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122 lines
3.5 KiB
122 lines
3.5 KiB
// Copyright 2013, Google Inc. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package sync2
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import (
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"sync"
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)
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// These are the three predefined states of a service.
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const (
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SERVICE_STOPPED = iota
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SERVICE_RUNNING
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SERVICE_SHUTTING_DOWN
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)
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var stateNames = []string{
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"Stopped",
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"Running",
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"ShuttingDown",
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}
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// ServiceManager manages the state of a service through its lifecycle.
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type ServiceManager struct {
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mu sync.Mutex
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wg sync.WaitGroup
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err error // err is the error returned from the service function.
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state AtomicInt64
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// shutdown is created when the service starts and is closed when the service
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// enters the SERVICE_SHUTTING_DOWN state.
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shutdown chan struct{}
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}
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// Go tries to change the state from SERVICE_STOPPED to SERVICE_RUNNING.
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//
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// If the current state is not SERVICE_STOPPED (already running), it returns
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// false immediately.
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//
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// On successful transition, it launches the service as a goroutine and returns
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// true. The service function is responsible for returning on its own when
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// requested, either by regularly checking svc.IsRunning(), or by waiting for
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// the svc.ShuttingDown channel to be closed.
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//
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// When the service func returns, the state is reverted to SERVICE_STOPPED.
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func (svm *ServiceManager) Go(service func(svc *ServiceContext) error) bool {
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svm.mu.Lock()
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defer svm.mu.Unlock()
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if !svm.state.CompareAndSwap(SERVICE_STOPPED, SERVICE_RUNNING) {
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return false
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}
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svm.wg.Add(1)
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svm.err = nil
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svm.shutdown = make(chan struct{})
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go func() {
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svm.err = service(&ServiceContext{ShuttingDown: svm.shutdown})
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svm.state.Set(SERVICE_STOPPED)
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svm.wg.Done()
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}()
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return true
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}
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// Stop tries to change the state from SERVICE_RUNNING to SERVICE_SHUTTING_DOWN.
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// If the current state is not SERVICE_RUNNING, it returns false immediately.
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// On successul transition, it waits for the service to finish, and returns true.
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// You are allowed to Go() again after a Stop().
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func (svm *ServiceManager) Stop() bool {
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svm.mu.Lock()
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defer svm.mu.Unlock()
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if !svm.state.CompareAndSwap(SERVICE_RUNNING, SERVICE_SHUTTING_DOWN) {
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return false
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}
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// Signal the service that we've transitioned to SERVICE_SHUTTING_DOWN.
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close(svm.shutdown)
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svm.shutdown = nil
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svm.wg.Wait()
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return true
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}
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// Wait waits for the service to terminate if it's currently running.
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func (svm *ServiceManager) Wait() {
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svm.wg.Wait()
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}
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// Join waits for the service to terminate and returns the value returned by the
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// service function.
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func (svm *ServiceManager) Join() error {
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svm.wg.Wait()
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return svm.err
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}
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// State returns the current state of the service.
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// This should only be used to report the current state.
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func (svm *ServiceManager) State() int64 {
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return svm.state.Get()
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}
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// StateName returns the name of the current state.
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func (svm *ServiceManager) StateName() string {
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return stateNames[svm.State()]
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}
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// ServiceContext is passed into the service function to give it access to
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// information about the running service.
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type ServiceContext struct {
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// ShuttingDown is a channel that the service can select on to be notified
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// when it should shut down. The channel is closed when the state transitions
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// from SERVICE_RUNNING to SERVICE_SHUTTING_DOWN.
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ShuttingDown chan struct{}
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}
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// IsRunning returns true if the ServiceContext.ShuttingDown channel has not
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// been closed yet.
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func (svc *ServiceContext) IsRunning() bool {
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select {
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case <-svc.ShuttingDown:
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return false
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default:
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return true
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}
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}
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