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200 lines
5.4 KiB
200 lines
5.4 KiB
package service
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import (
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"context"
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"errors"
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"sync/atomic"
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"github.com/tendermint/tendermint/libs/log"
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)
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var (
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// ErrAlreadyStarted is returned when somebody tries to start an already
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// running service.
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ErrAlreadyStarted = errors.New("already started")
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// ErrAlreadyStopped is returned when somebody tries to stop an already
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// stopped service (without resetting it).
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ErrAlreadyStopped = errors.New("already stopped")
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// ErrNotStarted is returned when somebody tries to stop a not running
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// service.
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ErrNotStarted = errors.New("not started")
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)
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// Service defines a service that can be started, stopped, and reset.
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type Service interface {
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// Start is called to start the service, which should run until
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// the context terminates. If the service is already running, Start
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// must report an error.
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Start(context.Context) error
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// Return true if the service is running
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IsRunning() bool
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// String representation of the service
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String() string
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// Wait blocks until the service is stopped.
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Wait()
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}
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// Implementation describes the implementation that the
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// BaseService implementation wraps.
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type Implementation interface {
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Service
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// Called by the Services Start Method
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OnStart(context.Context) error
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// Called when the service's context is canceled.
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OnStop()
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}
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/*
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Classical-inheritance-style service declarations. Services can be started, then
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stopped, then optionally restarted.
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Users can override the OnStart/OnStop methods. In the absence of errors, these
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methods are guaranteed to be called at most once. If OnStart returns an error,
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service won't be marked as started, so the user can call Start again.
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A call to Reset will panic, unless OnReset is overwritten, allowing
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OnStart/OnStop to be called again.
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The caller must ensure that Start and Stop are not called concurrently.
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It is ok to call Stop without calling Start first.
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Typical usage:
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type FooService struct {
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BaseService
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// private fields
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}
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func NewFooService() *FooService {
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fs := &FooService{
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// init
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}
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fs.BaseService = *NewBaseService(log, "FooService", fs)
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return fs
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}
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func (fs *FooService) OnStart(ctx context.Context) error {
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fs.BaseService.OnStart() // Always call the overridden method.
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// initialize private fields
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// start subroutines, etc.
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}
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func (fs *FooService) OnStop() error {
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fs.BaseService.OnStop() // Always call the overridden method.
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// close/destroy private fields
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// stop subroutines, etc.
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}
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*/
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type BaseService struct {
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logger log.Logger
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name string
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started uint32 // atomic
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stopped uint32 // atomic
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quit chan struct{}
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// The "subclass" of BaseService
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impl Implementation
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}
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// NewBaseService creates a new BaseService.
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func NewBaseService(logger log.Logger, name string, impl Implementation) *BaseService {
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return &BaseService{
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logger: logger,
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name: name,
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quit: make(chan struct{}),
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impl: impl,
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}
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}
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// Start starts the Service and calls its OnStart method. An error will be
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// returned if the service is already running or stopped. To restart a
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// stopped service, call Reset.
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func (bs *BaseService) Start(ctx context.Context) error {
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if atomic.CompareAndSwapUint32(&bs.started, 0, 1) {
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if atomic.LoadUint32(&bs.stopped) == 1 {
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bs.logger.Error("not starting service; already stopped", "service", bs.name, "impl", bs.impl.String())
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atomic.StoreUint32(&bs.started, 0)
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return ErrAlreadyStopped
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}
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bs.logger.Info("starting service", "service", bs.name, "impl", bs.impl.String())
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if err := bs.impl.OnStart(ctx); err != nil {
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// revert flag
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atomic.StoreUint32(&bs.started, 0)
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return err
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}
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go func(ctx context.Context) {
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select {
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case <-bs.quit:
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// someone else explicitly called stop
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// and then we shouldn't.
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return
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case <-ctx.Done():
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// if nothing is running, no need to
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// shut down again.
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if !bs.impl.IsRunning() {
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return
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}
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// the context was cancel and we
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// should stop.
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if err := bs.Stop(); err != nil {
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bs.logger.Error("stopped service",
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"err", err.Error(),
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"service", bs.name,
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"impl", bs.impl.String())
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}
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bs.logger.Info("stopped service",
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"service", bs.name,
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"impl", bs.impl.String())
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}
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}(ctx)
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return nil
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}
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bs.logger.Debug("not starting service; already started", "service", bs.name, "impl", bs.impl.String())
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return ErrAlreadyStarted
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}
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// Stop implements Service by calling OnStop (if defined) and closing quit
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// channel. An error will be returned if the service is already stopped.
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func (bs *BaseService) Stop() error {
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if atomic.CompareAndSwapUint32(&bs.stopped, 0, 1) {
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if atomic.LoadUint32(&bs.started) == 0 {
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bs.logger.Error("not stopping service; not started yet", "service", bs.name, "impl", bs.impl.String())
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atomic.StoreUint32(&bs.stopped, 0)
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return ErrNotStarted
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}
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bs.logger.Info("stopping service", "service", bs.name, "impl", bs.impl.String())
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bs.impl.OnStop()
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close(bs.quit)
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return nil
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}
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bs.logger.Debug("not stopping service; already stopped", "service", bs.name, "impl", bs.impl.String())
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return ErrAlreadyStopped
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}
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// IsRunning implements Service by returning true or false depending on the
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// service's state.
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func (bs *BaseService) IsRunning() bool {
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return atomic.LoadUint32(&bs.started) == 1 && atomic.LoadUint32(&bs.stopped) == 0
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}
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// Wait blocks until the service is stopped.
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func (bs *BaseService) Wait() { <-bs.quit }
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// String implements Service by returning a string representation of the service.
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func (bs *BaseService) String() string { return bs.name }
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