forked from mirrors/gotosocial
141 lines
3.2 KiB
Go
141 lines
3.2 KiB
Go
package nowish
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import (
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"sync"
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"sync/atomic"
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"time"
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"unsafe"
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)
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// Start returns a new Clock instance initialized and
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// started with the provided precision, along with the
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// stop function for it's underlying timer
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func Start(precision time.Duration) (*Clock, func()) {
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c := Clock{}
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return &c, c.Start(precision)
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}
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type Clock struct {
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noCopy noCopy //nolint noCopy because a copy will fuck with atomics
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// format stores the time formatting style string
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format string
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// valid indicates whether the current value stored in .Format is valid
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valid uint32
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// mutex protects writes to .Format, not because it would be unsafe, but
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// because we want to minimize unnnecessary allocations
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mutex sync.Mutex
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// Format is an unsafe pointer to the last-updated time format string
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Format unsafe.Pointer
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// Time is an unsafe pointer to the last-updated time.Time object
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Time unsafe.Pointer
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}
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// Start starts the clock with the provided precision, the
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// returned function is the stop function for the underlying timer
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func (c *Clock) Start(precision time.Duration) func() {
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// Create ticker from duration
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tick := time.NewTicker(precision)
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// Set initial time
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t := time.Now()
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atomic.StorePointer(&c.Time, unsafe.Pointer(&t))
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// Set initial format
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s := ""
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atomic.StorePointer(&c.Format, unsafe.Pointer(&s))
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// If formatting string unset, set default
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c.mutex.Lock()
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if c.format == "" {
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c.format = time.RFC822
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}
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c.mutex.Unlock()
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// Start main routine
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go c.run(tick)
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// Return stop fn
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return tick.Stop
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}
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// run is the internal clock ticking loop
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func (c *Clock) run(tick *time.Ticker) {
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for {
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// Wait on tick
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_, ok := <-tick.C
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// Channel closed
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if !ok {
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break
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}
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// Update time
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t := time.Now()
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atomic.StorePointer(&c.Time, unsafe.Pointer(&t))
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// Invalidate format string
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atomic.StoreUint32(&c.valid, 0)
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}
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}
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// Now returns a good (ish) estimate of the current 'now' time
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func (c *Clock) Now() time.Time {
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return *(*time.Time)(atomic.LoadPointer(&c.Time))
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}
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// NowFormat returns the formatted "now" time, cached until next tick and "now" updates
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func (c *Clock) NowFormat() string {
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// If format still valid, return this
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if atomic.LoadUint32(&c.valid) == 1 {
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return *(*string)(atomic.LoadPointer(&c.Format))
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}
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// Get mutex lock
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c.mutex.Lock()
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// Double check still invalid
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if atomic.LoadUint32(&c.valid) == 1 {
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c.mutex.Unlock()
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return *(*string)(atomic.LoadPointer(&c.Format))
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}
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// Calculate time format
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b := c.Now().AppendFormat(
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make([]byte, 0, len(c.format)),
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c.format,
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)
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// Update the stored value and set valid!
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atomic.StorePointer(&c.Format, unsafe.Pointer(&b))
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atomic.StoreUint32(&c.valid, 1)
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// Unlock and return
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c.mutex.Unlock()
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// Note:
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// it's safe to do this conversion here
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// because this byte slice will never change.
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// and we have the direct pointer to it, we're
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// not requesting it atomicly via c.Format
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return *(*string)(unsafe.Pointer(&b))
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}
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// SetFormat sets the time format string used by .NowFormat()
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func (c *Clock) SetFormat(format string) {
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// Get mutex lock
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c.mutex.Lock()
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// Update time format
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c.format = format
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// Invalidate current format string
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atomic.StoreUint32(&c.valid, 0)
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// Unlock
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c.mutex.Unlock()
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}
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