feat: basic infrastructure for connection pooling

connection.ts

@@ -34,10 +34,12 @@ export interface SendCommandOptions {
 }
 
 export interface Connection extends TypedEventTarget<ConnectionEventMap> {
+  /** @deprecated */
   name: string | null;
   isClosed: boolean;
   isConnected: boolean;
   close(): void;
+  [Symbol.dispose](): void;
   connect(): Promise<void>;
   reconnect(): Promise<void>;
   sendCommand(
@@ -95,7 +97,15 @@ interface PendingCommand {
   reject: (error: unknown) => void;
 }
 
-export class RedisConnection
+export function createRedisConnection(
+  hostname: string,
+  port: number | string | undefined,
+  options: RedisConnectionOptions,
+): Connection {
+  return new RedisConnection(hostname, port ?? 6379, options);
+}
+
+class RedisConnection
   implements Connection, TypedEventTarget<ConnectionEventMap> {
   name: string | null = null;
   private maxRetryCount = 10;
@@ -306,7 +316,11 @@ export class RedisConnection
   }
 
   close() {
-    this.#close(false);
+    return this[Symbol.dispose]();
+  }
+
+  [Symbol.dispose](): void {
+    return this.#close(false);
   }
 
   #close(canReconnect = false) {

deno.json

@@ -3,6 +3,7 @@
   "version": "0.37.1",
   "exports": {
     ".": "./mod.ts",
+    "./experimental/pool": "./experimental/pool/mod.ts",
     "./experimental/cluster": "./experimental/cluster/mod.ts",
     "./experimental/web-streams-connection": "./experimental/web_streams_connection/mod.ts"
   },

executor.ts

@@ -2,6 +2,9 @@ import type { Connection, SendCommandOptions } from "./connection.ts";
 import type { RedisReply, RedisValue } from "./protocol/shared/types.ts";
 
 export interface CommandExecutor {
+  /**
+   * @deprecated
+   */
   readonly connection: Connection;
   /**
    * @deprecated

experimental/pool/mod.ts

@@ -0,0 +1 @@
+export * from "../../pool/mod.ts";

pool/default_pool.ts

@@ -0,0 +1,103 @@
+import type { Pool } from "./pool.ts";
+
+class AlreadyRemovedFromPoolError extends Error {
+  constructor() {
+    super("This connection has already been removed from the pool.");
+  }
+}
+
+const kDefaultTimeout = 5_000;
+class DefaultPool<T extends Disposable> implements Pool<T> {
+  readonly #idle: Array<T> = [];
+  readonly #connections: Array<T> = [];
+  #connectionCount: number = 0;
+  readonly #deferredQueue: Array<PromiseWithResolvers<T>> = [];
+  readonly #options: Required<PoolOptions<T>>;
+
+  constructor(
+    {
+      maxConnections = 8,
+      acquire,
+    }: PoolOptions<T>,
+  ) {
+    this.#options = {
+      acquire,
+      maxConnections,
+    };
+  }
+
+  async acquire(signal?: AbortSignal): Promise<T> {
+    signal ||= AbortSignal.timeout(kDefaultTimeout);
+    signal.throwIfAborted();
+    if (this.#idle.length > 0) {
+      const conn = this.#idle.shift()!;
+      return Promise.resolve(conn);
+    }
+
+    if (this.#connectionCount < this.#options.maxConnections) {
+      this.#connectionCount++;
+      try {
+        const connection = await this.#options.acquire();
+        this.#connections.push(connection);
+        return connection;
+      } catch (error) {
+        this.#connectionCount--;
+        throw error;
+      }
+    }
+
+    const deferred = Promise.withResolvers<T>();
+    this.#deferredQueue.push(deferred);
+    const { promise, reject } = deferred;
+    const onAbort = () => {
+      const i = this.#deferredQueue.indexOf(deferred);
+      if (i === -1) return;
+      this.#deferredQueue.splice(i, 1);
+      reject(signal.reason);
+    };
+    signal.addEventListener("abort", onAbort, { once: true });
+    return promise;
+  }
+
+  #has(conn: T): boolean {
+    return this.#connections.includes(conn);
+  }
+
+  release(conn: T): void {
+    if (!this.#has(conn)) {
+      throw new AlreadyRemovedFromPoolError();
+    } else if (this.#deferredQueue.length > 0) {
+      const i = this.#deferredQueue.shift()!;
+      i.resolve(conn);
+    } else {
+      this.#idle.push(conn);
+    }
+  }
+
+  close() {
+    const errors: Array<unknown> = [];
+    for (const x of [...this.#connections]) {
+      try {
+        x[Symbol.dispose]();
+      } catch (error) {
+        errors.push(error);
+      }
+    }
+    this.#connections.length = 0;
+    this.#idle.length = 0;
+    if (errors.length > 0) {
+      throw new AggregateError(errors);
+    }
+  }
+}
+
+export interface PoolOptions<T extends Disposable> {
+  maxConnections?: number;
+  acquire(): Promise<T>;
+}
+
+export function createDefaultPool<T extends Disposable>(
+  options: PoolOptions<T>,
+): Pool<T> {
+  return new DefaultPool<T>(options);
+}

