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all, vendor: Switch back to non-forked thejerf/suture (#5171)

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This commit is contained in:
Jakob Borg
2018-09-08 11:56:56 +02:00
committed by Audrius Butkevicius
parent 8aa2d8d92c
commit 9e00b619ab
18 changed files with 47 additions and 44 deletions
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19
vendor/github.com/thejerf/suture/LICENSE generated vendored Normal file
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Copyright (c) 2014-2015 Barracuda Networks, Inc.
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

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vendor/github.com/thejerf/suture/doc.go generated vendored Normal file
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/*
Package suture provides Erlang-like supervisor trees.
This implements Erlang-esque supervisor trees, as adapted for Go. This is
intended to be an industrial-strength implementation, but it has not yet
been deployed in a hostile environment. (It's headed there, though.)
Supervisor Tree -> SuTree -> suture -> holds your code together when it's
trying to fall apart.
Why use Suture?
* You want to write bullet-resistant services that will remain available
despite unforeseen failure.
* You need the code to be smart enough not to consume 100% of the CPU
restarting things.
* You want to easily compose multiple such services in one program.
* You want the Erlang programmers to stop lording their supervision
trees over you.
Suture has 100% test coverage, and is golint clean. This doesn't prove it
free of bugs, but it shows I care.
A blog post describing the design decisions is available at
http://www.jerf.org/iri/post/2930 .
Using Suture
To idiomatically use Suture, create a Supervisor which is your top level
"application" supervisor. This will often occur in your program's "main"
function.
Create "Service"s, which implement the Service interface. .Add() them
to your Supervisor. Supervisors are also services, so you can create a
tree structure here, depending on the exact combination of restarts
you want to create.
As a special case, when adding Supervisors to Supervisors, the "sub"
supervisor will have the "super" supervisor's Log function copied.
This allows you to set one log function on the "top" supervisor, and
have it propagate down to all the sub-supervisors. This also allows
libraries or modules to provide Supervisors without having to commit
their users to a particular logging method.
Finally, as what is probably the last line of your main() function, call
.Serve() on your top level supervisor. This will start all the services
you've defined.
See the Example for an example, using a simple service that serves out
incrementing integers.
*/
package suture

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vendor/github.com/thejerf/suture/messages.go generated vendored Normal file
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package suture
// sum type pattern for type-safe message passing; see
// http://www.jerf.org/iri/post/2917
type supervisorMessage interface {
isSupervisorMessage()
}
type listServices struct {
c chan []Service
}
func (ls listServices) isSupervisorMessage() {}
type removeService struct {
id serviceID
notification chan struct{}
}
func (rs removeService) isSupervisorMessage() {}
func (s *Supervisor) sync() {
s.control <- syncSupervisor{}
}
type syncSupervisor struct {
}
func (ss syncSupervisor) isSupervisorMessage() {}
func (s *Supervisor) fail(id serviceID, err interface{}, stacktrace []byte) {
s.control <- serviceFailed{id, err, stacktrace}
}
type serviceFailed struct {
id serviceID
err interface{}
stacktrace []byte
}
func (sf serviceFailed) isSupervisorMessage() {}
func (s *Supervisor) serviceEnded(id serviceID, complete bool) {
s.sendControl(serviceEnded{id, complete})
}
type serviceEnded struct {
id serviceID
complete bool
}
func (s serviceEnded) isSupervisorMessage() {}
// added by the Add() method
type addService struct {
service Service
name string
response chan serviceID
}
func (as addService) isSupervisorMessage() {}
type stopSupervisor struct {
done chan struct{}
}
func (ss stopSupervisor) isSupervisorMessage() {}
func (s *Supervisor) panic() {
s.control <- panicSupervisor{}
}
type serviceTerminated struct {
id serviceID
}
func (st serviceTerminated) isSupervisorMessage() {}
type panicSupervisor struct {
}
func (ps panicSupervisor) isSupervisorMessage() {}

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vendor/github.com/thejerf/suture/service.go generated vendored Normal file
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package suture
/*
Service is the interface that describes a service to a Supervisor.
Serve Method
The Serve method is called by a Supervisor to start the service.
