Go cron定时任务的用法 / 开普饭

cron是什么cron的意思就是：计划任务，说白了就是定时任务。我和系统约个时间，你在几点几分几秒或者每隔几分钟跑一个任务(job)，就那么简单。cron表达式cron表达式是一个好东西，这个东西不仅Java的quartZ能用到，Go语言中也可以用到。我没有用过Linux的cron，但网上说Linux也是可以用crontab -e 命令来配置定时任务。Go语言和Java中都是可以精确到秒的，但是Linux中不行。cron表达式代表一个时间的集合，使用6个空格分隔的字段表示：字段名是否必须允许的值　允许的特定字符秒(Seconds)是0-59* / , -分(Minute)是0-59* / , -时(Hours)是0-23* / , -日(Day of month)是1-31* / , - ?月(Month)是1-12 或 JAN-DEC* / , -星期(Day of week)否0-6 或 SUM-SAT* / , - ?注：1.月(Month)和星期(Day of week)字段的值不区分大小写，如：SUN、Sun 和 sun 是一样的。2.星期(Day of week)字段如果没提供，相当于是 *

# ┌───────────── min (0 - 59) # │ ┌────────────── hour (0 - 23) # │ │ ┌─────────────── day of month (1 - 31) # │ │ │ ┌──────────────── month (1 - 12) # │ │ │ │ ┌───────────────── day of week (0 - 6) (0 to 6 are Sunday to # │ │ │ │ │ Saturday, or use names; 7 is also Sunday) # │ │ │ │ │ # │ │ │ │ │ # * * * * * command to execute

cron特定字符说明1）星号(*)表示 cron 表达式能匹配该字段的所有值。如在第5个字段使用星号(month)，表示每个月2）斜线(/)表示增长间隔，如第1个字段(minutes) 值是 3-59/15，表示每小时的第3分钟开始执行一次，之后每隔 15 分钟执行一次（即 3、18、33、48 这些时间点执行），这里也可以表示为：3/153）逗号(,)用于枚举值，如第6个字段值是 MON,WED,FRI，表示星期一、三、五执行4）连字号(-)表示一个范围，如第3个字段的值为 9-17 表示 9am 到 5pm 直接每个小时（包括9和17）5）问号(?)只用于日(Day of month) 和星期(Day of week)，表示不指定值，可以用于代替 *6）L，W，#Go中没有L，W，#的用法，下文作解释。cron举例说明每隔5秒执行一次：*/5 * * * * ?每隔1分钟执行一次：0 */1 * * * ?每天23点执行一次：0 0 23 * * ?每天凌晨1点执行一次：0 0 1 * * ?每月1号凌晨1点执行一次：0 0 1 1 * ?在26分、29分、33分执行一次：0 26,29,33 * * * ?每天的0点、13点、18点、21点都执行一次：0 0 0,13,18,21 * * ?下载安装控制台输入 go get github.com/robfig/cron 去下载定时任务的Go包，前提是你的 $GOPATH 已经配置好源码解析文件目录讲解

1 constantdelay.go #一个最简单的秒级别定时系统。与cron无关 2 constantdelay_test.go #测试 3 cron.go #Cron系统。管理一系列的cron定时任务（Schedule Job） 4 cron_test.go #测试 5 doc.go #说明文档 6 LICENSE #授权书 7 parser.go #解析器，解析cron格式字符串城一个具体的定时器（Schedule） 8 parser_test.go #测试 9 README.md #README10 spec.go #单个定时器（Schedule）结构体。如何计算自己的下一次触发时间11 spec_test.go #测试

cron.go结构体：

1 // Cron keeps track of any number of entries, invoking the associated func as 2 // specified by the schedule. It may be started, stopped, and the entries may 3 // be inspected while running. 4 // Cron保持任意数量的条目的轨道，调用相关的func时间表指定。它可以被启动，停止和条目，可运行的同时进行检查。 5 type Cron struct { 6 entries []*Entry 　　　　// 任务 7 stop chan struct{} // 叫停止的途径 8 add chan *Entry // 添加新任务的方式 9 snapshot chan []*Entry // 请求获取任务快照的方式10 running bool // 是否在运行11 ErrorLog *log.Logger // 出错日志(新增属性)12 location *time.Location // 所在地区(新增属性) 13 }

1 // Entry consists of a schedule and the func to execute on that schedule. 2 // 入口包括时间表和可在时间表上执行的func 3 type Entry struct { 4 // 计时器 5 Schedule Schedule 6 // 下次执行时间 7 Next time.Time 8 // 上次执行时间 9 Prev time.Time10 // 任务11 Job Job12 }

