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worker.go
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worker.go
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// Copyright (C) 2019-2023, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
package health
import (
"context"
"errors"
"fmt"
"sync"
"time"
"github.com/prometheus/client_golang/prometheus"
"go.uber.org/zap"
"golang.org/x/exp/maps"
"golang.org/x/exp/slices"
"github.com/MetalBlockchain/metalgo/utils"
"github.com/MetalBlockchain/metalgo/utils/logging"
"github.com/MetalBlockchain/metalgo/utils/set"
)
var (
allTags = []string{AllTag}
errRestrictedTag = errors.New("restricted tag")
errDuplicateCheck = errors.New("duplicated check")
)
type worker struct {
log logging.Logger
namespace string
metrics *metrics
checksLock sync.RWMutex
checks map[string]*taggedChecker
resultsLock sync.RWMutex
results map[string]Result
numFailingApplicationChecks int
tags map[string]set.Set[string] // tag -> set of check names
startOnce sync.Once
closeOnce sync.Once
wg sync.WaitGroup
closer chan struct{}
}
type taggedChecker struct {
checker Checker
isApplicationCheck bool
tags []string
}
func newWorker(
log logging.Logger,
namespace string,
registerer prometheus.Registerer,
) (*worker, error) {
metrics, err := newMetrics(namespace, registerer)
return &worker{
log: log,
namespace: namespace,
metrics: metrics,
checks: make(map[string]*taggedChecker),
results: make(map[string]Result),
closer: make(chan struct{}),
tags: make(map[string]set.Set[string]),
}, err
}
func (w *worker) RegisterCheck(name string, check Checker, tags ...string) error {
// We ensure [AllTag] isn't contained in [tags] to prevent metrics from
// double counting.
if slices.Contains(tags, AllTag) {
return fmt.Errorf("%w: %q", errRestrictedTag, AllTag)
}
w.checksLock.Lock()
defer w.checksLock.Unlock()
if _, ok := w.checks[name]; ok {
return fmt.Errorf("%w: %q", errDuplicateCheck, name)
}
w.resultsLock.Lock()
defer w.resultsLock.Unlock()
// Add the check to each tag
for _, tag := range tags {
names := w.tags[tag]
names.Add(name)
w.tags[tag] = names
}
// Add the special AllTag descriptor
names := w.tags[AllTag]
names.Add(name)
w.tags[AllTag] = names
applicationChecks := w.tags[ApplicationTag]
tc := &taggedChecker{
checker: check,
isApplicationCheck: applicationChecks.Contains(name),
tags: tags,
}
w.checks[name] = tc
w.results[name] = notYetRunResult
// Whenever a new check is added - it is failing
w.log.Info("registered new check and initialized its state to failing",
zap.String("namespace", w.namespace),
zap.String("name", name),
zap.Strings("tags", tags),
)
// If this is a new application-wide check, then all of the registered tags
// now have one additional failing check.
w.updateMetrics(tc, false /*=healthy*/, true /*=register*/)
return nil
}
func (w *worker) RegisterMonotonicCheck(name string, checker Checker, tags ...string) error {
var result utils.Atomic[any]
return w.RegisterCheck(name, CheckerFunc(func(ctx context.Context) (any, error) {
details := result.Get()
if details != nil {
return details, nil
}
details, err := checker.HealthCheck(ctx)
if err == nil {
result.Set(details)
}
return details, err
}), tags...)
