conntrim.py

# this would be called before adding a connection to the connection manager
# (presumably we just completed dial or accept routines to completion)
def before_adding_conn():
  if numconns < highwater:
    return
  # amortize the cost of evicting conns, drop connection count to the low water mark
  for numconns > lowwater:
    if not optimistic_evict():
      force_eviction()

# see if a subsystem is happy to lose a connection
def optimistic_evict():
  for ss in subsystems:
    if ss.optimistic_evict():
      return True
  return False

# evict a connection from the naughtiest subsystem for which only naughtier subsystems have a stake in the chosen connection
def force_evict():
  ordered_subsystems = sort(subsystems, key=suitability_for_eviction, reverse=True)
  for i, ss in enum(ordered_subsystems):
    # connections that are used by less naughty subsystems are not eligible for eviction by a naughtier subsystem.
    ineligible_conns = {conn for conn in oss.conns() for oss in ordered_subsystems[i+1:]}
    eligible_conns = set(ss.conns()) - ineligible_conns
    # if there are no eligible connections, we must let a less naughty subsystem choose
    if eligible_conns:
      ss.choose_evictee(eligible_conns)

# example implementation:
# determine a fair share of the total available conns for this subsystem,
# and return the difference with its actual usage.
def suitability_for_eviction(subsystem):
  return subsystem.num_conns() - total_conns*quota(subsystem)

# subsystems will implement this (Go)
type ConnEvictor interface{
  OptimisticEvict() (_ Conn, ok bool)
  ChooseEvictee([]Conn) Conn
}

# example for DHT
OptimisticEvict: return conn that's eligible for replacement in routing table
ChooseEvictee: return newest entry in fullest bucket