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serial-do.go
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serial-do.go
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/*
© 2021–present Harald Rudell <harald.rudell@gmail.com> (https://haraldrudell.github.io/haraldrudell/)
ISC License
*/
package parl
import (
"context"
"fmt"
"sync"
"time"
"github.com/haraldrudell/parl/perrors"
)
// SerialDo serializes a thunk.
//
type SerialDo struct {
thunk func(at time.Time)
eventReceiver func(event *SerialDoEvent)
errFn func(err error)
lock sync.Mutex
busySince time.Time // behind lock
pendingSince time.Time // behind lock
sdoID SerialDoID
wg WaitGroup
ctx context.Context
}
// NewSerialDo serializes .Do invocations
// eventFn must be thread-safe.
// errFn must be thread-safe.
func NewSerialDo(
thunk func(at time.Time),
eventFn func(event *SerialDoEvent),
errFn func(err error),
ctx context.Context) (sdo *SerialDo) {
if thunk == nil {
panic(perrors.Errorf("NewSerialDo with thunk nil"))
}
if errFn == nil {
panic(perrors.Errorf("NewSerialDo with errFn nil"))
}
return &SerialDo{
thunk: thunk,
eventReceiver: eventFn,
errFn: errFn,
sdoID: serialDoID.ID(),
ctx: ctx,
}
}
// Do invokes the thunk serially
// if SerialDo is idle, Do launches thunk via a thread
// if SerialDo is busy, Do makes it pending
// if SerialDo is already pending, Do does nothing
// Do returns true if SerialDo state is pending
// Do is non-blocking and thread-safe
func (sdo *SerialDo) Do(now ...time.Time) (isPending bool) {
// check state
if sdo.ctx.Err() != nil {
panic(perrors.Errorf("SerialDo#%s: Do after cancel", sdo.sdoID))
}
// ensure now0 non-zero time
var now0 time.Time
if len(now) > 0 {
now0 = now[0]
}
if now0.IsZero() {
now0 = time.Now()
}
var typ SerialDoType
if typ, isPending = sdo.performDo(now0); !typ.IsValid() {
return // was already pending: ignore Do invocation
}
// SerialDoPending: pending at now0
// SerialDoLaunch: busy at now0
// send event
sdo.invokeEventFn(typ, now0)
return // state changed return
}
func (sdo *SerialDo) State() (
busySince time.Time,
pendingSince time.Time,
isCancel bool,
isWaitComplete bool,
) {
if isCancel = sdo.ctx.Err() != nil; isCancel {
isWaitComplete = sdo.wg.IsZero()
}
sdo.lock.Lock()
defer sdo.lock.Unlock()
busySince = sdo.busySince
pendingSince = sdo.pendingSince
return
}
func (sdo *SerialDo) Wait() {
// wait for shutdown
<-sdo.ctx.Done()
// wait for thread to exit
sdo.wg.Wait()
}
func (sdo *SerialDo) String() (s string) {
s = "sdo#" + sdo.sdoID.String()
busySince, pendingSince, isCancel, isWaitComplete := sdo.State()
// check if done
if isWaitComplete {
return s + " done"
}
return fmt.Sprintf("%s busy: %s pend: %s can: %t",
s, Short(busySince), Short(pendingSince),
isCancel,
)
}
func (sdo *SerialDo) performDo(now time.Time) (typ SerialDoType, isPending bool) {
sdo.lock.Lock()
defer sdo.lock.Unlock()
// if already pending, ignore
if !sdo.pendingSince.IsZero() {
isPending = true
return // already pending
}
// if busy, mark pending
if !sdo.busySince.IsZero() {
sdo.pendingSince = now
return SerialDoPending, true
}
// launch thread
sdo.busySince = now
sdo.wg.Add(1)
go sdo.doThread(now)
typ = SerialDoLaunch
return
}
func (sdo *SerialDo) invokeEventFn(typ SerialDoType, t time.Time) {
defer Recover(Annotation(), nil, sdo.errFn)
if sdo.eventReceiver == nil {
return
}
sdo.eventReceiver(NewSerialDoEvent(typ, t, sdo))
}
func (sdo *SerialDo) invokeThunk(at time.Time) {
defer Recover(Annotation(), nil, sdo.errFn)
sdo.thunk(at)
}
func (sdo *SerialDo) doThread(at time.Time) {
defer sdo.wg.Done()
defer Recover(Annotation(), nil, sdo.errFn)
for {
sdo.invokeThunk(at)
var typ SerialDoType
typ, at = sdo.checkForMoreDo()
sdo.invokeEventFn(typ, at)
if typ == SerialDoIdle {
return
}
}
}
var timeTimeZeroValue time.Time
func (sdo *SerialDo) checkForMoreDo() (typ SerialDoType, t time.Time) {
sdo.lock.Lock()
defer sdo.lock.Unlock()
// check for cancel
if sdo.ctx.Err() != nil {
t = sdo.busySince
sdo.busySince = timeTimeZeroValue
sdo.pendingSince = timeTimeZeroValue
typ = SerialDoIdle
return
}
// if pending, relaunch thunk
if !sdo.pendingSince.IsZero() {
t = sdo.pendingSince
sdo.pendingSince = timeTimeZeroValue
typ = SerialDoPendingLaunch
return
}
// enter idle state
t = sdo.busySince
sdo.busySince = timeTimeZeroValue
typ = SerialDoIdle
return
}