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machinelock.go
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machinelock.go
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// Copyright 2018 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.
package machinelock
import (
"fmt"
"runtime/debug"
"sort"
"sync"
"time"
"github.com/juju/collections/deque"
"github.com/juju/errors"
"github.com/juju/lumberjack/v2"
"github.com/juju/mutex/v2"
"gopkg.in/yaml.v2"
"github.com/juju/juju/core/logger"
"github.com/juju/juju/core/paths"
)
// Filename represents the name of the logfile that is created in the LOG_DIR.
const Filename = "machine-lock.log"
// Lock is used to give external packages something to refer to.
type Lock interface {
Acquire(spec Spec) (func(), error)
Report(opts ...ReportOption) (string, error)
}
// Clock provides an interface for dealing with clocks.
type Clock interface {
// After waits for the duration to elapse and then sends the
// current time on the returned channel.
After(time.Duration) <-chan time.Time
// Now returns the current clock time.
Now() time.Time
}
// Config defines the attributes needed to correctly construct
// a machine lock.
type Config struct {
AgentName string
Clock Clock
Logger logger.Logger
LogFilename string
}
// Validate ensures that all the required config values are set.
func (c Config) Validate() error {
if c.AgentName == "" {
return errors.NotValidf("missing AgentName")
}
if c.Clock == nil {
return errors.NotValidf("missing Clock")
}
if c.Logger == nil {
return errors.NotValidf("missing Logger")
}
if c.LogFilename == "" {
return errors.NotValidf("missing LogFilename")
}
return nil
}
// New creates a new machine lock.
func New(config Config) (*lock, error) {
if err := config.Validate(); err != nil {
return nil, errors.Trace(err)
}
if err := paths.PrimeLogFile(config.LogFilename); err != nil {
// This isn't a fatal error so continue if priming fails.
_ = fmt.Sprintf("failed to create prime logfile in %s, because: %v", config.LogFilename, err)
}
lock := &lock{
agent: config.AgentName,
clock: config.Clock,
logger: config.Logger,
logFilename: config.LogFilename,
acquire: mutex.Acquire,
spec: mutex.Spec{
Name: "machine-lock",
Clock: config.Clock,
Delay: 250 * time.Millisecond,
// Cancel is added in Acquire.
},
waiting: make(map[int]*info),
history: deque.NewWithMaxLen(1000),
}
lock.setStartMessage()
return lock, nil
}
func (c *lock) setStartMessage() {
now := c.clock.Now().Format(timeFormat)
// The reason that we don't attempt to write the start message out immediately
// is that there may be multiple agents on the machine writing to the same log file.
// The way that we control this is to open and close the file while we hold the
// machine lock. We don't want to acquire the lock just to write out the agent
// has started as this would potentially hold up the agent starting while another
// agent holds the lock. However it is very useful to have the agent start time
// recorded in the central file, so we save it and write it out the first time.
c.startMessage = fmt.Sprintf("%s === agent %s started ===", now, c.agent)
}
// Spec is an argument struct for the `Acquire` method.
// It must have a Cancel channel and a Worker name defined.
type Spec struct {
Cancel <-chan struct{}
// The purpose of the NoCancel is to ensure that there isn't
// an accidental forgetting of the cancel channel. The primary
// use case for this is the reboot worker that doesn't want to
// pass in a cancel channel because it really wants to reboot.
NoCancel bool
Worker string
Comment string
Group string
}
// Validate ensures that a Cancel channel and a Worker name are defined.
func (s Spec) Validate() error {
if s.Cancel == nil {
if !s.NoCancel {
return errors.NotValidf("missing Cancel")
}
}
if s.Worker == "" {
return errors.NotValidf("missing Worker")
}
return nil
}
// Acquire will attempt to acquire the machine hook execution lock.
// The method returns an error if the spec is invalid, or if the Cancel
// channel is signalled before the lock is acquired.
func (c *lock) Acquire(spec Spec) (func(), error) {
if err := spec.Validate(); err != nil {
return nil, errors.Trace(err)
}
current := &info{
worker: spec.Worker,
comment: spec.Comment,
stack: string(debug.Stack()),
requested: c.clock.Now(),
}
c.mu.Lock()
id := c.next
c.next++
c.waiting[id] = current
mSpec := c.spec
mSpec.Cancel = spec.Cancel
if spec.Group != "" {
mSpec.Name = fmt.Sprintf("%s-%s", mSpec.Name, spec.Group)
}
c.mu.Unlock()
c.logger.Debugf("acquire machine lock %q for %s (%s)", mSpec.Name, spec.Worker, spec.Comment)
releaser, err := c.acquire(mSpec)
c.mu.Lock()
defer c.mu.Unlock()
// Remove from the waiting map.
delete(c.waiting, id)
if err != nil {
return nil, errors.Trace(err)
}
c.logger.Debugf("machine lock %q acquired for %s (%s)", mSpec.Name, spec.Worker, spec.Comment)
c.holder = current
current.acquired = c.clock.Now()
return func() {
// We need to acquire the mutex before we call the releaser
// to ensure that we move the current to the history before
// another pending acquisition overwrites the current value.
c.mu.Lock()
defer c.mu.Unlock()
// We write the log file entry before we release the execution
// lock to ensure that no other agent is attempting to write to the
// log file.
