resumer: periodically resume transaction

worker/resumer/resumer.go

Index: worker/resumer/resumer.go
=== added file 'worker/resumer/resumer.go'
--- worker/resumer/resumer.go	1970-01-01 00:00:00 +0000
+++ worker/resumer/resumer.go	2013-06-19 11:49:55 +0000
@@ -0,0 +1,71 @@
+// Copyright 2012, 2013 Canonical Ltd.
+// Licensed under the AGPLv3, see LICENCE file for details.
+
+package resumer
+
+import (
+	"fmt"
+	"launchpad.net/juju-core/log"
+	"launchpad.net/tomb"
+	"time"
+)
+
+// defaultInterval is the standard value for the interval setting.
+const defaultInterval = time.Minute
+
+// interval sets how often the resuming is called.
+var interval = defaultInterval
+
+// TransactionResumer defines the interface for types capable to
+// resume transactions.
+type TransactionResumer interface {
+	// ResumeTransactions resumes all pending transactions.
+	ResumeTransactions() error
+}
+
+// Resumer is responsible for a periodical resuming of pending transactions.
+type Resumer struct {
+	tomb tomb.Tomb
+	tr   TransactionResumer
+}
+
+// NewResumer periodically resumes pending transactions.
+func NewResumer(tr TransactionResumer) *Resumer {
+	rr := &Resumer{tr: tr}
+	go func() {
+		defer rr.tomb.Done()
+		rr.tomb.Kill(rr.loop())
+	}()
+	return rr
+}
+
+func (rr *Resumer) String() string {
+	return fmt.Sprintf("resumer")
+}
+
+func (rr *Resumer) Kill() {
+	rr.tomb.Kill(nil)
+}
+
+func (rr *Resumer) Stop() error {
+	rr.tomb.Kill(nil)
+	return rr.tomb.Wait()
+}
+
+func (rr *Resumer) Wait() error {
+	return rr.tomb.Wait()
+}
+
+func (rr *Resumer) loop() error {
+	for {
+		select {
+		case <-rr.tomb.Dying():
+			return tomb.ErrDying
+		case <-time.After(interval):
+			if err := rr.tr.ResumeTransactions(); err != nil {
+				log.Errorf("worker/resumer: cannot resume transactions: %v", err)
+			}
+		}
+	}
+	panic("unreachable")
+}