关键方法：

1 // 开始任务 2 // Start the cron scheduler in its own go-routine, or no-op if already started. 3 func (c *Cron) Start() { 4 if c.running { 5 return 6 } 7 c.running = true 8 go c.run() 9 }10 // 结束任务11 // Stop stops the cron scheduler if it is running; otherwise it does nothing.12 func (c *Cron) Stop() {13 if !c.running {14 return15 }16 c.stop <- struct{}{}17 c.running = false18 }19 20 // 执行定时任务21 // Run the scheduler.. this is private just due to the need to synchronize22 // access to the 'running' state variable.23 func (c *Cron) run() {24 // Figure out the next activation times for each entry.25 now := time.Now().In(c.location)26 for _, entry := range c.entries {27 entry.Next = entry.Schedule.Next(now)28 }29 // 无限循环30 for {31 //通过对下一个执行时间进行排序，判断那些任务是下一次被执行的，防在队列的前面.sort是用来做排序的32 sort.Sort(byTime(c.entries))33 34 var effective time.Time35 if len(c.entries) == 0 || c.entries[0].Next.IsZero() {36 // If there are no entries yet, just sleep - it still handles new entries37 // and stop requests.38 effective = now.AddDate(10, 0, 0)39 } else {40 effective = c.entries[0].Next41 }42 43 timer := time.NewTimer(effective.Sub(now))44 select {45 case now = <-timer.C: // 执行当前任务46 now = now.In(c.location)47 // Run every entry whose next time was this effective time.48 for _, e := range c.entries {49 if e.Next != effective {50 break51 }52 go c.runWithRecovery(e.Job)53 e.Prev = e.Next54 e.Next = e.Schedule.Next(now)55 }56 continue57 58 case newEntry := <-c.add: // 添加新的任务59 c.entries = append(c.entries, newEntry)60 newEntry.Next = newEntry.Schedule.Next(time.Now().In(c.location))61 62 case <-c.snapshot: // 获取快照63 c.snapshot <- c.entrySnapshot()64 65 case <-c.stop: // 停止任务66 timer.Stop()67 return68 }69 70 // 'now' should be updated after newEntry and snapshot cases.71 now = time.Now().In(c.location)72 timer.Stop()73 }74 }

spec.go结构体及关键方法：

1 // SpecSchedule specifies a duty cycle (to the second granularity), based on a 2 // traditional crontab specification. It is computed initially and stored as bit sets. 3 type SpecSchedule struct { 4 // 表达式中锁表明的，秒，分，时，日，月，周，每个都是uint64 5 // Dom:Day of Month,Dow:Day of week 6 Second, Minute, Hour, Dom, Month, Dow uint64 7 } 8 9 // bounds provides a range of acceptable values (plus a map of name to value).10 // 定义了表达式的结构体11 type bounds struct {12 min, max uint13 names map[string]uint14 }15 16 17 // The bounds for each field.18 // 这样就能看出各个表达式的范围19 var (20 seconds = bounds{0, 59, nil}21 minutes = bounds{0, 59, nil}22 hours = bounds{0, 23, nil}23 dom = bounds{1, 31, nil}24 months = bounds{1, 12, map[string]uint{25 "jan": 1,26 "feb": 2,27 "mar": 3,28 "apr": 4,29 "may": 5,30 "jun": 6,31 "jul": 7,32 "aug": 8,33 "sep": 9,34 "oct": 10,35 "nov": 11,36 "dec": 12,37 }}38 dow = bounds{0, 6, map[string]uint{39 "sun": 0,40 "mon": 1,41 "tue": 2,42 "wed": 3,43 "thu": 4,44 "fri": 5,45 "sat": 6,46 }}47 )48 49 const (50 // Set the top bit if a star was included in the expression.51 starBit = 1 << 6352 )

看了上面的东西肯定有人疑惑为什么秒分时这些都是定义了unit64,以及定义了一个常量starBit = 1 << 63这种写法，这是逻辑运算符。表示二进制1向左移动63位。原因如下：cron表达式是用来表示一系列时间的，而时间是无法逃脱自己的区间的，分，秒 0 - 59 ，时 0 - 23 ，天/月 0 - 31 ，天/周 0 - 6 ，月0 - 11 。这些本质上都是一个点集合，或者说是一个整数区间。那么对于任意的整数区间，可以描述cron的如下部分规则。* | ? 任意，对应区间上的所有点。（额外注意日/周，日 / 月的相互干扰。）纯数字，对应一个具体的点。/ 分割的两个数字 a , b，区间上符合 a + n * b 的所有点（ n >= 0 )。- 分割的两个数字，对应这两个数字决定的区间内的所有点。L | W 需要对于特定的时间特殊判断，无法通用的对应到区间上的点。至此， robfig/cron为什么不支持 L | W的原因已经明了了。去除这两条规则后，其余的规则其实完全可以使用点的穷举来通用表示。考虑到最大的区间也不过是60个点，那么使用一个uint64的整数的每一位来表示一个点便很合适了。所以定义unit64不为过下面是go中cron表达式的方法：

