Quality of Server Filter
The blocking nature of the standard servlet API makes it impossible to implement web applications that can guarantee some level of Quality of Service (QoS). Threads and memory are limited resources within a servlet container, yet with the standard servlet API, the only way to handle a HTTP request is with a thread allocated for the entire duration of the request. If a request is of low priority, or if other resources needed by the request are not available, then it is not possible to reuse the thread allocated to the request for high priority requests or requests that can proceed.
Jetty susports Suspendable Requests, which allows non-blocking handling of HTTP requests, so that that threads may be allocated in a managed way to provide application specific QoS. The QoSFilter is utility servlet filter that uses suspendable requests to implement some QoS features.