Documentation
¶
Overview ¶
Package time provides functionality for measuring and displaying time.
The calendrical calculations always assume a Gregorian calendar, with no leap seconds.
Monotonic Clocks ¶
Operating systems provide both a “wall clock,” which is subject to changes for clock synchronization, and a “monotonic clock,” which is not. The general rule is that the wall clock is for telling time and the monotonic clock is for measuring time. Rather than split the API, in this package the Time returned by time.Now contains both a wall clock reading and a monotonic clock reading; later time-telling operations use the wall clock reading, but later time-measuring operations, specifically comparisons and subtractions, use the monotonic clock reading.
For example, this code always computes a positive elapsed time of approximately 20 milliseconds, even if the wall clock is changed during the operation being timed:
start := time.Now() ... operation that takes 20 milliseconds ... t := time.Now() elapsed := t.Sub(start)
Other idioms, such as time.Since(start), time.Until(deadline), and time.Now().Before(deadline), are similarly robust against wall clock resets.
The rest of this section gives the precise details of how operations use monotonic clocks, but understanding those details is not required to use this package.
The Time returned by time.Now contains a monotonic clock reading. If Time t has a monotonic clock reading, t.Add adds the same duration to both the wall clock and monotonic clock readings to compute the result. Because t.AddDate(y, m, d), t.Round(d), and t.Truncate(d) are wall time computations, they always strip any monotonic clock reading from their results. Because t.In, t.Local, and t.UTC are used for their effect on the interpretation of the wall time, they also strip any monotonic clock reading from their results. The canonical way to strip a monotonic clock reading is to use t = t.Round(0).
If Times t and u both contain monotonic clock readings, the operations t.After(u), t.Before(u), t.Equal(u), and t.Sub(u) are carried out using the monotonic clock readings alone, ignoring the wall clock readings. If either t or u contains no monotonic clock reading, these operations fall back to using the wall clock readings.
On some systems the monotonic clock will stop if the computer goes to sleep. On such a system, t.Sub(u) may not accurately reflect the actual time that passed between t and u.
Because the monotonic clock reading has no meaning outside the current process, the serialized forms generated by t.GobEncode, t.MarshalBinary, t.MarshalJSON, and t.MarshalText omit the monotonic clock reading, and t.Format provides no format for it. Similarly, the constructors time.Date, time.Parse, time.ParseInLocation, and time.Unix, as well as the unmarshalers t.GobDecode, t.UnmarshalBinary. t.UnmarshalJSON, and t.UnmarshalText always create times with no monotonic clock reading.
Note that the Go == operator compares not just the time instant but also the Location and the monotonic clock reading. See the documentation for the Time type for a discussion of equality testing for Time values.
For debugging, the result of t.String does include the monotonic clock reading if present. If t != u because of different monotonic clock readings, that difference will be visible when printing t.String() and u.String().
Index ¶
- Constants
- func After(d Duration) <-chan Time
- func Sleep(d Duration)
- func Tick(d Duration) <-chan Time
- type Duration
- func (d Duration) Hours() float64
- func (d Duration) Microseconds() int64
- func (d Duration) Milliseconds() int64
- func (d Duration) Minutes() float64
- func (d Duration) Nanoseconds() int64
- func (d Duration) Round(m Duration) Duration
- func (d Duration) Seconds() float64
- func (d Duration) String() string
- func (d Duration) Truncate(m Duration) Duration
- type Month
- type Ticker
- type Time
- func (t Time) Add(d Duration) Time
- func (t Time) AddDate(years int, months int, days int) Time
- func (t Time) After(u Time) bool
- func (t Time) Before(u Time) bool
- func (t Time) Clock() (hour, min, sec int)
- func (t Time) Date() (year int, month Month, day int)
- func (t Time) Day() int
- func (t Time) Equal(u Time) bool
- func (t *Time) GobDecode(data []byte) error
- func (t Time) GobEncode() ([]byte, error)
- func (t Time) Hour() int
- func (t Time) ISOWeek() (year, week int)
- func (t Time) In(loc *Location) Time
- func (t Time) IsZero() bool
- func (t Time) Local() Time
- func (t Time) Location() *Location
- func (t Time) MarshalBinary() ([]byte, error)
- func (t Time) MarshalJSON() ([]byte, error)
- func (t Time) MarshalText() ([]byte, error)
- func (t Time) Minute() int
- func (t Time) Month() Month
- func (t Time) Nanosecond() int
- func (t Time) Round(d Duration) Time
- func (t Time) Second() int
- func (t Time) Sub(u Time) Duration
- func (t Time) Truncate(d Duration) Time
- func (t Time) UTC() Time
- func (t Time) Unix() int64
- func (t Time) UnixNano() int64
- func (t *Time) UnmarshalBinary(data []byte) error
- func (t *Time) UnmarshalJSON(data []byte) error
- func (t *Time) UnmarshalText(data []byte) error
- func (t Time) Weekday() Weekday
- func (t Time) Year() int
- func (t Time) YearDay() int
- func (t Time) Zone() (name string, offset int)
- type Timer
- type Weekday
Constants ¶
const ( Nanosecond Duration = 1 Microsecond = 1000 * Nanosecond Millisecond = 1000 * Microsecond Second = 1000 * Millisecond Minute = 60 * Second Hour = 60 * Minute )
Common durations. There is no definition for units of Day or larger to avoid confusion across daylight savings time zone transitions.
