Package org.eclipse.jetty.http2

Class BufferingFlowControlStrategy

  • All Implemented Interfaces:
    FlowControlStrategy, Dumpable
    @ManagedObject
public class BufferingFlowControlStrategy
extends AbstractFlowControlStrategy

    A flow control strategy that accumulates updates and emits window control frames when the accumulated value reaches a threshold.

    The sender flow control window is represented in the receiver as two buckets: a bigger bucket, initially full, that is drained when data is received, and a smaller bucket, initially empty, that is filled when data is consumed. Only the smaller bucket can refill the bigger bucket.

    The smaller bucket is defined as a fraction of the bigger bucket.

    For a more visual representation, see the rocking bamboo fountain.

    The algorithm works in this way.

    The initial bigger bucket (BB) capacity is 100, and let's imagine the smaller bucket (SB) being 40% of the bigger bucket: 40.

    The receiver receives a data frame of 60, so now BB=40; the data frame is passed to the application that consumes 25, so now SB=25. Since SB is not full, no window control frames are emitted.

    The application consumes other 20, so now SB=45. Since SB is full, its 45 are transferred to BB, which is now BB=85, and a window control frame is sent with delta=45.

    The application consumes the remaining 15, so now SB=15, and no window control frame is emitted.