Use a task queue to ensure code blocks are executed sequentially (#510)

* Only `await` on the last code block

This ensures that all of the blocks are sent over in a single sequential batch, with no way for anyone else to execute their own block between two of ours, which would cause ordering issues

* Introduce a task queue for running `blocks`

* Abstract out a `callback`

* Move the queue to its own file

* Simplify API and add ability to have multiple queues

* `await` calls to `run()`

* Switch to more official PQueue

Lmao at the fact that I implemented this from scratch

* Rename to `ExecuteQueue`

* Tweak docs

* Delete `queue.ts`

Author: DavisVaughan

apps/vscode/package.json

@@ -1356,6 +1356,7 @@
     "markdown-it": "^13.0.1",
     "markdown-it-highlightjs": "^4.0.1",
     "nanoid": "^4.0.0",
+    "p-queue": "^8.0.1",
     "picomatch": "^2.3.1",
     "quarto-core": "*",
     "quarto-lsp": "*",

apps/vscode/src/host/execute-queue.ts

@@ -0,0 +1,69 @@
+/*
+ * execute-queue.ts
+ *
+ * Copyright (C) 2024 by Posit Software, PBC
+ *
+ * Unless you have received this program directly from Posit Software pursuant
+ * to the terms of a commercial license agreement with Posit Software, then
+ * this program is licensed to you under the terms of version 3 of the
+ * GNU Affero General Public License. This program is distributed WITHOUT
+ * ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING THOSE OF NON-INFRINGEMENT,
+ * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Please refer to the
+ * AGPL (http://www.gnu.org/licenses/agpl-3.0.txt) for more details.
+ *
+ */
+
+import PQueue from 'p-queue';
+
+/**
+ * Language specific execution queue
+ *
+ * A singleton class that constructs and manages multiple execution queues, identified by
+ * their `key` (typically the language name).
+ */
+export class ExecuteQueue {
+  /// Singleton instance
+  private static _instance: ExecuteQueue;
+
+  /// Maps a `key` to its `queue`
+  private _queues = new Map<string, PQueue>();
+
+  /**
+   * Constructor
+   *
+   * Private since we only want one of these. Access using `instance()` instead.
+   */
+  private constructor() { }
+
+  /**
+   * Accessor for the singleton instance
+   *
+   * Creates it if it doesn't exist.
+   */
+  static get instance(): ExecuteQueue {
+    if (!ExecuteQueue._instance) {
+      // Initialize if we've never accessed it
+      ExecuteQueue._instance = new ExecuteQueue();
+    }
+
+    return ExecuteQueue._instance;
+  }
+
+  /**
+   * Add a `callback` for execution on `key`'s task queue
+   *
+   * Returns a promise that resolves when the task finishes
+   */
+  async add(key: string, callback: () => Promise<void>): Promise<void> {
+    let queue = this._queues.get(key);
+
+    if (queue === undefined) {
+      // If we've never initialized this key's queue, do so now.
+      // Limit `concurrency` to 1, because we don't want tasks run out of order.
+      queue = new PQueue({ concurrency: 1 });
+      this._queues.set(key, queue);
+    }
+
+    return queue.add(callback);
+  }
+}

apps/vscode/src/host/hooks.ts

@@ -18,6 +18,7 @@ import * as hooks from 'positron';
 
 import { ExtensionHost, HostWebviewPanel, HostStatementRangeProvider } from '.';
 import { CellExecutor, cellExecutorForLanguage, executableLanguages, isKnitrDocument, pythonWithReticulate } from './executors';
+import { ExecuteQueue } from './execute-queue';
 import { MarkdownEngine } from '../markdown/engine';
 import { virtualDoc, virtualDocUri, adjustedPosition } from "../vdoc/vdoc";
 
@@ -56,14 +57,26 @@ export function hooksExtensionHost() : ExtensionHost {
         case "r":
           return {
             execute: async (blocks: string[], _editorUri?: vscode.Uri) : Promise<void> => {
-              for (const block of blocks) {
-                let code = block;
-                if (language === "python" && isKnitrDocument(document, engine)) {
-                  language = "r";
-                  code = pythonWithReticulate(block);
+              const runtime = hooksApi()?.runtime;
+
+              if (runtime === undefined) {
+                // Can't do anything without a runtime
+                return;
+              }
+
+              if (language === "python" && isKnitrDocument(document, engine)) {
+                language = "r";
+                blocks = blocks.map(pythonWithReticulate);
+              }
+              
+              // Our callback executes each block sequentially
+              const callback = async () => {
+                for (const block of blocks) {
+                  await runtime.executeCode(language, block, false);
                 }
-                await hooksApi()?.runtime.executeCode(language, code, false);
-              } 
+              }
+
+              await ExecuteQueue.instance.add(language, callback);
             },
             executeSelection: async () : Promise<void> => {
               await vscode.commands.executeCommand('workbench.action.positronConsole.executeCode', {languageId: language});
@@ -166,4 +179,3 @@ async function getStatementRange(
     position
   );
 }
-

yarn.lock

@@ -4306,6 +4306,11 @@ eventemitter3@^4.0.0:
   resolved "https://registry.yarnpkg.com/eventemitter3/-/eventemitter3-4.0.7.tgz#2de9b68f6528d5644ef5c59526a1b4a07306169f"
   integrity sha512-8guHBZCwKnFhYdHr2ysuRWErTwhoN2X8XELRlrRwpmfeY2jjuUN4taQMsULKUVo1K4DvZl+0pgfyoysHxvmvEw==
 
+eventemitter3@^5.0.1:
+  version "5.0.1"
+  resolved "https://registry.yarnpkg.com/eventemitter3/-/eventemitter3-5.0.1.tgz#53f5ffd0a492ac800721bb42c66b841de96423c4"
+  integrity sha512-GWkBvjiSZK87ELrYOSESUYeVIc9mvLLf/nXalMOS5dYrgZq9o5OVkbZAVM06CVxYsCwH9BDZFPlQTlPA1j4ahA==
+
 exceljs@^4.3.0:
   version "4.3.0"
   resolved "https://registry.yarnpkg.com/exceljs/-/exceljs-4.3.0.tgz#939bc0d4c59c200acadb7051be34d25c109853c4"
@@ -6342,6 +6347,19 @@ p-locate@^5.0.0:
   dependencies:
     p-limit "^3.0.2"
 
+p-queue@^8.0.1:
+  version "8.0.1"
+  resolved "https://registry.yarnpkg.com/p-queue/-/p-queue-8.0.1.tgz#718b7f83836922ef213ddec263ff4223ce70bef8"
+  integrity sha512-NXzu9aQJTAzbBqOt2hwsR63ea7yvxJc0PwN/zobNAudYfb1B7R08SzB4TsLeSbUCuG467NhnoT0oO6w1qRO+BA==
+  dependencies:
+    eventemitter3 "^5.0.1"
+    p-timeout "^6.1.2"
+
+p-timeout@^6.1.2:
+  version "6.1.2"
+  resolved "https://registry.yarnpkg.com/p-timeout/-/p-timeout-6.1.2.tgz#22b8d8a78abf5e103030211c5fc6dee1166a6aa5"
+  integrity sha512-UbD77BuZ9Bc9aABo74gfXhNvzC9Tx7SxtHSh1fxvx3jTLLYvmVhiQZZrJzqqU0jKbN32kb5VOKiLEQI/3bIjgQ==
+
 pako@~1.0.2:
   version "1.0.11"
   resolved "https://registry.yarnpkg.com/pako/-/pako-1.0.11.tgz#6c9599d340d54dfd3946380252a35705a6b992bf"