forked from coreos/nsproxy
/
subscription.go
178 lines (149 loc) · 5.16 KB
/
subscription.go
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package dbus
import (
"errors"
"time"
"github.com/guelfey/go.dbus"
)
const (
cleanIgnoreInterval = int64(10 * time.Second)
ignoreInterval = int64(30 * time.Millisecond)
)
func (c *Conn) initSubscription() {
c.subscriber.ignore = make(map[dbus.ObjectPath]int64)
}
// Returns two unbuffered channels which will receive all changed units every
// @interval@ seconds. Deleted units are sent as nil.
func (c *Conn) SubscribeUnits(interval time.Duration) (<-chan map[string]*UnitStatus, <-chan error) {
return c.SubscribeUnitsCustom(interval, 0, func(u1, u2 *UnitStatus) bool { return *u1 != *u2 })
}
// SubscribeUnitsCustom is like SubscribeUnits but lets you specify the buffer
// size of the channels and the comparison function for detecting changes.
func (c *Conn) SubscribeUnitsCustom(interval time.Duration, buffer int, isChanged func(*UnitStatus, *UnitStatus) bool) (<-chan map[string]*UnitStatus, <-chan error) {
old := make(map[string]*UnitStatus)
statusChan := make(chan map[string]*UnitStatus, buffer)
errChan := make(chan error, buffer)
go func() {
for {
timerChan := time.After(interval)
units, err := c.ListUnits()
if err == nil {
cur := make(map[string]*UnitStatus)
for i := range units {
cur[units[i].Name] = &units[i]
}
// add all new or changed units
changed := make(map[string]*UnitStatus)
for n, u := range cur {
if oldU, ok := old[n]; !ok || isChanged(oldU, u) {
changed[n] = u
}
delete(old, n)
}
// add all deleted units
for oldN := range old {
changed[oldN] = nil
}
old = cur
statusChan <- changed
} else {
errChan <- err
}
<-timerChan
}
}()
return statusChan, errChan
}
type SubStateUpdate struct {
UnitName string
SubState string
}
// SetSubStateSubscriber writes to updateCh when any unit's substate changes.
// Althrough this writes to updateCh on every state change, the reported state
// may be more recent than the change that generated it (due to an unavoidable
// race in the systemd dbus interface). That is, this method provides a good
// way to keep a current view of all units' states, but is not guaranteed to
// show every state transition they go through. Furthermore, state changes
// will only be written to the channel with non-blocking writes. If updateCh
// is full, it attempts to write an error to errCh; if errCh is full, the error
// passes silently.
func (c *Conn) SetSubStateSubscriber(updateCh chan<- *SubStateUpdate, errCh chan<- error) {
c.subscriber.Lock()
defer c.subscriber.Unlock()
c.subscriber.updateCh = updateCh
c.subscriber.errCh = errCh
}
func (c *Conn) sendSubStateUpdate(path dbus.ObjectPath) {
c.subscriber.Lock()
defer c.subscriber.Unlock()
if c.subscriber.updateCh == nil {
return
}
if c.shouldIgnore(path) {
return
}
info, err := c.GetUnitInfo(path)
if err != nil {
select {
case c.subscriber.errCh <- err:
default:
}
}
name := info["Id"].Value().(string)
substate := info["SubState"].Value().(string)
update := &SubStateUpdate{name, substate}
select {
case c.subscriber.updateCh <- update:
default:
select {
case c.subscriber.errCh <- errors.New("update channel full!"):
default:
}
}
c.updateIgnore(path, info)
}
func (c *Conn) GetUnitInfo(path dbus.ObjectPath) (map[string]dbus.Variant, error) {
var err error
var props map[string]dbus.Variant
obj := c.sysconn.Object("org.freedesktop.systemd1", path)
err = obj.Call("GetAll", 0, "org.freedesktop.systemd1.Unit").Store(&props)
if err != nil {
return nil, err
}
return props, nil
}
// The ignore functions work around a wart in the systemd dbus interface.
// Requesting the properties of an unloaded unit will cause systemd to send a
// pair of UnitNew/UnitRemoved signals. Because we need to get a unit's
// properties on UnitNew (as that's the only indication of a new unit coming up
// for the first time), we would enter an infinite loop if we did not attempt
// to detect and ignore these spurious signals. The signal themselves are
// indistinguishable from relevant ones, so we (somewhat hackishly) ignore an
// unloaded unit's signals for a short time after requesting its properties.
// This means that we will miss e.g. a transient unit being restarted
// *immediately* upon failure and also a transient unit being started
// immediately after requesting its status (with systemctl status, for example,
// because this causes a UnitNew signal to be sent which then causes us to fetch
// the properties).
func (c *Conn) shouldIgnore(path dbus.ObjectPath) bool {
t, ok := c.subscriber.ignore[path]
return ok && t >= time.Now().UnixNano()
}
func (c *Conn) updateIgnore(path dbus.ObjectPath, info map[string]dbus.Variant) {
c.cleanIgnore()
// unit is unloaded - it will trigger bad systemd dbus behavior
if info["LoadState"].Value().(string) == "not-found" {
c.subscriber.ignore[path] = time.Now().UnixNano() + ignoreInterval
}
}
// without this, ignore would grow unboundedly over time
func (c *Conn) cleanIgnore() {
now := time.Now().UnixNano()
if c.subscriber.cleanIgnore < now {
c.subscriber.cleanIgnore = now + cleanIgnoreInterval
for p, t := range c.subscriber.ignore {
if t < now {
delete(c.subscriber.ignore, p)
}
}
}
}