[UIMA-5960] UIMA-DUCC: Modify pull service to synchronize threads

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.0.0-Ducc
• Component/s: DUCC
• Assignee: Jaroslaw Cwiklik
• Reporter: Jaroslaw Cwiklik
• Created: 15/Jan/19 20:41
• Updated: 04/Feb/19 18:37
• Resolved: 04/Feb/19 18:37

Description

Pull service is not polling for tasks correctly. Currently it allows threads to send GET requests concurrently. With many services running each with many threads the driver may get easily overrun. 

Instead each service should allow one GET request at a time. So there is only one thread pulling task at a time. Other threads block until a thread receives a task. If no task is given, a single thread will retry until a task becomes available or service is stopped. There will be no waiting on the driver/client side.