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manifold.go
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manifold.go
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// Copyright 2015 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.
package agent
import (
"github.com/juju/errors"
"launchpad.net/tomb"
"github.com/juju/juju/agent"
"github.com/juju/juju/worker"
"github.com/juju/juju/worker/dependency"
)
// Manifold returns a manifold that starts a worker proxying the supplied Agent
// for use by other workers.
func Manifold(a agent.Agent) dependency.Manifold {
return dependency.Manifold{
Start: startFunc(a),
Output: outputFunc,
}
}
// startFunc returns a StartFunc that starts a worker holding a reference to
// the supplied Agent.
func startFunc(a agent.Agent) dependency.StartFunc {
return func(_ dependency.Context) (worker.Worker, error) {
w := &agentWorker{agent: a}
go func() {
defer w.tomb.Done()
<-w.tomb.Dying()
}()
return w, nil
}
}
// outputFunc extracts an Agent from its *agentWorker.
func outputFunc(in worker.Worker, out interface{}) error {
inWorker, _ := in.(*agentWorker)
outPointer, _ := out.(*agent.Agent)
if inWorker == nil || outPointer == nil {
return errors.Errorf("expected %T->%T; got %T->%T", inWorker, outPointer, in, out)
}
*outPointer = inWorker.agent
return nil
}
// agentWorker is a degenerate worker.Worker that exists only to make an Agent
// accessible via the manifold's Output.
type agentWorker struct {
tomb tomb.Tomb
agent agent.Agent
}
// Kill is part of the worker.Worker interface.
func (w *agentWorker) Kill() {
w.tomb.Kill(nil)
}
// Wait is part of the worker.Worker interface.
func (w *agentWorker) Wait() error {
return w.tomb.Wait()
}