title: App Engine - Pull queues max_concurrent_requests limit?
body: <p>I'm using Google App Engine pull queues to send massive push notifications to APNS, GCM and OneSignal mostly following this architecture: <a href="https://cloudplatform.googleblog.com/2013/07/google-app-engine-takes-pain-out-of-sending-ios-push-notifications.html" rel="nofollow noreferrer">https://cloudplatform.googleblog.com/2013/07/google-app-engine-takes-pain-out-of-sending-ios-push-notifications.html</a></p>
  
  <p><a href="https://i.stack.imgur.com/IHF6Z.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IHF6Z.png" alt="enter image description here"></a></p>
  
  <p>The problem is that I'm hitting some kind of limit about how many tasks are leased at the same time: my Notification Workers lease 3 notifications at a time, but when there are more than about 30 workers running, <code>leaseTasks()</code> returns an empty array, even when there are hundreds or thousands of pending tasks. As far as I know, there is no limit about how many tasks are leased at the same time, so this behaviour is unexpected.</p>