To count the number of units in a Duration, divide:
second := time.Second fmt.Print(int64(second/time.Millisecond)) // prints 1000
To convert an integer number of units to a Duration, multiply:
seconds := 10 fmt.Print(time.Duration(seconds)*time.Second) // prints 10s
Variables ¶
This section is empty.
Functions ¶
func After ¶
After waits for the duration to elapse and then sends the current time on the returned channel. It is equivalent to NewTimer(d).C. The underlying Timer is not recovered by the garbage collector until the timer fires. If efficiency is a concern, use NewTimer instead and call Timer.Stop if the timer is no longer needed.
func Sleep ¶
func Sleep(d Duration)
Sleep pauses the current goroutine for at least the duration d. A negative or zero duration causes Sleep to return immediately.
func Tick ¶
Tick is a convenience wrapper for NewTicker providing access to the ticking channel only. While Tick is useful for clients that have no need to shut down the Ticker, be aware that without a way to shut it down the underlying Ticker cannot be recovered by the garbage collector; it "leaks". Unlike NewTicker, Tick will return nil if d <= 0.
Types ¶
type Duration ¶
type Duration int64
A Duration represents the elapsed time between two instants as an int64 nanosecond count. The representation limits the largest representable duration to approximately 290 years.
func (Duration) Microseconds ¶
Microseconds returns the duration as an integer microsecond count.
func (Duration) Milliseconds ¶
Milliseconds returns the duration as an integer millisecond count.
func (Duration) Nanoseconds ¶
Nanoseconds returns the duration as an integer nanosecond count.
func (Duration) Round ¶
Round returns the result of rounding d to the nearest multiple of m. The rounding behavior for halfway values is to round away from zero. If the result exceeds the maximum (or minimum) value that can be stored in a Duration, Round returns the maximum (or minimum) duration. If m <= 0, Round returns d unchanged.
func (Duration) String ¶
String returns a string representing the duration in the form "72h3m0.5s". Leading zero units are omitted. As a special case, durations less than one second format use a smaller unit (milli-, micro-, or nanoseconds) to ensure that the leading digit is non-zero. The zero duration formats as 0s.
type Ticker ¶
type Ticker struct {
C <-chan Time // The channel on which the ticks are delivered.
// contains filtered or unexported fields
}
A Ticker holds a channel that delivers “ticks” of a clock at intervals.
func NewTicker ¶
NewTicker returns a new Ticker containing a channel that will send the time on the channel after each tick. The period of the ticks is specified by the duration argument. The ticker will adjust the time interval or drop ticks to make up for slow receivers. The duration d must be greater than zero; if not, NewTicker will panic. Stop the ticker to release associated resources.
type Time ¶
type Time struct {
// contains filtered or unexported fields
}
A Time represents an instant in time with nanosecond precision.
Programs using times should typically store and pass them as values, not pointers. That is, time variables and struct fields should be of type time.Time, not *time.Time.
A Time value can be used by multiple goroutines simultaneously except that the methods GobDecode, UnmarshalBinary, UnmarshalJSON and UnmarshalText are not concurrency-safe.
