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package featureflag
import (
"context"
"sync"
"time"
"github.com/sirupsen/logrus"
"gitlab.com/gitlab-org/gitaly/v15/internal/helper/tick"
)
// Cache is an abstraction over feature flag management.
type Cache interface {
// Get returns true/false as a first return parameter is the feature flag is
// enabled/disabled. The second return parameter is true only if the feature
// flag was evaluated and false if it is not know (not in the Cache).
Get(context.Context, string) (bool, bool)
}
// NoopCache is a dummy implementation of the FlagCache that is used as a stub.
type NoopCache struct{}
// Get always returns the same result (false, false) to the caller.
func (NoopCache) Get(context.Context, string) (bool, bool) {
return false, false
}
var (
// flagCache is a storage of the feature flags evaluated somewhere and
// used to prevent potential performance troubles with triggering
// feature flag fetching too much often from the Provider.
flagCache Cache = NoopCache{}
flagCacheMtx sync.Mutex
)
// SetCache sets a Cache for the feature flags.
func SetCache(new Cache) {
flagCacheMtx.Lock()
defer flagCacheMtx.Unlock()
flagCache = new
}
// GetCache returns current Cache of the feature flags.
func GetCache() Cache {
flagCacheMtx.Lock()
defer flagCacheMtx.Unlock()
return flagCache
}
// Provider is an abstraction that is able to return a set of feature flags
// in their current state.
type Provider interface {
// GetAll returns all known feature flags and their state.
GetAll(ctx context.Context) (map[string]bool, error)
}
// RefreshableCache is a periodically refreshable cache for storing feature flags.
// To start auto-refresh the RefreshLoop method needs to be called.
type RefreshableCache struct {
mtx sync.RWMutex
logger logrus.FieldLogger
flags map[string]bool
provider Provider
}
// NewRefreshableCache returns a new instance of the RefreshableCache that is already initialized.
func NewRefreshableCache(
ctx context.Context,
logger logrus.FieldLogger,
provider Provider,
) *RefreshableCache {
c := &RefreshableCache{logger: logger, provider: provider}
c.refresh(ctx)
return c
}
// RefreshLoop is a blocking call that returns once passed in context is cancelled.
// It continuously reloads cache data. If data retrieval from the Provider returns
// an error the cache data remains the same without any changes.
func (rc *RefreshableCache) RefreshLoop(ctx context.Context, ticker tick.Ticker) {
ticker.Reset()
for {
select {
case <-ticker.C():
rc.refresh(ctx)
ticker.Reset()
case <-ctx.Done():
return
}
}
}
// Get returns current cached value for the feature flag and true as a second return parameter.
// If flag is not found the both return values are false.
func (rc *RefreshableCache) Get(_ context.Context, name string) (bool, bool) {
rc.mtx.RLock()
defer rc.mtx.RUnlock()
val, found := rc.flags[name]
return val, found
}
func (rc *RefreshableCache) refresh(ctx context.Context) {
ctx, cancel := context.WithTimeout(ctx, time.Second*5)
defer cancel()
newFlags, err := rc.provider.GetAll(ctx)
if err != nil {
rc.logger.Errorf("failure on fetching the state of the feature flags: %v", err)
// In case of an issue with flags retrieval, proceed without updating cached data.
return
}
flagsClone := make(map[string]bool, len(newFlags))
for k, v := range newFlags {
flagsClone[k] = v
}
rc.mtx.Lock()
defer rc.mtx.Unlock()
rc.flags = flagsClone
}
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