Re-enable WP-CLI execution in the child process

cli/commands/wp.ts

@@ -9,11 +9,6 @@ import { isServerRunning, sendWpCliCommand } from 'cli/lib/wordpress-server-mana
 import { Logger, LoggerError } from 'cli/logger';
 import { GlobalOptions } from 'cli/types';
 
-// Sending WP-CLI messages to the child process is controlled by this feature flag. We've disabled
-// it until we can figure out the problems with race conditions and `MaxPhpInstancesError`s from
-// Playground
-const IS_WP_CLI_CHILD_PROCESS_EXECUTION_ENABLED = false;
-
 const logger = new Logger< '' >();
 
 export async function runCommand(
@@ -30,7 +25,7 @@ export async function runCommand(
 	// a different PHP version, pass the command to it…
 	const useCustomPhpVersion = options.phpVersion && options.phpVersion !== site.phpVersion;
 
-	if ( IS_WP_CLI_CHILD_PROCESS_EXECUTION_ENABLED && ! useCustomPhpVersion ) {
+	if ( ! useCustomPhpVersion ) {
 		try {
 			await connect();
 

cli/lib/tests/pm2-manager.test.ts

@@ -281,7 +281,7 @@ describe( 'PM2 Manager', () => {
 
 			const message: ManagerMessage = {
 				topic: 'stop-server',
-				messageId: 1,
+				messageId: '1',
 			};
 
 			await sendMessageToProcess( 42, message );
@@ -302,7 +302,7 @@ describe( 'PM2 Manager', () => {
 
 			const message: ManagerMessage = {
 				topic: 'stop-server',
-				messageId: 1,
+				messageId: '1',
 			};
 
 			await expect( sendMessageToProcess( 42, message ) ).rejects.toThrow( 'Send failed' );

cli/lib/types/wordpress-server-ipc.ts

@@ -56,7 +56,7 @@ const _managerMessagePayloadSchema = z.discriminatedUnion( 'topic', [
 ] );
 export type ManagerMessagePayload = z.infer< typeof _managerMessagePayloadSchema >;
 
-const managerMessageBase = z.object( { messageId: z.number() } );
+const managerMessageBase = z.object( { messageId: z.string() } );
 export const managerMessageSchema = z.discriminatedUnion( 'topic', [
 	managerMessageBase.merge( managerMessageStartServer ),
 	managerMessageBase.merge( managerMessageRunBlueprint ),
@@ -75,13 +75,13 @@ const childMessageActivity = z.object( {
 } );
 
 const childMessageResult = z.object( {
-	originalMessageId: z.number(),
+	originalMessageId: z.string(),
 	topic: z.literal( 'result' ),
 	result: z.unknown(),
 } );
 
 const childMessageError = z.object( {
-	originalMessageId: z.number(),
+	originalMessageId: z.string(),
 	topic: z.literal( 'error' ),
 	errorMessage: z.string(),
 	errorStack: z.string().optional(),

cli/lib/wordpress-server-manager.ts

@@ -155,9 +155,8 @@ async function waitForReadyMessage( pmId: number ): Promise< void > {
  * - Checks periodically for inactivity
  * - Has both inactivity timeout and max total timeout
  */
-let nextMessageId = 0;
 const messageActivityTrackers = new Map<
-	number,
+	string,
 	{
 		activityCheckIntervalId: NodeJS.Timeout;
 	}
@@ -175,7 +174,7 @@ async function sendMessage(
 ): Promise< unknown > {
 	const { maxTotalElapsedTime = PLAYGROUND_CLI_MAX_TIMEOUT, logger } = options;
 	const bus = await getPm2Bus();
-	const messageId = nextMessageId++;
+	const messageId = crypto.randomUUID();
 	let responseHandler: ( packet: unknown ) => void;
 
 	return new Promise( ( resolve, reject ) => {
@@ -223,7 +222,10 @@ async function sendMessage(
 			} else if ( validPacket.raw.topic === 'console-message' ) {
 				lastActivityTimestamp = Date.now();
 				logger?.reportProgress( validPacket.raw.message );
-			} else if ( validPacket.raw.topic === 'error' ) {
+			} else if (
+				validPacket.raw.topic === 'error' &&
+				validPacket.raw.originalMessageId === messageId
+			) {
 				const error = new Error( validPacket.raw.errorMessage ) as Error & {
 					cliArgs?: Record< string, unknown >;
 				};

cli/wordpress-server-child.ts

@@ -25,6 +25,7 @@ import { sanitizeRunCLIArgs } from 'common/lib/cli-args-sanitizer';
 import { isWordPressDirectory } from 'common/lib/fs-utils';
 import { getMuPlugins } from 'common/lib/mu-plugins';
 import { formatPlaygroundCliMessage } from 'common/lib/playground-cli-messages';
+import { sequential } from 'common/lib/sequential';
 import { isWordPressDevVersion } from 'common/lib/wordpress-version-utils';
 import { z } from 'zod';
 import { getSqliteCommandPath, getWpCliPharPath } from 'cli/lib/server-files';
@@ -285,30 +286,31 @@ async function runBlueprint( config: ServerConfig ): Promise< void > {
 	}
 }
 