/* ------------------------------------------------------------ 第64位标记任意，用于日/周，日 / 月的相互干扰。 63 - 0 为表示区间 [63 , 0] 的每一个点。 ------------------------------------------------------------ 假设区间是 0 - 63 ，则有如下的例子：比如 0/3 的表示如下： (表示每隔两位为1) * / ? +---+--------------------------------------------------------+ | 0 | 1 0 0 1 0 0 1 ~~ ~~ 1 0 0 1 0 0 1 | +---+--------------------------------------------------------+ 63 ~ ~ ~~ 0 比如 2-5 的表示如下： (表示从右往左2-5位上都是1) * / ? +---+--------------------------------------------------------+ | 0 | 0 0 0 0 ~ ~ ~~ ~ 0 0 0 1 1 1 1 0 0 | +---+--------------------------------------------------------+ 63 ~ ~ ~~ 0 比如 * 的表示如下： (表示所有位置上都为1) * / ? +---+--------------------------------------------------------+ | 1 | 1 1 1 1 1 ~ ~ ~ 1 1 1 1 1 1 1 1 1 | +---+--------------------------------------------------------+ 63 ~ ~ ~~ 0 */

parser.go将字符串解析为SpecSchedule的类。

1 package cron 2 3 import ( 4 "fmt" 5 "math" 6 "strconv" 7 "strings" 8 "time" 9 ) 10 11 // Configuration options for creating a parser. Most options specify which 12 // fields should be included, while others enable features. If a field is not 13 // included the parser will assume a default value. These options do not change 14 // the order fields are parse in. 15 type ParseOption int 16 17 const ( 18 Second ParseOption = 1 << iota // Seconds field, default 0 19 Minute // Minutes field, default 0 20 Hour // Hours field, default 0 21 Dom // Day of month field, default * 22 Month // Month field, default * 23 Dow // Day of week field, default * 24 DowOptional // Optional day of week field, default * 25 Descriptor // Allow descriptors such as @monthly, @weekly, etc. 26 ) 27 28 var places = []ParseOption{ 29 Second, 30 Minute, 31 Hour, 32 Dom, 33 Month, 34 Dow, 35 } 36 37 var defaults = []string{ 38 "0", 39 "0", 40 "0", 41 "*", 42 "*", 43 "*", 44 } 45 46 // A custom Parser that can be configured. 47 type Parser struct { 48 options ParseOption 49 optionals int 50 } 51 52 // Creates a custom Parser with custom options. 53 // 54 // // Standard parser without descriptors 55 // specParser := NewParser(Minute | Hour | Dom | Month | Dow) 56 // sched, err := specParser.Parse("0 0 15 */3 *") 57 // 58 // // Same as above, just excludes time fields 59 // subsParser := NewParser(Dom | Month | Dow) 60 // sched, err := specParser.Parse("15 */3 *") 61 // 62 // // Same as above, just makes Dow optional 63 // subsParser := NewParser(Dom | Month | DowOptional) 64 // sched, err := specParser.Parse("15 */3") 65 // 66 func NewParser(options ParseOption) Parser { 67 optionals := 0 68 if options&DowOptional > 0 { 69 options |= Dow 70 optionals++ 71 } 72 return Parser{options, optionals} 73 } 74 75 // Parse returns a new crontab schedule representing the given spec. 76 // It returns a descriptive error if the spec is not valid. 77 // It accepts crontab specs and features configured by NewParser. 78 // 将字符串解析成为SpecSchedule 。 SpecSchedule符合Schedule接口 79 80 func (p Parser) Parse(spec string) (Schedule, error) { 81 　　// 直接处理特殊的特殊的字符串 82 if spec[0] == '@' && p.options&Descriptor > 0 { 83 return parseDescriptor(spec) 84 } 85 86 // Figure out how many fields we need 87 max := 0 88 for _, place := range places { 89 if p.options&place > 0 { 90 max++ 91 } 92 } 93 min := max - p.optionals 94 95 // cron利用空白拆解出独立的items。 