cluster: add scheduling policy to cluster.settings

doc/api/cluster.md

@@ -900,6 +900,9 @@ values are `'rr'` and `'none'`.
 <!-- YAML
 added: v0.7.1
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/49292
+    description: The `schedulingPolicy` option is supported now.
   - version:
      - v13.2.0
      - v12.16.0
@@ -931,6 +934,9 @@ changes:
     messages between processes. Possible values are `'json'` and `'advanced'`.
     See [Advanced serialization for `child_process`][] for more details.
     **Default:** `false`.
+  * `schedulingPolicy` {string} Scheduling policy to use between processes.
+    **Default:** `cluster.SCHED_RR`. See \[`cluster.schedulingPolicy`]\[] for
+    details.
   * `silent` {boolean} Whether or not to send output to parent's stdio.
     **Default:** `false`.
   * `stdio` {Array} Configures the stdio of forked processes. Because the

lib/internal/cluster/primary.js

@@ -44,7 +44,6 @@ cluster.SCHED_RR = SCHED_RR;      // Primary distributes connections.
 let ids = 0;
 let initialized = false;
 
-// XXX(bnoordhuis) Fold cluster.schedulingPolicy into cluster.settings?
 let schedulingPolicy = process.env.NODE_CLUSTER_SCHED_POLICY;
 if (schedulingPolicy === 'rr')
   schedulingPolicy = SCHED_RR;
@@ -65,6 +64,7 @@ cluster.setupPrimary = function(options) {
     exec: process.argv[1],
     execArgv: process.execArgv,
     silent: false,
+    schedulingPolicy: cluster.schedulingPolicy,
     ...cluster.settings,
     ...options,
   };
@@ -86,9 +86,10 @@ cluster.setupPrimary = function(options) {
     return process.nextTick(setupSettingsNT, settings);
 
   initialized = true;
-  schedulingPolicy = cluster.schedulingPolicy;  // Freeze policy.
+  schedulingPolicy = settings.schedulingPolicy;  // Freeze policy.
   assert(schedulingPolicy === SCHED_NONE || schedulingPolicy === SCHED_RR,
-         `Bad cluster.schedulingPolicy: ${schedulingPolicy}`);
+         `Bad settings.schedulingPolicy: ${schedulingPolicy}`);
+  cluster.schedulingPolicy = schedulingPolicy;  // Show to the world.
 
   process.nextTick(setupSettingsNT, settings);
 
@@ -158,6 +159,10 @@ function removeHandlesForWorker(worker) {
   });
 }
 
+cluster.getSettings = function() {
+  return { ...cluster.settings };
+};
+
 cluster.fork = function(env) {
   cluster.setupPrimary();
   const id = ++ids;

test/known_issues/test-cluster-import-scheduling-policy.mjs

@@ -0,0 +1,13 @@
+// Refs: https://github.com/nodejs/node/issues/49240
+// When importing cluster in ESM, cluster.schedulingPolicy cannot be set;
+// and the env variable doesn't work since imports are hoisted to the top.
+// Therefore the scheduling policy is still cluster.SCHED_RR.
+import '../common/index.mjs';
+import assert from 'node:assert';
+import * as cluster from 'cluster';
+
+
+assert.strictEqual(cluster.schedulingPolicy, cluster.SCHED_RR);
+cluster.setupPrimary({ schedulingPolicy: cluster.SCHED_NONE });
+const settings = cluster.getSettings();
+assert.strictEqual(settings.schedulingPolicy, cluster.SCHED_RR);

test/parallel/test-cluster-setup-primary-cumulative.js

@@ -35,6 +35,7 @@ assert.deepStrictEqual(cluster.settings, {
   exec: process.argv[1],
   execArgv: process.execArgv,
   silent: false,
+  schedulingPolicy: 2,
 });
 console.log('ok sets defaults');
 
@@ -58,5 +59,6 @@ assert.deepStrictEqual(cluster.settings, {
   exec: 'overridden',
   execArgv: ['baz', 'bang'],
   silent: false,
+  schedulingPolicy: 2,
 });
 console.log('ok preserves current settings');