脚本专栏 发布日期：2024/12/29 浏览次数：1
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 * / , - "htmlcode">
# ┌───────────── 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：3/15
3）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("htmlcode">
constantdelay.go #一个最简单的秒级别定时系统。与cron无关 constantdelay_test.go #测试 cron.go #Cron系统。管理一系列的cron定时任务（Schedule Job） cron_test.go #测试 doc.go #说明文档 LICENSE #授权书 parser.go #解析器，解析cron格式字符串城一个具体的定时器（Schedule） parser_test.go #测试 README.md #README 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 spec_test.go #测试
cron.go
结构体：
// Cron keeps track of any number of entries, invoking the associated func as
// specified by the schedule. It may be started, stopped, and the entries may
// be inspected while running.
// 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。
type Cron struct {
entries []*Entry // 任务
stop chan struct{} // 叫停止的途径
add chan *Entry // 添加新任务的方式
snapshot chan []*Entry // 请求获取任务快照的方式
running bool // 是否在运行
ErrorLog *log.Logger // 出错日志(新增属性)
location *time.Location // 所在地区(新增属性)
}
// Entry consists of a schedule and the func to execute on that schedule.
// 入口包括时间表和可在时间表上执行的func
type Entry struct {
// 计时器
Schedule Schedule
// 下次执行时间
Next time.Time
// 上次执行时间
Prev time.Time
// 任务
Job Job
}
关键方法：
// 开始任务
// Start the cron scheduler in its own go-routine, or no-op if already started.
func (c *Cron) Start() {
if c.running {
return
}
c.running = true
go c.run()
}
// 结束任务
// Stop stops the cron scheduler if it is running; otherwise it does nothing.
func (c *Cron) Stop() {
if !c.running {
return
}
c.stop <- struct{}{}
c.running = false
}
// 执行定时任务
// Run the scheduler.. this is private just due to the need to synchronize
// access to the 'running' state variable.
func (c *Cron) run() {
// Figure out the next activation times for each entry.
now := time.Now().In(c.location)
for _, entry := range c.entries {
entry.Next = entry.Schedule.Next(now)
}
// 无限循环
for {
//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
sort.Sort(byTime(c.entries))
var effective time.Time
if len(c.entries) == 0 || c.entries[0].Next.IsZero() {
// If there are no entries yet, just sleep - it still handles new entries
// and stop requests.
effective = now.AddDate(10, 0, 0)
} else {
effective = c.entries[0].Next
}
timer := time.NewTimer(effective.Sub(now))
select {
case now = <-timer.C: // 执行当前任务
now = now.In(c.location)
// Run every entry whose next time was this effective time.
for _, e := range c.entries {
if e.Next != effective {
break
}
go c.runWithRecovery(e.Job)
e.Prev = e.Next
e.Next = e.Schedule.Next(now)
}
continue
case newEntry := <-c.add: // 添加新的任务
c.entries = append(c.entries, newEntry)
newEntry.Next = newEntry.Schedule.Next(time.Now().In(c.location))
case <-c.snapshot: // 获取快照
c.snapshot <- c.entrySnapshot()
case <-c.stop: // 停止任务
timer.Stop()
return
}
// 'now' should be updated after newEntry and snapshot cases.
now = time.Now().In(c.location)
timer.Stop()
}
}
spec.go
结构体及关键方法：
// SpecSchedule specifies a duty cycle (to the second granularity), based on a
// traditional crontab specification. It is computed initially and stored as bit sets.
type SpecSchedule struct {
// 表达式中锁表明的，秒，分，时，日，月，周，每个都是uint64
// Dom:Day of Month,Dow:Day of week
Second, Minute, Hour, Dom, Month, Dow uint64
}
// bounds provides a range of acceptable values (plus a map of name to value).
// 定义了表达式的结构体
type bounds struct {
min, max uint
names map[string]uint
}
// The bounds for each field.
// 这样就能看出各个表达式的范围
var (
seconds = bounds{0, 59, nil}
minutes = bounds{0, 59, nil}
hours = bounds{0, 23, nil}
dom = bounds{1, 31, nil}
months = bounds{1, 12, map[string]uint{
"jan": 1,
"feb": 2,
"mar": 3,
"apr": 4,
"may": 5,
"jun": 6,
"jul": 7,
"aug": 8,
"sep": 9,
"oct": 10,
"nov": 11,
"dec": 12,
}}
dow = bounds{0, 6, map[string]uint{
"sun": 0,
"mon": 1,
"tue": 2,
"wed": 3,
"thu": 4,
"fri": 5,
"sat": 6,
}}
)
const (
// Set the top bit if a star was included in the expression.
