dm/appengine/mutate/record_completion.go

// Copyright 2015 The LUCI Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package mutate

import (
	"context"

	"go.chromium.org/luci/dm/api/service/v1"
	"go.chromium.org/luci/dm/appengine/model"
	ds "go.chromium.org/luci/gae/service/datastore"
	"go.chromium.org/luci/tumble"
)

// Attempt to complete attempts 64-at-a-time. Rely on tumble's
// tail-call optimization to save on transactions.
const completionLimit = 64

// RecordCompletion marks that fact that an Attempt is completed (Finished) on
// its corresponding BackDepGroup, and fires off additional AckFwdDep mutations
// for each incoming dependency that is blocked.
//
// In the case where an Attempt has hundreds or thousands of incoming
// dependencies, the naive implementation of this mutation could easily overfill
// a single datastore transaction. For that reason, the implementation here
// unblocks things 64 edges at a time, and keeps returning itself as a mutation
// until it unblocks less than 64 things (e.g. it does a tail-call).
//
// This relies on tumble's tail-call optimization to be performant in terms of
// the number of transactions, otherwise this would take 1 transaction per
// 64 dependencies. With the TCO, it could do hundreds or thousands of
// dependencies, but it will also be fair to other work (e.g. it will allow
// other Attempts to take dependencies on this Attempt while RecordCompletion
// is in between tail-calls).
type RecordCompletion struct {
	For *dm.Attempt_ID
}

// Root implements tumble.Mutation.
func (r *RecordCompletion) Root(c context.Context) *ds.Key {
	return ds.KeyForObj(c, &model.BackDepGroup{Dependee: *r.For})
}

// RollForward implements tumble.Mutation.
func (r *RecordCompletion) RollForward(c context.Context) (muts []tumble.Mutation, err error) {
	bdg := &model.BackDepGroup{Dependee: *r.For}
	if err = ds.Get(c, bdg); err != nil && err != ds.ErrNoSuchEntity {
		return
	}

	needProp := make([]*model.BackDep, 0, completionLimit)

	q := (ds.NewQuery("BackDep").
		Ancestor(ds.KeyForObj(c, bdg)).
		Eq("Propagated", false).
		Limit(completionLimit))

	if err = ds.GetAll(c, q, &needProp); err != nil {
		return
	}

	if len(needProp) > 0 {
		muts = make([]tumble.Mutation, len(needProp))

		for i, bdep := range needProp {
			bdep.Propagated = true
			muts[i] = &AckFwdDep{bdep.Edge()}
		}

		if len(needProp) == completionLimit {
			// Append ourself if there might be more to do!
			muts = append(muts, r)
		}

		if err = ds.Put(c, needProp); err != nil {
			return
		}
	}

	if !bdg.AttemptFinished {
		bdg.AttemptFinished = true
		if err = ds.Put(c, bdg); err != nil {
			return
		}
	}

	return
}

func init() {
	tumble.Register((*RecordCompletion)(nil))
}