRequest | string>
+  ): Promise<void> {
+    const requests_: Array<AsyncLocksMultiLockRequest<RWLockWriter>> = [];
+    for (const request of requests) {
+      if (Array.isArray(request)) {
+        const [key, ...lockingParams] = request;
+        const key_ = key.toString();
+        const lock = this._locks.get(key_);
+        // Default the lock type to `write`
+        const lockType = (lockingParams[0] = lockingParams[0] ?? 'write');
+        if (lock == null) {
+          requests_.push([key_, RWLockWriter, ...lockingParams]);
+        } else if (lock.type !== lockType) {
+          throw new errors.ErrorDBTransactionLockType();
+        }
+      } else {
+        const key_ = request.toString();
+        const lock = this._locks.get(key_);
+        if (lock == null) {
+          // Default to using `RWLockWriter` write lock for just string keys
+          requests_.push([key_, RWLockWriter, 'write']);
+        } else if (lock.type !== 'write') {
+          throw new errors.ErrorDBTransactionLockType();
+        }
+      }
+    }
+    if (requests_.length > 0) {
+      // Duplicates are eliminated, and the returned acquisitions are sorted
+      const lockAcquires = this.lockBox.lockMulti(...requests_);
+      for (const [key, lockAcquire, ...lockingParams] of lockAcquires) {
+        const [lockRelease, lock] = await lockAcquire();
+        // The `Map` will maintain insertion order
+        // these must be unlocked in reverse order
+        // when the transaction is destroyed
+        this._locks.set(key as string, {
+          lock: lock!,
+          type: lockingParams[0]!, // The `type` is defaulted to `write`
+          release: lockRelease,
+        });
+      }
+    }
+  }
+
+  /**
+   * Unlock a sequence of lock keys
+   * Unlocking will be done in the order of the keys
+   * A transaction instance is only allowed to unlock keys that it previously
+   * locked, all keys that are not part of the `this._locks` is ignored
+   * Unlocking the same keys is idempotent
+   */
+  public async unlock(...keys: Array<ToString>): Promise<void> {
+    for (const key of keys) {
+      const key_ = key.toString();
+      const lock = this._locks.get(key_);
+      if (lock == null) continue;
+      this._locks.delete(key_);
+      await lock.release();
+    }
+  }
+
   public async get<T>(
     keyPath: KeyPath | string | Buffer,
     raw?: false,
@@ -344,7 +443,7 @@ class DBTransaction {
     if (this._committed) {
       return;
     }
-    this.logger.debug(`Committing ${this.constructor.name} ${this._id}`);
+    this.logger.debug(`Committing ${this.constructor.name} ${this.id}`);
     for (const iterator of this._iteratorRefs) {
       await iterator.destroy();
     }
@@ -357,12 +456,14 @@ class DBTransaction {
       } catch (e) {
         if (e.code === 'TRANSACTION_CONFLICT') {
           this.logger.debug(
-            `Failed Committing ${this.constructor.name} ${this._id} due to ${errors.ErrorDBTransactionConflict.name}`,
+            `Failed Committing ${this.constructor.name} ${this.id} due to ${errors.ErrorDBTransactionConflict.name}`,
           );
-          throw new errors.ErrorDBTransactionConflict(undefined, { cause: e });
+          throw new errors.ErrorDBTransactionConflict(undefined, {
+            cause: e,
+          });
         } else {
           this.logger.debug(
-            `Failed Committing ${this.constructor.name} ${this._id} due to ${e.message}`,
+            `Failed Committing ${this.constructor.name} ${this.id} due to ${e.message}`,
           );
           throw e;
         }
@@ -376,7 +477,7 @@ class DBTransaction {
       }
     }
     await this.destroy();
-    this.logger.debug(`Committed ${this.constructor.name} ${this._id}`);
+    this.logger.debug(`Committed ${this.constructor.name} ${this.id}`);
   }
 
   @ready(new errors.ErrorDBTransactionDestroyed())
@@ -387,7 +488,7 @@ class DBTransaction {
     if (this._rollbacked) {
       return;
     }
-    this.logger.debug(`Rollbacking ${this.constructor.name} ${this._id}`);
+    this.logger.debug(`Rollbacking ${this.constructor.name} ${this.id}`);
     for (const iterator of this._iteratorRefs) {
       await iterator.destroy();
     }
@@ -405,7 +506,20 @@ class DBTransaction {
       }
     }
     await this.destroy();
-    this.logger.debug(`Rollbacked ${this.constructor.name} ${this._id}`);
+    this.logger.debug(`Rollbacked ${this.constructor.name} ${this.id}`);
+  }
+
+  /**
+   * Set the snapshot manually
+   * This ensures that consistent reads and writes start
+   * after this method is executed
+   * This is idempotent
+   * Note that normally snapshots are set lazily upon the first
+   * transaction db operation
+   */
+  @ready(new errors.ErrorDBTransactionDestroyed())
+  public setSnapshot(): void {
+    this.setupSnapshot();
   }
 
   /**

src/DBTransaction.ts

@@ -82,6 +82,11 @@ class ErrorDBTransactionConflict<T> extends ErrorDBTransaction<T> {
   static description = 'DBTransaction cannot commit due to conflicting writes';
 }
 
+class ErrorDBTransactionLockType<T> extends ErrorDBTransaction<T> {
+  static description =
+    'DBTransaction does not support upgrading or downgrading the lock type';
+}
+
 export {
   ErrorDB,
   ErrorDBRunning,
@@ -103,4 +108,5 @@ export {
   ErrorDBTransactionRollbacked,
   ErrorDBTransactionNotCommittedNorRollbacked,
   ErrorDBTransactionConflict,
+  ErrorDBTransactionLockType,
 };