The service should execute within the goroutine that this is
called in. If this function either returns or panics, the Supervisor
will call it again.
A Serve method SHOULD do as much cleanup of the state as possible,
to prevent any corruption in the previous state from crashing the
service again.
Stop Method
This method is used by the supervisor to stop the service. Calling this
directly on a Service given to a Supervisor will simply result in the
Service being restarted; use the Supervisor's .Remove(ServiceToken) method
to stop a service. A supervisor will call .Stop() only once. Thus, it may
be as destructive as it likes to get the service to stop.
Once Stop has been called on a Service, the Service SHOULD NOT be
reused in any other supervisor! Because of the impossibility of
guaranteeing that the service has actually stopped in Go, you can't
prove that you won't be starting two goroutines using the exact
same memory to store state, causing completely unpredictable behavior.
Stop should not return until the service has actually stopped.
"Stopped" here is defined as "the service will stop servicing any
further requests in the future". For instance, a common implementation
is to receive a message on a dedicated "stop" channel and immediately
returning. Once the stop command has been processed, the service is
stopped.
Another common Stop implementation is to forcibly close an open socket
or other resource, which will cause detectable errors to manifest in the
service code. Bear in mind that to perfectly correctly use this
approach requires a bit more work to handle the chance of a Stop
command coming in before the resource has been created.
If a service does not Stop within the supervisor's timeout duration, a log
entry will be made with a descriptive string to that effect. This does
not guarantee that the service is hung; it may still get around to being
properly stopped in the future. Until the service is fully stopped,
both the service and the spawned goroutine trying to stop it will be
"leaked".
Stringer Interface
When a Service is added to a Supervisor, the Supervisor will create a
string representation of that service used for logging.
If you implement the fmt.Stringer interface, that will be used.
If you do not implement the fmt.Stringer interface, a default
fmt.Sprintf("%#v") will be used.
Optional Interface
Services may optionally implement IsCompletable, which allows a service
to indicate to a supervisor that it does not need to be restarted if
it has terminated.
*/
type Service interface {
Serve()
Stop()
}
/*
IsCompletable is an optionally-implementable interface that allows a service
to report to a supervisor that it does not need to be restarted because it
has terminated normally. When a Service is going to be restarted, the
supervisor will check for this method, and if Complete returns true, the
service is removed from the supervisor instead of restarted.
This is only executed when the service is not running because it has
terminated, and has not yet been restarted.
*/
type IsCompletable interface {
Complete() bool
}

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vendor/github.com/thejerf/suture/supervisor.go generated vendored Normal file
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package suture
import (
"errors"
"fmt"
"log"
"math"
"runtime"
"sync"
"time"
)
const (
notRunning = iota
normal
paused
)
type supervisorID uint32
type serviceID uint32
type (
// BadStopLogger is called when a service fails to properly stop
BadStopLogger func(*Supervisor, Service, string)
// FailureLogger is called when a service fails
FailureLogger func(
supervisor *Supervisor,
service Service,
serviceName string,
currentFailures float64,
failureThreshold float64,
restarting bool,
error interface{},
stacktrace []byte,
)
// BackoffLogger is called when the supervisor enters or exits backoff mode
BackoffLogger func(s *Supervisor, entering bool)
)
var currentSupervisorIDL sync.Mutex
var currentSupervisorID uint32
// ErrWrongSupervisor is returned by the (*Supervisor).Remove method
// if you pass a ServiceToken from the wrong Supervisor.
var ErrWrongSupervisor = errors.New("wrong supervisor for this service token, no service removed")
// ErrTimeout is returned when an attempt to RemoveAndWait for a service to
// stop has timed out.
var ErrTimeout = errors.New("waiting for service to stop has timed out")
// ServiceToken is an opaque identifier that can be used to terminate a service that
// has been Add()ed to a Supervisor.
type ServiceToken struct {
id uint64
}
type serviceWithName struct {
Service Service
name string
}
/*
Supervisor is the core type of the module that represents a Supervisor.
Supervisors should be constructed either by New or NewSimple.