starBit = 1 << 63
)
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。
/* ------------------------------------------------------------ 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) * / "htmlcode">package cron import ( "fmt" "math" "strconv" "strings" "time" ) // Configuration options for creating a parser. Most options specify which // fields should be included, while others enable features. If a field is not // included the parser will assume a default value. These options do not change // the order fields are parse in. type ParseOption int const ( Second ParseOption = 1 << iota // Seconds field, default 0 Minute // Minutes field, default 0 Hour // Hours field, default 0 Dom // Day of month field, default * Month // Month field, default * Dow // Day of week field, default * DowOptional // Optional day of week field, default * Descriptor // Allow descriptors such as @monthly, @weekly, etc. ) var places = []ParseOption{ Second, Minute, Hour, Dom, Month, Dow, } var defaults = []string{ "0", "0", "0", "*", "*", "*", } // A custom Parser that can be configured. type Parser struct { options ParseOption optionals int } // Creates a custom Parser with custom options. // // // Standard parser without descriptors // specParser := NewParser(Minute | Hour | Dom | Month | Dow) // sched, err := specParser.Parse("0 0 15 */3 *") // // // Same as above, just excludes time fields // subsParser := NewParser(Dom | Month | Dow) // sched, err := specParser.Parse("15 */3 *") // // // Same as above, just makes Dow optional // subsParser := NewParser(Dom | Month | DowOptional) // sched, err := specParser.Parse("15 */3") // func NewParser(options ParseOption) Parser { optionals := 0 if options&DowOptional > 0 { options |= Dow optionals++ } return Parser{options, optionals} } // Parse returns a new crontab schedule representing the given spec. // It returns a descriptive error if the spec is not valid. // It accepts crontab specs and features configured by NewParser. // 将字符串解析成为SpecSchedule 。 SpecSchedule符合Schedule接口 func (p Parser) Parse(spec string) (Schedule, error) { // 直接处理特殊的特殊的字符串 if spec[0] == '@' && p.options&Descriptor > 0 { return parseDescriptor(spec) } // Figure out how many fields we need max := 0 for _, place := range places { if p.options&place > 0 { max++ } } min := max - p.optionals // cron利用空白拆解出独立的items。 fields := strings.Fields(spec) // 验证表达式取值范围 if count := len(fields); count < min || count > max { if min == max { return nil, fmt.Errorf("Expected exactly %d fields, found %d: %s", min, count, spec) } return nil, fmt.Errorf("Expected %d to %d fields, found %d: %s", min, max, count, spec) } // Fill in missing fields fields = expandFields(fields, p.options) var err error field := func(field string, r bounds) uint64 { if err != nil { return 0 } var bits uint64 bits, err = getField(field, r) return bits } var ( second = field(fields[0], seconds) minute = field(fields[1], minutes) hour = field(fields[2], hours) dayofmonth = field(fields[3], dom) month = field(fields[4], months) dayofweek = field(fields[5], dow) ) if err != nil { return nil, err } // 返回所需要的SpecSchedule return &SpecSchedule{ Second: second, Minute: minute, Hour: hour, Dom: dayofmonth, Month: month, Dow: dayofweek, }, nil } func expandFields(fields []string, options ParseOption) []string { n := 0 count := len(fields) expFields := make([]string, len(places)) copy(expFields, defaults) for i, place := range places { if options&place > 0 { expFields[i] = fields[n] n++ } if n == count { break } } return expFields } var standardParser = NewParser( Minute | Hour | Dom | Month | Dow | Descriptor, ) // ParseStandard returns a new crontab schedule representing the given standardSpec // (https://en.wikipedia.org/wiki/Cron). It differs from Parse requiring to always // pass 5 entries representing: minute, hour, day of month, month and day of week, // in that order. It returns a descriptive error if the spec is not valid. // // It accepts // - Standard crontab specs, e.g. "* * * * " // - Descriptors, e.g. "@midnight", "@every 1h30m" // 这里表示不仅可以使用cron表达式，也可以使用@midnight @every等方法 func ParseStandard(standardSpec string) (Schedule, error) { return standardParser.Parse(standardSpec) } var defaultParser = NewParser( Second | Minute | Hour | Dom | Month | DowOptional | Descriptor, ) // Parse returns a new crontab schedule representing the given spec. // It returns a descriptive error if the spec is not valid. // // It accepts // - Full crontab specs, e.g. "* * * * * " // - Descriptors, e.g. "@midnight", "@every 1h30m" func Parse(spec string) (Schedule, error) { return