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|
package runners
import (
"context"
"sync"
)
// 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 {
state uint32 // 0=stopped, 1=running, 2=stopping
mutex sync.Mutex // mutex protects overall state changes
wait sync.Mutex // wait is used as a single-entity wait-group, only ever locked within 'mutex'
ctx chan struct{} // ctx is the current context for running function (or nil if not running)
}
// 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)) bool {
// Attempt to start the svc
ctx, ok := svc.doStart()
if !ok {
return false
}
defer func() {
// unlock single wait
svc.wait.Unlock()
// ensure stopped
_ = svc.Stop()
}()
// Run with context.
fn(CancelCtx(ctx))
return true
}
// 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)) bool {
// Attempt to start the svc
ctx, ok := svc.doStart()
if !ok {
return false
}
go func() {
defer func() {
// unlock single wait
svc.wait.Unlock()
// ensure stopped
_ = svc.Stop()
}()
// Run with context.
fn(CancelCtx(ctx))
}()
return true
}
// RunWait is functionally the same as .Run(), but blocks until the first instance of .Run() returns.
func (svc *Service) RunWait(fn func(context.Context)) bool {
// Attempt to start the svc
ctx, ok := svc.doStart()
if !ok {
<-ctx // block
return false
}
defer func() {
// unlock single wait
svc.wait.Unlock()
// ensure stopped
_ = svc.Stop()
}()
// Run with context.
fn(CancelCtx(ctx))
return true
}
// 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 {
// Attempt to stop the svc
ctx, ok := svc.doStop()
if !ok {
return false
}
defer func() {
// Get svc lock
svc.mutex.Lock()
// Wait until stopped
svc.wait.Lock()
svc.wait.Unlock()
// Reset the svc
svc.ctx = nil
svc.state = 0
svc.mutex.Unlock()
}()
// Cancel ctx
close(ctx)
return true
}
// While allows you to execute given function guaranteed within current
// service state. Please note that this will hold the underlying service
// state change mutex open while executing the function.
func (svc *Service) While(fn func()) {
// Protect state change
svc.mutex.Lock()
defer svc.mutex.Unlock()
// Run
fn()
}
// doStart will safely set Service state to started, returning a ptr to this context insance.
func (svc *Service) doStart() (chan struct{}, bool) {
// Protect startup
svc.mutex.Lock()
if svc.ctx == nil {
// this will only have been allocated
// if svc.Done() was already called.
svc.ctx = make(chan struct{})
}
// Take our own ptr
ctx := svc.ctx
if svc.state != 0 {
// State was not stopped.
svc.mutex.Unlock()
return ctx, false
}
// Set started.
svc.state = 1
// Start waiter.
svc.wait.Lock()
// Unlock and return
svc.mutex.Unlock()
return ctx, true
}
// doStop will safely set Service state to stopping, returning a ptr to this cancelfunc instance.
func (svc *Service) doStop() (chan struct{}, bool) {
// Protect stop
svc.mutex.Lock()
if svc.state != 1 /* not started */ {
svc.mutex.Unlock()
return nil, false
}
// state stopping
svc.state = 2
// Take our own ptr
// and unlock state
ctx := svc.ctx
svc.mutex.Unlock()
return ctx, true
}
// Running returns if Service is running (i.e. state NOT stopped / stopping).
func (svc *Service) Running() bool {
svc.mutex.Lock()
state := svc.state
svc.mutex.Unlock()
return (state == 1)
}
// 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{} {
var done <-chan struct{}
svc.mutex.Lock()
switch svc.state {
// stopped
case 0:
if svc.ctx == nil {
// here we create a new context so that the
// returned 'done' channel here will still
// be valid for when Service is next started.
svc.ctx = make(chan struct{})
}
done = svc.ctx
// started
case 1:
done = svc.ctx
// stopping
case 2:
done = svc.ctx
}
svc.mutex.Unlock()
return done
}
|
