state, machiner: new style principal units watcher

state/unit.go

 package state
 
 import (
         "errors"
         "fmt"
         "labix.org/v2/mgo"
         "labix.org/v2/mgo/txn"
         "launchpad.net/juju-core/charm"
         "launchpad.net/juju-core/state/presence"
         "launchpad.net/juju-core/trivial"
@@ skipping 386 matching lines @@
 // It returns the started pinger.
 func (u *Unit) SetAgentAlive() (*presence.Pinger, error) {
         p := presence.NewPinger(u.st.presence, u.globalKey())
         err := p.Start()
         if err != nil {
                 return nil, err
         }
         return p, nil
 }
 
+// IsAssignedTo returns whether u is a principal assigned to machine m.
+// It panics if u is not a principal unit.
+func (u *Unit) IsAssignedTo(m *Machine) bool {

[rog, 2012/11/09 09:08:08]

is this necessary? can't we just use AssignedMachineId instead?

[aram, 2012/11/09 16:50:08]

It was impossible to use the previous version of AssignedMachineId, but I fixed
that function instead to return usable errors and I deleted this.

+        if !u.IsPrincipal() {
+                panic("unit is not a principal")
+        }
+        return u.doc.MachineId != nil && *u.doc.MachineId == m.doc.Id
+}
+
 // AssignedMachineId returns the id of the assigned machine.
 func (u *Unit) AssignedMachineId() (id int, err error) {
         defer trivial.ErrorContextf(&err, "cannot get machine id of unit %q", u)
         if u.IsPrincipal() {
                 if u.doc.MachineId == nil {
                         return 0, errors.New("unit not assigned to machine")
                 }
                 return *u.doc.MachineId, nil
         }
         pudoc := unitDoc{}
@@ skipping 239 matching lines @@
                 return p1.Protocol < p2.Protocol
         }
         return p1.Number < p2.Number
 }
 
 // SortPorts sorts the given ports, first by protocol,
 // then by number.
 func SortPorts(ports []Port) {
         sort.Sort(portSlice(ports))
 }