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package lifecycle
import (
"context"
"github.com/pkg/errors"
)
// A PauseResumer can be atomically paused and resumed.
type PauseResumer interface {
// Pause should result in pausing all operations if nil is returned.
//
// If a pause cannot complete within the context deadline,
// the context error should be returned, and normal operation should
// resume, as if pause was never called.
Pause(context.Context) error
// Resume should always result in normal operation.
//
// Context can be used for control of graceful operations,
// but Resume should not return until normal operation is restored.
//
// Operations that are required for resuming, should use a background context
// internally (possibly linking any trace spans).
Resume(context.Context) error
}
type prFunc struct{ pause, resume func(context.Context) error }
func (p prFunc) Pause(ctx context.Context) error { return p.pause(ctx) }
func (p prFunc) Resume(ctx context.Context) error { return p.resume(ctx) }
var _ PauseResumer = prFunc{}
// PauseResumerFunc is a convenience method that takes a pause and resume func
// and returns a PauseResumer.
func PauseResumerFunc(pause, resume func(context.Context) error) PauseResumer {
return prFunc{pause: pause, resume: resume}
}
// MultiPauseResume will join multiple PauseResumers where
// all will be paused, or none.
//
// Any that pause successfully, when another fails, will
// have Resume called.
func MultiPauseResume(pr ...PauseResumer) PauseResumer {
pause := func(ctx context.Context) error {
ctx, cancel := context.WithCancel(ctx)
defer cancel()
pass := make(chan struct{})
fail := make(chan struct{})
errCh := make(chan error, len(pr))
resumeErrCh := make(chan error, len(pr))
doPause := func(p PauseResumer) {
err := errors.Wrapf(p.Pause(ctx), "pause")
errCh <- err
select {
case <-pass:
resumeErrCh <- nil
case <-fail:
if err == nil {
resumeErrCh <- errors.Wrapf(p.Resume(ctx), "resume")
} else {
resumeErrCh <- nil
}
}
}
for _, p := range pr {
go doPause(p)
}
var hasErr bool
var errs []error
for range pr {
err := <-errCh
if err != nil {
errs = append(errs, err)
if !hasErr {
cancel()
close(fail)
hasErr = true
}
}
}
if !hasErr {
close(pass)
}
for range pr {
err := <-resumeErrCh
if err != nil {
errs = append(errs, err)
}
}
if len(errs) > 0 {
return errors.Errorf("multiple errors: %v", errs)
}
return nil
}
resume := func(ctx context.Context) error {
ch := make(chan error)
res := func(fn func(context.Context) error) { ch <- fn(ctx) }
for _, p := range pr {
go res(p.Resume)
}
var errs []error
for range pr {
err := <-ch
if err != nil {
errs = append(errs, err)
}
}
if len(errs) > 0 {
return errors.Errorf("multiple errors: %v", errs)
}
return nil
}
return PauseResumerFunc(pause, resume)
}
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