WIP

Author: CMCDragonkai

src/DB.ts

@@ -38,6 +38,7 @@ class DB {
     dbPath,
     crypto,
     fs = require('fs'),
+    deadlock = false,
     logger = new Logger(this.name),
     fresh = false,
     ...dbOptions
@@ -49,12 +50,14 @@ class DB {
     };
     fs?: FileSystem;
     logger?: Logger;
+    deadlock?: boolean;
     fresh?: boolean;
   } & DBOptions): Promise<DB> {
     logger.info(`Creating ${this.name}`);
     const db = new this({
       dbPath,
       fs,
+      deadlock,
       logger,
     });
     await db.start({
@@ -75,6 +78,7 @@ class DB {
   protected logger: Logger;
   protected workerManager?: DBWorkerManagerInterface;
   protected _lockBox: LockBox<RWLockWriter> = new LockBox();
+  protected _locksPending?: Map<string, { count: number}>;
   protected _db: RocksDBDatabase;
   /**
    * References to iterators
@@ -110,15 +114,20 @@ class DB {
   constructor({
     dbPath,
     fs,
+    deadlock,
     logger,
   }: {
     dbPath: string;
     fs: FileSystem;
+    deadlock: boolean;
     logger: Logger;
   }) {
     this.logger = logger;
     this.dbPath = dbPath;
     this.fs = fs;
+    if (deadlock) {
+      this._locksPending = new Map();
+    }
   }
 
   public async start({
@@ -213,6 +222,7 @@ class DB {
       const tran = new DBTransaction({
         db: this,
         lockBox: this._lockBox,
+        locksPending: this._locksPending,
         logger: this.logger,
       });
       return [

src/DBTransaction.ts

@@ -1,17 +1,12 @@
 import type { ResourceRelease } from '@matrixai/resources';
-import type {
-  LockBox,
-  MultiLockRequest as AsyncLocksMultiLockRequest,
-} from '@matrixai/async-locks';
+import type { LockBox } from '@matrixai/async-locks';
 import type DB from './DB';
 import type {
-  ToString,
   KeyPath,
   LevelPath,
   DBIteratorOptions,
   DBClearOptions,
   DBCountOptions,
-  MultiLockRequest,
 } from './types';
 import type {
   RocksDBTransaction,
@@ -20,7 +15,12 @@ import type {
 } from './native/types';
 import Logger from '@matrixai/logger';
 import { CreateDestroy, ready } from '@matrixai/async-init/dist/CreateDestroy';
-import { Lock, RWLockWriter } from '@matrixai/async-locks';
+import {
+  Monitor,
+  Lock,
+  RWLockWriter,
+  errors as asyncLocksErrors
+} from '@matrixai/async-locks';
 import DBIterator from './DBIterator';
 import { rocksdbP } from './native';
 import * as utils from './utils';
@@ -33,15 +33,7 @@ class DBTransaction {
 
   protected _db: DB;
   protected logger: Logger;
-  protected lockBox: LockBox<RWLockWriter>;
-  protected _locks: Map<
-    string,
-    {
-      lock: RWLockWriter;
-      type: 'read' | 'write';
-      release: ResourceRelease;
-    }
-  > = new Map();
+  protected monitor: Monitor<RWLockWriter>;
   protected _options: RocksDBTransactionOptions;
   protected _transaction: RocksDBTransaction;
   protected _snapshot: RocksDBTransactionSnapshot;
@@ -58,18 +50,25 @@ class DBTransaction {
   public constructor({
     db,
     lockBox,
+    locksPending,
     logger,
     ...options
   }: {
     db: DB;
     lockBox: LockBox<RWLockWriter>;
+    locksPending?: Map<string, { count: number }>;
     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;
+    // This creates the monitor that I care about
+    this.monitor = new Monitor(
+      lockBox,
+      RWLockWriter,
+      locksPending
+    );
     const options_ = {
       ...options,
       // Transactions should be synchronous
@@ -96,9 +95,7 @@ class DBTransaction {
     // this then allows the destruction to proceed
     await this.commitOrRollbackLock.waitForUnlock();
     this._db.transactionRefs.delete(this);
-    // Unlock all locked keys in reverse
-    const lockedKeys = [...this._locks.keys()].reverse();
-    await this.unlock(...lockedKeys);
+    await this.monitor.unlockAll();
     this.logger.debug(`Destroyed ${this.constructor.name} ${this.id}`);
   }
 
@@ -150,15 +147,8 @@ class DBTransaction {
     return this._rollbacked;
   }
 
-  get locks(): ReadonlyMap<
-    string,
-    {
-      lock: RWLockWriter;
-      type: 'read' | 'write';
-      release: ResourceRelease;
-    }
-  > {
-    return this._locks;
+  get locks(): Monitor<RWLockWriter>['locks'] {
+    return this.monitor.locks;
   }
 
   /**
@@ -168,78 +158,26 @@ class DBTransaction {
     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 | ToString>
+    ...params: Parameters<Monitor<RWLockWriter>['lock']>
   ): 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();
-        }
+    try {
+      await this.monitor.lock(...params)();
+    } catch (e) {
+      if (e instanceof asyncLocksErrors.ErrorAsyncLocksMonitorLockType) {
+        throw new errors.ErrorDBTransactionLockType(undefined, { cause: e });
       }
-    }
-    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,
-        });
+      if (e instanceof asyncLocksErrors.ErrorAsyncLocksMonitorDeadlock) {
+        throw new errors.ErrorDBTransactionDeadlock(undefined, { cause: e });
       }
+      throw e;
     }
   }
 
-  /**
-   * 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 unlock(
+    ...params: Parameters<Monitor<RWLockWriter>['unlock']>
+  ): Promise<void> {
+    await this.monitor.unlock(...params);
   }
 
   public async get<T>(

src/errors.ts

@@ -87,6 +87,11 @@ class ErrorDBTransactionLockType<T> extends ErrorDBTransaction<T> {
     'DBTransaction does not support upgrading or downgrading the lock type';
 }
 
+class ErrorDBTransactionDeadlock<T> extends ErrorDBTransaction<T> {
+  static description =
+    'DBTransaction encountered a pessimistic deadlock';
+}
+
 export {
   ErrorDB,
   ErrorDBRunning,
@@ -109,4 +114,5 @@ export {
   ErrorDBTransactionNotCommittedNorRollbacked,
   ErrorDBTransactionConflict,
   ErrorDBTransactionLockType,
+  ErrorDBTransactionDeadlock,
 };

src/types.ts

@@ -20,9 +20,9 @@ type POJO = { [key: string]: any };
 /**
  * Any type that can be turned into a string
  */
-interface ToString {
-  toString(): string;
-}
+// interface ToString {
+//   toString(): string;
+// }
 
 /**
  * Opaque types are wrappers of existing types
@@ -159,14 +159,14 @@ type DBOp =
 
 type DBOps = Array<DBOp>;
 
-type MultiLockRequest = [
-  key: ToString,
-  ...lockingParams: Parameters<RWLockWriter['lock']>,
-];
+// type MultiLockRequest = [
+//   key: ToString,
+//   ...lockingParams: Parameters<RWLockWriter['lock']>,
+// ];
 
 export type {
   POJO,
-  ToString,
+  // ToString,
   Opaque,
   Callback,
   Merge,
@@ -182,5 +182,5 @@ export type {
   DBBatch,
   DBOp,
   DBOps,
-  MultiLockRequest,
+  // MultiLockRequest,
 };