Fix: MaxListenersExceededWarning (fixes #105)

Author: mysticatea

bin/common/bootstrap.js

@@ -24,6 +24,13 @@ module.exports = function bootstrap(name) {
             return require("./version")(process.stdout)
 
         default:
+            // https://github.com/mysticatea/npm-run-all/issues/105
+            // Avoid MaxListenersExceededWarnings.
+            process.stdout.setMaxListeners(0)
+            process.stderr.setMaxListeners(0)
+            process.stdin.setMaxListeners(0)
+
+            // Main
             return require(`../${name}/main`)(
                 argv,
                 process.stdout,

docs/node-api.md

@@ -104,3 +104,9 @@ runAll(["clean", "lint", "build"])
         console.log(`${results[2].name}: ${results[2].code}`); // build: 0
     });
 ```
+
+## About MaxListenersExceededWarning
+
+- If you use `options.stdin`, `options.stdout`, or `options.stderr` in parallel mode, please configure max listeners by [emitter.setMaxListeners(n)](https://nodejs.org/api/events.html#events_emitter_setmaxlisteners_n) properly.
+- If you don't use those options and `process.stdXXX.isTTY` is `false`, please configure max listeners of the `process.stdXXX` properly. In that case, `npm-run-all` uses piping to connect to child processes.<br>
+  On the other hand, if `process.stdXXX.isTTY` is `true`, `npm-run-all` uses `inherit` option, so the configuration is unnecessary.

lib/index.js

@@ -208,7 +208,7 @@ function maxLength(length, name) {
  * @returns {Promise}
  *   A promise object which becomes fullfilled when all npm-scripts are completed.
  */
-module.exports = function npmRunAll(patternOrPatterns, options) {
+module.exports = function npmRunAll(patternOrPatterns, options) { //eslint-disable-line complexity
     const stdin = (options && options.stdin) || null
     const stdout = (options && options.stdout) || null
     const stderr = (options && options.stderr) || null

test/common.js

@@ -330,4 +330,27 @@ describe("[common]", () => {
             assert(false, "Should fail.")
         })
     })
+
+    // https://github.com/mysticatea/npm-run-all/issues/105
+    describe("should not print MaxListenersExceededWarning when it runs 10 tasks:", () => {
+        const tasks = Array.from({ length: 10 }, () => "test-task:append:a")
+
+        it("npm-run-all command", async () => {
+            const buf = new BufferStream()
+            await runAll(tasks, null, buf)
+            assert(buf.value.indexOf("MaxListenersExceededWarning") === -1)
+        })
+
+        it("run-s command", async () => {
+            const buf = new BufferStream()
+            await runSeq(tasks, null, buf)
+            assert(buf.value.indexOf("MaxListenersExceededWarning") === -1)
+        })
+
+        it("run-p command", async () => {
+            const buf = new BufferStream()
+            await runPar(tasks, null, buf)
+            assert(buf.value.indexOf("MaxListenersExceededWarning") === -1)
+        })
+    })
 })

test/fail.js

@@ -12,6 +12,7 @@
 const assert = require("power-assert")
 const nodeApi = require("../lib")
 const util = require("./lib/util")
+const delay = util.delay
 const removeResult = util.removeResult
 const runAll = util.runAll
 const runPar = util.runPar
@@ -43,6 +44,7 @@ describe("[fail] it should fail", () => {
     after(() => process.chdir(".."))
 
     beforeEach(removeResult)
+    afterEach(() => delay(1000))
 
     describe("if an invalid option exists.", () => {
         it("npm-run-all command", () => shouldFail(runAll(["--invalid"])))