-async function runWpCliCommand(
-	args: string[]
-): Promise< { stdout: string; stderr: string; exitCode: number } > {
-	await Promise.allSettled( [ startingPromise ] );
+const runWpCliCommand = sequential(
+	async ( args: string[] ): Promise< { stdout: string; stderr: string; exitCode: number } > => {
+		await Promise.allSettled( [ startingPromise ] );
 
-	if ( ! server ) {
-		throw new Error( `Failed to run WP CLI command because server is not running` );
-	}
+		if ( ! server ) {
+			throw new Error( `Failed to run WP CLI command because server is not running` );
+		}
 
-	const response = await server.playground.cli( [
-		'php',
-		'/tmp/wp-cli.phar',
-		`--path=${ await server.playground.documentRoot }`,
-		...args,
-	] );
-
-	return {
-		stdout: await response.stdoutText,
-		stderr: await response.stderrText,
-		exitCode: await response.exitCode,
-	};
-}
+		const response = await server.playground.cli( [
+			'php',
+			'/tmp/wp-cli.phar',
+			`--path=${ await server.playground.documentRoot }`,
+			...args,
+		] );
+
+		return {
+			stdout: await response.stdoutText,
+			stderr: await response.stderrText,
+			exitCode: await response.exitCode,
+		};
+	},
+	{ concurrent: 3, max: 10 }
+);
 
-function sendErrorMessage( messageId: number, error: unknown ) {
+function sendErrorMessage( messageId: string, error: unknown ) {
 	const errorResponse: ChildMessageRaw = {
 		originalMessageId: messageId,
 		topic: 'error',
@@ -325,7 +327,7 @@ async function ipcMessageHandler( packet: unknown ) {
 	if ( ! messageResult.success ) {
 		errorToConsole( 'Invalid message received:', messageResult.error );
 
-		const minimalMessageSchema = z.object( { id: z.number() } );
+		const minimalMessageSchema = z.object( { id: z.string() } );
 		const minimalMessage = minimalMessageSchema.safeParse( packet );
 		if ( minimalMessage.success ) {
 			sendErrorMessage( minimalMessage.data.id, messageResult.error );
@@ -349,7 +351,13 @@ async function ipcMessageHandler( packet: unknown ) {
 				result = await stopServer();
 				break;
 			case 'wp-cli-command':
-				result = await runWpCliCommand( validMessage.data.args );
+				try {
+					result = await runWpCliCommand( validMessage.data.args );
+				} catch ( wpCliError ) {
+					errorToConsole( `WP-CLI error:`, wpCliError );
+					sendErrorMessage( validMessage.messageId, wpCliError );
+					return; // Don't crash, just return error to caller
+				}
 				break;
 			default:
 				throw new Error( `Unknown message.` );

common/lib/sequential.ts

@@ -1,17 +1,28 @@
-const sequentialLocks = new Map< () => Promise< unknown >, Set< Promise< unknown > > >();
+type SequentialOptions = {
+	concurrent?: number;
+	max?: number;
+};
 
-// Ensures that calls to the provided function are executed sequentially
 export function sequential< Args extends unknown[], Return >(
-	fn: ( ...args: Args ) => Promise< Return >
+	fn: ( ...args: Args ) => Promise< Return >,
+	options?: SequentialOptions
 ) {
+	const concurrentCount = options?.concurrent ?? 1;
+	const maxQueueSize = options?.max;
+	const locks = new Set< Promise< Return > >();
+	let queueCount = 0;
+
 	return async ( ...args: Args ) => {
-		const locks = sequentialLocks.get( fn ) ?? new Set();
-		if ( ! sequentialLocks.has( fn ) ) {
-			sequentialLocks.set( fn, locks );
+		if ( maxQueueSize !== undefined && queueCount >= maxQueueSize ) {
+			throw new Error(
+				`Queue is full (${ maxQueueSize } pending commands). Please try again later.`
+			);
 		}
 
-		while ( locks.size ) {
+		while ( locks.size >= concurrentCount ) {
+			queueCount++;
 			await Promise.allSettled( [ ...locks ] );
+			queueCount--;
 		}
 
 		const fnPromise = fn( ...args );