Once constructed, a Supervisor should be started in one of three ways:
1. Calling .Serve().
2. Calling .ServeBackground().
3. Adding it to an existing Supervisor.
Calling Serve will cause the supervisor to run until it is shut down by
an external user calling Stop() on it. If that never happens, it simply
runs forever. I suggest creating your services in Supervisors, then making
a Serve() call on your top-level Supervisor be the last line of your main
func.
Calling ServeBackground will CORRECTLY start the supervisor running in a
new goroutine. You do not want to just:
go supervisor.Serve()
because that will briefly create a race condition as it starts up, if you
try to .Add() services immediately afterward.
The various Log function should only be modified while the Supervisor is
not running, to prevent race conditions.
*/
type Supervisor struct {
Name string
id supervisorID
failureDecay float64
failureThreshold float64
failureBackoff time.Duration
timeout time.Duration
log func(string)
services map[serviceID]serviceWithName
servicesShuttingDown map[serviceID]serviceWithName
lastFail time.Time
failures float64
restartQueue []serviceID
serviceCounter serviceID
control chan supervisorMessage
liveness chan struct{}
resumeTimer <-chan time.Time
recoverPanics bool
LogBadStop BadStopLogger
LogFailure FailureLogger
LogBackoff BackoffLogger
// avoid a dependency on github.com/thejerf/abtime by just implementing
// a minimal chunk.
getNow func() time.Time
getAfterChan func(time.Duration) <-chan time.Time
sync.Mutex
state uint8
}
// Spec is used to pass arguments to the New function to create a
// supervisor. See the New function for full documentation.
type Spec struct {
Log func(string)
FailureDecay float64
FailureThreshold float64
FailureBackoff time.Duration
Timeout time.Duration
LogBadStop BadStopLogger
LogFailure FailureLogger
LogBackoff BackoffLogger
PassThroughPanics bool
}
/*
New is the full constructor function for a supervisor.
The name is a friendly human name for the supervisor, used in logging. Suture
does not care if this is unique, but it is good for your sanity if it is.
If not set, the following values are used:
* Log: A function is created that uses log.Print.
* FailureDecay: 30 seconds
* FailureThreshold: 5 failures
* FailureBackoff: 15 seconds
* Timeout: 10 seconds
The Log function will be called when errors occur. Suture will log the
following:
* When a service has failed, with a descriptive message about the
current backoff status, and whether it was immediately restarted
* When the supervisor has gone into its backoff mode, and when it
exits it
* When a service fails to stop
The failureRate, failureThreshold, and failureBackoff controls how failures
are handled, in order to avoid the supervisor failure case where the
program does nothing but restarting failed services. If you do not
care how failures behave, the default values should be fine for the
vast majority of services, but if you want the details:
The supervisor tracks the number of failures that have occurred, with an
exponential decay on the count. Every FailureDecay seconds, the number of
failures that have occurred is cut in half. (This is done smoothly with an
exponential function.) When a failure occurs, the number of failures
is incremented by one. When the number of failures passes the
FailureThreshold, the entire service waits for FailureBackoff seconds
before attempting any further restarts, at which point it resets its
failure count to zero.
Timeout is how long Suture will wait for a service to properly terminate.
The PassThroughPanics options can be set to let panics in services propagate
and crash the program, should this be desirable.
