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// Copyright 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"
)
// stringsWorker is the internal implementation of the Worker
// interface, using a StringsWatcher for handling changes.
type stringsWorker struct {
tomb tomb.Tomb
// handler is what will be called when events are triggered.
handler StringsWatchHandler
}
// StringsWatchHandler implements the business logic triggered as part
// of watching a StringsWatcher.
type StringsWatchHandler 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 strings Worker will make sure to
// stop the watcher.
SetUp() (apiWatcher.StringsWatcher, 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(changes []string) error
}
// NewStringsWorker 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 NewStringsWorker(handler StringsWatchHandler) Worker {
sw := &stringsWorker{
handler: handler,
}
go func() {
defer sw.tomb.Done()
sw.tomb.Kill(sw.loop())
}()
return sw
}
// Kill the loop with no-error
func (sw *stringsWorker) Kill() {
sw.tomb.Kill(nil)
}
// Wait for the looping to finish
func (sw *stringsWorker) Wait() error {
return sw.tomb.Wait()
}
func (sw *stringsWorker) loop() error {
w, err := sw.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(sw.handler, &sw.tomb)
defer watcher.Stop(w, &sw.tomb)
for {
select {
case <-sw.tomb.Dying():
return tomb.ErrDying
case changes, ok := <-w.Changes():
if !ok {
return mustErr(w)
}
if err := sw.handler.Handle(changes); err != nil {
return err
}
}
}
}
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