1// Copyright 2021 The Gitea Authors. All rights reserved.
2// Use of this source code is governed by a MIT-style
3// license that can be found in the LICENSE file.
4
5package db
6
7import (
8	"errors"
9	"fmt"
10
11	"code.gitea.io/gitea/modules/setting"
12)
13
14// ResourceIndex represents a resource index which could be used as issue/release and others
15// We can create different tables i.e. issue_index, release_index and etc.
16type ResourceIndex struct {
17	GroupID  int64 `xorm:"pk"`
18	MaxIndex int64 `xorm:"index"`
19}
20
21// UpsertResourceIndex the function will not return until it acquires the lock or receives an error.
22func UpsertResourceIndex(e Engine, tableName string, groupID int64) (err error) {
23	// An atomic UPSERT operation (INSERT/UPDATE) is the only operation
24	// that ensures that the key is actually locked.
25	switch {
26	case setting.Database.UseSQLite3 || setting.Database.UsePostgreSQL:
27		_, err = e.Exec(fmt.Sprintf("INSERT INTO %s (group_id, max_index) "+
28			"VALUES (?,1) ON CONFLICT (group_id) DO UPDATE SET max_index = %s.max_index+1",
29			tableName, tableName), groupID)
30	case setting.Database.UseMySQL:
31		_, err = e.Exec(fmt.Sprintf("INSERT INTO %s (group_id, max_index) "+
32			"VALUES (?,1) ON DUPLICATE KEY UPDATE max_index = max_index+1", tableName),
33			groupID)
34	case setting.Database.UseMSSQL:
35		// https://weblogs.sqlteam.com/dang/2009/01/31/upsert-race-condition-with-merge/
36		_, err = e.Exec(fmt.Sprintf("MERGE %s WITH (HOLDLOCK) as target "+
37			"USING (SELECT ? AS group_id) AS src "+
38			"ON src.group_id = target.group_id "+
39			"WHEN MATCHED THEN UPDATE SET target.max_index = target.max_index+1 "+
40			"WHEN NOT MATCHED THEN INSERT (group_id, max_index) "+
41			"VALUES (src.group_id, 1);", tableName),
42			groupID)
43	default:
44		return fmt.Errorf("database type not supported")
45	}
46	return
47}
48
49var (
50	// ErrResouceOutdated represents an error when request resource outdated
51	ErrResouceOutdated = errors.New("resource outdated")
52	// ErrGetResourceIndexFailed represents an error when resource index retries 3 times
53	ErrGetResourceIndexFailed = errors.New("get resource index failed")
54)
55
56const (
57	// MaxDupIndexAttempts max retry times to create index
58	MaxDupIndexAttempts = 3
59)
60
61// GetNextResourceIndex retried 3 times to generate a resource index
62func GetNextResourceIndex(tableName string, groupID int64) (int64, error) {
63	for i := 0; i < MaxDupIndexAttempts; i++ {
64		idx, err := getNextResourceIndex(tableName, groupID)
65		if err == ErrResouceOutdated {
66			continue
67		}
68		if err != nil {
69			return 0, err
70		}
71		return idx, nil
72	}
73	return 0, ErrGetResourceIndexFailed
74}
75
76// DeleteResouceIndex delete resource index
77func DeleteResouceIndex(e Engine, tableName string, groupID int64) error {
78	_, err := e.Exec(fmt.Sprintf("DELETE FROM %s WHERE group_id=?", tableName), groupID)
79	return err
80}
81
82// getNextResourceIndex return the next index
83func getNextResourceIndex(tableName string, groupID int64) (int64, error) {
84	sess := x.NewSession()
85	defer sess.Close()
86	if err := sess.Begin(); err != nil {
87		return 0, err
88	}
89	var preIdx int64
90	_, err := sess.SQL(fmt.Sprintf("SELECT max_index FROM %s WHERE group_id = ?", tableName), groupID).Get(&preIdx)
91	if err != nil {
92		return 0, err
93	}
94
95	if err := UpsertResourceIndex(sess, tableName, groupID); err != nil {
96		return 0, err
97	}
98
99	var curIdx int64
100	has, err := sess.SQL(fmt.Sprintf("SELECT max_index FROM %s WHERE group_id = ? AND max_index=?", tableName), groupID, preIdx+1).Get(&curIdx)
101	if err != nil {
102		return 0, err
103	}
104	if !has {
105		return 0, ErrResouceOutdated
106	}
107	if err := sess.Commit(); err != nil {
108		return 0, err
109	}
110	return curIdx, nil
111}
112