Time instants can be compared using the Before, After, and Equal methods. The Sub method subtracts two instants, producing a Duration. The Add method adds a Time and a Duration, producing a Time.
The zero value of type Time is January 1, year 1, 00:00:00.000000000 UTC. As this time is unlikely to come up in practice, the IsZero method gives a simple way of detecting a time that has not been initialized explicitly.
Each Time has associated with it a Location, consulted when computing the presentation form of the time, such as in the Format, Hour, and Year methods. The methods Local, UTC, and In return a Time with a specific location. Changing the location in this way changes only the presentation; it does not change the instant in time being denoted and therefore does not affect the computations described in earlier paragraphs.
Representations of a Time value saved by the GobEncode, MarshalBinary, MarshalJSON, and MarshalText methods store the Time.Location's offset, but not the location name. They therefore lose information about Daylight Saving Time.
In addition to the required “wall clock” reading, a Time may contain an optional reading of the current process's monotonic clock, to provide additional precision for comparison or subtraction. See the “Monotonic Clocks” section in the package documentation for details.
Note that the Go == operator compares not just the time instant but also the Location and the monotonic clock reading. Therefore, Time values should not be used as map or database keys without first guaranteeing that the identical Location has been set for all values, which can be achieved through use of the UTC or Local method, and that the monotonic clock reading has been stripped by setting t = t.Round(0). In general, prefer t.Equal(u) to t == u, since t.Equal uses the most accurate comparison available and correctly handles the case when only one of its arguments has a monotonic clock reading.
func Date ¶
Date returns the Time corresponding to
yyyy-mm-dd hh:mm:ss + nsec nanoseconds
in the appropriate zone for that time in the given location.
The month, day, hour, min, sec, and nsec values may be outside their usual ranges and will be normalized during the conversion. For example, October 32 converts to November 1.
A daylight savings time transition skips or repeats times. For example, in the United States, March 13, 2011 2:15am never occurred, while November 6, 2011 1:15am occurred twice. In such cases, the choice of time zone, and therefore the time, is not well-defined. Date returns a time that is correct in one of the two zones involved in the transition, but it does not guarantee which.
Date panics if loc is nil.
func Unix ¶
Unix returns the local Time corresponding to the given Unix time, sec seconds and nsec nanoseconds since January 1, 1970 UTC. It is valid to pass nsec outside the range [0, 999999999]. Not all sec values have a corresponding time value. One such value is 1<<63-1 (the largest int64 value).
func (Time) AddDate ¶
AddDate returns the time corresponding to adding the given number of years, months, and days to t. For example, AddDate(-1, 2, 3) applied to January 1, 2011 returns March 4, 2010.
AddDate normalizes its result in the same way that Date does, so, for example, adding one month to October 31 yields December 1, the normalized form for November 31.
func (Time) Equal ¶
Equal reports whether t and u represent the same time instant. Two times can be equal even if they are in different locations. For example, 6:00 +0200 and 4:00 UTC are Equal. See the documentation on the Time type for the pitfalls of using == with Time values; most code should use Equal instead.
func (Time) ISOWeek ¶
ISOWeek returns the ISO 8601 year and week number in which t occurs. Week ranges from 1 to 53. Jan 01 to Jan 03 of year n might belong to week 52 or 53 of year n-1, and Dec 29 to Dec 31 might belong to week 1 of year n+1.
func (Time) In ¶
In returns a copy of t representing the same time instant, but with the copy's location information set to loc for display purposes.
In panics if loc is nil.
func (Time) IsZero ¶
IsZero reports whether t represents the zero time instant, January 1, year 1, 00:00:00 UTC.
func (Time) Location ¶
func (t Time) Location() *Location
Location returns the time zone information associated with t.
func (Time) MarshalBinary ¶
MarshalBinary implements the encoding.BinaryMarshaler interface.
func (Time) MarshalJSON ¶
MarshalJSON implements the json.Marshaler interface. The time is a quoted string in RFC 3339 format, with sub-second precision added if present.
func (Time) MarshalText ¶
MarshalText implements the encoding.TextMarshaler interface. The time is formatted in RFC 3339 format, with sub-second precision added if present.
func (Time) Minute ¶
Minute returns the minute offset within the hour specified by t, in the range [0, 59].
func (Time) Nanosecond ¶
Nanosecond returns the nanosecond offset within the second specified by t, in the range [0, 999999999].
func (Time) Round ¶
Round returns the result of rounding t to the nearest multiple of d (since the zero time). The rounding behavior for halfway values is to round up. If d <= 0, Round returns t stripped of any monotonic clock reading but otherwise unchanged.
