fix: allow concurrent prettier setups

CHANGES.md

@@ -13,6 +13,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 ### Changed
 * Use palantir-java-format 2.57.0 on Java 21. ([#2447](https://github.com/diffplug/spotless/pull/2447))
 * Re-try `npm install` with `--prefer-online` after `ERESOLVE` error. ([#2448](https://github.com/diffplug/spotless/pull/2448))
+* Allow multiple npm-based formatters having the same module dependencies, to share a `node_modules` dir without race conditions. [#2462](https://github.com/diffplug/spotless/pull/2462))
 
 ## [3.1.0] - 2025-02-20
 ### Added

lib/src/main/java/com/diffplug/spotless/npm/ExclusiveFolderAccess.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2025 DiffPlug
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.diffplug.spotless.npm;
+
+import java.io.File;
+import java.util.Objects;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+import javax.annotation.Nonnull;
+
+import com.diffplug.spotless.ThrowingEx;
+
+interface ExclusiveFolderAccess {
+
+	static ExclusiveFolderAccess forFolder(@Nonnull File folder) {
+		return forFolder(folder.getAbsolutePath());
+	}
+
+	static ExclusiveFolderAccess forFolder(@Nonnull String path) {
+		return new ExclusiveFolderAccessSharedMutex(Objects.requireNonNull(path));
+	}
+
+	void runExclusively(ThrowingEx.Runnable runnable);
+
+	class ExclusiveFolderAccessSharedMutex implements ExclusiveFolderAccess {
+
+		private static final ConcurrentHashMap<String, Lock> mutexes = new ConcurrentHashMap<>();
+
+		private final String path;
+
+		private ExclusiveFolderAccessSharedMutex(@Nonnull String path) {
+			this.path = Objects.requireNonNull(path);
+		}
+
+		private Lock getMutex() {
+			return mutexes.computeIfAbsent(path, k -> new ReentrantLock());
+		}
+
+		@Override
+		public void runExclusively(ThrowingEx.Runnable runnable) {
+			final Lock lock = getMutex();
+			try {
+				lock.lock();
+				runnable.run();
+			} catch (Exception e) {
+				throw ThrowingEx.asRuntime(e);
+			} finally {
+				lock.unlock();
+			}
+		}
+	}
+}

lib/src/main/java/com/diffplug/spotless/npm/NodeModulesCachingNpmProcessFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2023-2024 DiffPlug
+ * Copyright 2023-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@
 import java.io.File;
 import java.util.List;
 import java.util.Objects;
+import java.util.UUID;
 
 import javax.annotation.Nonnull;
 
@@ -65,8 +66,8 @@ public NpmProcess createNpmInstallProcess(NodeServerLayout nodeServerLayout, Npm
 	}
 
 	@Override
-	public NpmLongRunningProcess createNpmServeProcess(NodeServerLayout nodeServerLayout, NpmFormatterStepLocations formatterStepLocations) {
-		return StandardNpmProcessFactory.INSTANCE.createNpmServeProcess(nodeServerLayout, formatterStepLocations);
+	public NpmLongRunningProcess createNpmServeProcess(NodeServerLayout nodeServerLayout, NpmFormatterStepLocations formatterStepLocations, UUID nodeServerInstanceId) {
+		return StandardNpmProcessFactory.INSTANCE.createNpmServeProcess(nodeServerLayout, formatterStepLocations, nodeServerInstanceId);
 	}
 
 	private class CachingNmpInstall implements NpmProcess {

lib/src/main/java/com/diffplug/spotless/npm/NodeServeApp.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 DiffPlug
+ * Copyright 2023-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,6 +15,8 @@
  */
 package com.diffplug.spotless.npm;
 
+import java.util.UUID;
+
 import javax.annotation.Nonnull;
 
 import org.slf4j.Logger;
@@ -32,9 +34,9 @@ public NodeServeApp(@Nonnull NodeServerLayout nodeServerLayout, @Nonnull NpmConf
 		super(nodeServerLayout, npmConfig, formatterStepLocations);
 	}
 
-	ProcessRunner.LongRunningProcess startNpmServeProcess() {
+	ProcessRunner.LongRunningProcess startNpmServeProcess(UUID nodeServerInstanceId) {
 		return timedLogger.withInfo("Starting npm based server in {} with {}.", this.nodeServerLayout.nodeModulesDir(), this.npmProcessFactory.describe())
-				.call(() -> npmProcessFactory.createNpmServeProcess(nodeServerLayout, formatterStepLocations).start());
+				.call(() -> npmProcessFactory.createNpmServeProcess(nodeServerLayout, formatterStepLocations, nodeServerInstanceId).start());
 	}
 