defaultParser.Parse(spec) } // getField returns an Int with the bits set representing all of the times that // the field represents or error parsing field value. A "field" is a comma-separated // list of "ranges". func getField(field string, r bounds) (uint64, error) { var bits uint64 ranges := strings.FieldsFunc(field, func(r rune) bool { return r == ',' }) for _, expr := range ranges { bit, err := getRange(expr, r) if err != nil { return bits, err } bits |= bit } return bits, nil } // getRange returns the bits indicated by the given expression: // number | number "-" number [ "/" number ] // or error parsing range. func getRange(expr string, r bounds) (uint64, error) { var ( start, end, step uint rangeAndStep = strings.Split(expr, "/") lowAndHigh = strings.Split(rangeAndStep[0], "-") singleDigit = len(lowAndHigh) == 1 err error ) var extra uint64 if lowAndHigh[0] == "*" || lowAndHigh[0] == "" { start = r.min end = r.max extra = starBit } else { start, err = parseIntOrName(lowAndHigh[0], r.names) if err != nil { return 0, err } switch len(lowAndHigh) { case 1: end = start case 2: end, err = parseIntOrName(lowAndHigh[1], r.names) if err != nil { return 0, err } default: return 0, fmt.Errorf("Too many hyphens: %s", expr) } } switch len(rangeAndStep) { case 1: step = 1 case 2: step, err = mustParseInt(rangeAndStep[1]) if err != nil { return 0, err } // Special handling: "N/step" means "N-max/step". if singleDigit { end = r.max } default: return 0, fmt.Errorf("Too many slashes: %s", expr) } if start < r.min { return 0, fmt.Errorf("Beginning of range (%d) below minimum (%d): %s", start, r.min, expr) } if end > r.max { return 0, fmt.Errorf("End of range (%d) above maximum (%d): %s", end, r.max, expr) } if start > end { return 0, fmt.Errorf("Beginning of range (%d) beyond end of range (%d): %s", start, end, expr) } if step == 0 { return 0, fmt.Errorf("Step of range should be a positive number: %s", expr) } return getBits(start, end, step) | extra, nil } // parseIntOrName returns the (possibly-named) integer contained in expr. func parseIntOrName(expr string, names map[string]uint) (uint, error) { if names != nil { if namedInt, ok := names[strings.ToLower(expr)]; ok { return namedInt, nil } } return mustParseInt(expr) } // mustParseInt parses the given expression as an int or returns an error. func mustParseInt(expr string) (uint, error) { num, err := strconv.Atoi(expr) if err != nil { return 0, fmt.Errorf("Failed to parse int from %s: %s", expr, err) } if num < 0 { return 0, fmt.Errorf("Negative number (%d) not allowed: %s", num, expr) } return uint(num), nil } // getBits sets all bits in the range [min, max], modulo the given step size. func getBits(min, max, step uint) uint64 { var bits uint64 // If step is 1, use shifts. if step == 1 { return ^(math.MaxUint64 << (max + 1)) & (math.MaxUint64 << min) } // Else, use a simple loop. for i := min; i <= max; i += step { bits |= 1 << i } return bits } // all returns all bits within the given bounds. (plus the star bit) func all(r bounds) uint64 { return getBits(r.min, r.max, 1) | starBit } // parseDescriptor returns a predefined schedule for the expression, or error if none matches. func parseDescriptor(descriptor string) (Schedule, error) { switch descriptor { case "@yearly", "@annually": return &SpecSchedule{ Second: 1 << seconds.min, Minute: 1 << minutes.min, Hour: 1 << hours.min, Dom: 1 << dom.min, Month: 1 << months.min, Dow: all(dow), }, nil case "@monthly": return &SpecSchedule{ Second: 1 << seconds.min, Minute: 1 << minutes.min, Hour: 1 << hours.min, Dom: 1 << dom.min, Month: all(months), Dow: all(dow), }, nil case "@weekly": return &SpecSchedule{ Second: 1 << seconds.min, Minute: 1 << minutes.min, Hour: 1 << hours.min, Dom: all(dom), Month: all(months), Dow: 1 << dow.min, }, nil case "@daily", "@midnight": return &SpecSchedule{ Second: 1 << seconds.min, Minute: 1 << minutes.min, Hour: 1 << hours.min, Dom: all(dom), Month: all(months), Dow: all(dow), }, nil case "@hourly": return &SpecSchedule{ Second: 1 << seconds.min, Minute: 1 << minutes.min, Hour: all(hours), Dom: all(dom), Month: all(months), Dow: all(dow), }, nil } const every = "@every " if strings.HasPrefix(descriptor, every) { duration, err := time.ParseDuration(descriptor[len(every):]) if err != nil { return nil, fmt.Errorf("Failed to parse duration %s: %s", descriptor, err) } return Every(duration), nil } return nil, fmt.Errorf("Unrecognized descriptor: %s", descriptor) }项目中应用
package main import ( "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。
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