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package runners
import (
"context"
"sync"
"sync/atomic"
"unsafe"
)
// Service provides a means of tracking a single long-running Service, provided protected state
// changes and preventing multiple instances running. Also providing Service state information.
type Service struct{ p atomic_pointer }
// Run will run the supplied function until completion, using given context to propagate cancel.
// Immediately returns false if the Service is already running, and true after completed run.
func (svc *Service) Run(fn func(context.Context)) (ok bool) {
var ptr *svc_instance
// Attempt to start.
ptr, ok = svc.start()
if !ok {
return
}
// Run given function.
defer svc.on_done(ptr)
fn(CancelCtx(ptr.done))
return
}
// GoRun will run the supplied function until completion in a goroutine, using given context to
// propagate cancel. Immediately returns boolean indicating success, or that service is already running.
func (svc *Service) GoRun(fn func(context.Context)) (ok bool) {
var ptr *svc_instance
// Attempt to start.
ptr, ok = svc.start()
if !ok {
return
}
go func() {
// Run given function.
defer svc.on_done(ptr)
fn(CancelCtx(ptr.done))
}()
return
}
// RunWait is functionally the same as .Run(), but blocks until the first instance of .Run() returns.
func (svc *Service) RunWait(fn func(context.Context)) (ok bool) {
var ptr *svc_instance
// Attempt to start.
ptr, ok = svc.start()
if !ok {
<-ptr.done
return
}
// Run given function.
defer svc.on_done(ptr)
fn(CancelCtx(ptr.done))
return
}
// GoRunWait is functionally the same as .RunWait(), but blocks until the first instance of RunWait() returns.
func (svc *Service) GoRunWait(fn func(context.Context)) (ok bool) {
var ptr *svc_instance
// Attempt to start.
ptr, ok = svc.start()
if !ok {
<-ptr.done
return
}
go func() {
// Run given function.
defer svc.on_done(ptr)
fn(CancelCtx(ptr.done))
}()
return
}
// Stop will attempt to stop the service, cancelling the running function's context. Immediately
// returns false if not running, and true only after Service is fully stopped.
func (svc *Service) Stop() bool {
return svc.must_get().stop()
}
// Running returns if Service is running (i.e. NOT fully stopped, but may be *stopping*).
func (svc *Service) Running() bool {
return svc.must_get().running()
}
// Done returns a channel that's closed when Service.Stop() is called. It is
// the same channel provided to the currently running service function.
func (svc *Service) Done() <-chan struct{} {
return svc.must_get().done
}
func (svc *Service) start() (*svc_instance, bool) {
ptr := svc.must_get()
return ptr, ptr.start()
}
func (svc *Service) on_done(ptr *svc_instance) {
// Ensure stopped.
ptr.stop_private()
// Free service.
svc.p.Store(nil)
}
func (svc *Service) must_get() *svc_instance {
var newptr *svc_instance
for {
// Try to load existing instance.
ptr := (*svc_instance)(svc.p.Load())
if ptr != nil {
return ptr
}
if newptr == nil {
// Allocate new instance.
newptr = new(svc_instance)
newptr.done = make(chan struct{})
}
// Attempt to acquire slot by setting our ptr.
if !svc.p.CAS(nil, unsafe.Pointer(newptr)) {
continue
}
return newptr
}
}
type svc_instance struct {
wait sync.WaitGroup
done chan struct{}
state atomic.Uint32
}
const (
started_bit = uint32(1) << 0
stopping_bit = uint32(1) << 1
finished_bit = uint32(1) << 2
)
func (i *svc_instance) start() (ok bool) {
// Acquire start by setting 'started' bit.
switch old := i.state.Or(started_bit); {
case old&finished_bit != 0:
// Already finished.
case old&started_bit == 0:
// Successfully started!
i.wait.Add(1)
ok = true
}
return
}
// NOTE: MAY ONLY BE CALLED BY STARTING GOROUTINE.
func (i *svc_instance) stop_private() {
// Attempt set both stopping and finished bits.
old := i.state.Or(stopping_bit | finished_bit)
// Only if we weren't already
// stopping do we close channel.
if old&stopping_bit == 0 {
close(i.done)
}
// Release
// waiters.
i.wait.Done()
}
func (i *svc_instance) stop() (ok bool) {
// Attempt to set the 'stopping' bit.
switch old := i.state.Or(stopping_bit); {
case old&finished_bit != 0:
// Already finished.
return
case old&started_bit == 0:
// This was never started
// to begin with, just mark
// as fully finished here.
_ = i.state.Or(finished_bit)
return
case old&stopping_bit == 0:
// We succesfully stopped
// instance, close channel.
close(i.done)
ok = true
}
// Wait on stop.
i.wait.Wait()
return
}
// running returns whether service was started and
// is not yet finished. that indicates that it may
// have been started and not yet stopped, or that
// it was started, stopped and not yet returned.
func (i *svc_instance) running() bool {
val := i.state.Load()
return val&started_bit != 0 &&
val&finished_bit == 0
}
|
