feat: emit event on job lock extend failure

REFERENCE.md

@@ -955,6 +955,12 @@ A queue emits also some useful events:
   // workers that crash or pause the event loop.
 })
 
+.on('lock-extension-failed', function (job, err) {
+  // A job failed to extend lock. This will be useful to debug redis 
+  // connection issues and jobs getting restarted because workers
+  // are not able to extend locks.
+});
+
 .on('progress', function (job, progress) {
   // A job's progress was updated!
 })

lib/queue.js

@@ -1078,8 +1078,8 @@ Queue.prototype.processJob = function(job, notFetch = false) {
               lockExtender();
             }
           })
-          .catch((/*err*/) => {
-            // Somehow tell the worker this job should stop processing...
+          .catch(err => {
+            this.emit('lock-extension-failed', job, err);
           });
       }
     );

test/test_events.js

@@ -211,6 +211,27 @@ describe('events', () => {
     });
   });
 
+  it('should emit an event if a job fails to extend lock', done => {
+    const LOCK_RENEW_TIME = 1;
+    queue = utils.buildQueue('queue fails to extend lock', {
+      settings: {
+        lockRenewTime: LOCK_RENEW_TIME
+      }
+    });
+    queue.once('lock-extension-failed', (lockingFailedJob, error) => {
+      expect(lockingFailedJob.data.foo).to.be.equal('lockingFailedJobFoo');
+      expect(error.message).to.be.equal('Connection is closed.');
+      queue.close().then(done);
+    });
+    queue.isReady().then(() => {
+      queue.process(() => {
+        utils.simulateDisconnect(queue);
+        return delay(LOCK_RENEW_TIME + 0.25);
+      });
+      queue.add({ foo: 'lockingFailedJobFoo' });
+    });
+  });
+
   it('should listen to global events', done => {
     const queue1 = utils.buildQueue();
     const queue2 = utils.buildQueue();