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package nowish
import (
"sync"
"sync/atomic"
"time"
)
// Timeout provides a reusable structure for enforcing timeouts with a cancel
type Timeout struct {
noCopy noCopy //nolint noCopy because a copy will mess with atomics
tk *time.Timer // tk is the underlying timeout-timer
ch syncer // ch is the cancel synchronization channel
wg sync.WaitGroup // wg is the waitgroup to hold .Start() until timeout goroutine started
st timeoutState // st stores the current timeout state (and protects concurrent use)
}
// NewTimeout returns a new Timeout instance
func NewTimeout() Timeout {
tk := time.NewTimer(time.Minute)
tk.Stop() // don't keep it running
return Timeout{
tk: tk,
ch: make(syncer),
}
}
func (t *Timeout) runTimeout(hook func()) {
t.wg.Add(1)
go func() {
cancelled := false
// Signal started
t.wg.Done()
select {
// Timeout reached
case <-t.tk.C:
if !t.st.stop() /* a sneaky cancel! */ {
t.ch.recv()
cancelled = true
defer t.ch.send()
}
// Cancel called
case <-t.ch:
cancelled = true
defer t.ch.send()
}
// Ensure timer stopped
if cancelled && !t.tk.Stop() {
<-t.tk.C
}
// Defer reset state
defer t.st.reset()
// If timed out call hook
if !cancelled {
hook()
}
}()
t.wg.Wait()
}
// Start starts the timer with supplied timeout. If timeout is reached before
// cancel then supplied timeout hook will be called. Error may be called if
// Timeout is already running when this function is called
func (t *Timeout) Start(d time.Duration, hook func()) {
if !t.st.start() {
panic("nowish: timeout already started")
}
t.runTimeout(hook)
t.tk.Reset(d)
}
// Cancel cancels the currently running timer. If a cancel is achieved, then
// this function will return after the timeout goroutine is finished
func (t *Timeout) Cancel() {
if !t.st.stop() {
return
}
t.ch.send()
t.ch.recv()
}
// timeoutState provides a thread-safe timeout state mechanism
type timeoutState uint32
// start attempts to start the state, must be already reset, returns success
func (t *timeoutState) start() bool {
return atomic.CompareAndSwapUint32((*uint32)(t), 0, 1)
}
// stop attempts to stop the state, must already be started, returns success
func (t *timeoutState) stop() bool {
return atomic.CompareAndSwapUint32((*uint32)(t), 1, 2)
}
// reset is fairly self explanatory
func (t *timeoutState) reset() {
atomic.StoreUint32((*uint32)(t), 0)
}
// syncer provides helpful receiver methods for a synchronization channel
type syncer (chan struct{})
// send blocks on sending an empty value down channel
func (s syncer) send() {
s <- struct{}{}
}
// recv blocks on receiving (and dropping) empty value from channel
func (s syncer) recv() {
<-s
}
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