cluster: add schedulingPolicy to settings

doc/api/cluster.md

@@ -947,6 +947,8 @@ changes:
     primary's `process.debugPort`.
   * `windowsHide` {boolean} Hide the forked processes console window that would
     normally be created on Windows systems. **Default:** `false`.
+  * `schedulingPolicy` {string} policy to distribute load among the
+    secondary processes.
 
 After calling [`.setupPrimary()`][] (or [`.fork()`][]) this settings object will
 contain the settings, including the default values.

lib/internal/cluster/primary.js

@@ -42,32 +42,37 @@ cluster.SCHED_RR = SCHED_RR;      // Primary distributes connections.
 let ids = 0;
 let debugPortOffset = 1;
 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;
-else if (schedulingPolicy === 'none')
-  schedulingPolicy = SCHED_NONE;
-else if (process.platform === 'win32') {
-  // Round-robin doesn't perform well on
-  // Windows due to the way IOCP is wired up.
-  schedulingPolicy = SCHED_NONE;
-} else
-  schedulingPolicy = SCHED_RR;
-
-cluster.schedulingPolicy = schedulingPolicy;
+let schedulingPolicy = SCHED_RR;
+
+const SCHEDULE_POLICY_NAME_MAP = new SafeMap()
+  .set('rr', SCHED_RR)
+  .set('none', SCHED_NONE);
+
+function processSchedulingPolicy(settings = {}) {
+  const schedulingPolicy = process.env.NODE_CLUSTER_SCHED_POLICY || settings.schedulingPolicy;
+  if (schedulingPolicy === 'rr' || schedulingPolicy === 'none')
+    return schedulingPolicy;
+  if (process.platform === 'win32') {
+    // Round-robin doesn't perform well on
+    // Windows due to the way IOCP is wired up.
+    return 'none';
+  }
+  return 'rr';
+}
 
 cluster.setupPrimary = function(options) {
   const settings = {
     args: ArrayPrototypeSlice(process.argv, 2),
     exec: process.argv[1],
     execArgv: process.execArgv,
     silent: false,
+    schedulingPolicy: cluster.schedulingPolicy || processSchedulingPolicy(options),
     ...cluster.settings,
     ...options
   };
 
+  assert(settings.schedulingPolicy);
+
   // Tell V8 to write profile data for each process to a separate file.
   // Without --logfile=v8-%p.log, everything ends up in a single, unusable
   // file. (Unusable because what V8 logs are memory addresses and each
@@ -85,9 +90,7 @@ cluster.setupPrimary = function(options) {
     return process.nextTick(setupSettingsNT, settings);
 
   initialized = true;
-  schedulingPolicy = cluster.schedulingPolicy;  // Freeze policy.
-  assert(schedulingPolicy === SCHED_NONE || schedulingPolicy === SCHED_RR,
-         `Bad cluster.schedulingPolicy: ${schedulingPolicy}`);
+  schedulingPolicy = SCHEDULE_POLICY_NAME_MAP.get(cluster.schedulingPolicy); // Freeze policy.
 
   process.nextTick(setupSettingsNT, settings);
 

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

@@ -34,6 +34,7 @@ assert.deepStrictEqual(cluster.settings, {
   args: process.argv.slice(2),
   exec: process.argv[1],
   execArgv: process.execArgv,
+  schedulingPolicy: 'rr',
   silent: false,
 });
 console.log('ok sets defaults');
@@ -57,6 +58,7 @@ assert.deepStrictEqual(cluster.settings, {
   args: ['foo', 'bar'],
   exec: 'overridden',
   execArgv: ['baz', 'bang'],
+  schedulingPolicy: 'rr',
   silent: false,
 });
 console.log('ok preserves current settings');