Gin Practice Serial 11 Cron timed tasks

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Cron timed Tasks

Project Address: Https://github.com/EDDYCJY/go ...

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In real-world applications, the use of timed tasks is common. Have you ever had a question about Golang how to do a timed task, or is it a poll?

In this article we will talk about Cron in conjunction with our project

Introduced

We will use the Cron package, which implements the Cron Spec parser and task Runner, simply to include the functions required for the scheduled task

Cron-expression format

Field name	is required	allowable Values	allowed special characters
Seconds (Seconds)	Yes	0-59	* / , -
Points (Minutes)	Yes	0-59	* / , -
Time (Hours)	Yes	0-23	* / , -
One of the one months (day of month)	Yes	1-31	* / , - ?
Monthly (month)	Yes	1-12 or Jan-dec	* / , -
Day of the week (Day of week)	Yes	0-6 or Sun-sat	* / , - ?

A cron expression represents a set of times, using 6 space-delimited fields

Can notice that the Golang Cron more than Crontab a second level, and then meet the second-level requirements of the time is convenient

Cron Special Characters

1. asterisk (*)

An asterisk indicates that all values of the field will be matched

2. Slash (/)

A slash user describes the increment of the range, expressed as "n-max/x", the form of first-last/x, for example 3-59/15 represents the third minute at this time and thereafter every 15 minutes, to 59 minutes. Starting with N, the increment is used until the end of that particular range. It won't repeat

3, comma (,)

Commas are used to separate items in the list. For example, using "Mon,wed,fri" on day of week will mean Monday, Wednesday and Friday

4. Hyphen (-)

Hyphens are used to define ranges. For example, 9-17 means every hour from 9 o'clock in the morning to 5 o'clock in the afternoon

5. Question mark (?)

Do not specify a value, instead of "*", similar to the existence of "_", it is not difficult to understand

Pre-defined Cron schedule

input	Brief Introduction	equivalent
@yearly (or @annually)	Run once at midnight January 1	0 0 0 1 1 *
@monthly	Every month at midnight, the first month of each month runs	0 0 0 1
@weekly	Once a week, run at midnight in Sunday	0 0 0 0
@daily (or @midnight)	Run once a day at midnight	0 0 0 *
@hourly	Run once per hour	0 0

Installation

$ go get -u github.com/robfig/cron

Practice

In the previous chapter gin practice serial 10 Custom GORM callbacks, we used the GORM callback to implement soft deletion, but also introduced another problem

Is how I hard delete, when do I hard delete? This is often related to business scenarios and is roughly

• Another set of hard-deleted interfaces
• Timed task Cleanup (or transfer, backup) invalid data

Here we use the second solution to practice

Writing hard-deleted code

Open the Tag.go, Article.go file under the models directory, and add the following code separately

1, Tag.go

func CleanAllTag() bool {    db.Unscoped().Where("deleted_on != ? ", 0).Delete(&Tag{})    return true}

2, Article.go

func CleanAllArticle() bool {    db.Unscoped().Where("deleted_on != ? ", 0).Delete(&Article{})    return true}

Note the hard delete to use Unscoped() , which is the GORM convention

Write cron

Create a new Cron.go file under the project root to write the code for the timed task and write the contents of the file

package mainimport (    "time"    "log"    "github.com/robfig/cron"    "github.com/EDDYCJY/go-gin-example/models")func main() {    log.Println("Starting...")    c := cron.New()    c.AddFunc("* * * * * *", func() {        log.Println("Run models.CleanAllTag...")        models.CleanAllTag()    })    c.AddFunc("* * * * * *", func() {        log.Println("Run models.CleanAllArticle...")        models.CleanAllArticle()    })    c.Start()    t1 := time.NewTimer(time.Second * 10)    for {        select {        case <-t1.C:            t1.Reset(time.Second * 10)        }    }}

In this program, we do the following things

1, Cron. New ()

A new (blank) Cron job is created based on local time runner

func New() *Cron {    return NewWithLocation(time.Now().Location())}// NewWithLocation returns a new Cron job runner.func NewWithLocation(location *time.Location) *Cron {    return &Cron{        entries:  nil,        add:      make(chan *Entry),        stop:     make(chan struct{}),        snapshot: make(chan []*Entry),        running:  false,        ErrorLog: nil,        location: location,    }}

2, C.addfunc ()

Addfunc will add a func to the Cron job runner to run on a given schedule

func (c *Cron) AddJob(spec string, cmd Job) error {    schedule, err := Parse(spec)    if err != nil {        return err    }    c.Schedule(schedule, cmd)    return nil}

The timesheet will be parsed first, and if a problem is filled, err will be added directly to the Schedule queue for execution

func (c *Cron) Schedule(schedule Schedule, cmd Job) {    entry := &Entry{        Schedule: schedule,        Job:      cmd,    }    if !c.running {        c.entries = append(c.entries, entry)        return    }    c.add <- entry}

3, C.start ()

Starts the Cron scheduler in the currently executing program. In fact, the main body here is Goroutine + for + select + Timer scheduling control OH

func (c *Cron) Run() {    if c.running {        return    }    c.running = true    c.run()}

4, time. Newtimer + for + select + T1. Reset

If you are a beginner, you will probably have questions, what is it for?

(1) time. Newtimer

A new timer is created, and a channel message is sent after you set the time D

(2) for + Select

Block Select waits for Channel

(3) T1. Reset

Resets the timer to start the timer again.
(Note that this article applies to "T.C has been taken away and can be used directly with Reset")

In general, this procedure is designed to block the main program, I hope you have questions to think, there is no other way?

Yes, you select{} can directly complete this requirement:)

Verify

$ go run cron.go 2018/04/29 17:03:34 [info] replacing callback `gorm:update_time_stamp` from /Users/eddycjy/go/src/github.com/EDDYCJY/go-gin-example/models/models.go:562018/04/29 17:03:34 [info] replacing callback `gorm:update_time_stamp` from /Users/eddycjy/go/src/github.com/EDDYCJY/go-gin-example/models/models.go:572018/04/29 17:03:34 [info] replacing callback `gorm:delete` from /Users/eddycjy/go/src/github.com/EDDYCJY/go-gin-example/models/models.go:582018/04/29 17:03:34 Starting...2018/04/29 17:03:35 Run models.CleanAllArticle...2018/04/29 17:03:35 Run models.CleanAllTag...2018/04/29 17:03:36 Run models.CleanAllArticle...2018/04/29 17:03:36 Run models.CleanAllTag...2018/04/29 17:03:37 Run models.CleanAllTag...2018/04/29 17:03:37 Run models.CleanAllArticle...

Check output log is normal, simulate soft deleted data, scheduled task work OK

Summary

Timing tasks are common, I hope you can understand golang how to achieve a simple scheduled task scheduling management

Can not rely on the system's Crontab settings, which day to use it?

Reference

Sample code for this series

• Go-gin-example

Catalog of this series

• Gin Practice Serial One Golang introduction and environment installation
• Gin Practice Two Build blog API ' s (i)
• Gin Practice three Build blog API ' s (ii)
• Gin Practice Four Build blog API ' s (iii)
• Gin Practice Five Build blog API ' s (iv)
• Gin Practice Six Build blog API ' s (v)
• Gin Practice serial Seven Golang graceful restart HTTP service
• Gin practice serial Eight for it plus swagger
• Gin practice nine deploying Golang applications to Docker
• Gin Practice serial 10 Custom GORM callbacks
• Gin Practice Serial 11 Cron timed tasks
• Gin Practice Golang Cross-compiling