 }

lib/src/main/java/com/diffplug/spotless/npm/NpmFormatterStepStateBase.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2024 DiffPlug
+ * Copyright 2016-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,13 +25,15 @@
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import com.diffplug.spotless.FormatterFunc;
+import com.diffplug.spotless.ProcessRunner;
 import com.diffplug.spotless.ProcessRunner.LongRunningProcess;
 import com.diffplug.spotless.ThrowingEx;
 
@@ -87,14 +89,17 @@ protected void prepareNodeServer() throws IOException {
 		}
 
 		protected void assertNodeServerDirReady() throws IOException {
-			if (needsPrepareNodeServerLayout()) {
-				// reinstall if missing
-				prepareNodeServerLayout();
-			}
-			if (needsPrepareNodeServer()) {
-				// run npm install if node_modules is missing
-				prepareNodeServer();
-			}
+			ExclusiveFolderAccess.forFolder(nodeServerLayout.nodeModulesDir())
+					.runExclusively(() -> {
+						if (needsPrepareNodeServerLayout()) {
+							// reinstall if missing
+							prepareNodeServerLayout();
+						}
+						if (needsPrepareNodeServer()) {
+							// run npm install if node_modules is missing
+							prepareNodeServer();
+						}
+					});
 		}
 
 		protected boolean needsPrepareNodeServer() {
@@ -109,12 +114,13 @@ protected ServerProcessInfo npmRunServer() throws ServerStartException, IOExcept
 			assertNodeServerDirReady();
 			LongRunningProcess server = null;
 			try {
-				// The npm process will output the randomly selected port of the http server process to 'server.port' file
+				final UUID nodeServerInstanceId = UUID.randomUUID();
+				// The npm process will output the randomly selected port of the http server process to 'server-<id>.port' file
 				// so in order to be safe, remove such a file if it exists before starting.
-				final File serverPortFile = new File(this.nodeServerLayout.nodeModulesDir(), "server.port");
+				final File serverPortFile = new File(this.nodeServerLayout.nodeModulesDir(), String.format("server-%s.port", nodeServerInstanceId));
 				NpmResourceHelper.deleteFileIfExists(serverPortFile);
 				// start the http server in node
-				server = nodeServeApp.startNpmServeProcess();
+				server = nodeServeApp.startNpmServeProcess(nodeServerInstanceId);
 
 				// await the readiness of the http server - wait for at most 60 seconds
 				try {
@@ -124,10 +130,12 @@ protected ServerProcessInfo npmRunServer() throws ServerStartException, IOExcept
 					try {
 						if (server.isAlive()) {
 							server.destroyForcibly();
-							server.waitFor();
+							ProcessRunner.Result result = server.result();
+							logger.info("Launching npm server process failed. Process result:\n{}", result);
 						}
 					} catch (Throwable t) {
-						// ignore
+						ProcessRunner.Result result = ThrowingEx.get(server::result);
+						logger.debug("Unable to forcibly end the server process. Process result:\n{}", result, t);
 					}
 					throw timeoutException;
 				}

lib/src/main/java/com/diffplug/spotless/npm/NpmProcessFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 DiffPlug
+ * Copyright 2023-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,6 +15,8 @@
  */
 package com.diffplug.spotless.npm;
 
+import java.util.UUID;
+
 public interface NpmProcessFactory {
 
 	enum OnlinePreferrence {
@@ -33,7 +35,7 @@ public String option() {
 
 	NpmProcess createNpmInstallProcess(NodeServerLayout nodeServerLayout, NpmFormatterStepLocations formatterStepLocations, OnlinePreferrence onlinePreferrence);
 
-	NpmLongRunningProcess createNpmServeProcess(NodeServerLayout nodeServerLayout, NpmFormatterStepLocations formatterStepLocations);
+	NpmLongRunningProcess createNpmServeProcess(NodeServerLayout nodeServerLayout, NpmFormatterStepLocations formatterStepLocations, UUID nodeServerInstanceId);
 
 	default String describe() {
 		return getClass().getSimpleName();

lib/src/main/java/com/diffplug/spotless/npm/StandardNpmProcessFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 DiffPlug
+ * Copyright 2023-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@
 import java.io.IOException;
 import java.util.List;
 import java.util.Map;
+import java.util.UUID;
 import java.util.concurrent.ExecutionException;
 
 import com.diffplug.spotless.ProcessRunner;
@@ -37,8 +38,8 @@ public NpmProcess createNpmInstallProcess(NodeServerLayout nodeServerLayout, Npm
 	}
 
