Refactor current GAE abstraction library to be free of the SDK*

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"
-        "sync"
-
-        "golang.org/x/net/context"
-
-        "appengine/datastore"
-)
-
-type memContextObj interface {
-        sync.Locker
-        canApplyTxn(m memContextObj) bool
-        applyTxn(c context.Context, m memContextObj)
-
-        endTxn()
-        mkTxn(*datastore.TransactionOptions) (memContextObj, error)
-}
-
-type memContext []memContextObj
-
-var _ = memContextObj((memContext)(nil))
-
-func newMemContext() memContext {
-        return memContext{
-                newTaskQueueData(),
-                newDataStoreData(),
-        }
-}
-
-type memContextIdx int
-
-const (
-        memContextTQIdx memContextIdx = iota
-        memContextDSIdx
-)
-
-func (m memContext) Get(itm memContextIdx) memContextObj {
-        return m[itm]
-}
-
-func (m memContext) Lock() {
-        for _, itm := range m {
-                itm.Lock()
-        }
-}
-
-func (m memContext) Unlock() {
-        for i := len(m) - 1; i >= 0; i-- {
-                m[i].Unlock()
-        }
-}
-
-func (m memContext) endTxn() {
-        for _, itm := range m {
-                itm.endTxn()
-        }
-}
-
-func (m memContext) mkTxn(o *datastore.TransactionOptions) (memContextObj, error) {
-        ret := make(memContext, len(m))
-        for i, itm := range m {
-                newItm, err := itm.mkTxn(o)
-                if err != nil {
-                        return nil, err
-                }
-                ret[i] = newItm
-        }
-        return ret, nil
-}
-
-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(c context.Context, txnCtxObj memContextObj) {
-        txnCtx := txnCtxObj.(memContext)
-        for i := range m {
-                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
-//
-// These can be retrieved with the "gae/wrapper".Get functions.
-//
-// The implementations are all backed by an in-memory implementation, and start
-// with an empty state.
-//
-// Using this more than once per context.Context will cause a panic.
-func Use(c context.Context) context.Context {
-        if c.Value(memContextKey) != nil {
-                panic(errors.New("memory.Use: called twice on the same Context"))
-        }
-        c = context.WithValue(
-                context.WithValue(c, memContextKey, newMemContext()),
-                giContextKey, &globalInfoData{})
-        return useTQ(useDS(useMC(useGI(c))))
-}
-
-func cur(c context.Context) (p memContext) {
-        p, _ = c.Value(memContextKey).(memContext)
-        return
-}
-
-type memContextKeyType int
-
-var memContextKey memContextKeyType
-
-// weird stuff
-
-// RunInTransaction is here because it's really a service-wide transaction, not
-// just in the datastore. TaskQueue behaves differently in a transaction in
-// a couple ways, for example.
-//
-// It really should have been appengine.Context.RunInTransaction(func(tc...)),
-// but because it's not, this method is on dsImpl instead to mirror the official
-// API.
-//
-// The fake implementation also differs from the real implementation because the
-// fake TaskQueue is NOT backed by the fake Datastore. This is done to make the
-// test-access API for TaskQueue better (instead of trying to reconstitute the
-// state of the task queue from a bunch of datastore accesses).
-func (d *dsImpl) RunInTransaction(f func(context.Context) error, o *datastore.TransactionOptions) error {
-        curMC := cur(d.c)
-
-        txnMC, err := curMC.mkTxn(o)
-        if err != nil {
-                return err
-        }
-
-        defer func() {
-                txnMC.Lock()
-                defer txnMC.Unlock()
-
-                txnMC.endTxn()
-        }()
-
-        if err = f(context.WithValue(d.c, memContextKey, txnMC)); err != nil {
-                return err
-        }
-
-        txnMC.Lock()
-        defer txnMC.Unlock()
-
-        if curMC.canApplyTxn(txnMC) {
-                curMC.applyTxn(d.c, txnMC)
-        } else {
-                return datastore.ErrConcurrentTransaction
-        }
-        return nil
-}