*/
func New(name string, spec Spec) (s *Supervisor) {
s = new(Supervisor)
s.Name = name
currentSupervisorIDL.Lock()
currentSupervisorID++
s.id = supervisorID(currentSupervisorID)
currentSupervisorIDL.Unlock()
if spec.Log == nil {
s.log = func(msg string) {
log.Print(fmt.Sprintf("Supervisor %s: %s", s.Name, msg))
}
} else {
s.log = spec.Log
}
if spec.FailureDecay == 0 {
s.failureDecay = 30
} else {
s.failureDecay = spec.FailureDecay
}
if spec.FailureThreshold == 0 {
s.failureThreshold = 5
} else {
s.failureThreshold = spec.FailureThreshold
}
if spec.FailureBackoff == 0 {
s.failureBackoff = time.Second * 15
} else {
s.failureBackoff = spec.FailureBackoff
}
if spec.Timeout == 0 {
s.timeout = time.Second * 10
} else {
s.timeout = spec.Timeout
}
s.recoverPanics = !spec.PassThroughPanics
// overriding these allows for testing the threshold behavior
s.getNow = time.Now
s.getAfterChan = time.After
s.control = make(chan supervisorMessage)
s.liveness = make(chan struct{})
s.services = make(map[serviceID]serviceWithName)
s.servicesShuttingDown = make(map[serviceID]serviceWithName)
s.restartQueue = make([]serviceID, 0, 1)
s.resumeTimer = make(chan time.Time)
// set up the default logging handlers
if spec.LogBadStop == nil {
s.LogBadStop = func(sup *Supervisor, _ Service, name string) {
s.log(fmt.Sprintf(
"%s: Service %s failed to terminate in a timely manner",
sup.Name,
name,
))
}
} else {
s.LogBadStop = spec.LogBadStop
}
if spec.LogFailure == nil {
s.LogFailure = func(
sup *Supervisor,
_ Service,
svcName string,
f float64,
thresh float64,
restarting bool,
err interface{},
st []byte,
) {
var errString string
e, canError := err.(error)
if canError {
errString = e.Error()
} else {
errString = fmt.Sprintf("%#v", err)
}
s.log(fmt.Sprintf(
"%s: Failed service '%s' (%f failures of %f), restarting: %#v, error: %s, stacktrace: %s",
sup.Name,
svcName,
f,
thresh,
restarting,
errString,
string(st),
))
}
} else {
s.LogFailure = spec.LogFailure
}
if spec.LogBackoff == nil {
s.LogBackoff = func(s *Supervisor, entering bool) {
if entering {
s.log("Entering the backoff state.")
} else {
s.log("Exiting backoff state.")
}
}
} else {
s.LogBackoff = spec.LogBackoff
}
return
}
func serviceName(service Service) (serviceName string) {
stringer, canStringer := service.(fmt.Stringer)
if canStringer {
serviceName = stringer.String()
} else {
serviceName = fmt.Sprintf("%#v", service)
}
return
}
// NewSimple is a convenience function to create a service with just a name
// and the sensible defaults.
func NewSimple(name string) *Supervisor {
return New(name, Spec{})
}
/*
Add adds a service to this supervisor.
If the supervisor is currently running, the service will be started
immediately. If the supervisor is not currently running, the service
will be started when the supervisor is.
The returned ServiceID may be passed to the Remove method of the Supervisor
to terminate the service.
As a special behavior, if the service added is itself a supervisor, the
supervisor being added will copy the Log function from the Supervisor it
is being added to. This allows factoring out providing a Supervisor
from its logging. This unconditionally overwrites the child Supervisor's
logging functions.
*/
func (s *Supervisor) Add(service Service) ServiceToken {
if s == nil {
panic("can't add service to nil *suture.Supervisor")
}
if supervisor, isSupervisor := service.(*Supervisor); isSupervisor {
supervisor.LogBadStop = s.LogBadStop
supervisor.LogFailure = s.LogFailure
supervisor.LogBackoff = s.LogBackoff
}
s.Lock()
if s.state == notRunning {
id := s.serviceCounter
s.serviceCounter++
s.services[id] = serviceWithName{service, serviceName(service)}
s.restartQueue = append(s.restartQueue, id)
s.Unlock()
return ServiceToken{uint64(s.id)<<32 | uint64(id)}
}
s.Unlock()
response := make(chan serviceID)
s.control <- addService{service, serviceName(service), response}
return ServiceToken{uint64(s.id)<<32 | uint64(<-response)}
}
// ServeBackground starts running a supervisor in its own goroutine. This
// method does not return until it is safe to use .Add() on the Supervisor.
func (s *Supervisor) ServeBackground() {
go s.Serve()
s.sync()
}
/*
Serve starts the supervisor. You should call this on the top-level supervisor,
but nothing else.
*/
func (s *Supervisor) Serve() {
if s == nil {
panic("Can't serve with a nil *suture.Supervisor")
}
if s.id == 0 {
panic("Can't call Serve on an incorrectly-constructed *suture.Supervisor")
}
defer func() {
s.Lock()
s.state = notRunning
s.Unlock()
}()
s.Lock()
if s.state != notRunning {
s.Unlock()
panic("Running a supervisor while it is already running?")