Round operates on the time as an absolute duration since the zero time; it does not operate on the presentation form of the time. Thus, Round(Hour) may return a time with a non-zero minute, depending on the time's Location.
func (Time) Second ¶
Second returns the second offset within the minute specified by t, in the range [0, 59].
func (Time) Sub ¶
Sub returns the duration t-u. If the result exceeds the maximum (or minimum) value that can be stored in a Duration, the maximum (or minimum) duration will be returned. To compute t-d for a duration d, use t.Add(-d).
func (Time) Truncate ¶
Truncate returns the result of rounding t down to a multiple of d (since the zero time). If d <= 0, Truncate returns t stripped of any monotonic clock reading but otherwise unchanged.
Truncate operates on the time as an absolute duration since the zero time; it does not operate on the presentation form of the time. Thus, Truncate(Hour) may return a time with a non-zero minute, depending on the time's Location.
func (Time) Unix ¶
Unix returns t as a Unix time, the number of seconds elapsed since January 1, 1970 UTC. The result does not depend on the location associated with t. Unix-like operating systems often record time as a 32-bit count of seconds, but since the method here returns a 64-bit value it is valid for billions of years into the past or future.
func (Time) UnixNano ¶
UnixNano returns t as a Unix time, the number of nanoseconds elapsed since January 1, 1970 UTC. The result is undefined if the Unix time in nanoseconds cannot be represented by an int64 (a date before the year 1678 or after 2262). Note that this means the result of calling UnixNano on the zero Time is undefined. The result does not depend on the location associated with t.
func (*Time) UnmarshalBinary ¶
UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.
func (*Time) UnmarshalJSON ¶
UnmarshalJSON implements the json.Unmarshaler interface. The time is expected to be a quoted string in RFC 3339 format.
func (*Time) UnmarshalText ¶
UnmarshalText implements the encoding.TextUnmarshaler interface. The time is expected to be in RFC 3339 format.
type Timer ¶
type Timer struct {
C <-chan Time
// contains filtered or unexported fields
}
Timer 类型表示了一个单一的事件。 当 Timer 过期时，除非 Timer 在 AfterFunc 之后创建，当前时间将发送到 C。 一个 Timer 必须通过 NewTimer 或 AfterFunc 进行创建。
func AfterFunc ¶
AfterFunc waits for the duration to elapse and then calls f in its own goroutine. It returns a Timer that can be used to cancel the call using its Stop method.
func NewTimer ¶
NewTimer creates a new Timer that will send the current time on its channel after at least duration d.
func (*Timer) Reset ¶
Reset changes the timer to expire after duration d. It returns true if the timer had been active, false if the timer had expired or been stopped.
Reset should be invoked only on stopped or expired timers with drained channels. If a program has already received a value from t.C, the timer is known to have expired and the channel drained, so t.Reset can be used directly. If a program has not yet received a value from t.C, however, the timer must be stopped and—if Stop reports that the timer expired before being stopped—the channel explicitly drained:
if !t.Stop() {
<-t.C
}
t.Reset(d)
This should not be done concurrent to other receives from the Timer's channel.
Note that it is not possible to use Reset's return value correctly, as there is a race condition between draining the channel and the new timer expiring. Reset should always be invoked on stopped or expired channels, as described above. The return value exists to preserve compatibility with existing programs.
func (*Timer) Stop ¶
Stop prevents the Timer from firing. It returns true if the call stops the timer, false if the timer has already expired or been stopped. Stop does not close the channel, to prevent a read from the channel succeeding incorrectly.
To ensure the channel is empty after a call to Stop, check the return value and drain the channel. For example, assuming the program has not received from t.C already:
if !t.Stop() {
<-t.C
}
This cannot be done concurrent to other receives from the Timer's channel or other calls to the Timer's Stop method.
For a timer created with AfterFunc(d, f), if t.Stop returns false, then the timer has already expired and the function f has been started in its own goroutine; Stop does not wait for f to complete before returning. If the caller needs to know whether f is completed, it must coordinate with f explicitly.
Source Files