pool/default_pool_test.ts

@@ -0,0 +1,85 @@
+import { assert, assertEquals, assertRejects } from "../deps/std/assert.ts";
+import { createDefaultPool } from "./default_pool.ts";
+
+class FakeConnection implements Disposable {
+  #isClosed = false;
+  isClosed() {
+    return this.#isClosed;
+  }
+  [Symbol.dispose]() {
+    if (this.#isClosed) {
+      throw new Error("Already closed");
+    }
+    this.#isClosed = true;
+  }
+}
+
+Deno.test({
+  name: "DefaultPool",
+  permissions: "none",
+  fn: async () => {
+    const openConnections: Array<FakeConnection> = [];
+    const pool = createDefaultPool({
+      acquire: () => {
+        const connection = new FakeConnection();
+        openConnections.push(connection);
+        return Promise.resolve(connection);
+      },
+      maxConnections: 2,
+    });
+    assertEquals(openConnections, []);
+
+    const signal = AbortSignal.timeout(200);
+
+    const conn1 = await pool.acquire(signal);
+    assertEquals(openConnections, [conn1]);
+    assert(openConnections.every((x) => !x.isClosed()));
+    assert(!signal.aborted);
+
+    const conn2 = await pool.acquire(signal);
+    assertEquals(openConnections, [conn1, conn2]);
+    assert(!conn2.isClosed());
+    assert(openConnections.every((x) => !x.isClosed()));
+    assert(!signal.aborted);
+
+    {
+      // Tests timeout handling
+      await assertRejects(
+        () => pool.acquire(signal),
+        "Intentionally aborted",
+      );
+      assert(signal.aborted);
+      assertEquals(openConnections, [conn1, conn2]);
+      assert(openConnections.every((x) => !x.isClosed()));
+    }
+
+    {
+      // Tests `release()`
+      pool.release(conn2);
+      assertEquals(openConnections, [conn1, conn2]);
+
+      const conn = await pool.acquire(new AbortController().signal);
+      assert(conn === conn2, "A new connection should not be created");
+      assertEquals(openConnections, [conn1, conn2]);
+    }
+
+    {
+      // `Pool#acquire` should wait for an active connection to be released.
+      const signal = AbortSignal.timeout(3_000);
+      const promise = pool.acquire(signal);
+      setTimeout(() => {
+        pool.release(conn1);
+      }, 50);
+      const conn = await promise;
+      assert(conn === conn1, "A new connection should not be created");
+      assertEquals(openConnections, [conn1, conn2]);
+      assert(!signal.aborted);
+    }
+
+    {
+      // `Pool#close` closes all connections
+      pool.close();
+      assert(openConnections.every((x) => x.isClosed()));
+    }
+  },
+});