}
s.state = normal
s.Unlock()
// for all the services I currently know about, start them
for _, id := range s.restartQueue {
namedService, present := s.services[id]
if present {
s.runService(namedService.Service, id)
}
}
s.restartQueue = make([]serviceID, 0, 1)
for {
select {
case m := <-s.control:
switch msg := m.(type) {
case serviceFailed:
s.handleFailedService(msg.id, msg.err, msg.stacktrace)
case serviceEnded:
service, monitored := s.services[msg.id]
if monitored {
if msg.complete {
delete(s.services, msg.id)
go func() {
service.Service.Stop()
}()
} else {
s.handleFailedService(msg.id, fmt.Sprintf("%s returned unexpectedly", service), []byte("[unknown stack trace]"))
}
}
case addService:
id := s.serviceCounter
s.serviceCounter++
s.services[id] = serviceWithName{msg.service, msg.name}
s.runService(msg.service, id)
msg.response <- id
case removeService:
s.removeService(msg.id, msg.notification, s.control)
case serviceTerminated:
delete(s.servicesShuttingDown, msg.id)
case stopSupervisor:
s.stopSupervisor()
msg.done <- struct{}{}
return
case listServices:
services := []Service{}
for _, service := range s.services {
services = append(services, service.Service)
}
msg.c <- services
case syncSupervisor:
// this does nothing on purpose; its sole purpose is to
// introduce a sync point via the channel receive
case panicSupervisor:
// used only by tests
panic("Panicking as requested!")
}
case _ = <-s.resumeTimer:
// We're resuming normal operation after a pause due to
// excessive thrashing
// FIXME: Ought to permit some spacing of these functions, rather
// than simply hammering through them
s.Lock()
s.state = normal
s.Unlock()
s.failures = 0
s.LogBackoff(s, false)
for _, id := range s.restartQueue {
namedService, present := s.services[id]
if present {
s.runService(namedService.Service, id)
}
}
s.restartQueue = make([]serviceID, 0, 1)
}
}
}
// Stop stops the Supervisor.
//
// This function will not return until either all Services have stopped, or
// they timeout after the timeout value given to the Supervisor at creation.
func (s *Supervisor) Stop() {
done := make(chan struct{})
if s.sendControl(stopSupervisor{done}) {
<-done
}
}
func (s *Supervisor) handleFailedService(id serviceID, err interface{}, stacktrace []byte) {
now := s.getNow()
if s.lastFail.IsZero() {
s.lastFail = now
s.failures = 1.0
} else {
sinceLastFail := now.Sub(s.lastFail).Seconds()
intervals := sinceLastFail / s.failureDecay
s.failures = s.failures*math.Pow(.5, intervals) + 1
}
if s.failures > s.failureThreshold {
s.Lock()
s.state = paused
s.Unlock()
s.LogBackoff(s, true)
s.resumeTimer = s.getAfterChan(s.failureBackoff)
}
s.lastFail = now
failedService, monitored := s.services[id]
// It is possible for a service to be no longer monitored
// by the time we get here. In that case, just ignore it.
if monitored {
// this may look dangerous because the state could change, but this
// code is only ever run in the one goroutine that is permitted to
// change the state, so nothing else will.
