go get -u github.com/1pkg/gohalt

Gohalt is simple and convenient yet powerful and efficient throttling go library. Gohalt provides various throttlers and surronding tools to build throttling pipelines and rate limiters of any complexity adjusted to your specific needs. Gohalt provides an easy way to integrate throttling and rate limiting with your infrastructure through built in middlewares.

Gohalt uses Throttler as the core interface for all derived throttlers and surronding tools.

// Throttler defines core gohalt throttler abstraction and exposes pair of counterpart methods: `Acquire` and `Release`.
type Throttler interface {
	// Acquire takes a part of throttling quota or returns error if throttling quota is drained
	// it needs to be called right before shared resource acquire.
	Acquire(context.Context) error
	// Release puts a part of throttling quota back or returns error if this is not possible
	// it needs to be called just after shared resource release.
	Release(context.Context) error
}

Throttler interface exposes pair of counterpart methods: Acquire takes a part of throttling quota or returns error if throttling quota is drained and needs to be called right before shared resource acquire; Release puts a part of throttling quota back or returns error if this is not possible and needs to be called just after shared resource release; Note: all derived throttler implementations are thread safe, so they could be used concurrently without additional locking. Note: all acquired throttlers should be released exatly the same amount of times they have been acquired. Note: despite throttler Release method has the same signature as Acquire has, Release implementations should try to handle any internal error gracefully and return error back rarely, nevertheless all errors returned by Release should be handeled by client.

In Gohalt throtllers could be easily combined with each other to build complex pipelines. There are multiple composite throttlers (all, any, ring, pattern, not, generator, etc) as well as leaf throttlers (timed, latency, monitor, metric, percentile, etc) to work with in Gohalt. If you don't find in existing throttlers the one that fits your needs you can create custom throttler by implementing Throttler interface. Such custom throttler should work with existing Gohalt throttlers and tools out of box.

Gohalt includes multiple supporting surrounding tools to make throttling more sugary.

// Runnable defined by typical abstract async func signature.
// Runnable is used by `Runner` as a subject for execution.
type Runnable func(context.Context) error
// Runner defines abstraction to execute a set of `Runnable`
// and return possible execution error back.
// Runner is designed to simplify work with throttlers
// by managing `Acquire`/`Release` loop.
type Runner interface {
	// Run executes single prodived `Runnable` instance.
	Run(Runnable)
	// Result returns possible execution error back.
	Result() error
}

Runnable and Runner define slim abstraction for executable and executor in Gohalt. Runner insterface aims to provide similar interface as errgroup.Group does. So to run a single executable use Run to wait and get result use Result. There are two runners implementations in Gohalt:

• sync func NewRunnerSync(ctx context.Context, thr Throttler) Runner
• async func NewRunnerAsync(ctx context.Context, thr Throttler) Runner Both implementation accept throttler and context as input arguments and handle all throttling cycle internaly. This way client donesn't need to call neither Acquire nor Release manually, all this is done by the runner. This way the only thing that needs to be done to add throttling to existing code wrap existing executable by Runnable. The only difference between sync and async runner is that the async runner starts each new Runnable inside new goroutine and uses locks for its imternal state. Note: You can't use sync runner in async fashion with go syncr.Run(func(context.Context) error{}) this will cause data race, use async runner instead async.Run(func(context.Context) error{}).

Last but not least Gohalt uses context heavily inside and there are multiple helpers to provide data via context for throttles, see throttles list to know when to use them.

// WithTimestamp adds the provided timestamp to the provided context
// to determine latency between `Acquire` and `Release`.
// Resulted context is used by: `latency` and `percentile` throtttlers.
func WithTimestamp(ctx context.Context, ts time.Time) context.Context
// WithPriority adds the provided priority to the provided context
// to differ `Acquire` priority levels.
// Resulted context is used by: `priority` throtttler.
func WithPriority(ctx context.Context, priority uint8) context.Context
// WithWeight adds the provided weight to the provided context
// to differ `Acquire` weight levels.
// Resulted context is used by: `semaphore` and `cellrate` throtttlers.
func WithWeight(ctx context.Context, weight int64) context.Context
// WithKey adds the provided key to the provided context
// to add additional call identifier to context.
// Resulted context is used by: `before`, `after`, `timed`, `adaptive`, `semaphore`, `cellrate` and `bucket` throtttlers.
func WithKey(ctx context.Context, key string) context.Context
// WithMessage adds the provided message to the provided context
// to add additional message that need to be used to context.
// Resulted context is used by: `enqueue` throtttler.
func WithMessage(ctx context.Context, message interface{}) context.Context
// WithMarshaler adds the provided marshaler to the provided context
// to add additional message marshaler that need to be used to context.
// Resulted context is used by: `enqueue` throtttler.
// Used in pair with `WithMessage`.
func WithMarshaler(ctx context.Context, mrsh Marshaler) context.Context
// WithParams facade call that respectively calls:
// - `WithTimestamp`
// - `WithPriority`
// - `WithWeight`
// - `WithKey`
// - `WithMessage`
// - `WithMarshaler`
func WithParams(ctx context.Context, ts time.Time, priority uint8, weight int64, key string, message interface{}, marshaler Marshaler) context.Context

Also there is yet another throttling sugar func WithThrottler(ctx context.Context, thr Throttler, freq time.Duration) context.Context related to context. Which defines context implementation that uses parrent context plus throttler internally. Using it you can keep typical context patterns for cancelation handling and apply and combine it with throttling.

select {
	case <-ctx.Done():
		return ctx.Error()
	default:
}

If internal context throttler is throttling context done channel will be closed respectively. Note such behavior is implemented by throttler long pooling with the specified frequency, so efficiently there will be additional throttling user in form of long pooling goroutine.

// complex throttler example
thr := NewThrottlerAll( // throttles only if all children throttle
	NewThrottlerPattern(
		Pattern{ // use throttler only if provided key matches `192.*.*.*` submask
			Pattern: regexp.MustCompile(`192\.[0-9]+\.[0-9]+\.[0-9]+`),
			Throttler: NewThrottlerAny( // throttles if any children throttles
				// throttles only if latency is above 50 millisecond
				NewThrottlerLatency(50*time.Millisecond, 5*time.Second),
				// throttles only if cpu usage is above 70%
				NewThrottlerMonitor(NewMonitorSystem(time.Minute), Stats{CPUUsage: 0.7}),
			),
		},
	),
	// throttles each not 3rd call
	NewThrottlerNot(NewThrottlerEach(3)),
	// enqueues provided message to queue
	NewThrottlerEnqueue(NewEnqueuerRabbit("amqp://user:pass@localhost:5672/vhost", "queue", time.Minute)),
)

In gohalt v0.4.0 breaking change is introduced to replace all untyped errors with two major error types:

• ErrorThreshold which defines error type that occurs if throttler reaches specified threshold.
• ErrorInternal which defines error type that occurs if throttler internal error happens. You can find list of returning error types for all existing throttlers in throttlers table bellow or in documentation.
  Note: not every gohalt throttler must return error; some throttlers might cause different side effects like logging or call to time.Sleep instead.

Gohalt is licensed under the MIT License.
See LICENSE for the full license text.