Add context-aware "time" library wrapper.

go/src/infra/gae/libs/wrapper/memory/context.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 memory
 
 import (
         "errors"
-        "infra/gae/libs/wrapper"
-        "math/rand"
         "sync"
 
         "golang.org/x/net/context"
 
         "appengine/datastore"
 )
 
 type memContextObj interface {
         sync.Locker
         canApplyTxn(m memContextObj) bool
-        applyTxn(rnd *rand.Rand, m memContextObj)
+        applyTxn(c context.Context, m memContextObj)
 
         endTxn()
         mkTxn(*datastore.TransactionOptions) (memContextObj, error)
 }
 
 type memContext []memContextObj
 
 var _ = memContextObj((memContext)(nil))
 
 func newMemContext() memContext {
@@ skipping 47 matching lines @@
 func (m memContext) canApplyTxn(txnCtxObj memContextObj) bool {
         txnCtx := txnCtxObj.(memContext)
         for i := range m {
                 if !m[i].canApplyTxn(txnCtx[i]) {
                         return false
                 }
         }
         return true
 }
 
-func (m memContext) applyTxn(rnd *rand.Rand, txnCtxObj memContextObj) {
+func (m memContext) applyTxn(c context.Context, txnCtxObj memContextObj) {
         txnCtx := txnCtxObj.(memContext)
         for i := range m {
-                m[i].applyTxn(rnd, txnCtx[i])
+                m[i].applyTxn(c, txnCtx[i])
         }
 }
 
 // Use adds implementations for the following gae/wrapper interfaces to the
 // context:
 //   * wrapper.Datastore
 //   * wrapper.TaskQueue
 //   * wrapper.Memcache
 //   * wrapper.GlobalInfo
 //
@@ skipping 52 matching lines @@
         }()
 
         if err = f(context.WithValue(d.c, memContextKey, txnMC)); err != nil {
                 return err
         }
 
         txnMC.Lock()
         defer txnMC.Unlock()
 
         if curMC.canApplyTxn(txnMC) {
-                curMC.applyTxn(wrapper.GetMathRand(d.c), txnMC)
+                curMC.applyTxn(d.c, txnMC)
         } else {
                 return datastore.ErrConcurrentTransaction
         }
         return nil
 }