s.Lock()
curState := s.state
s.Unlock()
if curState == normal {
s.runService(failedService.Service, id)
s.LogFailure(s, failedService.Service, failedService.name, s.failures, s.failureThreshold, true, err, stacktrace)
} else {
// FIXME: When restarting, check that the service still
// exists (it may have been stopped in the meantime)
s.restartQueue = append(s.restartQueue, id)
s.LogFailure(s, failedService.Service, failedService.name, s.failures, s.failureThreshold, false, err, stacktrace)
}
}
}
func (s *Supervisor) runService(service Service, id serviceID) {
go func() {
if s.recoverPanics {
defer func() {
if r := recover(); r != nil {
buf := make([]byte, 65535, 65535)
written := runtime.Stack(buf, false)
buf = buf[:written]
s.fail(id, r, buf)
}
}()
}
service.Serve()
complete := false
if completable, ok := service.(IsCompletable); ok && completable.Complete() {
complete = true
}
s.serviceEnded(id, complete)
}()
}
func (s *Supervisor) removeService(id serviceID, notificationChan chan struct{}, removedChan chan supervisorMessage) {
namedService, present := s.services[id]
if present {
delete(s.services, id)
s.servicesShuttingDown[id] = namedService
go func() {
successChan := make(chan struct{})
go func() {
namedService.Service.Stop()
close(successChan)
if notificationChan != nil {
notificationChan <- struct{}{}
}
}()
select {
case <-successChan:
// Life is good!
case <-s.getAfterChan(s.timeout):
s.LogBadStop(s, namedService.Service, namedService.name)
}
removedChan <- serviceTerminated{id}
}()
} else {
if notificationChan != nil {
notificationChan <- struct{}{}
}
}
}
func (s *Supervisor) stopSupervisor() {
notifyDone := make(chan serviceID)
for id := range s.services {
namedService, present := s.services[id]
if present {
delete(s.services, id)
s.servicesShuttingDown[id] = namedService
go func(sID serviceID) {
namedService.Service.Stop()
notifyDone <- sID
}(id)
}
}
timeout := s.getAfterChan(s.timeout)
SHUTTING_DOWN_SERVICES:
for len(s.servicesShuttingDown) > 0 {
select {
case id := <-notifyDone:
delete(s.servicesShuttingDown, id)
case <-timeout:
for _, namedService := range s.servicesShuttingDown {
s.LogBadStop(s, namedService.Service, namedService.name)
}
// failed remove statements will log the errors.
break SHUTTING_DOWN_SERVICES
}
}
close(s.liveness)
return
}
// String implements the fmt.Stringer interface.
func (s *Supervisor) String() string {
return s.Name
}
func (s *Supervisor) sendControl(sm supervisorMessage) bool {
select {
case s.control <- sm:
return true
case _, _ = <-s.liveness:
return false
}
}
/*
Remove will remove the given service from the Supervisor, and attempt to Stop() it.
The ServiceID token comes from the Add() call. This returns without waiting
for the service to stop.
*/
func (s *Supervisor) Remove(id ServiceToken) error {
sID := supervisorID(id.id >> 32)
if sID != s.id {
return ErrWrongSupervisor
}
// no meaningful error handling if this is false
_ = s.sendControl(removeService{serviceID(id.id & 0xffffffff), nil})
return nil
}
/*
RemoveAndWait will remove the given service from the Supervisor and attempt
to Stop() it. It will wait up to the given timeout value for the service to
terminate. A timeout value of 0 means to wait forever.
If a nil error is returned from this function, then the service was
terminated normally. If either the supervisor terminates or the timeout
passes, ErrTimeout is returned. (If this isn't even the right supervisor
ErrWrongSupervisor is returned.)
*/
func (s *Supervisor) RemoveAndWait(id ServiceToken, timeout time.Duration) error {
sID := supervisorID(id.id >> 32)
if sID != s.id {
return ErrWrongSupervisor
}
var timeoutC <-chan time.Time
if timeout > 0 {
timer := time.NewTimer(timeout)
defer timer.Stop()
timeoutC = timer.C
}
notificationC := make(chan struct{})
sentControl := s.sendControl(removeService{serviceID(id.id & 0xffffffff), notificationC})
if sentControl == false {
return ErrTimeout
}
select {
case <-notificationC:
// normal case; the service is terminated.
return nil
// This occurs if the entire supervisor ends without the service
// having terminated, and includes the timeout the supervisor
// itself waited before closing the liveness channel.
case _, _ = <-s.liveness:
return ErrTimeout
// The local timeout.
case <-timeoutC:
return ErrTimeout
}
}
/*
Services returns a []Service containing a snapshot of the services this
Supervisor is managing.
*/
func (s *Supervisor) Services() []Service {
ls := listServices{make(chan []Service)}
if s.sendControl(ls) {
return <-ls.c
}
return nil
}