LogDog: Add collector service implementation.

common/retry/retry.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package retry
 
 import (
         "time"
 
         "github.com/luci/luci-go/common/clock"
         "golang.org/x/net/context"
 )
 
 // Stop is a sentinel value returned by a Iterator to indicate that no more
 // attempts should be made.
 const Stop time.Duration = -1
 
 // Callback is a callback function that Retry will invoke every time an
 // attempt fails prior to sleeping.
 type Callback func(error, time.Duration)
 
 // Iterator describes a stateful implementation of retry logic.
 type Iterator interface {
         // Returns the next retry delay, or Stop if no more retries should be made.
         Next(context.Context, error) time.Duration
 }
 
+// Generator is a function that produces an Iterator instance.
+type Generator func() Iterator

[dnj (Google), 2016/01/21 04:36:24]

This concept is used enough, we might as well codify it.

+
 // Retry executes a function 'f'. If the function returns an error, it will
 // be re-executed according to a retry plan.
 //
 // If the supplied context is canceled, retry will stop executing. Retry will
 // not execute the supplied function at all if the context is canceled when
 // Retry is invoked.
 //
 // If 'callback' is not nil, it will be invoked if an error occurs (prior to
 // sleeping).
 func Retry(ctx context.Context, it Iterator, f func() error, callback Callback) (err error) {
@@ skipping 27 matching lines @@
                         select {
                         case <-ctx.Done():
                                 return ctx.Err()
 
                         case <-clock.After(ctx, delay):
                                 break
                         }
                 }
         }
 }