current.released = c.clock.Now()
c.writeLogEntry()
c.logger.Debugf("machine lock %q released for %s (%s)", mSpec.Name, spec.Worker, spec.Comment)
releaser.Release()
c.history.PushFront(current)
c.holder = nil
}, nil
}
func (c *lock) writeLogEntry() {
// At the time this method is called, the holder is still set and the lock's
// mutex is held.
writer := &lumberjack.Logger{
Filename: c.logFilename,
MaxSize: 10, // megabytes
MaxBackups: 5,
Compress: true,
}
c.logger.Debugf("created rotating log file %q with max size %d MB and max backups %d",
writer.Filename, writer.MaxSize, writer.MaxBackups)
defer func() { _ = writer.Close() }()
if c.startMessage != "" {
_, err := fmt.Fprintln(writer, c.startMessage)
if err != nil {
c.logger.Warningf("unable to write startMessage: %s", err.Error())
}
c.startMessage = ""
}
_, err := fmt.Fprintln(writer, simpleInfo(c.agent, c.holder, c.clock.Now()))
if err != nil {
c.logger.Warningf("unable to release message: %s", err.Error())
}
}
type info struct {
// worker is the worker that wants or has the lock.
worker string
// comment is provided by the worker to say what they are doing.
comment string
// stack trace for additional debugging
stack string
requested time.Time
acquired time.Time
released time.Time
}
type lock struct {
agent string
clock Clock
logger logger.Logger
logFilename string
startMessage string
acquire func(mutex.Spec) (mutex.Releaser, error)
spec mutex.Spec
mu sync.Mutex
next int
holder *info
waiting map[int]*info
history *deque.Deque
}
type ReportOption int
const (
ShowHistory ReportOption = iota
ShowStack
ShowDetailsYAML
)
func contains(opts []ReportOption, opt ReportOption) bool {
for _, value := range opts {
if value == opt {
return true
}
}
return false
}
type reportInfo struct {
Worker string `yaml:"worker"`
Comment string `yaml:"comment,omitempty"`
Requested string `yaml:"requested,omitempty"`
Acquired string `yaml:"acquired,omitempty"`
Released string `yaml:"released,omitempty"`
WaitTime time.Duration `yaml:"wait-time,omitempty"`
HoldTime time.Duration `yaml:"hold-time,omitempty"`
Stack string `yaml:"stack,omitempty"`
}
type report struct {
Holder interface{} `yaml:"holder"`
Waiting []interface{} `yaml:"waiting,omitempty"`
History []interface{} `yaml:"history,omitempty"`
}
func (c *lock) Report(opts ...ReportOption) (string, error) {
includeStack := contains(opts, ShowStack)
detailsYAML := contains(opts, ShowDetailsYAML)
c.mu.Lock()
defer c.mu.Unlock()
now := c.clock.Now()
r := report{
Holder: displayInfo(c.holder, includeStack, detailsYAML, now),
}
// Show the waiting with oldest first, which will have the smallest
// map key.
for _, key := range sortedKeys(c.waiting) {
r.Waiting = append(r.Waiting, displayInfo(c.waiting[key], includeStack, detailsYAML, now))
}
if contains(opts, ShowHistory) {
iter := c.history.Iterator()
var v *info
for iter.Next(&v) {
r.History = append(r.History, displayInfo(v, includeStack, detailsYAML, now))
}
}
output := map[string]report{c.agent: r}
out, err := yaml.Marshal(output)
if err != nil {
return "", errors.Trace(err)
}
return string(out), nil
}
func sortedKeys(m map[int]*info) []int {
values := make([]int, 0, len(m))
for key := range m {
values = append(values, key)
}
sort.Ints(values)
return values
}
func timeOutput(t time.Time) string {
if t.IsZero() {
return ""
}
return t.String()
}
func displayInfo(info *info, includeStack, detailsYAML bool, now time.Time) interface{} {
if !detailsYAML {
return simpleInfo("", info, now)
}
if info == nil {
return nil
}
output := reportInfo{
Worker: info.worker,
Comment: info.comment,
Requested: timeOutput(info.requested),
Acquired: timeOutput(info.acquired),
Released: timeOutput(info.released),
}
var other time.Time
if info.acquired.IsZero() {
other = now
} else {
if info.released.IsZero() {
other = now
} else {
other = info.released
}
output.HoldTime = other.Sub(info.acquired).Round(time.Second)
// Now set other for the wait time.
other = info.acquired
}
output.WaitTime = other.Sub(info.requested).Round(time.Second)
return &output
}
func simpleInfo(agent string, info *info, now time.Time) string {
if info == nil {
return "none"
}
msg := info.worker
if info.comment != "" {
msg += " (" + info.comment + ")"
}
// We pass in agent when writing to the file, but not for the report.
// This allows us to have the agent in the file but keep the first column
// aligned for timestamps.
if agent != "" {
msg = agent + ": " + msg
}
if info.acquired.IsZero() {
waiting := now.Sub(info.requested).Round(time.Second)
return fmt.Sprintf("%s, waiting %s", msg, waiting)
}
if info.released.IsZero() {
holding := now.Sub(info.acquired).Round(time.Second)
return fmt.Sprintf("%s, holding %s", msg, holding)
}
ts := info.released.Format(timeFormat)
waited := info.acquired.Sub(info.requested).Round(time.Second)
held := info.released.Sub(info.acquired).Round(time.Second)
return fmt.Sprintf("%s %s, waited %s, held %s", ts, msg, waited, held)
}
const timeFormat = "2006-01-02 15:04:05"