track poller running state

use setTimeout, and wait for the search and job processing to complete before polling for jobs again

src/worker.js

@@ -37,6 +37,7 @@ export default class Worker extends events.EventEmitter {
     this._poller = {
       timer: false,
       enabled: true,
+      running: false,
     };
 
     this.debug(`Created worker for job type ${this.jobtype}`);
@@ -250,23 +251,33 @@ export default class Worker extends events.EventEmitter {
   }
 
   _startJobPolling() {
-    if (!this._poller.enabled) {
+    if (!this._poller.enabled || this._poller.running) {
       return;
     }
 
-    this._poller.timer = setInterval(() => {
-      this._getPendingJobs().then((jobs) => this._claimPendingJobs(jobs));
+    this._poller.timer = setTimeout(() => {
+      this._getPendingJobs().then((jobs) => {
+        if (!this._poller.running) return;
+
+        const foundJobs = (!jobs || jobs.length === 0);
+        const task = foundJobs ? Promise.resolve() : this._claimPendingJobs(jobs);
+
+        task.then(() => {
+          this._poller.running = false;
+          this._startJobPolling();
+        });
+      });
     } , this.checkInterval);
+
+    this._poller.running = true;
   }
 
   _stopJobPolling() {
-    clearInterval(this._poller.timer);
+    this._poller.running = false;
+    clearTimeout(this._poller.timer);
   }
 
-  _claimPendingJobs(jobs) {
-    if (!jobs || jobs.length === 0) return;
-
-    this._stopJobPolling();
+  _claimPendingJobs(jobs = []) {
     let claimed = false;
 
     // claim a single job, stopping after first successful claim
@@ -292,10 +303,8 @@ export default class Worker extends events.EventEmitter {
       this.debug(`Claimed job ${claimedJob._id}`);
       return this._performJob(claimedJob);
     })
-    .then(() => this._startJobPolling())
     .catch((err) => {
       this.debug('Error claiming jobs', err);
-      this._startJobPolling();
     });
   }