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// Copyright 2012, 2013 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.
package worker
import (
"launchpad.net/tomb"
apiWatcher "launchpad.net/juju-core/state/api/watcher"
"launchpad.net/juju-core/state/watcher"
)
// mustErr is defined as a variable to allow the test suite
// to override it.
var mustErr = watcher.MustErr
// notifyWorker is the internal implementation of the Worker
// interface, using a NotifyWatcher for handling changes.
type notifyWorker struct {
tomb tomb.Tomb
// handler is what will handle when events are triggered
handler NotifyWatchHandler
}
// NotifyWatchHandler implements the business logic that is triggered
// as part of watching a NotifyWatcher.
type NotifyWatchHandler interface {
// SetUp starts the handler, this should create the watcher we
// will be waiting on for more events. SetUp can return a Watcher
// even if there is an error, and the notify Worker will make sure
// to stop the watcher.
SetUp() (apiWatcher.NotifyWatcher, error)
// TearDown should cleanup any resources that are left around
TearDown() error
// Handle is called when the Watcher has indicated there are
// changes, do whatever work is necessary to process it
Handle() error
}
// NewNotifyWorker starts a new worker running the business logic from
// the handler. The worker loop is started in another goroutine as a
// side effect of calling this.
func NewNotifyWorker(handler NotifyWatchHandler) Worker {
nw := ¬ifyWorker{
handler: handler,
}
go func() {
defer nw.tomb.Done()
nw.tomb.Kill(nw.loop())
}()
return nw
}
// Kill the loop with no-error
func (nw *notifyWorker) Kill() {
nw.tomb.Kill(nil)
}
// Wait for the looping to finish
func (nw *notifyWorker) Wait() error {
return nw.tomb.Wait()
}
type tearDowner interface {
TearDown() error
}
// propagateTearDown tears down the handler, but ensures any error is
// propagated through the tomb's Kill method.
func propagateTearDown(handler tearDowner, t *tomb.Tomb) {
if err := handler.TearDown(); err != nil {
t.Kill(err)
}
}
func (nw *notifyWorker) loop() error {
w, err := nw.handler.SetUp()
if err != nil {
if w != nil {
// We don't bother to propagate an error, because we
// already have an error
w.Stop()
}
return err
}
defer propagateTearDown(nw.handler, &nw.tomb)
defer watcher.Stop(w, &nw.tomb)
for {
select {
case <-nw.tomb.Dying():
return tomb.ErrDying
case _, ok := <-w.Changes():
if !ok {
return mustErr(w)
}
if err := nw.handler.Handle(); err != nil {
return err
}
}
}
}
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