119 lines
2.7 KiB
Go
119 lines
2.7 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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)
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// Timeout provides a reusable structure for enforcing timeouts with a cancel
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type Timeout struct {
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noCopy noCopy //nolint noCopy because a copy will mess with atomics
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tk *time.Timer // tk is the underlying timeout-timer
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ch syncer // ch is the cancel synchronization channel
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wg sync.WaitGroup // wg is the waitgroup to hold .Start() until timeout goroutine started
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st timeoutState // st stores the current timeout state (and protects concurrent use)
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}
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// NewTimeout returns a new Timeout instance
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func NewTimeout() Timeout {
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tk := time.NewTimer(time.Minute)
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tk.Stop() // don't keep it running
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return Timeout{
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tk: tk,
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ch: make(syncer),
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}
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}
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func (t *Timeout) runTimeout(hook func()) {
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t.wg.Add(1)
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go func() {
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cancelled := false
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// Signal started
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t.wg.Done()
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select {
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// Timeout reached
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case <-t.tk.C:
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if !t.st.stop() /* a sneaky cancel! */ {
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t.ch.recv()
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cancelled = true
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defer t.ch.send()
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}
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// Cancel called
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case <-t.ch:
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cancelled = true
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defer t.ch.send()
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}
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// Ensure timer stopped
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if cancelled && !t.tk.Stop() {
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<-t.tk.C
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}
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// Defer reset state
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defer t.st.reset()
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// If timed out call hook
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if !cancelled {
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hook()
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}
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}()
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t.wg.Wait()
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}
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// Start starts the timer with supplied timeout. If timeout is reached before
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// cancel then supplied timeout hook will be called. Error may be called if
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// Timeout is already running when this function is called
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func (t *Timeout) Start(d time.Duration, hook func()) {
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if !t.st.start() {
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panic("nowish: timeout already started")
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}
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t.runTimeout(hook)
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t.tk.Reset(d)
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}
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// Cancel cancels the currently running timer. If a cancel is achieved, then
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// this function will return after the timeout goroutine is finished
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func (t *Timeout) Cancel() {
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if !t.st.stop() {
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return
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}
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t.ch.send()
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t.ch.recv()
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}
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// timeoutState provides a thread-safe timeout state mechanism
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type timeoutState uint32
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// start attempts to start the state, must be already reset, returns success
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func (t *timeoutState) start() bool {
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return atomic.CompareAndSwapUint32((*uint32)(t), 0, 1)
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}
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// stop attempts to stop the state, must already be started, returns success
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func (t *timeoutState) stop() bool {
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return atomic.CompareAndSwapUint32((*uint32)(t), 1, 2)
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}
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// reset is fairly self explanatory
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func (t *timeoutState) reset() {
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atomic.StoreUint32((*uint32)(t), 0)
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}
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// syncer provides helpful receiver methods for a synchronization channel
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type syncer (chan struct{})
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// send blocks on sending an empty value down channel
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func (s syncer) send() {
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s <- struct{}{}
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}
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// recv blocks on receiving (and dropping) empty value from channel
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func (s syncer) recv() {
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<-s
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}
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