96 fields := strings.Fields(spec) 97 98 // 验证表达式取值范围 99 if count := len(fields); count < min || count > max {100 if min == max {101 return nil, fmt.Errorf("Expected exactly %d fields, found %d: %s", min, count, spec)102 }103 return nil, fmt.Errorf("Expected %d to %d fields, found %d: %s", min, max, count, spec)104 }105 106 // Fill in missing fields107 fields = expandFields(fields, p.options)108 109 var err error110 field := func(field string, r bounds) uint64 {111 if err != nil {112 return 0113 }114 var bits uint64115 bits, err = getField(field, r)116 return bits117 }118 119 var (120 second = field(fields[0], seconds)121 minute = field(fields[1], minutes)122 hour = field(fields[2], hours)123 dayofmonth = field(fields[3], dom)124 month = field(fields[4], months)125 dayofweek = field(fields[5], dow)126 )127 if err != nil {128 return nil, err129 }130 // 返回所需要的SpecSchedule131 return &SpecSchedule{132 Second: second,133 Minute: minute,134 Hour: hour,135 Dom: dayofmonth,136 Month: month,137 Dow: dayofweek,138 }, nil139 }140 141 func expandFields(fields []string, options ParseOption) []string {142 n := 0143 count := len(fields)144 expFields := make([]string, len(places))145 copy(expFields, defaults)146 for i, place := range places {147 if options&place > 0 {148 expFields[i] = fields[n]149 n++150 }151 if n == count {152 break153 }154 }155 return expFields156 }157 158 var standardParser = NewParser(159 Minute | Hour | Dom | Month | Dow | Descriptor,160 )161 162 // ParseStandard returns a new crontab schedule representing the given standardSpec163 // (https://en.wikipedia.org/wiki/Cron). It differs from Parse requiring to always164 // pass 5 entries representing: minute, hour, day of month, month and day of week,165 // in that order. It returns a descriptive error if the spec is not valid.166 //167 // It accepts168 // - Standard crontab specs, e.g. "* * * * ?"169 // - Descriptors, e.g. "@midnight", "@every 1h30m"170 // 这里表示不仅可以使用cron表达式，也可以使用@midnight @every等方法171 172 func ParseStandard(standardSpec string) (Schedule, error) {173 return standardParser.Parse(standardSpec)174 }175 176 var defaultParser = NewParser(177 Second | Minute | Hour | Dom | Month | DowOptional | Descriptor,178 )179 180 // Parse returns a new crontab schedule representing the given spec.181 // It returns a descriptive error if the spec is not valid.182 //183 // It accepts184 // - Full crontab specs, e.g. "* * * * * ?"185 // - Descriptors, e.g. "@midnight", "@every 1h30m"186 func Parse(spec string) (Schedule, error) {187 return defaultParser.Parse(spec)188 }189 190 // getField returns an Int with the bits set representing all of the times that191 // the field represents or error parsing field value. A "field" is a comma-separated192 // list of "ranges".193 func getField(field string, r bounds) (uint64, error) {194 var bits uint64195 ranges := strings.FieldsFunc(field, func(r rune) bool { return r == ',' })196 for _, expr := range ranges {197 bit, err := getRange(expr, r)198 if err != nil {199 return bits, err200 }201 bits |= bit202 }203 return bits, nil204 }205 206 // getRange returns the bits indicated by the given expression:207 // number | number "-" number [ "/" number ]208 // or error parsing range.209 func getRange(expr string, r bounds) (uint64, error) {210 var (211 start, end, step uint212 rangeAndStep = strings.Split(expr, "/")213 lowAndHigh = strings.Split(rangeAndStep[0], "-")214 singleDigit = len(lowAndHigh) == 1215 err error216 )217 218 var extra uint64219 if lowAndHigh[0] == "*" || lowAndHigh[0] == "?" {220 start = r.min221 end = r.max222 extra = starBit223 } else {224 start, err = parseIntOrName(lowAndHigh[0], r.names)225 if err != nil {226 return 0, err227 }228 switch len(lowAndHigh) {229 case 1:230 end = start231 case 2:232 end, err = parseIntOrName(lowAndHigh[1], r.names)233 if err != nil {234 return 0, err235 }236 default:237 return 0, fmt.Errorf("Too many hyphens: %s", expr)238 }239 }240 241 switch len(rangeAndStep) {242 case 1:243 step = 1244 case 2:245 step, err = mustParseInt(rangeAndStep[1])246 if err != nil {247 return 0, err248 }249 250 // Special handling: "N/step" means "N-max/step".251 if singleDigit {252 end = r.max253 }254 default:255 return 0, fmt.Errorf("Too many slashes: %s", expr)256 }257 258 if start < r.min {259 return 0, fmt.Errorf("Beginning of range (%d) below minimum (%d): %s", start, r.min, expr)260 }261 if