feat: add app launch in parallel limit

lib/API/schema.json

@@ -148,6 +148,11 @@
     "docDefault": false,
     "docDescription": "Make the process wait for a process.send('ready')"
   },
+  "launch_limit": {
+    "type": "number",
+    "docDefault": 1,
+    "docDescription": "Maximum number of launching processes at a time"
+  },
   "instances": {
     "type": "number",
     "docDefault": 1,

lib/God.js

@@ -136,7 +136,14 @@ God.prepare = function prepare (env, cb) {
     env.instances = 1;
   }
 
-  timesLimit(env.instances, 1, function (n, next) {
+  // app launch in parallel limit
+  if (env.launch_limit != null) {
+    env.launch_limit = parseInt(env.launch_limit);
+  }
+  if (!env.launch_limit || env.launch_limit < 0) {
+    env.launch_limit = 1;
+  }
+  timesLimit(env.instances, env.launch_limit, function (n, next) {
     env.vizion_running = false;
     if (env.env && env.env.vizion_running) {
       env.env.vizion_running = false;

test/programmatic/graceful.mocha.js

@@ -173,6 +173,70 @@ describe('Wait ready / Graceful start / restart', function() {
 
   });
 
+  describe('(Cluster): Launching limit feature', function () {
+    this.timeout(10000);
+
+    after(function(done) {
+      pm2.delete('all', done);
+    });
+
+    it('Should launch app processes in parallel', function(done) {
+      pm2.start({
+        script         : './wait-ready.js',
+        instances      : 3,
+        launch_limit: 2,
+        exec_mode      : 'cluster',
+        name           : 'launching-limit-1'
+      });
+
+      setTimeout(function() {
+        pm2.list(function(err, apps) {
+          should(apps[0].pm2_env.status).eql('online');
+          should(apps[1].pm2_env.status).eql('online');
+          should(apps[2].pm2_env.status).eql('online');
+          pm2.delete('all', done);
+        })
+      }, 500);
+    });
+
+    it('Should launch app processes in parallel and limit launching processes on wait ready', function(done) {
+      pm2.start({
+        script         : './wait-ready.js',
+        listen_timeout : 2000,
+        wait_ready     : true,
+        instances      : 3,
+        launch_limit: 2,
+        exec_mode      : 'cluster',
+        name           : 'launching-limit-2'
+      });
+
+      setTimeout(function() {
+        pm2.list(function(err, apps) {
+          should(apps[0].pm2_env.status).eql('launching');
+          should(apps[1].pm2_env.status).eql('launching');
+          should(apps[2]).undefined();
+        });
+      }, 500);
+
+      setTimeout(function() {
+        pm2.list(function(err, apps) {
+          should(apps[0].pm2_env.status).eql('online');
+          should(apps[1].pm2_env.status).eql('online');
+          should(apps[2].pm2_env.status).eql('launching');
+        })
+      }, 1500);
+
+      setTimeout(function() {
+        pm2.list(function(err, apps) {
+          should(apps[0].pm2_env.status).eql('online');
+          should(apps[1].pm2_env.status).eql('online');
+          should(apps[2].pm2_env.status).eql('online');
+          done();
+        })
+      }, 2500);
+    });
+  });
+
   describe('(Cluster): Wait ready feature', function () {
     this.timeout(10000);
 

types/index.d.ts

@@ -383,6 +383,10 @@ export interface StartOptions {
    * when you want your application to be considered as ready.
    */
   wait_ready?: boolean;
+  /**
+   * (Default: 1) Maximum number of launching processes at a time on application startup.
+   */
+  launch_limit?: number;
   /**
    * (Default: 1600)
    * The number of milliseconds to wait after a stop or restart command issues a SIGINT signal to kill the
@@ -446,7 +450,7 @@ export interface StartOptions {
 
 interface ReloadOptions {
   /**
-   * (Default: false) If true is passed in, pm2 will reload it’s environment from process.env 
+   * (Default: false) If true is passed in, pm2 will reload it’s environment from process.env
    * before reloading your process.
    */
   updateEnv?: boolean;