}
func (w *worker) Results(tags ...string) (map[string]Result, bool) {
w.resultsLock.RLock()
defer w.resultsLock.RUnlock()
// if no tags are specified, return all checks
if len(tags) == 0 {
tags = allTags
}
names := set.Set[string]{}
tagSet := set.Of(tags...)
tagSet.Add(ApplicationTag) // we always want to include the application tag
for tag := range tagSet {
if set, ok := w.tags[tag]; ok {
names.Union(set)
}
}
results := make(map[string]Result, names.Len())
healthy := true
for name := range names {
if result, ok := w.results[name]; ok {
results[name] = result
healthy = healthy && result.Error == nil
}
}
return results, healthy
}
func (w *worker) Start(ctx context.Context, freq time.Duration) {
w.startOnce.Do(func() {
detachedCtx := utils.Detach(ctx)
w.wg.Add(1)
go func() {
ticker := time.NewTicker(freq)
defer func() {
ticker.Stop()
w.wg.Done()
}()
w.runChecks(detachedCtx)
for {
select {
case <-ticker.C:
w.runChecks(detachedCtx)
case <-w.closer:
return
}
}
}()
})
}
func (w *worker) Stop() {
w.closeOnce.Do(func() {
close(w.closer)
w.wg.Wait()
})
}
func (w *worker) runChecks(ctx context.Context) {
w.checksLock.RLock()
// Copy the [w.checks] map to collect the checks that we will be running
// during this iteration. If [w.checks] is modified during this iteration of
// [runChecks], then the added check will not be run until the next
// iteration.
checks := maps.Clone(w.checks)
w.checksLock.RUnlock()
var wg sync.WaitGroup
wg.Add(len(checks))
for name, check := range checks {
go w.runCheck(ctx, &wg, name, check)
}
wg.Wait()
}
func (w *worker) runCheck(ctx context.Context, wg *sync.WaitGroup, name string, check *taggedChecker) {
defer wg.Done()
start := time.Now()
// To avoid any deadlocks when [RegisterCheck] is called with a lock
// that is grabbed by [check.HealthCheck], we ensure that no locks
// are held when [check.HealthCheck] is called.
details, err := check.checker.HealthCheck(ctx)
end := time.Now()
result := Result{
Details: details,
Timestamp: end,
Duration: end.Sub(start),
}
w.resultsLock.Lock()
defer w.resultsLock.Unlock()
prevResult := w.results[name]
if err != nil {
errString := err.Error()
result.Error = &errString
result.ContiguousFailures = prevResult.ContiguousFailures + 1
if prevResult.ContiguousFailures > 0 {
result.TimeOfFirstFailure = prevResult.TimeOfFirstFailure
} else {
result.TimeOfFirstFailure = &end
}
if prevResult.Error == nil {
w.log.Warn("check started failing",
zap.String("namespace", w.namespace),
zap.String("name", name),
zap.Strings("tags", check.tags),
zap.Error(err),
)
w.updateMetrics(check, false /*=healthy*/, false /*=register*/)
}
} else if prevResult.Error != nil {
w.log.Info("check started passing",
zap.String("namespace", w.namespace),
zap.String("name", name),
zap.Strings("tags", check.tags),
)
w.updateMetrics(check, true /*=healthy*/, false /*=register*/)
}
w.results[name] = result
}
// updateMetrics updates the metrics for the given check. If [healthy] is true,
// then the check is considered healthy and the metrics are decremented.
// Otherwise, the check is considered unhealthy and the metrics are incremented.
// [register] must be true only if this is the first time the check is being
// registered.
func (w *worker) updateMetrics(tc *taggedChecker, healthy bool, register bool) {
if tc.isApplicationCheck {
// Note: [w.tags] will include AllTag.
for tag := range w.tags {
gauge := w.metrics.failingChecks.WithLabelValues(tag)
if healthy {
gauge.Dec()
} else {
gauge.Inc()
}
}
if healthy {
w.numFailingApplicationChecks--
} else {
w.numFailingApplicationChecks++
}
} else {
for _, tag := range tc.tags {
gauge := w.metrics.failingChecks.WithLabelValues(tag)
if healthy {
gauge.Dec()
} else {
gauge.Inc()
// If this is the first time this tag was registered, we also need to
// account for the currently failing application-wide checks.
if register && w.tags[tag].Len() == 1 {
gauge.Add(float64(w.numFailingApplicationChecks))
}
}
}
gauge := w.metrics.failingChecks.WithLabelValues(AllTag)
if healthy {
gauge.Dec()
} else {
gauge.Inc()
}
}
}