go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/buildbucket/appengine/model/sequence.go (about)

     1  // Copyright 2020 The LUCI Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package model
    16  
    17  import (
    18  	"context"
    19  
    20  	"go.chromium.org/luci/common/errors"
    21  	"go.chromium.org/luci/gae/service/datastore"
    22  )
    23  
    24  // NumberSequence stores the next number in a named sequence of numbers.
    25  type NumberSequence struct {
    26  	_     datastore.PropertyMap `gae:"-,extra"`
    27  	_kind string                `gae:"$kind,NumberSequence"`
    28  	ID    string                `gae:"$id"`
    29  
    30  	Next int32 `gae:"next_number,noindex"`
    31  }
    32  
    33  // GenerateSequenceNumbers generates n numbers for the given sequence name,
    34  // returning the smallest number the caller may use. For a returned number
    35  // i, the caller may use [i, i+n).
    36  func GenerateSequenceNumbers(ctx context.Context, name string, n int) (int32, error) {
    37  	// TODO(crbug/1042991): Migrate old -> new build number sequence entity key.
    38  	// TODO(crbug/1042991): Report metric for sequence number generation time.
    39  	seq := &NumberSequence{
    40  		ID: name,
    41  	}
    42  	var res int32
    43  	err := datastore.RunInTransaction(ctx, func(ctx context.Context) error {
    44  		switch err := datastore.Get(ctx, seq); {
    45  		case err == datastore.ErrNoSuchEntity:
    46  			seq.Next = 1
    47  		case err != nil:
    48  			return errors.Annotate(err, "error fetching number sequence %q", seq.ID).Err()
    49  		}
    50  		res = seq.Next
    51  		seq.Next += int32(n)
    52  		if err := datastore.Put(ctx, seq); err != nil {
    53  			return errors.Annotate(err, "error updating number sequence %q", seq.ID).Err()
    54  		}
    55  		return nil
    56  	}, nil)
    57  	if err != nil {
    58  		return 0, err
    59  	}
    60  	return res, nil
    61  }