end > r.max {262 return 0, fmt.Errorf("End of range (%d) above maximum (%d): %s", end, r.max, expr)263 }264 if start > end {265 return 0, fmt.Errorf("Beginning of range (%d) beyond end of range (%d): %s", start, end, expr)266 }267 if step == 0 {268 return 0, fmt.Errorf("Step of range should be a positive number: %s", expr)269 }270 271 return getBits(start, end, step) | extra, nil272 }273 274 // parseIntOrName returns the (possibly-named) integer contained in expr.275 func parseIntOrName(expr string, names map[string]uint) (uint, error) {276 if names != nil {277 if namedInt, ok := names[strings.ToLower(expr)]; ok {278 return namedInt, nil279 }280 }281 return mustParseInt(expr)282 }283 284 // mustParseInt parses the given expression as an int or returns an error.285 func mustParseInt(expr string) (uint, error) {286 num, err := strconv.Atoi(expr)287 if err != nil {288 return 0, fmt.Errorf("Failed to parse int from %s: %s", expr, err)289 }290 if num < 0 {291 return 0, fmt.Errorf("Negative number (%d) not allowed: %s", num, expr)292 }293 294 return uint(num), nil295 }296 297 // getBits sets all bits in the range [min, max], modulo the given step size.298 func getBits(min, max, step uint) uint64 {299 var bits uint64300 301 // If step is 1, use shifts.302 if step == 1 {303 return ^(math.MaxUint64 << (max + 1)) & (math.MaxUint64 << min)304 }305 306 // Else, use a simple loop.307 for i := min; i <= max; i += step {308 bits |= 1 << i309 }310 return bits311 }312 313 // all returns all bits within the given bounds. (plus the star bit)314 func all(r bounds) uint64 {315 return getBits(r.min, r.max, 1) | starBit316 }317 318 // parseDescriptor returns a predefined schedule for the expression, or error if none matches.319 func parseDescriptor(descriptor string) (Schedule, error) {320 switch descriptor {321 case "@yearly", "@annually":322 return &SpecSchedule{323 Second: 1 << seconds.min,324 Minute: 1 << minutes.min,325 Hour: 1 << hours.min,326 Dom: 1 << dom.min,327 Month: 1 << months.min,328 Dow: all(dow),329 }, nil330 331 case "@monthly":332 return &SpecSchedule{333 Second: 1 << seconds.min,334 Minute: 1 << minutes.min,335 Hour: 1 << hours.min,336 Dom: 1 << dom.min,337 Month: all(months),338 Dow: all(dow),339 }, nil340 341 case "@weekly":342 return &SpecSchedule{343 Second: 1 << seconds.min,344 Minute: 1 << minutes.min,345 Hour: 1 << hours.min,346 Dom: all(dom),347 Month: all(months),348 Dow: 1 << dow.min,349 }, nil350 351 case "@daily", "@midnight":352 return &SpecSchedule{353 Second: 1 << seconds.min,354 Minute: 1 << minutes.min,355 Hour: 1 << hours.min,356 Dom: all(dom),357 Month: all(months),358 Dow: all(dow),359 }, nil360 361 case "@hourly":362 return &SpecSchedule{363 Second: 1 << seconds.min,364 Minute: 1 << minutes.min,365 Hour: all(hours),366 Dom: all(dom),367 Month: all(months),368 Dow: all(dow),369 }, nil370 }371 372 const every = "@every "373 if strings.HasPrefix(descriptor, every) {374 duration, err := time.ParseDuration(descriptor[len(every):])375 if err != nil {376 return nil, fmt.Errorf("Failed to parse duration %s: %s", descriptor, err)377 }378 return Every(duration), nil379 }380 381 return nil, fmt.Errorf("Unrecognized descriptor: %s", descriptor)382 }

项目中应用

package mainimport ( "github.com/robfig/cron" "log")func main() { i := 0 c := cron.New() spec := "*/5 * * * * ?" c.AddFunc(spec, func() { i++ log.Println("cron running:", i) }) c.AddFunc("@every 1h1m", func() { i++ log.Println("cron running:", i) }) c.Start()}

注： @every 用法比较特殊，这是Go里面比较特色的用法。同样的还有 @yearly @annually @monthly @weekly @daily @midnight @hourly 这里面就不一一赘述了。希望大家能够自己探索。参考网站：http://blog.studygolang.com/2014/02/go_crontab/http://blog.csdn.net/cchd0001/article/details/51076922 https://en.wikipedia.org/wiki/Cron https://github.com/robfig/cron

Go cron定时任务的用法

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