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/*
Classical-inheritance-style service declarations.
Services can be started, then stopped, then optionally restarted.
Users can override the OnStart/OnStop methods.
By default, these methods are guaranteed to be called at most once.
A call to Reset will panic, unless OnReset is overwritten, allowing OnStart/OnStop to be called again.
Caller must ensure that Start() and Stop() are not called concurrently.
It is ok to call Stop() without calling Start() first.
Services cannot be re-started unless OnReset is overwritten to allow it.
Typical usage:
type FooService struct {
BaseService
// private fields
}
func NewFooService() *FooService {
fs := &FooService{
// init
}
fs.BaseService = *NewBaseService(log, "FooService", fs)
return fs
}
func (fs *FooService) OnStart() error {
fs.BaseService.OnStart() // Always call the overridden method.
// initialize private fields
// start subroutines, etc.
}
func (fs *FooService) OnStop() error {
fs.BaseService.OnStop() // Always call the overridden method.
// close/destroy private fields
// stop subroutines, etc.
}
*/
package common
import (
"sync/atomic"
"github.com/tendermint/log15"
)
type Service interface {
Start() (bool, error)
OnStart() error
Stop() bool
OnStop()
Reset() (bool, error)
OnReset() error
IsRunning() bool
String() string
}
type BaseService struct {
log log15.Logger
name string
started uint32 // atomic
stopped uint32 // atomic
// The "subclass" of BaseService
impl Service
}
func NewBaseService(log log15.Logger, name string, impl Service) *BaseService {
return &BaseService{
log: log,
name: name,
impl: impl,
}
}
// Implements Servce
func (bs *BaseService) Start() (bool, error) {
if atomic.CompareAndSwapUint32(&bs.started, 0, 1) {
if atomic.LoadUint32(&bs.stopped) == 1 {
if bs.log != nil {
bs.log.Warn(Fmt("Not starting %v -- already stopped", bs.name), "impl", bs.impl)
}
return false, nil
} else {
if bs.log != nil {
bs.log.Info(Fmt("Starting %v", bs.name), "impl", bs.impl)
}
}
err := bs.impl.OnStart()
return true, err
} else {
if bs.log != nil {
bs.log.Debug(Fmt("Not starting %v -- already started", bs.name), "impl", bs.impl)
}
return false, nil
}
}
// Implements Service
func (bs *BaseService) OnStart() error { return nil }
// Implements Service
func (bs *BaseService) Stop() bool {
if atomic.CompareAndSwapUint32(&bs.stopped, 0, 1) {
if bs.log != nil {
bs.log.Info(Fmt("Stopping %v", bs.name), "impl", bs.impl)
}
bs.impl.OnStop()
return true
} else {
if bs.log != nil {
bs.log.Debug(Fmt("Stopping %v (ignoring: already stopped)", bs.name), "impl", bs.impl)
}
return false
}
}
// Implements Service
func (bs *BaseService) OnStop() {}
// Implements Service
func (bs *BaseService) Reset() (bool, error) {
if atomic.CompareAndSwapUint32(&bs.stopped, 1, 0) {
// whether or not we've started, we can reset
atomic.CompareAndSwapUint32(&bs.started, 1, 0)
return true, bs.impl.OnReset()
} else {
if bs.log != nil {
bs.log.Debug(Fmt("Can't reset %v. Not stopped", bs.name), "impl", bs.impl)
}
return false, nil
}
// never happens
return false, nil
}
// Implements Service
func (bs *BaseService) OnReset() error {
PanicSanity("The service cannot be reset")
return nil
}
// Implements Service
func (bs *BaseService) IsRunning() bool {
return atomic.LoadUint32(&bs.started) == 1 && atomic.LoadUint32(&bs.stopped) == 0
}
// Implements Servce
func (bs *BaseService) String() string {
return bs.name
}
//----------------------------------------
type QuitService struct {
BaseService
Quit chan struct{}
}
func NewQuitService(log log15.Logger, name string, impl Service) *QuitService {
return &QuitService{
BaseService: *NewBaseService(log, name, impl),
Quit: nil,
}
}
// NOTE: when overriding OnStart, must call .QuitService.OnStart().
func (qs *QuitService) OnStart() error {
qs.Quit = make(chan struct{})
return nil
}
// NOTE: when overriding OnStop, must call .QuitService.OnStop().
func (qs *QuitService) OnStop() {
if qs.Quit != nil {
close(qs.Quit)
}
}