pool/executor.ts

@@ -0,0 +1,51 @@
+import type { Connection, SendCommandOptions } from "../connection.ts";
+import type { Pool } from "./pool.ts";
+import type { CommandExecutor } from "../executor.ts";
+import { DefaultExecutor } from "../executor.ts";
+import type { RedisReply, RedisValue } from "../protocol/shared/types.ts";
+
+export function createPooledExecutor(pool: Pool<Connection>): CommandExecutor {
+  return new PooledExecutor(pool);
+}
+
+class PooledExecutor implements CommandExecutor {
+  readonly #pool: Pool<Connection>;
+  constructor(pool: Pool<Connection>) {
+    this.#pool = pool;
+  }
+
+  get connection(): Connection {
+    throw new Error("PooledExecutor.connection is not supported");
+  }
+
+  async exec(
+    command: string,
+    ...args: RedisValue[]
+  ): Promise<RedisReply> {
+    const connection = await this.#pool.acquire();
+    try {
+      const executor = new DefaultExecutor(connection);
+      return await executor.exec(command, ...args);
+    } finally {
+      this.#pool.release(connection);
+    }
+  }
+
+  async sendCommand(
+    command: string,
+    args?: RedisValue[],
+    options?: SendCommandOptions,
+  ): Promise<RedisReply> {
+    const connection = await this.#pool.acquire();
+    try {
+      const executor = new DefaultExecutor(connection);
+      return await executor.sendCommand(command, args, options);
+    } finally {
+      this.#pool.release(connection);
+    }
+  }
+
+  close(): void {
+    return this.#pool.close();
+  }
+}

pool/mod.ts

@@ -0,0 +1,30 @@
+import type { Redis, RedisConnectOptions } from "../redis.ts";
+import { create } from "../redis.ts";
+import type { Connection } from "../connection.ts";
+import { createRedisConnection } from "../connection.ts";
+import { createDefaultPool } from "./default_pool.ts";
+import { createPooledExecutor } from "./executor.ts";
+
+export interface CreatePoolClientOptions {
+  connection: RedisConnectOptions;
+  maxConnections?: number;
+}
+
+export function createPoolClient(
+  options: CreatePoolClientOptions,
+): Promise<Redis> {
+  const pool = createDefaultPool<Connection>({
+    acquire,
+    maxConnections: options.maxConnections ?? 8,
+  });
+  const executor = createPooledExecutor(pool);
+  const client = create(executor);
+  return Promise.resolve(client);
+
+  async function acquire(): Promise<Connection> {
+    const { hostname, port, ...connectionOptions } = options.connection;
+    const connection = createRedisConnection(hostname, port, connectionOptions);
+    await connection.connect();
+    return connection;
+  }
+}

pool/pool.ts

@@ -0,0 +1,5 @@
+export interface Pool<T extends Disposable> {
+  acquire(signal?: AbortSignal): Promise<T>;
+  release(item: T): void;
+  close(): void;
+}

redis.ts

@@ -43,7 +43,7 @@ import type {
   ZScanOpts,
   ZUnionstoreOpts,
 } from "./command.ts";
-import { RedisConnection } from "./connection.ts";
+import { createRedisConnection } from "./connection.ts";
 import type { Connection, SendCommandOptions } from "./connection.ts";
 import type { RedisConnectionOptions } from "./connection.ts";
 import type { CommandExecutor } from "./executor.ts";
@@ -2452,7 +2452,8 @@ export interface RedisConnectOptions extends RedisConnectionOptions {
  * ```
  */
 export async function connect(options: RedisConnectOptions): Promise<Redis> {
-  const connection = createRedisConnection(options);
+  const { hostname, port, ...connectionOptions } = options;
+  const connection = createRedisConnection(hostname, port, connectionOptions);
   await connection.connect();
   const executor = new DefaultExecutor(connection);
   return create(executor);
@@ -2471,7 +2472,8 @@ export async function connect(options: RedisConnectOptions): Promise<Redis> {
  * ```
  */
 export function createLazyClient(options: RedisConnectOptions): Redis {
-  const connection = createRedisConnection(options);
+  const { hostname, port, ...connectionOptions } = options;
+  const connection = createRedisConnection(hostname, port, connectionOptions);
   const executor = createLazyExecutor(connection);
   return create(executor);
 }
@@ -2519,11 +2521,6 @@ export function parseURL(url: string): RedisConnectOptions {
   };
 }
 
-function createRedisConnection(options: RedisConnectOptions): Connection {
-  const { hostname, port = 6379, ...opts } = options;
-  return new RedisConnection(hostname, port, opts);
-}
-
 function createLazyExecutor(connection: Connection): CommandExecutor {
   let executor: CommandExecutor | null = null;
   return {