 	@Override
-	public NpmLongRunningProcess createNpmServeProcess(NodeServerLayout nodeServerLayout, NpmFormatterStepLocations formatterStepLocations) {
-		return new NpmServe(nodeServerLayout.nodeModulesDir(), formatterStepLocations);
+	public NpmLongRunningProcess createNpmServeProcess(NodeServerLayout nodeServerLayout, NpmFormatterStepLocations formatterStepLocations, UUID nodeServerInstanceId) {
+		return new NpmServe(nodeServerLayout.nodeModulesDir(), formatterStepLocations, nodeServerInstanceId);
 	}
 
 	private static abstract class AbstractStandardNpmProcess {
@@ -119,16 +120,21 @@ public ProcessRunner.Result waitFor() {
 
 	private static class NpmServe extends AbstractStandardNpmProcess implements NpmLongRunningProcess {
 
-		public NpmServe(File workingDir, NpmFormatterStepLocations formatterStepLocations) {
+		private final UUID nodeServerInstanceId;
+
+		public NpmServe(File workingDir, NpmFormatterStepLocations formatterStepLocations, UUID nodeServerInstanceId) {
 			super(workingDir, formatterStepLocations);
+			this.nodeServerInstanceId = nodeServerInstanceId;
 		}
 
 		@Override
 		protected List<String> commandLine() {
 			return List.of(
 					npmExecutable(),
 					"start",
-					"--scripts-prepend-node-path=true");
+					"--scripts-prepend-node-path=true",
+					"--",
+					"--node-server-instance-id=" + nodeServerInstanceId);
 		}
 
 		@Override

lib/src/main/resources/com/diffplug/spotless/npm/common-serve.js

@@ -4,7 +4,7 @@ const GracefulShutdownManager = require("@moebius/http-graceful-shutdown").Grace
 const express = require("express");
 const app = express();
 
-app.use(express.json({ limit: "50mb" }));
+app.use(express.json({limit: "50mb"}));
 
 const fs = require("fs");
 
@@ -14,13 +14,33 @@ function debugLog() {
 	}
 }
 
+function getInstanceId() {
+	const args = process.argv.slice(2);
+
+	// Look for the --node-server-instance-id option
+	let instanceId;
+
+	args.forEach(arg => {
+		if (arg.startsWith('--node-server-instance-id=')) {
+			instanceId = arg.split('=')[1];
+		}
+	});
+
+	// throw if instanceId is not set
+	if (!instanceId) {
+		throw new Error("Missing --node-server-instance-id argument");
+	}
+	return instanceId;
+}
+
 var listener = app.listen(0, "127.0.0.1", () => {
-	debugLog("Server running on port " + listener.address().port);
-	fs.writeFile("server.port.tmp", "" + listener.address().port, function(err) {
+	const instanceId = getInstanceId();
+	debugLog("Server running on port " + listener.address().port + " for instance " + instanceId);
+	fs.writeFile("server.port.tmp", "" + listener.address().port, function (err) {
 		if (err) {
 			return console.log(err);
 		} else {
-			fs.rename("server.port.tmp", "server.port", function(err) {
+			fs.rename("server.port.tmp", `server-${instanceId}.port`, function (err) {
 				if (err) {
 					return console.log(err);
 				}
@@ -32,7 +52,7 @@ const shutdownManager = new GracefulShutdownManager(listener);
 
 app.post("/shutdown", (req, res) => {
 	res.status(200).send("Shutting down");
-	setTimeout(function() {
+	setTimeout(function () {
 		shutdownManager.terminate(() => debugLog("graceful shutdown finished."));
 	}, 200);
 });

plugin-gradle/CHANGES.md

@@ -7,6 +7,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 * Use palantir-java-format 2.57.0 on Java 21. ([#2447](https://github.com/diffplug/spotless/pull/2447))
 * Re-try `npm install` with `--prefer-online` after `ERESOLVE` error. ([#2448](https://github.com/diffplug/spotless/pull/2448))
 * Apply Gradle's strict plugin types validation to the Spotless plugin. ([#2454](https://github.com/diffplug/spotless/pull/2454))
+* Allow multiple npm-based formatters having the same module dependencies, to share a `node_modules` dir without race conditions. [#2462](https://github.com/diffplug/spotless/pull/2462))
 
 ## [7.0.2] - 2025-01-14
 ### Fixed

plugin-maven/CHANGES.md

@@ -6,6 +6,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 ### Changed
 * Use palantir-java-format 2.57.0 on Java 21. ([#2447](https://github.com/diffplug/spotless/pull/2447))
 * Re-try `npm install` with `--prefer-online` after `ERESOLVE` error. ([#2448](https://github.com/diffplug/spotless/pull/2448))
+* Allow multiple npm-based formatters having the same module dependencies, to share a `node_modules` dir without race conditions. [#2462](https://github.com/diffplug/spotless/pull/2462))
 
 ## [2.44.3] - 2025-02-20
 * Support for `clang-format` ([#2406](https://github.com/diffplug/spotless/pull/2406))