func()

in swim/memberlist.go [519:629]

• 68 lines of code
• 17 McCabe index (conditional complexity)

func (m *memberlist) Update(changes []Change) (applied []Change) {
	if m.node.Stopped() || len(changes) == 0 {
		return nil
	}

	// validate incoming changes
	for i, change := range changes {
		changes[i] = change.validateIncoming()
	}

	m.node.EmitEvent(MemberlistChangesReceivedEvent{changes})

	var memberChanges []membership.MemberChange

	m.Lock()

	// run through all changes received and figure out if they need to be accepted
	m.members.Lock()
	for _, change := range changes {
		member, has := m.members.byAddress[change.Address]

		// transform the change into a member that we can test against existing
		// members
		gossip := Member{}
		gossip.populateFromChange(&change)

		// test to see if we need to process the gossip
		if shouldProcessGossip(member, &gossip) {
			// the gossip overwrites the know state about the member

			if gossip.Address == m.local.Address {
				// if the gossip is about the local member it needs to be
				// countered by increasing the incarnation number and gossip the
				// new state to the network.
				change = m.bumpIncarnation()
				m.node.EmitEvent(RefuteUpdateEvent{})
			} else {
				// otherwise it can be applied to the memberlist

				// prepare the change and collect if there is an outside
				// observable change eg. changes that involve active
				// participants of the membership (pingable)
				memberChange := membership.MemberChange{}
				if has && member.isReachable() {
					memberChange.Before = *member
				}
				if gossip.isReachable() {
					memberChange.After = gossip
				}
				if memberChange.Before != nil || memberChange.After != nil {
					memberChanges = append(memberChanges, memberChange)
				}

				if !has {
					// if the member was not already present in the list we will
					// add it and assign it a random position in the list to ensure
					// guarantees for pinging
					m.members.byAddress[gossip.Address] = &gossip
					i := m.getJoinPosition()
					m.members.list = append(m.members.list[:i], append([]*Member{&gossip}, m.members.list[i:]...)...)
				} else {
					// copy the value of the gossip into the already existing
					// struct. This operation is by value, not by reference.
					// this is to keep both the list and byAddress map in sync
					// without tedious lookup operations.
					*member = gossip
				}

			}

			// keep track of the change that it has been applied
			applied = append(applied, change)

		}
	}
	m.members.Unlock()

	if len(applied) > 0 {
		// when there are changes applied we need to recalculate our checksum
		oldChecksum := m.Checksum()
		m.ComputeChecksum()

		for _, change := range applied {
			if change.Source != m.node.address {
				m.logger.WithFields(bark.Fields{
					"remote": change.Source,
				}).Debug("ringpop applied remote update")
			}
		}

		m.node.EmitEvent(MemberlistChangesAppliedEvent{
			Changes:     applied,
			OldChecksum: oldChecksum,
			NewChecksum: m.Checksum(),
			NumMembers:  m.NumMembers(),
		})
		m.node.handleChanges(applied)

	}

	// if there are changes that are important for outside observers of the
	// membership emit those
	if len(memberChanges) > 0 {
		m.node.EmitEvent(membership.ChangeEvent{
			Changes: memberChanges,
		})
	}

	m.Unlock()
	return applied
}